Polymers

In this work, the finite element technique is employed to evaluate the effects of thermal relaxation durations on temperature, displacements, and stresses in a two-dimensional, polymeric, orthotropic, elastic medium. The problem is considered in a homogeneous, polymeric, orthotropic medium in the context of the Green and Lindsay model with two thermal relaxation times. The bounding surface of the half-space was subjected to a heat flux with an exponentially decaying pulse. Finite element techniques were used to solve the governing formulations, with eight-node isoparametric rectangular elements with three degrees of freedom (DOF) per node. The developed method was calculated using numerical results applied to the polymeric, orthotropic medium. The findings were implemented and visually shown. Finally, the results were displayed to demonstrate the differences between classical dynamic coupling (CT), the Lord–Shulman (LS) and the Green and Lindsay (GL) models. Full article

The sustainability, performance, and cost of production in the plywood industry depend on wood adhesives and the hot-pressing process. In this study, a cold-setting plywood adhesive was developed based on polyvinyl alcohol (PVOH), high-purity lignin, and hexamine. The influence of lignin content (10%, 15%, and 20%) and cold-pressing time (3, 6, 12, and 24 h) on cohesion, adhesion, and formaldehyde emission of plywood were investigated through physical, chemical, thermal, and mechanical analyses. The increased lignin addition level lowered the solids content, which resulted in reduced average viscosity of the adhesive. As a result, the cohesion strength of the adhesive formulation with 10% lignin addition was greater than those of 15% and 20% lignin content. Markedly, the adhesive formulation containing a 15% lignin addition level exhibited superior thermo-mechanical properties than the blends with 10% and 20% lignin content. This study showed that 10% and 15% lignin content in the adhesive resulted in better cohesion strength than that with 20% lignin content. However, statistical analysis revealed that the addition of 20% lignin in the adhesive and using a cold-pressing time of 24 h could produce plywood that was comparable to the control polyurethane resins, i.e., dry tensile shear strength (TSS) value of 0.95 MPa, modulus of rupture (MOR) ranging from 35.8 MPa, modulus of elasticity (MOE) values varying from 3980 MPa, and close-to-zero formaldehyde emission (FE) of 0.1 mg/L, which meets the strictest emission standards. This study demonstrated the feasibility of fabricating eco-friendly plywood bonded with PVOH–lignin–hexamine-based adhesive using cold pressing as an alternative to conventional plywood. Full article

This study describes the fabrication of an electrospun, U-shaped optical fiber sensor for temperature measurements. The sensor is based on single mode fibers and was fabricated into a U-shaped optical fiber sensor through flame heating. This study applied electrospinning to coat PVA, a polymer, onto the sensor layer to reduce its sensitivity to humidity. The sensor is used to measure temperature variations ranging from 30 °C to 100 °C. The objectives of this study were to analyze the sensitivity variation of the sensor with different sensor layer thicknesses resulting from different electrospinning durations, as well as to simulate the wavelength signals generated at different electrospinning durations using COMSOL. The results revealed that the maximum wavelength sensitivity, transmission loss sensitivity, and linearity of the sensor were 25 dBm/°C, 70 pm/°C, and 0.956, respectively. Longer electrospinning durations resulted in thicker sensor layers and higher sensor sensitivity, that wavelength sensitivity of the sensor increased by 42%. Full article

The aim of this paper is to propose ecological thermal insulation materials that meet the goals of sustainability but also fulfill the imposed thermal performance requirements. This paper studies new composite materials based on sheep wool from the perspective of thermal conductivity. The composites were prepared using two types of binder: acrylic-polyurethane resin and natural rubber latex, which were applied to the wool fibres through different methods and percentages. Based on the obtained results of thermal conductivity, two types of samples were selected for further analysis, which aimed to determine the microstructure, chemical composition, water absorption, attack of microorganisms, water vapour permeability, hygrothermal adsorption characteristics and sound absorption of the samples. In order to analyse the variation of thermal conductivity, the following parameters were taken into account: thickness, density, type of binder and percentage of binder. Following the obtained results, it was observed that the value of the thermal conductivity of the samples varies between 0.0324 and 0.0436 W/mK. It was found that all the samples prepared and analysed in this study fulfil the national criteria for the thermal performance of thermal insulation material. After conducting the in-depth analysis of the two selected sample types, it was concluded that both materials have good sound absorption characteristics over the considered frequency range. In addition, as it was expected from the natural fibres, the samples had low resistance against the attack of microorganisms and water-related tests. Full article

