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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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17 pages, 6111 KiB  
Article
Effect of Aging on Unidirectional Composite Laminate Polyethylene for Body Armor
by Amy Engelbrecht-Wiggans, Zois Tsinas, Ajay Krishnamurthy and Amanda L. Forster
Polymers 2023, 15(6), 1347; https://doi.org/10.3390/polym15061347 - 8 Mar 2023
Cited by 5 | Viewed by 2299
Abstract
The construction of ballistic-resistant body armor is experiencing an increasing use of flexible unidirectional (UD) composite laminates that comprise multiple layers. Each UD layer contains hexagonally packed high-performance fibers with a very low modulus matrix (sometimes referred to as binder resins). Laminates are [...] Read more.
The construction of ballistic-resistant body armor is experiencing an increasing use of flexible unidirectional (UD) composite laminates that comprise multiple layers. Each UD layer contains hexagonally packed high-performance fibers with a very low modulus matrix (sometimes referred to as binder resins). Laminates are then made from orthogonal stacks of these layers, and these laminate-based armor packages offer significant performance advantages over standard woven materials. When designing any armor system, the long-term reliability of the armor materials is critical, particularly with regard to stability with exposure to temperature and humidity, as these are known causes of degradation in commonly used body armor materials. To better inform future armor designers, this work investigates the tensile behavior of an ultra-high molar mass polyethylene (UHMMPE) flexible UD laminate that was aged for at least 350 d at two accelerated conditions: 70 °C at 76% relative humidity (RH) and 70 °C in a desiccator. Tensile tests were performed at two different loading rates. The mechanical properties of the material after ageing demonstrated less than 10% degradation in tensile strength, indicating high reliability for armor made from this material. Full article
(This article belongs to the Special Issue Durability and Degradation of Polymeric Materials II)
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14 pages, 2185 KiB  
Article
Feasibility of Valorization of Post-Consumer Recycled Flexible Polypropylene by Adding Fumed Nanosilica for Its Potential Use in Food Packaging toward Sustainability
by Eliezer Velásquez, Carol López de Dicastillo, Cristian Patiño Vidal, Guillermo Copello, Cristopher Reyes, Abel Guarda and María José Galotto
Polymers 2023, 15(5), 1081; https://doi.org/10.3390/polym15051081 - 21 Feb 2023
Cited by 12 | Viewed by 2699
Abstract
The food industry has a current challenge of increasing the recycling of post-consumer plastics to reduce plastic waste towards a circular economy, especially flexible polypropylene, which is highly demanded in food packaging. However, recycling post-consumer plastics is limited because service life and reprocessing [...] Read more.
The food industry has a current challenge of increasing the recycling of post-consumer plastics to reduce plastic waste towards a circular economy, especially flexible polypropylene, which is highly demanded in food packaging. However, recycling post-consumer plastics is limited because service life and reprocessing degrade their physical-mechanical properties and modify the migration of components from the recycled material to the food. This research evaluated the feasibility of valorization of post-consumer recycled flexible polypropylene (PCPP) by incorporating fumed nanosilica (NS). For this purpose, the effect of concentration and type (hydrophilic and hydrophobic) of NS on the morphological, mechanical, sealing, barrier and overall migration properties of PCPP films was studied. Incorporating NS improved Young’s modulus and, more significantly, tensile strength at 0.5 wt% and 1 wt%, where a better particle dispersion was confirmed by EDS-SEM, but it diminished elongation at breakage of the films. Interestingly, NS tended to increase the seal strength of PCPP nanocomposite films more significantly at higher NS content, showing a seal failure of the adhesive peel type which is preferred for flexible packaging. NS at 1 wt% did not affect the water vapor and oxygen permeabilities of the films. Overall migration of PCPP and nanocomposites exceeded the limit value of 10 mg dm−2 allowed by European legislation at the studied concentrations of 1% and 4 wt%. Nonetheless, NS reduced the overall migration of PCPP from 17.3 to 15 mg dm−2 in all nanocomposites. In conclusion, PCPP with 1 wt% of hydrophobic NS presented an improved overall performance of the studied packaging properties. Full article
(This article belongs to the Special Issue Polymers for Recycling and Valorization of Soft and Hard Materials)
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21 pages, 497 KiB  
Review
Hydrothermal Ageing of Glass Fibre Reinforced Vinyl Ester Composites: A Review
by James Thomason and Georgios Xypolias
Polymers 2023, 15(4), 835; https://doi.org/10.3390/polym15040835 - 8 Feb 2023
Cited by 25 | Viewed by 3884
Abstract
The use of glass fibre-reinforced polymer (GFRP) composites in load-carrying constructions has significantly increased over the last few decades. Such GFRP composite structures may undergo significant changes in performance as a consequence of long-term environmental exposure. Vinyl ester (VE) resins are a class [...] Read more.
The use of glass fibre-reinforced polymer (GFRP) composites in load-carrying constructions has significantly increased over the last few decades. Such GFRP composite structures may undergo significant changes in performance as a consequence of long-term environmental exposure. Vinyl ester (VE) resins are a class of thermosetting polymers increasingly being used in such structural composites. This increasing use of VE-based GFRPs in such applications has led to an increasing need to better understand the consequences of long-term environmental exposure on their performance. The reliable validation of the environmental durability of new VE-based GFRPs can be a time- and resource-consuming process involving costly testing programs. Accelerated hydrothermal ageing is often used in these investigations. This paper reviews the relevant literature on the hydrothermal ageing of vinyl ester-based GFRP with special attention to the fundamental background of moisture-induced ageing of GFRP, the important role of voids, and the fibre-matrix interface, on composite mechanical performance. Full article
(This article belongs to the Special Issue Durability and Degradation of Polymeric Materials II)
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20 pages, 3343 KiB  
Article
Enzyme-Catalyzed Polymerization of Kraft Lignin from Eucalyptus globulus: Comparison of Bacterial and Fungal Laccases Efficacy
by Luisa García-Fuentevilla, Gabriela Domínguez, Raquel Martín-Sampedro, Manuel Hernández, María E. Arias, José I. Santos, David Ibarra and María E. Eugenio
Polymers 2023, 15(3), 513; https://doi.org/10.3390/polym15030513 - 18 Jan 2023
Cited by 5 | Viewed by 3237
Abstract
Kraft lignin, a side-stream from the pulp and paper industry, can be modified by laccases for the synthesis of high added-value products. This work aims to study different laccase sources, including a bacterial laccase from Streptomyces ipomoeae (SiLA) and a fungal laccase from [...] Read more.
Kraft lignin, a side-stream from the pulp and paper industry, can be modified by laccases for the synthesis of high added-value products. This work aims to study different laccase sources, including a bacterial laccase from Streptomyces ipomoeae (SiLA) and a fungal laccase from Myceliophthora thermophila (MtL), for kraft lignin polymerization. To study the influence of some variables in these processes, a central composite design (CCD) with two continuous variables (enzyme concentration and reaction time) and three levels for each variable was used. The prediction of the behavior of the output variables (phenolic content and molecular weight of lignins) were modelled by means of response surface methodology (RSM). Moreover, characterization of lignins was performed by Fourier-transform infrared (FTIR) spectroscopy and different nuclear magnetic resonance (NMR) spectroscopy techniques. In addition, antioxidant activity was also analyzed. Results showed that lignin polymerization (referring to polymerization as lower phenolic content and higher molecular weight) occurred by the action of both laccases. The enzyme concentration was the most influential variable in the lignin polymerization reaction within the range studied for SiLA laccase, while the most influential variable for MtL laccase was the reaction time. FTIR and NMR characterization analysis corroborated lignin polymerization results obtained from the RSM. Full article
(This article belongs to the Special Issue Development of Bio-Based Materials: Synthesis, Characterization, and Applications II)
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44 pages, 19950 KiB  
Review
Hybridization of Wide-Angle X-ray and Neutron Diffraction Techniques in the Crystal Structure Analyses of Synthetic Polymers
by Kohji Tashiro, Katsuhiro Kusaka, Hiroko Yamamoto, Takaaki Hosoya, Shuji Okada and Takashi Ohhara
Polymers 2023, 15(2), 465; https://doi.org/10.3390/polym15020465 - 16 Jan 2023
Cited by 3 | Viewed by 3213
Abstract
The development in the crystal structure analysis of synthetic polymers using the hybridized combination of wide-angle X-ray and neutron diffraction (WAXD and WAND, respectively) techniques has been reviewed with many case studies performed by the authors. At first, the technical development was reviewed, [...] Read more.
The development in the crystal structure analysis of synthetic polymers using the hybridized combination of wide-angle X-ray and neutron diffraction (WAXD and WAND, respectively) techniques has been reviewed with many case studies performed by the authors. At first, the technical development was reviewed, in which the usage of high-energy synchrotron X-ray source was emphasized for increasing the total number of the observable diffraction peaks, and several examples were introduced. Secondly, the usage of the WAND method was introduced, in which the successful extraction of hydrogen atomic positions was described. The third example is to show the importance for the hybrid combination of these two diffraction methods. The quantitative WAXD data analysis gave the crystal structures of at-poly(vinyl alcohol) (at-PVA) and at-PVA-iodine complex. However, the thus-proposed structure models were found not to reproduce the observed WAND data very much. The reason came from the remarkable difference in the atomic scattering powers of the constituting atomic species between WAXD and WAND phenomena. The introduction of statistical disorder solved this serious problem, which reproduced both of the observed WAXD and WAND data consistently. The more systematic combination of WAXD and WAND methods, or the so-called X-N method, was applied also to the quantitative evaluation of the bonded electron density distribution along the skeletal chains, where the results about polydiacetylene single crystals were presented as the first successful study. Finally, the application of WAND technique in the trace of structural changes induced under the application of external stress or temperature was described. The future perspective is described for the development of structural science of synthetic polymers on the basis of the combined WAXD/WAND techniques. Full article
(This article belongs to the Special Issue State-of-the-Art Polymer Science and Technology in Japan (2021,2022))
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16 pages, 3086 KiB  
Article
Insight into Degrading Effects of Two Fungi on Polyurethane Coating Failure in a Simulated Atmospheric Environment
by Xiangping Hao, Kexin Yang, Dawei Zhang and Lin Lu
Polymers 2023, 15(2), 328; https://doi.org/10.3390/polym15020328 - 9 Jan 2023
Cited by 3 | Viewed by 2497
Abstract
Two different fungi, Talaromyces funiculosus (T. funiculosus) and Phanerochaete chrysosporium (P. chrysosporium), were collected from the Xishuangbanna atmospheric corrosion site and incubated on a polyurethane (PU) coating at 30 °C for two weeks under 95% relative humidity (RH). The biodegrading [...] Read more.
Two different fungi, Talaromyces funiculosus (T. funiculosus) and Phanerochaete chrysosporium (P. chrysosporium), were collected from the Xishuangbanna atmospheric corrosion site and incubated on a polyurethane (PU) coating at 30 °C for two weeks under 95% relative humidity (RH). The biodegrading effects of these fungi on the coating failure were investigated from aspects of metabolism and electrochemistry. The results showed that T. funiculosus contributed more to the degradation of the PU coating failure than P. chrysosporium, and two factors played dominant roles. First, the weight of the T. funiculosus mycelium was nearly 3 times more than that of P. chrysosporium, indicating there was more substrate mycelium of T. funiculosus deep into the coatings to get more nutrition in atmospheric during colonization. Second, T. funiculosus secreted carboxylic acids, such as citric, propanoic, succinic, and tartaric acids, and accelerated the hydrolysis of the ester and urethane bonds in the PU coatings. As a result, the mycelium of T. funiculosus readily penetrated the interface of the coating and substrate resulting in a rapid proliferation. Thus, the |Z|0.01Hz value of the coating decreased to 5.1 × 104 Ω·cm2 after 14 days of colonization by T. funiculosus while the value remained at 7.2 × 107 Ω·cm2 after colonization by P. chrysosporium. These insights suggest that the biodegradation process in simulated atmospheric environments would provide theoretical guidance and directions for the design of antifungal PU coatings. Full article
(This article belongs to the Special Issue Durability and Degradation of Polymeric Materials II)
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9 pages, 2286 KiB  
Article
Self- and Cross-Fusing of Furan-Based Polyurea Gels Dynamically Cross-Linked with Maleimides
by Takuya Kumakura, Kenji Takada and Tatsuo Kaneko
Polymers 2023, 15(2), 341; https://doi.org/10.3390/polym15020341 - 9 Jan 2023
Cited by 1 | Viewed by 2362
Abstract
Bio-based polyureas (PUs) with main-chain furan rings were synthesized by the polyaddition of 2,5-bis(aminomethyl)furan with various diisocyanates, such as methylene diphenyl diisocyanate. Several PU’s were soluble in polar organic solvents, and were cast to form thermomechanically stable films with softening temperatures of over [...] Read more.
