Search Results (34)

This study explores the development of long fiber-reinforced thermoplastic (LFT) composites based on blends of poly(lactic acid) (PLA) and polyhydroxyalkanoate (PHA), reinforced with sisal fibers. A novel lab-scale LFT line was employed to fabricate the long fiber composites, effectively addressing the challenges associated with dispersing and processing high-aspect-ratio natural fibers. The rheological, mechanical, thermal, and morphological properties of the resulting bio-LFT composites were systematically characterized using FTIR, SEM, rotational rheology, mechanical testing, DSC, and TGA. The results demonstrated generally homogeneous fiber dispersion, although limited interfacial adhesion between the fibers and polymer matrix was observed. Mechanical tests revealed that sisal fiber incorporation significantly enhanced tensile strength and stiffness, while impact toughness decreased. Thermal analyses showed improved crystallinity and thermal stability with increasing PHA content and fiber reinforcement. Overall, this work highlights the potential of natural fibers to create high-performance, sustainable biocomposites and lays a solid foundation for future advancements in developing eco-friendly structural materials. Full article

The immiscibility of thermoplastic starch (TPS) and polybutylene succinate (PBS) complicates the thermal processing of these materials. This study provides the first comparative assessment of two compatibilizers with differing reaction mechanisms, Joncryl^® ADR 4468 and epoxidized linseed oil (ELO), for the optimization of biobased TPS/PBS blends. A total of 13 batches, varying in compatibilizer and blend composition, were processed via hot melt extrusion and injection molding to produce pellets. Blends were analyzed using tensile and impact testing, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), rheology, and scanning electron microscopy (SEM). The findings suggest that both compatibilizers can improve the compatibility of these blends, as evidenced by higher glass transition temperatures (T_g) compared to the reference batch (100-0-N/A). Joncryl^® ADR 4468 batches exhibit superior tensile strength and Young’s moduli, while ELO batches demonstrate greater elongation at break. The enhanced processability observed in Joncryl^® ADR 4468 is attributed to the increased polymer chain entanglement and molecular weight, whereas ELO facilitates greater chain mobility due to its plasticizing effect. These differences arise from the distinct mechanisms of action: Joncryl^® ADR 4468 promotes chain extension and crosslinking, whereas ELO mainly enhances flexibility through plasticization. Overall, this study provides a comparative assessment of these compatibilizers in TPS/PBS blends, laying the groundwork for future investigations into optimizing compatibilizer concentration and blend composition. Full article

We modified native wheat starch using 15, 30, and 60 min of acid hydrolysis (AH). The non-modified and AH-modified starches were converted to highly homogeneous thermoplastic starches (TPSs) using our two-step preparation protocol consisting of solution casting and melt mixing. Our main objective was to verify if AH can decrease the processing temperature of TPS. All samples were characterized in detail by microscopic, spectroscopic, diffraction, thermomechanical, rheological, and micromechanical methods, including in situ measurements of torque and temperature during the final melt mixing step. The experimental results showed that (i) AH decreased the average molecular weight preferentially in the amorphous regions, (ii) the lower-viscosity matrix in the AH-treated starches resulted in slightly higher crystallinity, and (iii) all AH-modified TPSs with a less viscous amorphous phase and higher content of crystalline phase exhibited similar properties. The effect of the higher crystallinity predominated at a laboratory temperature and low deformations, resulting in slightly stiffer material. The effect of the lower viscosity dominated during the melt mixing, where the shorter molecules acted as a lubricant and decreased the in situ measured processing temperature. The AH-induced decrease in the processing temperature could be beneficial for energy savings and/or possible temperature-sensitive admixtures for TPS systems. Full article

The rheology of wood thermoplastics is a crucial factor in enhancing wood utilization efficiency, significantly impacting the various applications of wood. The rheological properties of these thermoplastics are influenced by several variables, including moisture content, temperature, and fiber morphology. This study aims to investigate the rheological characteristics of wood under differing moisture levels (from absolute drying to water-impregnated states), thicknesses (ranging from 3 to 15 mm), compression methods, and compression conditions through a series of compression tests. The results show that moisture content and thickness substantially affect the rheological properties of wood thermoplastics, whereas thermal compression conditions exert a comparatively minor influence. Additionally, analysis of the content of the three primary elements in wood, alongside microscopic morphological examination, reveals that increased fiber length and higher length–diameter ratio are associated with enhanced rheological properties of wood thermoplastics. Notably, the influence of cellulose content (ranging from 40%–50%) on these rheological characteristics appears to be limited. Full article