Pack integrity is essential for the success of modified atmosphere packaging of food products. Colorimetric oxygen leak indicators or tags are simple and smart tools that can depict the presence or absence of oxygen within a package. However, not many bio-based electrospun materials were explored for this purpose. Ultraviolet light-activated kappa-carrageenan-based smart oxygen indicating tag was developed using the electrospinning technique in this study and its stability during storage was determined. Kappa-carrageenan was used with redox dye, sacrificial electron donor, photocatalyst, and solvent for preparing oxygen indicating electrospun tag. Parameters of electrospinning namely flow rate of the polymer solution, the distance between spinneret and collector, and voltage applied were optimized using Taguchi L9 orthogonal design. Rheological and microstructural studies revealed that the electrospinning solution was pseudoplastic and the mat fibers were compact and non-woven with an average fiber size of 1–2 microns. Oxygen sensitivity at different oxygen concentrations revealed that the tag was sensitive enough to detect as low as 0.4% oxygen. The developed tag was stable for at least 60 days when stored in dark at 25 °C and 65% RH. The developed mat could be highly useful in modified atmosphere packaging applications to check seal integrity in oxygen devoid packages. Full article

Three-dimensional printed surgical guides increase the precision of orthodontic mini-implant placement. The purpose of this research was to investigate the effects of disinfection and of two types of autoclave sterilization on the mechanical properties of 3D printed surgical guides obtained via the SLA (stereolithography) and DLP (digital light processing) printing methods. A total of 96 standard specimens (48 SLA and 48 DLP) were printed to analyze the tensile and flexural properties of the materials. A total of 80 surgical guide (40 SLA and 40 DLP) specimens from each printing method were classified into four groups: CG (control group); G1, disinfected with 4% Gigasept (Gigasept Instru AF; Schülke & Mayer Gmbh, Norderstedt, Germany); G2, autoclave-sterilized (121 °C); and G3, autoclave-sterilized (134 °C). Significant differences in the maximum compressive load were determined between the groups comprising the DLP-(p < 0.001) and the SLA- (p < 0.001) printed surgical guides. Groups G2 (p = 0.001) and G3 (p = 0.029) showed significant parameter modifications compared with the CG. Disinfection with 4% Gigasept (Gigasept Instru AF; Schülke & Mayer Gmbh, Norderstedt, Germany) is suitable both for SLA- and DLP-printed surgical guides. Heat sterilization at both 121 °C and 134 °C modified the mechanical properties of the surgical guides. Full article

Injection molding, in addition to extrusion, is the most important technology in the polymer processing industry. When modeling injection molding, the global approach is necessary to take into account the solid polymer transport, polymer melting and the polymer melt flow. The model of polymer melting is fundamental for the development of such a global injection molding model. In the paper, the state-of-the-art of modeling and experimentation of the flow and melting in injection molding machines has been presented and discussed. It has been concluded that the existing mathematical models have no strong experimental basis. Therefore, experimentation of the polymer flow and melting in the injection molding machine has been performed, and the effect of processing conditions: the screw speed, the plasticating stroke and the back pressure on the process course has been investigated. Starving in the beginning sections of the screw has been observed, which was not presented in the literature so far. The novel concepts of injection molding modeling have been discussed. Full article

Fused filament fabrication (FFF) systems utilize a wide variety of commercially available filaments, including Acrylonitrile Butadiene Styrene (ABS), as well as their variants. However, the effect of filament composition, reinforcements (chopped fibers and nanotubes), and 3-D printing variables on the microstructure and thermomechanical behavior is not well understood, and systematic studies are needed. In this work, different types of ABS materials with and without carbon fiber and carbon nanotube reinforcements were printed with multiple print layer heights. The microstructure, elastic behavior, tensile behavior, and fracture toughness of 3-D printed materials were characterized. ABS material systems printed at a low print layer height of 0.1 mm outperformed those printed at a larger height of 0.2 mm. Carbon nanotube reinforcements result in significant improvement in the strength and elastic modulus of ABS materials. Printed coupons of ABS with carbon nanotubes achieve an ultimate strength of 34.18 MPa, while a premium grade ABS coupon achieved 28.75 MPa when printed with the same print layer heights. Samples of ABS with chopped carbon fiber show an ultimate strength of 27.25 MPa, due primarily to the significant porosity present in the filament. Elastic moduli and fracture toughness measured using dynamic and mechanical methods show similar trends as a function of layer height. The effects of different materials, reinforcements, and printing parameters on the microstructure and mechanical properties are discussed in detail. Full article