Bio-based polyureas (PUs) with main-chain furan rings were synthesized by the polyaddition of 2,5-bis(aminomethyl)furan with various diisocyanates, such as methylene diphenyl diisocyanate. Several PU’s were soluble in polar organic solvents, and were cast to form thermomechanically stable films with softening temperatures of over 100 °C. The furan rings of the PU main chains underwent a dynamic Diels-Alder (DA) reaction with bismaleimide (BMI) cross-linkers. While the mixed solution of PU and BMI did not show any apparent signs of reaction at room temperature, the DA reaction proceeded to form gels upon heating to 60 °C, which became a solution again by further heating to 80 °C (retro-DA reaction). The solution phase was maintained by rapid quenching from 80 °C to room temperature, while the gel was reformed upon slow cooling. The recovered gels exhibited self-healing properties. A scratch made by a hot knife at temperatures above 80 °C disappeared spontaneously. When two different gels were cut using a knife at room temperature, placed in contact with each other, and heated to 60 °C, they fused. The ability to control the DA/retro-DA reaction allowed gels of varying composition to heal. Full article
(This article belongs to the Special Issue State-of-the-Art Polymer Science and Technology in Japan (2021,2022))
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15 pages, 2393 KiB  
Article
Studying the Physical and Chemical Properties of Polydimethylsiloxane Matrix Reinforced by Nanostructured TiO2 Supported on Mesoporous Silica
by Sari Katz, Noa Lachman, Nir Hafif, Lilach Rosh, Alexander Pevzner, Amir Lybman, Tal Amitay-Rosen, Ido Nir and Hadar Rotter
Polymers 2023, 15(1), 81; https://doi.org/10.3390/polym15010081 - 25 Dec 2022
Cited by 9 | Viewed by 4971
Abstract
In this study, a reactive adsorbent filler was integrated into a polymeric matrix as a novel reactive protective barrier without undermining its mechanical, thermal, and chemical properties. For this purpose, newly synthesized TiO2/MCM/polydimethylsiloxane (PDMS) composites were prepared, and their various properties [...] Read more.
In this study, a reactive adsorbent filler was integrated into a polymeric matrix as a novel reactive protective barrier without undermining its mechanical, thermal, and chemical properties. For this purpose, newly synthesized TiO2/MCM/polydimethylsiloxane (PDMS) composites were prepared, and their various properties were thoroughly studied. The filler, TiO2/MCM, is based on a (45 wt%) TiO2 nanoparticle catalyst inside the pores of ordered mesoporous silica, MCM-41, which combines a high adsorption capacity and catalytic capability. This study shows that the incorporation of TiO2/MCM significantly enhances the composite’s Young’s modulus in terms of tensile strength, as an optimal measurement of 1.6 MPa was obtained, compared with that of 0.8 MPa of pristine PDMS. The composites also showed a higher thermal stability, a reduction in the coefficient of thermal expansion (from 290 to 110 ppm/°C), a 25% reduction in the change in the normalized specific heat capacity, and an increase in the thermal degradation temperatures. The chemical stability in organic environments was improved, as toluene swelling decreased by 40% and the contact angle increased by ~15°. The enhanced properties of the novel synthesized TiO2/MCM/PDMS composite can be used in various applications where a high adsorption capacity and catalytic/photocatalytic activity are required, such as in protective equipment, microfluidic applications, and chemical sensor devices. Full article
(This article belongs to the Special Issue Durability and Degradation of Polymeric Materials II)
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26 pages, 7618 KiB  
Article
Plastic Deformation of High Density Polyethylene with Extended-Chain Crystal Morphology
by Alina Vozniak and Zbigniew Bartczak
Polymers 2023, 15(1), 66; https://doi.org/10.3390/polym15010066 - 24 Dec 2022
Cited by 8 | Viewed by 4005
Abstract
Samples of polyethylene with extended-chain crystal morphology, obtained by crystallization under high pressure, were subjected to uniaxial compression to various strains. Accompanying structural changes were analyzed using scanning electron microscopy. At the true strain of e = 0.2–0.3 the microbuckling instability was observed [...] Read more.
Samples of polyethylene with extended-chain crystal morphology, obtained by crystallization under high pressure, were subjected to uniaxial compression to various strains. Accompanying structural changes were analyzed using scanning electron microscopy. At the true strain of e = 0.2–0.3 the microbuckling instability was observed in longitudinally loaded lamellae, resulting in the formation of angular kinks. This induced a rapid reorientation of the lamellae, facilitating their further deformation by crystallographic slip. Microbuckling instability was found to occur earlier than in samples with folded-chain crystal morphology (e = 0.3–0.4) due to a smaller ratio of the amorphous to crystalline layer thickness. SEM observations demonstrated that the microbuckling instability begins with small undulation in long lamellae. Sharp angular lamellar kinks develop from the initial undulation through intense plastic deformation by crystallographic slip along the chain direction. The same slip system was found to operate throughout the kink, including the tip region as well as both limbs. In contrast to thin folded-chain lamellae that often undergo fragmentation during deformation, the thick extended-chain lamellae deform stably by chain slip and retain their continuity up to high strains, e > 1.6. This stability of deformation is related to the large thickness of extended-chain lamellae. Full article
(This article belongs to the Special Issue Plastics II)
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24 pages, 7223 KiB  
Review
Review on Heat Generation of Rubber Composites
by Ying Liu, Wenduo Chen and Dazhi Jiang
Polymers 2023, 15(1), 2; https://doi.org/10.3390/polym15010002 - 20 Dec 2022
Cited by 23 | Viewed by 5322
Abstract
Rubber composites are extensively used in industrial applications for their exceptional elasticity. The fatigue temperature rise occurs during operation, resulting in a serious decline in performance. Reducing heat generation of the composites during cyclic loading will help to avoid substantial overheating that most [...] Read more.
Rubber composites are extensively used in industrial applications for their exceptional elasticity. The fatigue temperature rise occurs during operation, resulting in a serious decline in performance. Reducing heat generation of the composites during cyclic loading will help to avoid substantial overheating that most likely results in the degradation of materials. Herein, we discuss the two main reasons for heat generation, including viscoelasticity and friction. Influencing factors of heat generation are highlighted, including the Payne effect, Mullins effect, interface interaction, crosslink density, bond rubber content, and fillers. Besides, theoretical models to predict the temperature rise are also analyzed. This work provides a promising way to achieve advanced rubber composites with high performance in the future. Full article
(This article belongs to the Special Issue Polymer Composite Analysis and Characterization II)
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15 pages, 10839 KiB  
Article
Advances in Rubber Compounds Using ZnO and MgO as Co-Cure Activators
by Md Najib Alam, Vineet Kumar and Sang-Shin Park
Polymers 2022, 14(23), 5289; https://doi.org/10.3390/polym14235289 - 3 Dec 2022
Cited by 34 | Viewed by 8903
Abstract
Zinc oxide performs as the best cure activator in sulfur-based vulcanization of rubber, but it is regarded as a highly toxic material for aquatic organisms. Hence, the toxic cure activator should be replaced by a non-toxic one. Still, there is no suitable alternative [...] Read more.
Zinc oxide performs as the best cure activator in sulfur-based vulcanization of rubber, but it is regarded as a highly toxic material for aquatic organisms. Hence, the toxic cure activator should be replaced by a non-toxic one. Still, there is no suitable alternative industrially. However, binary activators combining ZnO and another metal oxide such as MgO can largely reduce the level of ZnO with some improved benefits in the vulcanization of rubber as investigated in this research. Curing, mechanical, and thermal characteristics were investigated to find out the suitability of MgO in the vulcanization of rubber. Curing studies reveal that significant reductions in the optimum curing times are found by using MgO as a co-cure activator. Especially, the rate of vulcanization with conventional 5 phr (per hundred grams) ZnO can be enhanced by more than double, going from 0.3 Nm/min to 0.85 Nm/min by the use of a 3:2 ratio of MgO to ZnO cure activator system that should have high industrial importance. Mechanical and thermal properties investigations suggest that MgO as a co-cure activator used at 60% can provide 7.5% higher M100 (modulus at 100% strain) (0.58 MPa from 0.54 MPa), 20% higher tensile strength (23.7 MPa from 19.5 MPa), 15% higher elongation at break (1455% from 1270%), 68% higher fracture toughness (126 MJ/m3 from 75 MJ/m3), and comparable thermal stability than conventionally using 100 % ZnO. Especially, MgO as a co-cure activator could be very useful for improving the fracture toughness in rubber compounds compared to ZnO as a single-site curing activator. The significant improvements in the curing and mechanical properties suggest that MgO and ZnO undergo chemical interactions during vulcanization. Such rubber compounds can be useful in advanced tough and stretchable applications. Full article
(This article belongs to the Special Issue Advances in Functional Rubber and Elastomer Composites)
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21 pages, 7289 KiB  
Article
Efficient Physical Mixing of Small Amounts of Nanosilica Dispersion and Waterborne Polyurethane by Using Mild Stirring Conditions
by María Echarri-Giacchi and José Miguel Martín-Martínez
Polymers 2022, 14(23), 5136; https://doi.org/10.3390/polym14235136 - 25 Nov 2022
Cited by 4 | Viewed by 2716
Abstract
Good dispersion of nanosilica particles in waterborne polyurethane was obtained by mild mechanical stirring when 0.1–0.5 wt.% nanosilica in aqueous dispersion was added. The addition of small amounts of nanosilica produced more negative Z-potential values, increased the surface tension and decreased the Brookfield [...] Read more.
Good dispersion of nanosilica particles in waterborne polyurethane was obtained by mild mechanical stirring when 0.1–0.5 wt.% nanosilica in aqueous dispersion was added. The addition of small amounts of nanosilica produced more negative Z-potential values, increased the surface tension and decreased the Brookfield viscosity, as well as the extent of shear thinning of the waterborne polyurethane. Depending on the amount of nanosilica, the particle-size distributions of the waterborne polyurethanes changed differently and the addition of only 0.1 wt.% nanosilica noticeably increased the percentage of the particles of 298 nm in diameter. The DSC curves showed two melting peaks at 46 °C and 52 °C, as well as an increase in the melting enthalpy. In addition, when nanosilica was added, the crystallization peak of the waterborne polyurethane was displaced to a higher temperature and showed higher enthalpy. Furthermore, the addition of 0.1–0.5 wt.% nanosilica displaced the temperature of decomposition of the soft domains to higher temperatures due to the intercalation of the particles among the soft segments; this led to a change in the degree of phase separation of the waterborne polyurethanes. As a consequence, improved thermal stability and viscoelastic and mechanical properties of the waterborne polyurethanes were obtained. However, the addition of small amounts of nanosilica was detrimental for the wettability and adhesion of the waterborne polyurethanes due to the existence of acrylic moieties on the nanosilica particles, which seemed to migrate to the interface once the polyurethane was cross-linked. In fact, the final T-peel strength values of the joints made with the waterborne polyurethanes containing nanosilica were significantly lower than the one obtained with the waterborne polyurethane without nanosilica; the higher the nanosilica content, the lower the final adhesion. The better the nanosilica dispersion in the waterborne polyurethane+nanosilica, the higher the final T-peel strength value. Full article
(This article belongs to the Special Issue Advances in Multifunctional Polymer-Based Nanocomposites)
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22 pages, 7308 KiB  
Article
The Influence of Different Sustainable Silk-Based Fillers on the Thermal and Mechanical Properties of Polylactic Acid Composites
by José Miguel Ferri, Miguel Aldas, Emilio Rayon, Maria Dolores Samper and Antonio Abel Lozano-Pérez
Polymers 2022, 14(22), 5016; https://doi.org/10.3390/polym14225016 - 18 Nov 2022
Cited by 8 | Viewed by 3032
Abstract
In this work, different silk fillers combined with maleinized corn oil (MCO), as environmentally friendly plasticizers, were used to modify the mechanical and thermal properties of polylactic acid (PLA) composites. Melt extrusion and injection were used to obtain samples with a content of [...] Read more.