This study aimed to enhance the initial adhesion performance of reactive polyurethane hot-melt adhesives by using a bio-based polycarbonate polyol instead of traditional polyester or polyether polyols and by incorporating thermoplastic polyurethane (TPU) in varied proportions. Adhesives synthesized from bio-based polycarbonate polyols and polypropylene glycol with MDI as the isocyanate were characterized chemically, thermally, and mechanically (FTIR, DSC, plate–plate rheology, DMA, and T-peel strength test). Adding 10–15 wt.% TPU significantly improved green strength and initial adhesion at room temperature and after accelerated cooling. The bio-based polycarbonate polyol promotes superior flexibility at low temperatures compared to fossil-derived alternatives, aligning with sustainability objectives. The results showed that 10 wt.% TPU maximized green strength without compromising flexibility, whereas 15 wt.% TPU, though enhancing adhesion, reduced flexibility due to increased crystallinity. T-peel tests on footwear materials indicated that all the adhesives exceeded the EN 15307:2015 requirements, with the highest peel strength achieved after curing. These findings highlight the benefit of bio-based polycarbonate polyols and TPUs in achieving strong, flexible, and eco-friendly adhesives suitable for demanding applications. Full article

This work describes the preparation of highly homogeneous thermoplastic starches (TPS’s) with the addition of 0, 5, or 10 wt.% of maltodextrin (MD) and 0 or 3 wt.% of TiO₂ nanoparticles. The TPS preparation was based on a two-step preparation protocol, which consisted in solution casting (SC) followed by melt mixing (MM). Rheology measurements at the typical starch processing temperature (120 °C) demonstrated that maltodextrin acted as a lubricating agent, which decreased the viscosity of the system. Consequently, the in situ measurement during the MM confirmed that the torque moments and real processing temperatures of all TPS/MD systems decreased in comparison with the pure TPS. The detailed characterization of morphology, thermomechanical properties, and local mechanical properties revealed that the viscosity decrease was accompanied by a slight decrease in the system homogeneity. The changes in the real processing temperatures might be quite moderate (ca 2–3 °C), but maltodextrin is a cheap and easy-to-add modifier, and the milder processing conditions are advantageous for both technical applications (energy savings) and biomedical applications (beneficial for temperature-sensitive additives, such as antibiotics). Full article

Skin wounds often form scar tissue during healing. Early intervention with tissue-engineered materials and cell therapies may promote scar-free healing. Exosomes and extracellular vesicles (EV) secreted by mesenchymal stromal cells (MSC) are believed to have high regenerative capacity. EV bioactivity is preserved after lyophilization and storage to enable use in remote and typically resource-constrained environments. We developed a bioprinted bandage containing reconstituted EVs that can be fabricated at the point-of-need. An alginate/carboxymethyl cellulose (CMC) biomaterial ink was prepared, and printability and mechanical properties were assessed with rheology and compression testing. Three-dimensional printed constructs were evaluated for Young’s modulus relative to infill density and crosslinking to yield material with stiffness suitable for use as a wound dressing. We purified EVs from human MSC-conditioned media and characterized them with nanoparticle tracking analysis and mass spectroscopy, which gave a peak size of 118 nm and identification of known EV proteins. Fluorescently labeled EVs were mixed to form bio-ink and bioprinted to characterize EV release. EV bandages were bioprinted on both a commercial laboratory bioprinter and a custom ruggedized 3D printer with bioprinting capabilities, and lyophilized EVs, biomaterial ink, and thermoplastic filament were deployed to an austere Arctic environment and bioprinted. This work demonstrates that EVs can be bioprinted with an alginate/CMC hydrogel and released over time when in contact with a skin-like substitute. The technology is suitable for operational medical applications, notably in resource-limited locations, including large-scale natural disasters, humanitarian crises, and combat zones. Full article

High-performance engineering thermoplastics offer lightweight and excellent mechanical performance in a wide temperature range. Their composites with carbon nanotubes are expected to enhance mechanical performance, while providing thermal and electrical conductivity. These are interesting attributes that may endow additional functionalities to the nanocomposites. The present work investigates the optimal conditions to prepare polyether ether ketone (PEEK)/multi-walled carbon nanotube (MWCNT) nanocomposites, minimizing the MWCNT agglomerate size while maximizing the nanocomposite electrical conductivity. The aim is to achieve PEEK/MWCNT nanocomposites that are suitable for melt-spinning of electrically conductive multifilament’s. Nanocomposites were prepared with compositions ranging from 0.5 to 7 wt.% MWCNT, showing an electrical percolation threshold between 1 and 2 wt.% MWCNT (10⁷–10² S/cm) and a rheological percolation in the same range (1 to 2 wt.% MWCNT), confirming the formation of an MWCNT network in the nanocomposite. Considering the large drop in electrical conductivity typically observed during melt-spinning and the drawing of filaments, the composition PEEK/5 wt.% MWCNT was selected for further investigation. The effect of the melt extrusion parameters, namely screw speed, temperature, and throughput, was studied by evaluating the morphology of MWCNT agglomerates, the nanocomposite rheology, and electrical properties. It was observed that the combination of the higher values of screw speed and temperature profile leads to the smaller number of MWCNT agglomerates with smaller size, albeit at a slightly lower electrical conductivity. Generally, all processing conditions tested yielded nanocomposites with electrical conductivity in the range of 0.50–0.85 S/cm. The nanocomposite processed at higher temperature and screw speed presented the lowest value of elastic modulus, perhaps owing to higher matrix degradation and lower connectivity between the agglomerates. From all the process parameters studied, the screw speed was identified to have the higher impact on nanocomposite properties. Full article