The hexavalent chromium (Cr(VI)) ion adsorption properties were conferred to porous silica beads by introducing alkylamine chains through functionalization with an aminosilane coupling agent, [3-(2-aminoethylamino)propyl]triethoxysilane (AEAPTES), or with an epoxysilane coupling agent, (3-glycidyloxypropyl)triethoxysilane (GOPTES), and polyfunctional amine compounds or poly-ethylenimines (PEIs). The presence of amino groups on the silica beads was confirmed by XPS and the amount of amino groups increased to 0.270 mmol/g by increasing the AEAPTES concentration and/or reaction time. The adsorption capacity of the silica beads functionalized with AEAPTES was the maximum at the initial pH value of 3.0 and the initial adsorption rate increased with an increase in the temperature. The adsorption capacity increased with an increase in the amount of amino groups at pH 3.0 and 30 °C. The adsorption behavior obeyed the pseudo-second order kinetic model and was well expressed by the Langmuir isotherm. These results support that Cr(VI) ion adsorption is accomplished through the electrostatic interaction between protonated amino groups and HCrO₄^- ions. In addition, the adsorption capacity further increased to 0.192–0.320 mmol/g by treating the GOPTES-treated silica beads with triethylenetetramine, pentaethylenehexamine, or PEI. These empirical, equilibria, and kinetic aspects obtained in this study support that the porous silica-based adsorbents prepared in this study can be applied to the removal of Cr(VI) ions. Full article

Using polyhydroxyalkanoate (PHA) materials for ruminal boluses could allow for longer sustained release of drugs and hormones that would reduce administration time and unneeded animal discomfort caused by continuous administration. The objective of this study was to determine ruminal degradability and kinetics of biodegradable polymers and blends. A proprietary PHA-based polymer, poly(butylene succinate-co-adipate) (PBSA), PBSA:PHA melt blends, and forage controls were incubated in rumen fluid for up to 240 h. Mass loss was measured after each incubation time, and digestion kinetic parameters were estimated. Thermogravimetric, differential scanning calorimetry, and intrinsic viscosity analyses were conducted on incubated samples. Generally, across treatments, mass loss was significant by 96 h with a minimum increase of 0.25% compared to 0 h but did not change thereafter. Degradation kinetics demonstrated that polymer treatments were still in the exponential degradation phase at 240 h with a maximum disappearance rate of 0.0031 %/h. Melting temperature increased, onset thermal degradation temperature decreased, and intrinsic viscosity decreased with incubation time, indicating structural changes to the polymers. Based on these preliminary findings, the first stage of degradation occurs within 24 h and PHA degrades slowly. However, further ruminal degradation studies of biodegradable polymers are warranted to elucidate maximum degradation and its characteristics. Full article

In recent times, developments in polymer application properties have required the design of different polymer structures more than ever. Cross-linked polymers (CPs) could be considered a good candidate material for potential applications when used in conjunction with nanoparticles. Cross-linked polymethyl methacrylate nanocomposites are considered to be one of the most commonly polymeric adsorbents due to their varied and simple modification methods. A new class of C-PMMA/SnO_2(a–d) nanocomposites have been fabricated as surface-selective adsorbents of Cr (III) with a good yield and different loading of SnO₂ nanoparticles. The morphology, molecular structures, and thermal stability of the new cross-linked polymers were examined using a Scanning electron microscope (SEM), the Fourier Transform Infrared method (FTIR), X-ray diffraction (XRD), and Thermogravimetric Analysis (TGA). The adsorption study of C-PMMA/SnO₂ was investigated, and an efficient level of adsorption for Cr (III) cations was detected. To evaluate the potential for the new polymers to be used as adsorbents against Cr (III) ions, the contact time, the initial concentration of Cr (III), and the effects of pH were studied. The introduction of SnO₂ into the polymer network enhanced the efficiency of the adsorption of heavy metals. The C-PMMA/SnO₂ is highly efficient at removing Cr (III) ions in wastewater samples at pH 6 for one hour. The adsorption study demonstrated that the adsorption capacity of C-PMMA/SnO₂c for Cr (III) was 1.76 mg /g, and its adsorption isotherm agreed with the Langmuir adsorption model. Full article