In this work, different silk fillers combined with maleinized corn oil (MCO), as environmentally friendly plasticizers, were used to modify the mechanical and thermal properties of polylactic acid (PLA) composites. Melt extrusion and injection were used to obtain samples with a content of 10 wt.% of MCO and 0.5 phr of different silk fillers: crushed silk (CS), silk fibroin microparticles (SFM), and silk fibroin nanoparticles (SFN). PLA formulation with 10 wt.% of MCO and 0.5 g of CS per hundred grams of composite (phr) showed the highest increase in mechanical ductile properties with an increase in elongation at break of approximately 1400%, compared with PLA. Differential scanning calorimetry (DSC) showed a decrease of 2 °C in their glass transition temperature with the addition of different silk fillers. In addition, SFM and SFN increase the degree of crystallinity of PLA. This increment was also confirmed by infrared spectroscopy analysis. Field emission scanning electron microscopy (FESEM) images revealed a good dispersion of the different silk fillers. Among them, PLA formulation with 10 wt.% MCO and 0.5 phr of SFN, showed an optimal balance between maximum resistance and elongation at break, with 52.0 MPa and 10.8%, respectively, improving elongation at break by 635%. Furthermore, all samples were satisfactorily disintegrated under composting conditions. Full article
(This article belongs to the Special Issue Polylactic Acid (PLA)-Based Materials)
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24 pages, 5772 KiB  
Article
Bio-Based Electrospun Fibers from Chitosan Schiff Base and Polylactide and Their Cu2+ and Fe3+ Complexes: Preparation and Antibacterial and Anticancer Activities
by Milena Ignatova, Ina Anastasova, Nevena Manolova, Iliya Rashkov, Nadya Markova, Rositsa Kukeva, Radostina Stoyanova, Ani Georgieva and Reneta Toshkova
Polymers 2022, 14(22), 5002; https://doi.org/10.3390/polym14225002 - 18 Nov 2022
Cited by 12 | Viewed by 2506
Abstract
The Schiff base derivative (Ch-8Q) of chitosan (Ch) and 8-hydroxyquinoline-2-carboxaldehyde (8QCHO) was prepared and fibrous mats were obtained by the electrospinning of Ch-8Q/polylactide (PLA) blend solutions in trifluoroacetic acid (TFA). Complexes of the mats were prepared by immersing them in a solution of [...] Read more.
The Schiff base derivative (Ch-8Q) of chitosan (Ch) and 8-hydroxyquinoline-2-carboxaldehyde (8QCHO) was prepared and fibrous mats were obtained by the electrospinning of Ch-8Q/polylactide (PLA) blend solutions in trifluoroacetic acid (TFA). Complexes of the mats were prepared by immersing them in a solution of CuCl2 or FeCl3. Electron paramagnetic resonance (EPR) analysis was performed to examine the complexation of Cu2+(Fe3+) in the Ch-8Q/PLA mats complexes. The morphology of the novel materials and their surface chemical composition were studied by scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The performed microbiological screening demonstrated that in contrast to the neat PLA mats, the Ch-8Q-containing mats and their complexes were able to kill all S. aureus bacteria within 3 h of contact. These fibrous materials had efficiency in suppressing the adhesion of pathogenic bacteria S. aureus. In addition, Ch-8Q/PLA mats and their complexes exerted good anticancer efficacy in vitro against human cervical HeLa cells and human breast MCF-7 cells. The Ch-8Q-containing fibrous materials had no cytotoxicity against non-cancer BALB/c 3T3 mouse fibroblast cells. These properties render the prepared materials promising as wound dressings as well as for application in local cancer treatment. Full article
(This article belongs to the Special Issue Development of Bio-Based Materials: Synthesis, Characterization, and Applications II)
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21 pages, 6288 KiB  
Article
Influence of Binder Composition and Material Extrusion (MEX) Parameters on the 3D Printing of Highly Filled Copper Feedstocks
by Mahrukh Sadaf, Santiago Cano, Joamin Gonzalez-Gutierrez, Mario Bragaglia, Stephan Schuschnigg, Christian Kukla, Clemens Holzer, Lilla Vály, Michael Kitzmantel and Francesca Nanni
Polymers 2022, 14(22), 4962; https://doi.org/10.3390/polym14224962 - 16 Nov 2022
Cited by 25 | Viewed by 4135
Abstract
This work aims to better understand the type of thermoplastic binders required to produce highly loaded copper filaments that can be successfully printed via low-cost filament-based material extrusion (MEX). Compounding feedstock material with 55 vol.% of copper and three multi-component binder systems has [...] Read more.
This work aims to better understand the type of thermoplastic binders required to produce highly loaded copper filaments that can be successfully printed via low-cost filament-based material extrusion (MEX). Compounding feedstock material with 55 vol.% of copper and three multi-component binder systems has been performed. The MEX behavior of these feedstocks was evaluated by depositing material at different speeds and appropriately selecting the extrusion temperature depending on the binder composition. The rest of the MEX parameters remained constant to evaluate the printing quality for the different feedstocks. Printable filaments were produced with low ovality and good surface quality. The filaments showed good dispersion of the powder and polymeric binder system in SEM analysis. The feedstock mechanical properties, i.e., the tensile strength of the filament, were sufficient to ensure proper feeding in the MEX machine. The viscosity of the feedstock systems at the adjusted printing temperatures lies in the range of 102–103 Pa·s at the shear rate of 100–1000 s−1, which appears to be sufficient to guarantee the correct flowability and continuous extrusion. The tensile properties vary greatly (e.g., ultimate tensile strength 3–9.8 MPa, elongation at break 1.5–40.5%), and the most fragile filament could not be reliably printed at higher speeds. Micrographs of the cross-section of printed parts revealed that as the printing speed increased, the porosity was minimized because the volumetric flow of the feedstock material increased, which can help to fill pores. This study offers new insights into the feedstock requirements needed to produce low-cost intricate copper components of high quality in a reliable and efficient manner. Such components can find many applications in the electronics, biomedical, and many other industries. Full article
(This article belongs to the Special Issue Sustainable Polymeric Composites: Fabrication and Application)
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15 pages, 5776 KiB  
Article
Analysis of Wear Phenomena Produced by Erosion with Abrasive Particles against Fluoropolymeric Coatings
by Guillermo Guerrero-Vaca and Oscar Rodríguez-Alabanda
Polymers 2022, 14(21), 4617; https://doi.org/10.3390/polym14214617 - 31 Oct 2022
Cited by 8 | Viewed by 2444
Abstract
To date, PTFE, PFA, and FEP-based fluoropolymer coatings have proven unbeatable in many services due to their excellent chemical inertness, very low wettability, thermal resistance, high non-stick properties, and good applicability. In use, these coatings usually suffer service cycles with consequent deterioration, and [...] Read more.
To date, PTFE, PFA, and FEP-based fluoropolymer coatings have proven unbeatable in many services due to their excellent chemical inertness, very low wettability, thermal resistance, high non-stick properties, and good applicability. In use, these coatings usually suffer service cycles with consequent deterioration, and it is of great interest to determine the intensity and type of wear caused in addition to the deterioration that occurs in their properties. In this work, the response of three polymeric coatings of interest applied to aluminum substrates, after being subjected to the action of abrasive particles of aluminum corundum, glass, and plastic projected under pressure, has been studied. During the application of a given wear cycle, the hardness, surface roughness, surface texture, and thickness of the coating have been measured, in addition to the slip angle and surface transmittance to analyze the evolution of each type of coating. The results allowed a concise evaluation of the performance of three fluoropolymeric coatings of great interest, differentiating the induced erosive wear phenomena and contributing complete information to facilitate the correct selection for users with practical application purposes and as a basis for future research work focused on advancements in this field. Full article
(This article belongs to the Special Issue Durability and Degradation of Polymeric Materials II)
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19 pages, 3853 KiB  
Article
Electrochemical Performance of Biopolymer-Based Hydrogel Electrolyte for Supercapacitors with Eco-Friendly Binders
by Giovanni Landi, Luca La Notte, Alessandro Lorenzo Palma and Giovanni Puglisi
Polymers 2022, 14(20), 4445; https://doi.org/10.3390/polym14204445 - 20 Oct 2022
Cited by 23 | Viewed by 3550
Abstract
An environmentally friendly hydrogel based on gelatin has been investigated as a gel polymer electrolyte in a symmetric carbon-based supercapacitor. To guarantee the complete sustainability of the devices, biomaterials from renewable resources (such as chitosan, casein and carboxymethyl cellulose) and activated carbon (from [...] Read more.
An environmentally friendly hydrogel based on gelatin has been investigated as a gel polymer electrolyte in a symmetric carbon-based supercapacitor. To guarantee the complete sustainability of the devices, biomaterials from renewable resources (such as chitosan, casein and carboxymethyl cellulose) and activated carbon (from coconut shells) have been used as a binder and filler within the electrode, respectively. The electrochemical properties of the devices have been compared by using cyclic voltammetry, galvanostatic charge/discharge curves and impedance spectroscopy. Compared to the liquid electrolyte, the hydrogel supercapacitors show similar energy performance with an enhancement of stability up to 12,000 cycles (e.g., chitosan as a binder). The most performant device can deliver ca. 5.2 Wh/kg of energy at a high power density of 1256 W/kg. A correlation between the electrochemical performances and charge storage mechanisms (involving faradaic and non-faradaic processes) at the interface electrode/hydrogel has been discussed. Full article
(This article belongs to the Special Issue Recent Progress on Polymer Electrolytes for Solar Cells and Supercapacitors)
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33 pages, 5442 KiB  
Review
Temperature-Responsive Polymer Brush Coatings for Advanced Biomedical Applications
by Svyatoslav Nastyshyn, Yuriy Stetsyshyn, Joanna Raczkowska, Yuriy Nastishin, Yuriy Melnyk, Yuriy Panchenko and Andrzej Budkowski
Polymers 2022, 14(19), 4245; https://doi.org/10.3390/polym14194245 - 10 Oct 2022
Cited by 45 | Viewed by 5273
Abstract
Modern biomedical technologies predict the application of materials and devices that not only can comply effectively with specific requirements, but also enable remote control of their functions. One of the most prospective materials for these advanced biomedical applications are materials based on temperature-responsive [...] Read more.
Modern biomedical technologies predict the application of materials and devices that not only can comply effectively with specific requirements, but also enable remote control of their functions. One of the most prospective materials for these advanced biomedical applications are materials based on temperature-responsive polymer brush coatings (TRPBCs). In this review, methods for the fabrication and characterization of TRPBCs are summarized, and possibilities for their application, as well as the advantages and disadvantages of the TRPBCs, are presented in detail. Special attention is paid to the mechanisms of thermo-responsibility of the TRPBCs. Applications of TRPBCs for temperature-switchable bacteria killing, temperature-controlled protein adsorption, cell culture, and temperature-controlled adhesion/detachment of cells and tissues are considered. The specific criteria required for the desired biomedical applications of TRPBCs are presented and discussed. Full article
(This article belongs to the Special Issue Polymer Brushes: Synthesis, Properties and Structure)
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15 pages, 5785 KiB  
Article
Synthesis of Optically and Redox Active Polyenaminones from Diamines and α,α’-Bis[(dimethylamino)methylidene]cyclohexanediones
by Urša Štanfel, Tomaž Kotnik, Sebastijan Ričko, Uroš Grošelj, Bogdan Štefane, Klemen Pirnat, Ema Žagar, Boštjan Genorio and Jurij Svete
Polymers 2022, 14(19), 4120; https://doi.org/10.3390/polym14194120 - 1 Oct 2022
Cited by 1 | Viewed by 2121
Abstract
New oligo- and polyenaminones with Mw ~ 7–50 KDa were prepared in high yields by transaminative amino-enaminone polymerization of regioisomeric bis[(dimethylamino)methylidene]cyclohexanediones with alkylene and phenylenediamines. The polymers obtained are practically insoluble in aqueous and organic solvents and exhibit film-forming properties, UV light [...] Read more.