This paper investigated the upcycling process of thermoplastic waste polystyrene (WPS) into thermosetting particleboard adhesive using two cross-linkers, namely methylene diphenyl diisocyanate (MDI) and maleic anhydride (MA). The WPS was dissolved in an organic co-solvent. The weight ratio of WPS/co-solvent was 1:9, and 10% of cross-linkers based on the WPS solids content were added subsequently at 60 °C under continuous stirring for 30 min. The adhesive properties, cohesion strength, and thermo-mechanical properties of WPS-based adhesives were examined to investigate the change of thermoplastic WPS to thermosetting adhesives. The bonding strength of WPS-based adhesives was evaluated in particleboard made of sengon (Falcataria moluccana (Miq.) Barneby & J.W. Grimes) wood and rice straw particles at different weight ratios according to the Japanese Industrial Standard (JIS) A 5908:2003. Rheology and Dynamic Mechanical Analysis revealed that modification with MDI and MA resulted in thermosetting properties in WPS-based adhesives by increasing the viscosity at a temperature above 72.7 °C and reaching the maximum storage modulus above 90.8 °C. WPS modified with MDI had a lower activation energy (Ea) value (83.4 kJ/mole) compared to the WPS modified with MA (150.8 kJ/mole), indicating the cross-linking with MDI was much faster compared with MA. Particleboard fabricated from 100% sengon wood particles bonded with WPS modified with MDI fulfilled the minimum requirement of JIS A 5908:2003 for interior applications. Full article

The effectiveness of layered particles as processing aid agents in molten polystyrene was studied. Three graphene grades and two clays of different lateral size were selected for this purpose. The morphologies of the composites were observed using scanning electron microscopy. Steady shear measurements were carried out and the Carreau–Yasuda model with yield stress was applied to the experimental results. A decrease in viscosity was observed at 2 wt.% of particle content for almost all composites. The most efficient particle for reducing viscosity was found to be graphene in a loose agglomerated configuration. Graphene and clay particles with similar dispersion states had a similar effect on the viscosity, inducing a decrease by 29% and 22%, respectively, suggesting comparable efficiency as processing aid agents. The observed decrease in viscosity is attributed to the phenomenon of superlubricity, which is a lubricating mechanism that is closely linked to the atomic structure of the particles. Full article

The complex multiphase morphology of thermoplastic elastomers based on styrene-block copolymers (TPSs) affects their flow behavior significantly and in a way which may not be considered by commonly used characterization and evaluation procedures. To evaluate the relevance of non-Newtonian flow phenomena for the validity of rheometric data in processing, three commercially available TPSs with comparable hardness of about 60 Shore A but with different application fields were selected and characterized using parallel plate and high-pressure capillary rheometry. The validity of the rheometric data is assessed by modeling the flow in a high-pressure capillary rheometer by a computational fluid dynamics (CFD) simulation. The results were discussed in conjunction with close-up images of samples taken after the measurement. The materials show clearly different rheological behaviors but depend on the respective shear and geometrical conditions. In particular, for the material with the lowest viscosity, doubling the capillary diameter resulted in a disproportionate increase of the pressure loss by up to one third. Only the capillary flow of this material could not be reproduced by the CFD simulation. The results indicate that conventionally determined rheometric data of TPSs are of limited use in evaluating process flows for various material grades. Full article

Polyethylene terephthalate (PET) is a thermoplastic material that is widely used in many application fields, such as packaging, construction and household products. Due to the relevant contribution of PET to global yearly solid waste, the recycling of such material has become an important issue. Disposed PET does not maintain the mechanical properties of virgin material, as exposure to water and other substances can cause multiple chain scissions, with subsequent degradation of the viscoelastic properties. For this reason, chain extension is needed to improve the final properties of the recycled product. Chain extension is generally performed through reactive extrusion. As the latter involves structural modification and flow of PET molecules, rheology is a relevant asset for understanding the process and tailoring the mechanical properties of the final products. This paper briefly reviews relevant rheological studies associated with the recycling of polyethylene terephthalate through the reactive extrusion process. Full article