New oligo- and polyenaminones with Mw ~ 7–50 KDa were prepared in high yields by transaminative amino-enaminone polymerization of regioisomeric bis[(dimethylamino)methylidene]cyclohexanediones with alkylene and phenylenediamines. The polymers obtained are practically insoluble in aqueous and organic solvents and exhibit film-forming properties, UV light absorption at wavelengths below 500 nm, and redox activity. These properties indicate a promising application potential of these polymers, which could find use in optical and optoelectronic applications and in energy storage devices. Full article
(This article belongs to the Special Issue Structural and Dynamic Properties of Synthetic Polymers in Complex Environments)
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14 pages, 3033 KiB  
Article
The Synthesis of Bio-Based Michael Donors from Tall Oil Fatty Acids for Polymer Development
by Ralfs Pomilovskis, Inese Mierina, Hynek Beneš, Olga Trhlíková, Arnis Abolins, Anda Fridrihsone and Mikelis Kirpluks
Polymers 2022, 14(19), 4107; https://doi.org/10.3390/polym14194107 - 30 Sep 2022
Cited by 6 | Viewed by 2634
Abstract
In this study, the synthesis of a Michael donor compound from cellulose production by-products—tall oil fatty acids—was developed. The developed Michael donor compounds can be further used to obtain polymeric materials after nucleophilic polymerization through the Michael reaction. It can be a promising [...] Read more.
In this study, the synthesis of a Michael donor compound from cellulose production by-products—tall oil fatty acids—was developed. The developed Michael donor compounds can be further used to obtain polymeric materials after nucleophilic polymerization through the Michael reaction. It can be a promising alternative method for conventional polyurethane materials, and the Michael addition polymerization reaction takes place under milder conditions than non-isocyanate polyurethane production technology, which requires high pressure, high temperature and a long reaction time. Different polyols, the precursors for Michael donor components, were synthesized from epoxidized tall oil fatty acids by an oxirane ring-opening and esterification reaction with different alcohols (trimethylolpropane and 1,4-butanediol). The addition of functional groups necessary for the Michael reaction was carried out by a transesterification reaction of polyol hydroxyl groups with tert-butyl acetoacetate ester. The following properties of the developed polyols and their acetoacetates were analyzed: hydroxyl value, acid value, moisture content and viscosity. The chemical structure was analyzed using Fourier transform infrared spectroscopy, gel permeation chromatography, size-exclusion chromatography and nuclear magnetic resonance. Matrix-assisted laser desorption/ionization analysis was used for structure identification for this type of acetoacetate for the first time. Full article
(This article belongs to the Special Issue Recent Advances in Polyurethane Materials)
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13 pages, 1480 KiB  
Article
Synthesis and Characterization of Quadrupolar-Hydrogen-Bonded Polymeric Ionic Liquids for Potential Self-Healing Electrolytes
by Chenming Li, Rajesh Bhandary, Anja Marinow, Dmitrii Ivanov, Mengxue Du, René Androsch and Wolfgang H. Binder
Polymers 2022, 14(19), 4090; https://doi.org/10.3390/polym14194090 - 29 Sep 2022
Cited by 9 | Viewed by 2935
Abstract
Within the era of battery technology, the urgent demand for improved and safer electrolytes is immanent. In this work, novel electrolytes, based on pyrrolidinium-bistrifluoromethanesulfonyl-imide polymeric ionic liquids (POILs), equipped with quadrupolar hydrogen-bonding moieties of ureido-pyrimidinone (UPy) to mediate self-healing properties were synthesized. Reversible [...] Read more.
Within the era of battery technology, the urgent demand for improved and safer electrolytes is immanent. In this work, novel electrolytes, based on pyrrolidinium-bistrifluoromethanesulfonyl-imide polymeric ionic liquids (POILs), equipped with quadrupolar hydrogen-bonding moieties of ureido-pyrimidinone (UPy) to mediate self-healing properties were synthesized. Reversible addition–fragmentation chain-transfer (RAFT) polymerization was employed using S,S-dibenzyl trithiocarbonate as the chain transfer agent to produce precise POILs with a defined amount of UPy and POIL-moieties. Kinetic studies revealed an excellent control over molecular weight and polydispersity in all polymerizations, with a preferable incorporation of UPy monomers in the copolymerizations together with the ionic monomers. Thermogravimetric analysis proved an excellent thermal stability of the polymeric ionic liquids up to 360 °C. By combining the results from differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS), and rheology, a decoupled conductivity of the POILs from glass transition was revealed. While the molecular weight was found to exert the main influence on ionic conductivity, the ultimate strength and the self-healing efficiency (of up to 88%) were also affected, as quantified by tensile tests for both pristine and self-healed samples, evidencing a rational design of self-healing electrolytes bearing both hydrogen bonding moieties and low-molecular-weight polymeric ionic liquids. Full article
(This article belongs to the Special Issue Polymeric Self-Healing Materials)
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17 pages, 2912 KiB  
Article
Ionic Push–Pull Polythiophenes: A Further Step towards Eco-Friendly BHJ Organic Solar Cells
by Martina Marinelli, Massimiliano Lanzi, Filippo Pierini, Yasamin Ziai, Alberto Zanelli, Debora Quadretti, Francesca Di Maria and Elisabetta Salatelli
Polymers 2022, 14(19), 3965; https://doi.org/10.3390/polym14193965 - 22 Sep 2022
Cited by 4 | Viewed by 2740
Abstract
Four new conjugated polymers alternating benzothiadiazole units and thiophene moieties functionalized with ionic phosphonium or sulfonic acid salts in the side chains were synthesized by a postfunctionalization approach of polymeric precursors. The introduction of ionic groups makes the conjugated polymers soluble in water [...] Read more.
Four new conjugated polymers alternating benzothiadiazole units and thiophene moieties functionalized with ionic phosphonium or sulfonic acid salts in the side chains were synthesized by a postfunctionalization approach of polymeric precursors. The introduction of ionic groups makes the conjugated polymers soluble in water and/or polar solvents, allowing for the fabrication of bulk heterojunction (BHJ) solar cells using environmentally friendly conditions. All polymers were fully characterized by spectroscopic, thermal, electrochemical, X-ray diffraction, scanning electron, and atomic force techniques. BHJ solar cells were obtained from halogen-free solvents (i.e., ethanol and/or anisole) by blending the synthesized ionic push–pull polymers with a serinol-fullerene derivative or an ionic homopolymer acting as electron-acceptor (EA) or electron-donor (ED) counterparts, respectively. The device with the highest optical density and the smoothest surface of the active layer was the best-performing, showing a 4.76% photoconversion efficiency. Full article
(This article belongs to the Special Issue Advance in New Energy Materials and Devices)
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13 pages, 4098 KiB  
Article
Quantitative Assessment of Tensile Strength and Degradation Coefficient of m-Aramid/p-Aramid Blended Yarns Used for Outer Layers of Firefighter Clothing under Ultraviolet Light and Correlation with Fabrics Data
by Kaoru Wakatsuki, Souta Onoda, Minami Matsubara, Norimichi Watanabe, Limin Bao and Hideaki Morikawa
Polymers 2022, 14(19), 3948; https://doi.org/10.3390/polym14193948 - 21 Sep 2022
Cited by 5 | Viewed by 2185
Abstract
The quantitative relationship between the fraction of UV exposure energy and the retention fraction of tensile strength was investigated on the m-Aramid/p-Aramid blend ratio of spun yarn. An exponential equation to calculate tensile strength from an arbitrary UV exposure energy is evaluated for [...] Read more.
The quantitative relationship between the fraction of UV exposure energy and the retention fraction of tensile strength was investigated on the m-Aramid/p-Aramid blend ratio of spun yarn. An exponential equation to calculate tensile strength from an arbitrary UV exposure energy is evaluated for yarns and fabrics. The spun yarns were exposed to UV light using a xenon-arc weathering meter. The retention fraction of tensile strength decreased exponentially with increasing the fraction of UV exposure energy. Curve fitting of the retention fraction of tensile strength to the fraction of UV exposure energy revealed two groups of degradation coefficients based on the blending ratio of m-Aramid/p-Aramid. The correlation between the degradation coefficients (αy and αf) of spun yarn and fabrics can be linearly regressed. The constant of proportionality in linear regression is considered to be the gap between the structure and the breaking mechanism of the fabric relative to yarn breakage. Based on the correlation between the degradation coefficients of spun yarn and fabrics and a mathematical model of the tensile strength of the spun yarn, the tensile strength of fabrics at a given UV exposure energy can be estimated from the tensile strength of the yarn. Full article
(This article belongs to the Special Issue Recent Development in Textiles and Fibers)
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27 pages, 9084 KiB  
Article
Biobased Copolyamides 56/66: Synthesis, Characterization and Crystallization Kinetics
by Chia-Hsiung Tseng and Ping-Szu Tsai
Polymers 2022, 14(18), 3879; https://doi.org/10.3390/polym14183879 - 17 Sep 2022
Cited by 18 | Viewed by 3762
Abstract
This study synthesized a series of new biobased copolyamides (co-PAs), namely PA56/PA66 with various comonomer ratios, by using in situ polycondensation. The structures, compositions, behaviors, and crystallization kinetics of the co-PAs were investigated through proton nuclear magnetic resonance (1H NMR) spectroscopy, [...] Read more.
This study synthesized a series of new biobased copolyamides (co-PAs), namely PA56/PA66 with various comonomer ratios, by using in situ polycondensation. The structures, compositions, behaviors, and crystallization kinetics of the co-PAs were investigated through proton nuclear magnetic resonance (1H NMR) spectroscopy, gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD). The influence of the composition of co-PAs on their mechanical properties and thermal stability was investigated. The co-PAs exhibited a eutectic melting point when the PA56 content was 50 mol%, with the crystallization temperature decreasing from 229 to a minimum 188 °C and the melting temperature from 253 to a minimum 218 °C. The results indicated that the tensile strength and flexural modulus first decreased and then increased as the PA66 content increased. The nonisothermal crystallization kinetics of the PA56/PA66 co-PAs were analyzed using both the Avrami equation modifications presented by Jeziorny and Mo. The results also indicated that the crystallization rate of the PA56/PA66 co-PAs was higher than that of PA56. Full article
(This article belongs to the Section Polymer Analysis and Characterization)
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17 pages, 6144 KiB  
Article
Cell-Laden Composite Hydrogel Bioinks with Human Bone Allograft Particles to Enhance Stem Cell Osteogenesis
by Hadis Gharacheh and Murat Guvendiren
Polymers 2022, 14(18), 3788; https://doi.org/10.3390/polym14183788 - 10 Sep 2022
Cited by 12 | Viewed by 3908
Abstract
There is a growing demand for bone graft substitutes that mimic the extracellular matrix properties of the native bone tissue to enhance stem cell osteogenesis. Composite hydrogels containing human bone allograft particles are particularly interesting due to inherent bioactivity of the allograft tissue. [...] Read more.
There is a growing demand for bone graft substitutes that mimic the extracellular matrix properties of the native bone tissue to enhance stem cell osteogenesis. Composite hydrogels containing human bone allograft particles are particularly interesting due to inherent bioactivity of the allograft tissue. Here, we report a novel photocurable composite hydrogel bioink for bone tissue engineering. Our composite bioink is formulated by incorporating human allograft bone particles in a methacrylated alginate formulation to enhance adult human mesenchymal stem cell (hMSC) osteogenesis. Detailed rheology and printability studies confirm suitability of our composite bioinks for extrusion-based 3D bioprinting technology. In vitro studies reveal high cell viability (~90%) for hMSCs up to 28 days of culture within 3D bioprinted composite scaffolds. When cultured within bioprinted composite scaffolds, hMSCs show significantly enhanced osteogenic differentiation as compared to neat scaffolds based on alkaline phosphatase activity, calcium deposition, and osteocalcin expression. Full article
(This article belongs to the Special Issue Composite Hydrogels towards Next-Generation Functional Materials and Devices)
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13 pages, 2481 KiB  
Article
Generation of Polyamide 12 Coatings on Stainless Steel Substrates by Directed Energy Deposition with a Thulium-Doped Fiber Laser (DED-LB/P)
by Alexander Wittmann, Oliver Hentschel, Alexander Sommereyns and Michael Schmidt
Polymers 2022, 14(18), 3729; https://doi.org/10.3390/polym14183729 - 7 Sep 2022
Cited by 7 | Viewed by 3043
Abstract
Due to their good material properties (e.g., corrosion and wear resistance, biocompatibility), thermoplastic materials like polyamide 12 (PA12) are interesting for functional coatings on metallic components. To ensure a spatially resolved coating and to shorten the process chain, directed energy deposition of polymer [...] Read more.
Due to their good material properties (e.g., corrosion and wear resistance, biocompatibility), thermoplastic materials like polyamide 12 (PA12) are interesting for functional coatings on metallic components. To ensure a spatially resolved coating and to shorten the process chain, directed energy deposition of polymer powders by means of a laser beam (DED-LB/P) offers a promising approach. Due to characteristic absorption bands, the use of a thulium fiber laser with a wavelength of 1.94 μm is investigated in a DED-LB/P setup to generate PA12 coatings on stainless steel substrates without the need to add any absorbing additives. The influence of the energy density and powder mass flow was analyzed by infrared thermography. Furthermore, the coatings were characterized by differential scanning calorimetry, laser-scanning-microscopy, optical microscopy and cross-cutting tests. The results in this study demonstrate for the first time the basic feasibility of an absorber-free DED-LB/P process by using a thulium fiber laser. PA12 coatings with a low porosity and good adhesion are achievable. Depending on the application-specific requirements, a trade-off must be made between the density and surface quality of the PA12 coatings. The use of infrared thermography is appropriate for in-situ detection of process instabilities caused by an excessive energy input. Full article
(This article belongs to the Section Polymer Processing and Engineering)
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13 pages, 4076 KiB  
Article
Bio-Based pH Indicator Films for Intelligent Food Packaging Applications
by Iulia Păușescu, Diana-Maria Dreavă, Ioan Bîtcan, Raluca Argetoianu, Diana Dăescu and Mihai Medeleanu
Polymers 2022, 14(17), 3622; https://doi.org/10.3390/polym14173622 - 1 Sep 2022
Cited by 17 | Viewed by 6735
Abstract
The widespread concerns about the environmental problems caused by conventional plastic food packaging and food waste led to a growing effort to develop active and intelligent systems produced from renewable biodegradable polymers for food packaging applications. Among intelligent systems, the most widely used [...] Read more.
The widespread concerns about the environmental problems caused by conventional plastic food packaging and food waste led to a growing effort to develop active and intelligent systems produced from renewable biodegradable polymers for food packaging applications. Among intelligent systems, the most widely used are pH indicators, which are generally based on a pH-sensitive dye incorporated into a solid support. The objective of this study was to develop new intelligent systems based on renewable biodegradable polymers and a new bio-inspired pH-sensitive dye. The structure of the dye was elucidated through FT-IR and 1D and 2D NMR spectroscopic analyses. UV-VIS measurements of the dye solutions at various pH values proved their halochromic properties. Their toxicity was evaluated through theoretical calculations, and no toxicity risks were found. The new anthocyanidin was used for the development of biodegradable intelligent systems based on chitosan blends. The obtained polymeric films were characterized through UV-VIS and FT-IR spectroscopy. Their thermal properties were assessed through a thermogravimetric analysis, which showed a better stability of chitosan–PVA–dye and chitosan–starch–dye films compared to those of chitosan–cellulose–dye films and the dye itself. The films’ sensitivity to pH variations was evaluated through immersion in buffer solutions with pH values ranging from 2 to 12, and visible color changes were observed. Full article
(This article belongs to the Special Issue Biodegradable Polymer Composites: Fabrication and Applications)
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28 pages, 4424 KiB  
Article
Modeling of Hexavalent Chromium Removal with Hydrophobically Modified Cellulose Nanofibers
by Francisco de Borja Ojembarrena, Jose Luis Sánchez-Salvador, Sergio Mateo, Ana Balea, Angeles Blanco, Noemí Merayo and Carlos Negro
Polymers 2022, 14(16), 3425; https://doi.org/10.3390/polym14163425 - 22 Aug 2022
Cited by 14 | Viewed by 3052
Abstract
Cellulose nanofibers (CNF) are sustainable nanomaterials, obtained by the mechanical disintegration of cellulose, whose properties make them an interesting adsorbent material due to their high specific area and active groups. CNF are easily functionalized to optimize the performance for different uses. The hypothesis [...] Read more.
Cellulose nanofibers (CNF) are sustainable nanomaterials, obtained by the mechanical disintegration of cellulose, whose properties make them an interesting adsorbent material due to their high specific area and active groups. CNF are easily functionalized to optimize the performance for different uses. The hypothesis of this work is that hydrophobization can be used to improve their ability as adsorbents. Therefore, hydrophobic CNF was applied to adsorb hexavalent chromium from wastewater. CNF was synthetized by TEMPO-mediated oxidation, followed by mechanical disintegration. Hydrophobization was performed using methyl trimetoxysilane (MTMS) as a hydrophobic coating agent. The adsorption treatment of hexavalent chromium with hydrophobic CNF was optimized by studying the influence of contact time, MTMS dosage (0–3 mmol·g−1 CNF), initial pH of the wastewater (3–9), initial chromium concentration (0.10–50 mg·L−1), and adsorbent dosage (250–1000 mg CNF·L−1). Furthermore, the corresponding adsorption mechanism was identified. Complete adsorption of hexavalent chromium was achieved with CNF hydrophobized with 1.5 mmol MTMS·g−1 CNF with the faster adsorption kinetic, which proved the initial hypothesis that hydrophobic CNF improves the adsorption capacity of hydrophilic CNF. The optimal adsorption conditions were pH 3 and the adsorbent dosage was over 500 mg·L−1. The maximum removal was found for the initial concentrations of hexavalent chromium below 1 mg·L−1 and a maximum adsorption capacity of 70.38 mg·g−1 was achieved. The kinetic study revealed that pseudo-second order kinetics was the best fitting model at a low concentration while the intraparticle diffusion model fit better for higher concentrations, describing a multi-step mechanism of hexavalent chromium onto the adsorbent surface. The Freundlich isotherm was the best adjustment model. Full article
(This article belongs to the Special Issue Polymeric Materials for Wastewater Treatment Applications)
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15 pages, 2920 KiB  
Article
Investigation into Biosorption of Pharmaceuticals from Aqueous Solutions by Biocomposite Material Based on Microbial Biomass and Natural Polymer: Process Variables Optimization and Kinetic Studies
by Lăcrămioara Rusu, Cristina-Gabriela Grigoraș, Andrei-Ionuț Simion, Elena-Mirela Suceveanu, Carol Schnakovszky and Lidia Favier
Polymers 2022, 14(16), 3388; https://doi.org/10.3390/polym14163388 - 19 Aug 2022
Cited by 1 | Viewed by 2563
Abstract
Biosorbtive removal of the antibacterial drug, ethacridine lactate (EL), from aqueous solutions was investigated using as biosorbent Saccharomyces pastorianus residual biomass immobilized in calcium alginate. The aim of this work was to optimize the biosorption process and to evaluate the biosorption capacity in [...] Read more.
Biosorbtive removal of the antibacterial drug, ethacridine lactate (EL), from aqueous solutions was investigated using as biosorbent Saccharomyces pastorianus residual biomass immobilized in calcium alginate. The aim of this work was to optimize the biosorption process and to evaluate the biosorption capacity in the batch system. Response surface methodology, based on a Box–Behnken design, was used to optimize the EL biosorption parameters. Two response functions (removal efficiency and biosorption capacity) were maximized dependent on three factors: initial concentration of EL solution, contact time, and agitation speed. The highest values for the studied functions (89.49%, 26.04 mg/g) were obtained in the following operational conditions: EL initial concentration: 59.73 mg/L; contact time: 94.26 min; agitation speed: 297.57 rpm. A number of nonlinear kinetic models, including pseudo-first-order, pseudo-second-order, Elovich, and Avrami, were utilized to validate the biosorption kinetic behavior of EL in the optimized conditions. The kinetic data fitted the pseudo-first-order and Avrami models. The experimental results demonstrated that the optimized parameters (especially the agitation speed) significantly affect biosorption and should be considered important in such studies. Full article
(This article belongs to the Special Issue Polymer Composites for Biomedical and Environmental Applications)
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19 pages, 3748 KiB  
Article
Improvement of Interfacial Adhesion and Thermomechanical Properties of PLA Based Composites with Wheat/Rice Bran
by Vito Gigante, Laura Aliotta, Ilaria Canesi, Marco Sandroni, Andrea Lazzeri, Maria-Beatrice Coltelli and Patrizia Cinelli
Polymers 2022, 14(16), 3389; https://doi.org/10.3390/polym14163389 - 19 Aug 2022
Cited by 13 | Viewed by 3137
Abstract
The present work aims to enhance the use of agricultural byproducts for the production of bio-composites by melt extrusion. It is well known that in the production of such bio-composites, the weak point is the filler-matrix interface, for this reason the adhesion between [...] Read more.
The present work aims to enhance the use of agricultural byproducts for the production of bio-composites by melt extrusion. It is well known that in the production of such bio-composites, the weak point is the filler-matrix interface, for this reason the adhesion between a polylactic acid (PLA)/poly(butylene succinate)(PBSA) blend and rice and wheat bran platelets was enhanced by a treatment method applied on the fillers using a suitable beeswax. Moreover, the coupling action of beeswax and inorganic fillers (such as talc and calcium carbonate) were investigated to improve the thermo-mechanical properties of the final composites. Through rheological (MFI), morphological (SEM), thermal (TGA, DSC), mechanical (Tensile, Impact), thermomechanical (HDT) characterizations and the application of analytical models, the optimum among the tested formulations was then selected. Full article
(This article belongs to the Special Issue Biobased and Biodegradable Polymer Blends and Composites)
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19 pages, 4362 KiB  
Article
First Insights into the Antiviral Activity of Chitosan-Based Bioactive Polymers towards the Bacteriophage Phi6: Physicochemical Characterization, Inactivation Potential, and Inhibitory Mechanisms
by Olivija Plohl, Katja Fric, Arijana Filipić, Polona Kogovšek, Magda Tušek Žnidarič and Lidija Fras Zemljič
Polymers 2022, 14(16), 3357; https://doi.org/10.3390/polym14163357 - 17 Aug 2022
Cited by 11 | Viewed by 2765
Abstract
The outbreak of the worrisome coronavirus disease in 2019 has caused great concern among the global public, especially regarding the need for personal protective equipment with applied antiviral agents to reduce the spread and transmission of the virus. Thus, in our research, chitosan-based [...] Read more.
The outbreak of the worrisome coronavirus disease in 2019 has caused great concern among the global public, especially regarding the need for personal protective equipment with applied antiviral agents to reduce the spread and transmission of the virus. Thus, in our research, chitosan-based bioactive polymers as potential antiviral agents were first evaluated as colloidal macromolecular solutions by elemental analysis and charge. Three different types of low and high molecular weight chitosan (LMW Ch, HMW Ch) and a LMW Ch derivative, i.e., quaternary chitosan (quart-LMW Ch), were used. To explore their antiviral activity for subsequent use in the form of coatings, the macromolecular Chs dispersions were incubated with the model virus phi6 (surrogate for SARS-CoV-2), and the success of virus inactivation was determined. Inactivation of phi6 with some chitosan-based compounds was very successful (>6 log), and the mechanisms behind this were explored. The changes in viral morphology after incubation were observed and the changes in infrared bands position were determined. In addition, dynamic and electrophoretic light scattering studies were performed to better understand the interaction between Chs and phi6. The results allowed us to better understand the antiviral mode of action of Chs agents as a function of their physicochemical properties. Full article
(This article belongs to the Section Biobased and Biodegradable Polymers)
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15 pages, 6853 KiB  
Article
A Tumor Accelerator Based on Multicomponent Bone Scaffolds and Cancer Cell Homing
by Chen-Ji Huang, Pei-Kuan Chou, Zong-Yi Sher, You-Rong Chen, Tan-Yueh Chen and Guo-Chung Dong
Polymers 2022, 14(16), 3340; https://doi.org/10.3390/polym14163340 - 16 Aug 2022
Cited by 1 | Viewed by 2265
Abstract
Bone tissue attracts cancer cell homing biologically, mechanically, or chemically. It is difficult and time consuming to identify their complex cross-talk using existed methods. In this study, a multi-component bone matrix was fabricated using gelatin, hydroxyapatite (HAp), and epidermal growth factor (EGF) as [...] Read more.