Incorporating thermally labile active pharmaceutical ingredients for manufacturing multifunctional polymeric medical devices is restricted due to their tendency to degrade in the hot melt extrusion process. In this study, the potential of sub- and near-critical carbon dioxide (CO₂) as a reversible plasticiser was explored by injecting it into a twin-screw hot melt extrusion process of Pellethane thermoplastic polyurethane to decrease its melt process temperature. Its morphological, throughput, thermal, rheological, and mechanical performances were also evaluated. The resultant extrudates were characterised using scanning electron microscopy, parallel plate rotational rheometer, differential scanning calorimetry, thermogravimetric analysis, and tensile testing. The process temperature decreased from 185 to 160 °C. The rheology indicated that the reduction in melt viscosity was from 690 Pa.s to 439 Pa.s (36%) and 414 Pa.s (40%) at 4.14 and 6.89 MPa, respectively. The tensile modulus in the elastomeric region is enhanced from 5.93 MPa, without CO₂ to 7.71 MPa with CO₂ at both 4.14 and 6.89 MPa. The results indicate that the employment of both sub- and near-critical CO₂ as a processing aid is a viable addition to conventional hot melt extrusion and that they offer more opportunities for thermosensitive drugs to be more stable in the molten stream of Pellethane thermoplastic polyurethane. Full article

The limited number of materials and mechanical weakness of fused deposition modeling (FDM) parts are deficiencies of FDM technology. The preparation of polymer composites parts with suitable filler is a promising method to improve the properties of the 3D printed parts. However, the agglomerate of filler makes its difficult disperse in the matrix. In this work, graphene nanoplatelets (GnPs) were surface modified with chemical, low-temperature plasma and in situ methods, in order to apply them as fillers for thermoplastic polyurethane (TPU). Following its modification, the surface chemical composition of GnPs was analyzed. Three wt% of surface-modified GnPs were incorporated into TPU to produce FDM filaments using a melting compounding process. Their effects on rheology properties and electrical conductivity on TPU/GnPs composites, as well as the dimensional accuracy and mechanical properties of FDM parts, are compared. The images of sample facture surfaces were examined by scanning electron microscope (SEM) to determine the dispersion of GnPs. Results indicate that chemical treatment of GnPs with zwitterionic surfactant is a good candidate to significantly enhance TPU filaments, when considering the FDM parts demonstrated the highest mechanical properties and lowest dimensional accuracy. Full article

Microorganism biomass is a sustainable and innovative source of biopolymers, such as proteins and polysaccharides, that is suitable for the development of biodegradable films. The aim of this research was to evaluate the synthesis, morphology, rheology, and morphological and mechanical properties on the production of edible biofilms based on water kefir grains, and compare them with edible films based on thermoplastic compounds from starch (TPS) obtained from taro (Colocasia esculenta) and cassava (Manihot esculenta). Edible biofilms were prepared in solution with 30% wt/wt glycerol relative to starch mass and kefir grain biofilms using the casting method. A stationary rheological analysis was performed on the film-forming suspensions of kefir, taro starch, and cassava starch. Once the films were obtained, a physicochemical and morphological characterization was carried out. Results of the characterization showed the following main aspects: The results indicated an increase in biomass production using muscovado and pineapple peel. The film-forming suspensions had a dilating behavior; however, the results obtained not only show the viscoelastic behavior but also the elastic limit (σ₀), which varied from 0.077 to 0.059 Pa for suspensions of water kefir grains and from 0.077 to 0.072 Pa for starch suspensions. These elastic limit variations can be defined as the minimum shear stress required to start the flow, and all these rheological data were adjusted to the Herschel–Bulkley model; the morphological and mechanical characterization of the films obtained showed homogeneous surfaces with transparency and without cracks; regarding the water activity, values lower than 6 were obtained, which indicates that there will be no growth of any microorganism, and the hardness data showed differences between those obtained from kefir and taro and cassava starch. The similar results of the rheological characterization in the formation of the kefir biofilm and the conventional edible starch films, in addition to the similar results in the water activity below 6 and the hardness, points to an attractive alternative capable of replacing the conventional materials with a mass production of biofilms of probiotic microorganisms. The results also revealed that water kefir grains biomass is a viable and innovative source of biodegradable materials, and these grains can be an alternative to conventional established starch materials. Full article