Bone tissue attracts cancer cell homing biologically, mechanically, or chemically. It is difficult and time consuming to identify their complex cross-talk using existed methods. In this study, a multi-component bone matrix was fabricated using gelatin, hydroxyapatite (HAp), and epidermal growth factor (EGF) as raw materials to investigate how “acellular” bone matrix affects cancer cell homing in bone. Then, EGF-responsive cancer cells were cultured with the scaffold in a dynamical bioreactor. For different culture periods, the effects of HAp, gelatin, and EGF on the cell adhesion, proliferation, 3D growth, and migration of cancer were evaluated. The results indicated that a small amount of calcium ion released from the scaffolds accelerated cancer MDA-MB-231 adhesion on the surface of inner pores. Moreover, degradable gelatin key caused cancer cell growth on the scaffold surface to turn into a 3D aggregation. Despite this, the formation of cancer spheroids was slow, and required 14 days of dynamic culture. Thankfully, EGF promoted cancer cell adhesion, proliferation, and migration, and cancer spheroids were observed only after 3-day culture. We concluded that the combination of the multiple components in this scaffold allows cancer cells to meet multiple requirements of cancer dynamic progression. Full article
(This article belongs to the Special Issue Nanomaterials Template for Organic or Composite Polymers in Biomedical Application II)
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16 pages, 4703 KiB  
Article
AI-Based Soft Module for Safe Human–Robot Interaction towards 4D Printing
by Ali Zolfagharian, Mohammad Reza Khosravani, Hoang Duong Vu, Minh Khoi Nguyen, Abbas Z. Kouzani and Mahdi Bodaghi
Polymers 2022, 14(16), 3302; https://doi.org/10.3390/polym14163302 - 13 Aug 2022
Cited by 12 | Viewed by 3313
Abstract
Soft robotic modules have potential use for therapeutic and educational purposes. To do so, they need to be safe, soft, smart, and customizable to serve individuals’ different preferences and personalities. A safe modular robotic product made of soft materials, particularly silicon, programmed by [...] Read more.
Soft robotic modules have potential use for therapeutic and educational purposes. To do so, they need to be safe, soft, smart, and customizable to serve individuals’ different preferences and personalities. A safe modular robotic product made of soft materials, particularly silicon, programmed by artificial intelligence algorithms and developed via additive manufacturing would be promising. This study focuses on the safe tactile interaction between humans and robots by means of soft material characteristics for translating physical communication to auditory. The embedded vibratory sensors used to stimulate touch senses transmitted through soft materials are presented. The soft module was developed and verified successfully to react to three different patterns of human–robot contact, particularly users’ touches, and then communicate the type of contact with sound. The study develops and verifies a model that can classify different tactile gestures via machine learning algorithms for safe human–robot physical interaction. The system accurately recognizes the gestures and shapes of three-dimensional (3D) printed soft modules. The gestures used for the experiment are the three most common, including slapping, squeezing, and tickling. The model builds on the concept of how safe human–robot physical interactions could help with cognitive and behavioral communication. In this context, the ability to measure, classify, and reflect the behavior of soft materials in robotic modules represents a prerequisite for endowing robotic materials in additive manufacturing for safe interaction with humans. Full article
(This article belongs to the Special Issue Frontiers in 3D and 4D Printing for Polymers and Polymeric Composites)
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17 pages, 9664 KiB  
Article
A Sustainable Approach to a Cleaner Production of Antimicrobial and Biocompatible Protein Fibers
by Angela Danila, Mariana Costea, Lenuta Profire, Cristina Mihaela Rimbu, Mihaela Baican, Florentina Lupascu, Simona-Maria Tatarusanu, Bianca-Stefania Profire and Emil-Ioan Muresan
Polymers 2022, 14(15), 3194; https://doi.org/10.3390/polym14153194 - 5 Aug 2022
Cited by 2 | Viewed by 2465
Abstract
This study presents the production, characterization, and application of celandine (Chelidonium majus L.) extracts (aqueous, acidic, alcoholic, and ultrasound) on wool fibers and their characterization. The study aims to obtain an ecologically dyed wool support that possesses biocompatible and antimicrobial activities. The [...] Read more.
This study presents the production, characterization, and application of celandine (Chelidonium majus L.) extracts (aqueous, acidic, alcoholic, and ultrasound) on wool fibers and their characterization. The study aims to obtain an ecologically dyed wool support that possesses biocompatible and antimicrobial activities. The plant extracts were characterized based on pH, total polyphenol content, and berberine content. Ecologically dyed wool supports were characterized based on scanning electron microscopy, levelness index, color measurements, contact angle indirect biocompatibility, and antibacterial analysis. According to the obtained results, celandine extract can be considered a potential candidate for the sustainable dyeing and functionalization of wool fibers. Full article
(This article belongs to the Special Issue Advances in Sustainable Polymers: Processing, Modeling, Properties and Applications)
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16 pages, 6424 KiB  
Article
Biochar Particles Obtained from Agricultural Carob Waste as a Suitable Filler for Sustainable Biocomposite Formulations
by Giulia Infurna, Luigi Botta, Marco Maniscalco, Elisabetta Morici, Giuseppe Caputo, Salvatore Marullo, Francesca D’Anna and Nadka Tz. Dintcheva
Polymers 2022, 14(15), 3075; https://doi.org/10.3390/polym14153075 - 29 Jul 2022
Cited by 15 | Viewed by 2701
Abstract
In the context of sustainable and circular economy, the recovery of biowaste for sustainable biocomposites formulation is a challenging issue. The aim of this work is to give a new life to agricultural carob waste after glucose extraction carried out by a local [...] Read more.
In the context of sustainable and circular economy, the recovery of biowaste for sustainable biocomposites formulation is a challenging issue. The aim of this work is to give a new life to agricultural carob waste after glucose extraction carried out by a local factory for carob candy production. A pyrolysis process was carried out on bio-waste to produce biofuel and, later, the solid residual fraction of pyrolysis process was used as interesting filler for biocomposites production. In this work, biochar particles (BC) as a pyrolysis product, after fuels recovery of organic biowaste, specifically, pyrolyzed carobs after glucose extraction, were added on poly(butylene-adipate-co-terephthalate), (PBAT), at two different concentrations, i.e., 10 and 20 wt%. The BC have been produced using three pyrolysis processing temperatures (i.e., 280, 340 and 400 °C) to optimize the compositions of produced solid fractions and biofuels. The resulting particles from the pyrolysis process (BC280, BC340 and BC400) were considered as suitable fillers for PBAT. Firstly, the BC particles properties were characterized by elemental composition and spectroscopy analysis, particle size measurements and evaluation of radical scavenging activity and efficiency. Moreover, PBAT/BC composites were subjected to analysis of their rheological and thermal behavior, morphologies and mechanical properties. In addition, accelerated weathering, monitored by both tensile test and spectroscopic analysis, was carried out, and obtained results show that the biochar particles can exert a beneficial effect on photo-oxidation delay of PBAT matrix. Full article
(This article belongs to the Special Issue Biodegradable Polymer Composites)
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30 pages, 1610 KiB  
Review
Novel Trends in Hydrogel Development for Biomedical Applications: A Review
by Pablo Sánchez-Cid, Mercedes Jiménez-Rosado, Alberto Romero and Víctor Pérez-Puyana
Polymers 2022, 14(15), 3023; https://doi.org/10.3390/polym14153023 - 26 Jul 2022
Cited by 192 | Viewed by 15716
Abstract
Nowadays, there are still numerous challenges for well-known biomedical applications, such as tissue engineering (TE), wound healing and controlled drug delivery, which must be faced and solved. Hydrogels have been proposed as excellent candidates for these applications, as they have promising properties for [...] Read more.
Nowadays, there are still numerous challenges for well-known biomedical applications, such as tissue engineering (TE), wound healing and controlled drug delivery, which must be faced and solved. Hydrogels have been proposed as excellent candidates for these applications, as they have promising properties for the mentioned applications, including biocompatibility, biodegradability, great absorption capacity and tunable mechanical properties. However, depending on the material or the manufacturing method, the resulting hydrogel may not be up to the specific task for which it is designed, thus there are different approaches proposed to enhance hydrogel performance for the requirements of the application in question. The main purpose of this review article was to summarize the most recent trends of hydrogel technology, going through the most used polymeric materials and the most popular hydrogel synthesis methods in recent years, including different strategies of enhancing hydrogels’ properties, such as cross-linking and the manufacture of composite hydrogels. In addition, the secondary objective of this review was to briefly discuss other novel applications of hydrogels that have been proposed in the past few years which have drawn a lot of attention. Full article
(This article belongs to the Collection Hydrogels)
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22 pages, 7645 KiB  
Article
Development of an Injection Molding Process for Long Glass Fiber-Reinforced Phenolic Resins
by Robert Maertens, Wilfried V. Liebig, Kay A. Weidenmann and Peter Elsner
Polymers 2022, 14(14), 2890; https://doi.org/10.3390/polym14142890 - 16 Jul 2022
Cited by 6 | Viewed by 4152
Abstract
Glass fiber-reinforced phenolic resins are well suited to substitute aluminum die-cast materials. They meet the high thermomechanical and chemical demands that are typically found in combustion engine and electric drive train applications. An injection molding process development for further improving their mechanical properties [...] Read more.
Glass fiber-reinforced phenolic resins are well suited to substitute aluminum die-cast materials. They meet the high thermomechanical and chemical demands that are typically found in combustion engine and electric drive train applications. An injection molding process development for further improving their mechanical properties by increasing the glass fiber length in the molded part was conducted. A novel screw mixing element was developed to improve the homogenization of the long fibers in the phenolic resin. The process operation with the mixing element is a balance between the desired mixing action, an undesired preliminary curing of the phenolic resin, and the reduction of the fiber length. The highest mixing energy input leads to a reduction of the initial fiber length L0 = 5000 μm to a weighted average fiber length of Lp = 571 μm in the molded part. This is an improvement over Lp = 285 μm for a short fiber-reinforced resin under comparable processing conditions. The mechanical characterization shows that for the long fiber-reinforced materials, the benefit of the increased homogeneity outweighs the disadvantages of the reduced fiber length. This is evident from the increase in tensile strength from σm = 21 MPa to σm = 57 MPa between the lowest and the highest mixing energy input parameter settings. Full article
(This article belongs to the Special Issue Injection Molding of Polymers and Polymer Composites)
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20 pages, 6258 KiB  
Article
The Effect of Physical Aging and Degradation on the Re-Use of Polyamide 12 in Powder Bed Fusion
by Benjamin Sanders, Edward Cant, Hoda Amel and Michael Jenkins
Polymers 2022, 14(13), 2682; https://doi.org/10.3390/polym14132682 - 30 Jun 2022
Cited by 22 | Viewed by 5187
Abstract
Powder bed fusion (PBF) is an additive manufacturing (AM) technique which offers efficient part-production, light-weighting, and the ability to create complex geometries. However, during a build cycle, multiple aging and degradation processes occur which may affect the reusability of the Polyamide 12 (PA-12) [...] Read more.
Powder bed fusion (PBF) is an additive manufacturing (AM) technique which offers efficient part-production, light-weighting, and the ability to create complex geometries. However, during a build cycle, multiple aging and degradation processes occur which may affect the reusability of the Polyamide 12 (PA-12) powder. Limited understanding of these phenomena can result in discarding re-usable powder unnecessarily, or the production of parts with insufficient properties, both of which lead to significant amounts of waste. This paper examines the thermal, chemical, and mechanical characteristics of PA-12 via an oven storage experiment that simulates multi jet fusion (MJF) conditions. Changes in the properties of PA-12 powder during oven storage showed two separate, time-dependent trends. Initially, differential scanning calorimetry showed a 4.2 °C increase in melting temperature (Tm) and a rise in crystallinity (Xc). This suggests that secondary crystallisation is occurring instead of, or in addition to, the more commonly reported further polycondensation process. However, with extended storage time, there were substantial reductions in Tm and Xc, whilst an 11.6 °C decrease in crystallisation temperature was observed. Fourier transform infrared spectroscopy, a technique rarely used in PBF literature, shows an increased presence of imide bonds—a key marker of thermo-oxidative degradation. Discolouration of samples, an 81% reduction in strength and severe material embrittlement provided further evidence that thermo-oxidative degradation becomes the dominant process following extended storage times beyond 100 h. An additional pre-drying experiment showed how moisture present within PA-12 can also accelerate degradation via hydrolysis. Full article
(This article belongs to the Special Issue Structure-Property Relationship of Polymer Materials)
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15 pages, 6104 KiB  
Article
Chitin Nanocrystal Hydrophobicity Adjustment by Fatty Acid Esterification for Improved Polylactic Acid Nanocomposites
by Ivanna Colijn, Murat Yanat, Geertje Terhaerdt, Karin Molenveld, Carmen G. Boeriu and Karin Schroën
Polymers 2022, 14(13), 2619; https://doi.org/10.3390/polym14132619 - 28 Jun 2022
Cited by 15 | Viewed by 3152
Abstract
Bioplastics may solve environmental issues related to the current linear plastic economy, but they need improvement to be viable alternatives. To achieve this, we aimed to add chitin nanocrystals (ChNC) to polylactic acid (PLA), which is known to alter material properties while maintaining [...] Read more.
Bioplastics may solve environmental issues related to the current linear plastic economy, but they need improvement to be viable alternatives. To achieve this, we aimed to add chitin nanocrystals (ChNC) to polylactic acid (PLA), which is known to alter material properties while maintaining a fully bio-based character. However, ChNC are not particularly compatible with PLA, and surface modification with fatty acids was used to improve this. We used fatty acids that are different in carbon chain length (C4–C18) and degree of saturation (C18:2). We successfully used Steglich esterification and confirmed covalent attachment of fatty acids to the ChNC with FTIR and solid-state 13C NMR. The morphology of the ChNC remained intact after surface modification, as observed by TEM. ChNC modified with C4 and C8 showed higher degrees of substitution compared to fatty acids with a longer aliphatic tail, while particles modified with the longest fatty acid showed the highest hydrophobicity. The addition of ChNC to the PLA matrix resulted in brown color formation that was reduced when using modified particles, leading to higher transparency, most probably as a result of better dispersibility of modified ChNC, as observed by SEM. In general, addition of ChNC provided high UV-protection to the base polymer material, which is an additional feature that can be created through the addition of ChNC, which is not at the expense of the barrier properties, or the mechanical strength. Full article
(This article belongs to the Special Issue Bio-Based and Biodegradable Polymeric Composites: Synthesis, Characterization and Applications)
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19 pages, 4294 KiB  
Article
Influence of Thermal Annealing Temperatures on Powder Mould Effectiveness to Avoid Deformations in ABS and PLA 3D-Printed Parts
by Joaquín Lluch-Cerezo, María Desamparados Meseguer, Juan Antonio García-Manrique and Rut Benavente
Polymers 2022, 14(13), 2607; https://doi.org/10.3390/polym14132607 - 27 Jun 2022
Cited by 21 | Viewed by 3515
Abstract
Fused deposition modelling (FDM)-printed parts can be treated with various post-processes to improve their mechanical properties, dimensional accuracy and surface finish. Samples of polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) parts are treated with annealing to study a ceramic powder mould’s effectiveness [...] Read more.
Fused deposition modelling (FDM)-printed parts can be treated with various post-processes to improve their mechanical properties, dimensional accuracy and surface finish. Samples of polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) parts are treated with annealing to study a ceramic powder mould’s effectiveness in order to avoid dimensional part deformation. The variables chosen are annealing temperatures and the usage of a ceramic powder mould to avoid part deformations. A flexural strength test was carried out to evaluate the mould’s influence on the mechanical properties of the part. The effectiveness of the mould has been evaluated mainly attending to the length of the part, because this is the dimension most affected by deformation. A polynomial approximation to a deformation’s length and the effectiveness of the mould allows for their prediction. Results obtained show that effectiveness increases with the annealing temperature. Nevertheless, mould effectiveness decreases when parts are fabricated with PLA, because it is a semi-crystalline thermoplastic, and it suffers a lower shrinkage during thermal post-process than amorphous polymers such as ABS. Attending to the flexural strength test, mould has no significant influence on the mechanical properties of the treated parts in both materials studied. Full article
(This article belongs to the Special Issue New Advances in Polymer Materials for Product Design Processes and Additive Manufacturing)
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12 pages, 1120 KiB  
Article
Experimental Investigation of the Different Polyacrylamide Dosages on Soil Water Movement under Brackish Water Infiltration
by Jihong Zhang, Quanjiu Wang, Weiyi Mu, Kai Wei, Yi Guo and Yan Sun
Polymers 2022, 14(12), 2495; https://doi.org/10.3390/polym14122495 - 19 Jun 2022
Cited by 11 | Viewed by 2260
Abstract
The use of soil conditioners in conjunction with brackish water irrigation is critical for the efficient development and use of brackish water as well as the enhancement of the structure of saline soil and stimulating crop growth. This study investigated the effects of [...] Read more.
The use of soil conditioners in conjunction with brackish water irrigation is critical for the efficient development and use of brackish water as well as the enhancement of the structure of saline soil and stimulating crop growth. This study investigated the effects of different polyacrylamide (PAM) dosages (0, 0.02%, 0.04%, and 0.06%) on the water flow properties of sandy loam during brackish water infiltration using one-dimensional vertical and horizontal soil column infiltration experiments. The results showed that: (1) PAM could lower the soil infiltration rate and increase soil water retention performance under brackish water infiltration conditions. (2) PAM had a significant effect on the parameters of the Philip and Kostiakov infiltration models. The soil sorption rate S and the empirical coefficient λ were the smallest, and the empirical index β was the largest when the PAM dosage was 0.04%. (3) PAM dosage displayed a quadratic polynomial connection with the soil saturated water content and the saturated hydraulic conductivity. The soil saturated water content was highest when the PAM dosage was 0.04%, the intake suction hd of the Brooks-Corey model increased by 15.30%, and the soil water holding capacity was greatly improved. (4) Soil treated with PAM could absorb more water under the same soil water suction, whereas the soil unsaturated hydraulic conductivity and its growth rate decreased. The soil saturated diffusion rate Ds, as well as the soil water diffusion threshold, rose. Finally, the 0.04% PAM dosage could improve soil hydrodynamic characteristics under brackish water infiltration, which is beneficial for the efficient utilization of brackish water. Full article
(This article belongs to the Special Issue Preparation, Structure and Characterization of Polymer/Cement Composites)
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13 pages, 2698 KiB  
Article
Synthesis and Thermal Analysis of Non-Covalent PS-b-SC-b-P2VP Triblock Terpolymers via Polylactide Stereocomplexation
by Ameen Arkanji, Viko Ladelta, Konstantinos Ntetsikas and Nikos Hadjichristidis
Polymers 2022, 14(12), 2431; https://doi.org/10.3390/polym14122431 - 15 Jun 2022
Cited by 6 | Viewed by 2541
Abstract
Polylactides (PLAs) are thermoplastic materials known for their wide range of applications. Moreover, the equimolar mixtures of poly(L-Lactide) (PLLA) and poly(D-Lactide) (PDLA) can form stereocomplexes (SCs), which leads to the formation of new non-covalent complex macromolecular architectures. In this work, we report the [...] Read more.
Polylactides (PLAs) are thermoplastic materials known for their wide range of applications. Moreover, the equimolar mixtures of poly(L-Lactide) (PLLA) and poly(D-Lactide) (PDLA) can form stereocomplexes (SCs), which leads to the formation of new non-covalent complex macromolecular architectures. In this work, we report the synthesis and characterization of non-covalent triblock terpolymers of polystyrene-b-stereocomplex PLA-b-poly(2-vinylpyridine) (PS-b-SC-b-P2VP). Well-defined ω-hydroxy-PS and P2VP were synthesized by “living” anionic polymerization high-vacuum techniques with sec-BuLi as initiator, followed by termination with ethylene oxide. The resulting PS-OH and P2VP-OH were used as macroinitiators for the ring-opening polymerization (ROP) of DLA and LLA with Sn(Oct)2 as a catalyst to afford PS-b-PDLA and P2VP-b-PLLA, respectively. SC formation was achieved by mixing PS-b-PDLA and P2VP-b-PLLA chloroform solutions containing equimolar PLAs segments, followed by precipitation into n-hexane. The molecular characteristics of the resulting block copolymers (BCPs) were determined by 1H NMR, size exclusion chromatography, and Fourier-transform infrared spectroscopy. The formation of PS-b-SC-b-P2VP and the effect of molecular weight variation of PLA blocks on the resulting polymers, were investigated by differential scanning calorimetry, X-ray powder diffraction, and circular dichroism spectroscopies. Full article
(This article belongs to the Special Issue Advances and Applications of Block Copolymers)
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14 pages, 3187 KiB  
Article
Simple, One-Pot Method for Preparing Transparent Ethyl Cellulose Films with Good Mechanical Properties
by Gabrijela Horvat, Klara Žvab, Željko Knez and Zoran Novak
Polymers 2022, 14(12), 2399; https://doi.org/10.3390/polym14122399 - 14 Jun 2022
Cited by 11 | Viewed by 4779
Abstract
In this research, ethyl cellulose films were prepared by a simple, easy, controlled one-pot method using either ethanol or ethyl lactate as solvents, the films being formed at 6 °C. Titanium dioxide nanoparticles were incorporated to improve the oxygen transmission and water vapour [...] Read more.
In this research, ethyl cellulose films were prepared by a simple, easy, controlled one-pot method using either ethanol or ethyl lactate as solvents, the films being formed at 6 °C. Titanium dioxide nanoparticles were incorporated to improve the oxygen transmission and water vapour transmission rates of the obtained films. This method used no plasticizers, and flexible materials with good mechanical properties were obtained. The resulting solvent-free and transparent ethyl cellulose films exhibited good mechanical properties and unique free-shapable properties. The obtained materials had similar properties to those reported in the literature, where plasticizers were incorporated into ethyl cellulose films with an elastic modulus of 528 MPa. Contact angles showed the hydrophobic nature of all the prepared materials, with contact angles between 80 and 108°. Micrographs showed the smooth surfaces of the prepared samples and porous intersections with honeycomb-like structures. The oxygen and water vapor transmission rates were the lowest for the ethyl cellulose films prepared in ethyl lactate, these being 615 cm3·m−2·day−1 and 7.8 gm−2·day−1, respectively, showing that the films have promise for food packaging applications. Full article
(This article belongs to the Special Issue Smart Polymeric Films and Coatings for Food Packaging Applications)
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14 pages, 4403 KiB  
Article
Anisotropic Tensile Characterisation of Eucalyptus nitens Timber above Its Fibre Saturation Point, and Its Application
by Xudong Chen, Yingyao Cheng, Andrew Chan, Damien Holloway and Gregory Nolan
Polymers 2022, 14(12), 2390; https://doi.org/10.3390/polym14122390 - 13 Jun 2022
Cited by 5 | Viewed by 2267
Abstract
Plantation-grown Eucalyptus nitens (E. nitens) has been grown predominantly for the pulp and paper industry. In this study, the suitability of E. nitens as a structural material is examined using static tensile tests in a universal testing machine. The anisotropic tensile [...] Read more.
Plantation-grown Eucalyptus nitens (E. nitens) has been grown predominantly for the pulp and paper industry. In this study, the suitability of E. nitens as a structural material is examined using static tensile tests in a universal testing machine. The anisotropic tensile behaviour of 240 Eucalyptus nitens small clear wood samples with a diversity of grain angles was examined in both dry and wet conditions. The samples had a highly anisotropic tensile characterisation in the context of both a low moisture content (MC = 12%) and a high moisture content (MC > its fibre saturation point, FSP). The results showed that, in a high moisture content condition, the wood showed a lower failure strength and more ductility at all grain angles than in a low moisture content condition. The underlying failure mechanism of Eucalyptusnitens timber in tension was determined in detail from the perspective of the microstructure of wood cellulose polymer composites. The mean tensile failure strengths perpendicular and parallel to the fibre direction were, respectively, 5.6 and 91.6 MPa for the low MC and 3.8 and 62.1 MPa for the high MC condition. This research provides a basis for using E. nitens as a potential structural tensile member. The moisture modification factors of Eucalyptus timber at a mean level are higher than those of the traditional construction material, Pinus radiata, implying that E. nitens is promising as a material to be used for tensile members in water saturated conditions. Full article
(This article belongs to the Special Issue Wood Polymer Composites: Processing, Properties, and Applications)
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16 pages, 4964 KiB  
Article
Intrinsically Stretchable Poly(3,4-ethylenedioxythiophene) Conducting Polymer Film for Flexible Electronics
by Lucija Fiket, Marin Božičević, Lana Brkić, Patricia Žagar, Anamarija Horvat and Zvonimir Katančić
Polymers 2022, 14(12), 2340; https://doi.org/10.3390/polym14122340 - 9 Jun 2022
Cited by 3 | Viewed by 3001
Abstract
The aim of this study was to synthesize an intrinsically stretchable conductive polymer (CP) by atom transfer radical polymerization (ATRP). For this purpose, poly(3,4-ethyilenedioxythiophene) (PEDOT) was synthesized as a backbone, while poly(acrylate-urethane) (PAU) was grafted onto the PEDOT backbone to form graft polymers [...] Read more.
The aim of this study was to synthesize an intrinsically stretchable conductive polymer (CP) by atom transfer radical polymerization (ATRP). For this purpose, poly(3,4-ethyilenedioxythiophene) (PEDOT) was synthesized as a backbone, while poly(acrylate-urethane) (PAU) was grafted onto the PEDOT backbone to form graft polymers PEDOT-g-PAU. Different concentrations of acrylate-urethane (AU) were used to synthesize PAU side chains of different lengths. The successful synthesis of the obtained intermediates and products (PEDOT-g-PAU) was confirmed by infrared spectroscopy and nuclear magnetic resonance. Thermal properties were evaluated by differential scanning calorimetry and thermogravimetric analysis, while conductivity was determined by four-point probe measurement. A simple tensile test was performed to characterize the ductility of the samples. PEDOT-g-PAU has shown high stretchability of up to 500% and, therefore, could potentially be used in skin-worn flexible electronics, while additional subsequent doping is required to improve the deterioration of electrical properties after the addition of the insulating urethane layer. Full article
(This article belongs to the Special Issue Advanced Polymeric Materials for Flexible Electronics Energy Storage Devices and Biosensors)
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15 pages, 2483 KiB  
Article
Faraday Instability in Viscous Fluids Covered with Elastic Polymer Films
by Junxiu Liu, Wenqiang Song, Gan Ma and Kai Li
Polymers 2022, 14(12), 2334; https://doi.org/10.3390/polym14122334 - 9 Jun 2022
Cited by 1 | Viewed by 2754
Abstract
Faraday instability has great application value in the fields of controlling polymer processing, micromolding colloidal lattices on structured suspensions, organizing particle layers, and conducting cell culture. To regulate Faraday instability, in this article, we attempt to introduce an elastic polymer film covering the [...] Read more.
Faraday instability has great application value in the fields of controlling polymer processing, micromolding colloidal lattices on structured suspensions, organizing particle layers, and conducting cell culture. To regulate Faraday instability, in this article, we attempt to introduce an elastic polymer film covering the surface of a viscous fluid layer and theoretically study the behaviors of the Faraday instability phenomenon and the effect of the elastic polymer film. Based on hydrodynamic theory, the Floquet theory is utilized to formulate its stability criterion, and the critical acceleration amplitude and critical wave number are calculated numerically. The results show that the critical acceleration amplitude for Faraday instability increases with three increasing bending stiffness of the elastic polymer film, and the critical wave number decreases with increasing bending stiffness. In addition, surface tension and viscosity also have important effects on the critical acceleration amplitude and critical wave number. The strategy of controlling Faraday instability by covering an elastic polymer film proposed in this paper has great application potential in new photonic devices, metamaterials, alternative energy, biology, and other fields. Full article
(This article belongs to the Special Issue Mathematical Modeling and Computer Simulation of Polymer Systems)
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17 pages, 4412 KiB  
Article
Synthesis and Characterization of Porous Chitosan/Saccharomycetes Adsorption Microspheres
by Wei Song, Qingzhu Zhang, Yuxin Guan, Wanyan Li, Siyu Xie, Jin Tong, Mo Li and Lili Ren
Polymers 2022, 14(11), 2292; https://doi.org/10.3390/polym14112292 - 5 Jun 2022
Cited by 7 | Viewed by 3239
Abstract
Porous chitosan/saccharomycetes adsorption microspheres were successfully prepared by using silica gel as porogen. The morphology of porous chitosan/saccharomycetes microspheres was characterized by scanning electron microscopy, the interaction between molecules was characterized by Fourier transform infrared spectroscopy, and the crystallization property of the microspheres [...] Read more.
Porous chitosan/saccharomycetes adsorption microspheres were successfully prepared by using silica gel as porogen. The morphology of porous chitosan/saccharomycetes microspheres was characterized by scanning electron microscopy, the interaction between molecules was characterized by Fourier transform infrared spectroscopy, and the crystallization property of the microspheres was characterized by X-ray diffraction. The results showed that the adsorption sites of amino and hydroxyl groups had been provided by the porous chitosan/saccharomycetes microspheres for the removal of preservatives, pigments, and other additives in food. The surface roughness of microspheres could be improved by increasing the mass ratio of saccharomycetes. The increase in silica gels could make the microsphere structure more compact. The porous chitosan/saccharomycetes microspheres could be used as adsorbents to adsorb doxycycline in wastewater. Full article
(This article belongs to the Section Polymer Chemistry)
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9 pages, 1069 KiB  
Article
Meso- and Rac-[bis(3-phenyl-6-tert-butylinden-1-yl)dimethylsilyl]zirconium Dichloride: Precatalysts for the Production of Differentiated Polyethylene Products with Enhanced Properties
by Kaitie A. Giffin, Virginie Cirriez, Orlando Santoro, Alexandre Welle, Evgueni Kirillov and Jean-François Carpentier
Polymers 2022, 14(11), 2217; https://doi.org/10.3390/polym14112217 - 30 May 2022
Cited by 1 | Viewed by 2803
Abstract
Ansa-zirconocene complexes are widely employed as precatalysts for olefin polymerization. Their synthesis generally leads to mixtures of their rac and meso isomers, whose separation is often problematic. In this contribution, we report on the synthesis of a novel silyl-bridged bis(indenyl)-based metallocene, and [...] Read more.
Ansa-zirconocene complexes are widely employed as precatalysts for olefin polymerization. Their synthesis generally leads to mixtures of their rac and meso isomers, whose separation is often problematic. In this contribution, we report on the synthesis of a novel silyl-bridged bis(indenyl)-based metallocene, and on the separation of its rac and meso isomers by simple recrystallization from toluene. The two complexes, activated by methylaluminoxane (MAO), have been used as precatalysts in ethylene/1-hexene copolymerization. Regardless of the reaction conditions, the meso complex outperformed its rac congener. A similar trend was observed by performing the process in the presence of the silica-supported versions of the complexes. This is remarkable, since meso metallocenes generally display lower activities than their rac analogues. Furthermore, the meso isomer generates polymer products that are more in line with the targets for the preparation of a bimodal PE grade made of a lower-MW high-density (HDPE) fraction and a higher-MW linear low-density (LLDPE) fraction. Full article
(This article belongs to the Special Issue Polyolefins: The Ever-Thriving Thermoplastics)
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13 pages, 3423 KiB  
Article
Room-Temperature Solid-State UV Cross-Linkable Vitrimer-like Polymers for Additive Manufacturing
by Jian Chen, Ya Wen, Lingyi Zeng, Xinchun Wang, Hongmei Chen, Wei Min Huang, Yuefeng Bai, Wenhao Yu, Keqing Zhao and Ping Hu
Polymers 2022, 14(11), 2203; https://doi.org/10.3390/polym14112203 - 29 May 2022
Cited by 6 | Viewed by 3267
Abstract
In this paper, a UV cross-linkable vitrimer-like polymer, ureidopyrimidinone functionalized telechelic polybutadiene, is reported. It is synthesized in two steps. First, 2(6-isocyanatohexylaminocarbonylamino)-6-methyl-4[1H]-pyrimidinone (UPy-NCO) reacts with hydroxy-functionalized polybutadiene (HTPB) to obtain UPy-HTPB-UPy, and then the resulted UPy-HTPB-UPy is cross-linked under 365 nm UV light [...] Read more.
In this paper, a UV cross-linkable vitrimer-like polymer, ureidopyrimidinone functionalized telechelic polybutadiene, is reported. It is synthesized in two steps. First, 2(6-isocyanatohexylaminocarbonylamino)-6-methyl-4[1H]-pyrimidinone (UPy-NCO) reacts with hydroxy-functionalized polybutadiene (HTPB) to obtain UPy-HTPB-UPy, and then the resulted UPy-HTPB-UPy is cross-linked under 365 nm UV light (photo-initiator: bimethoxy-2-phenylacetophenone, DMPA). Further investigation reveals that the density of cross-linking and mechanical properties of the resulting polymers can be tailored via varying the amount of photo-initiator and UV exposure time. Before UV cross-linking, UPy-HTPB-UPy is found to be vitrimer-like due to the quadruple hydrogen-bonding interactions. The UPy groups at the end of the chain also enable for rapid solidification upon the evaporation of the solvent. The unsaturated double bonds in the HTPB chains enable UPy-HTPB-UPy to be UV cross-linkable in the solid state at room temperature. After cross-linking, the polymers have good shape memory effect (SME). Here, we demonstrate that this type of polymer can have many potential applications in additive manufacturing. In the cases of fused deposition modelling (FDM) and direct ink writing (DIW), not only the strength of the interlayer bonding but also the strength of the polymer itself can be enhanced via UV exposure (from thermoplastic to thermoset) either during printing or after printing. The SME after cross-linking further helps to achieve rapid volumetric additive manufacturing anytime and anywhere. Full article
(This article belongs to the Special Issue Shape Memory Polymers IV)
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10 pages, 3688 KiB  
Article
Manipulation of Elastic Instability of Viscoelastic Fluid in a Rhombus Cross Microchannel
by Meng Zhang, Zihuang Wang, Yanhua Zheng, Bifeng Zhu, Bingzhi Zhang, Xiaohui Fang, Wenli Shang and Wu Zhang
Polymers 2022, 14(11), 2152; https://doi.org/10.3390/polym14112152 - 25 May 2022
Cited by 1 | Viewed by 1864
Abstract
This paper reports the manipulation of elastic instability of the viscoelastic fluid in a rhombus cross microchannel (RCM) structure. The bistable instability and unsteady instability of the flow is firstly demonstrated in a standard cross microchannel (SCM) for reference. We then keep the [...] Read more.
This paper reports the manipulation of elastic instability of the viscoelastic fluid in a rhombus cross microchannel (RCM) structure. The bistable instability and unsteady instability of the flow is firstly demonstrated in a standard cross microchannel (SCM) for reference. We then keep the bi-stable instability over a much wider injection rate range in the RCM, which is attributed to the stabilizing effect of the rhombus structure. A semi-bistable instability was also established in the RCM at a high enough injection rate. In addition, the unsteady elastic instability is realized in the RCM through an asymmetric injection rate condition. Full article
(This article belongs to the Special Issue Microfluidics as a Platform to Manufacture, Manipulate and Test Polymeric Entities)
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