Automation and mass-production are two of the many limitations in the tissue engineering industry. Textile fabrication methods such as electrospinning are used extensively in this field because of the resemblance of the extracellular matrix to the fiber structure. However, electrospinning has many limitations, including the ability to mass-produce, automate, and reproduce products. For this reason, this study evaluates the potential use of a traditional textile method such as spinning. Apart from mass production, these methods are also easy, efficient, and cost-effective. This study uses bovine-derived collagen fibers to create yarns using the traditional ring spinning method. The collagen yarns are proven to be biocompatible. Enzymatic biodegradability was also confirmed for its potential use in vivo. The results of this study prove the safety and efficacy of the material and the fabrication method. The material encourages higher cell proliferation and migration compared to tissue culture-treated plastic plates. The process is not only simple but is also streamlined and replicable, resulting in standardized products that can be reproduced. Full article

New three fabricated chitosan (CS) loaded with fly ash (FA) films were developed in this study. The shell waste of white shrimp was used as a precursor for the isolation of chitin and converted into chitosan by carrying out a deacetylation process. The formation of chitosan was conducted by various preparation steps deproteinization, demineralization, and deacetylation. The degree of deacetylation was found to be 95.2%. The obtained chitosan was used to prepare three different chitosan loaded-fly ash films. The prepared films contained various fly ash: chitosan ratios (2:1, FA-CSF1), (1:1, FA-CSF2), and (1:2, FA-CSF3). The obtained films were characterized using FTIR, XRD, and SEM. The micrograph images of the formed films showed spherical particles with an average size of 10 µm. The surface area, adsorption-desorption properties, thermal stability, and water/fat binding features of the fabricated chitosan films were studied. The results revealed that the prepared films displayed typical BET graphs with surface areas ranging from 2.436 m² g⁻¹ to 8.490 m² g⁻¹. The fabricated FA-CSF films also showed high thermal stability at temperatures up to 284.9 °C and excellent water/fat binding capacities. The antibacterial potential of the designed films was screened against E. coli (Gram-negative) and B. cereus (Gram-positive) bacterial strains. The tested solution of CS (1%) exhibited inhibition zones for E. coli and B. cereus as 18.51 mm and 14.81 mm, respectively, while in FA solution (1%), the inhibition zones were found to be 10.16 mm, and 13.57 mm, respectively. The results encourage and open up the new and promising areas of research for applying chitosan extracted from waste materials in biological applications. Full article

There is a need to create next-generation polymer composites having high property, unique function, and intelligent behaviors, such as shape memory effect (SME) and self-healing (SH) capability. Rare earth complexes can provide luminescence for polymers, and their dispersion is highly affected by ligand structures. Here, we created three different REOCs with different ligands before studying the effects of ligands on REOC dispersion in polyurea–urethane (PUU) with disulfide bonds in main chains. In addition, the effects of different REOCs on mechanical properties, luminescent functions, and intelligent behaviors of PUU composites were studied. The results showed that REOC I (Sm(TTA)₃phen: TTA, thenoyltrifluoroacetone; phen, 1,10-phenanthroline) has incompatible ligands with the PUU matrix. REOC I and REOC III (Sm(BUBA)₃phen: BUBA, 4-benzylurea-benzoic acid) with amine and urea groups facilitate their dispersion. It was REOC III that helped the maintenance of mechanical properties of PUU composites due to the good dispersion and the needle-like morphologies. Due to more organic ligands of REOC III, the fluorescence intensity of composite materials is reduced. The shape recovery ratio of the composite was not as good as that of pure PUU when a large amount of fillers was added. Besides, REOC I reduced the self-healing efficiency of PUU composites due to poor dispersion, and the other two REOCs increased the self-healing efficiency. The results showed that ligands in REOCs are important for their dispersion in the PUU matrix. The poor dispersion of REOC I is unbeneficial for mechanical properties and intelligent behavior. The high miscibility of REOC II (Sm(PABA)₃phen: PABA, 4-aminobenzoic acid) decreases mechanical properties as well but ensures the good shape recovery ratio and self-healing efficiency. The mediate miscibility and needle-like morphology of REOC III are good for mechanical properties. The shape recovery ratio, however, was decreased. Full article

The musculoskeletal (MS) system consists of bone, cartilage, tendon, ligament, and skeletal muscle, which forms the basic framework of the human body. This system plays a vital role in appropriate body functions, including movement, the protection of internal organs, support, hematopoiesis, and postural stability. Therefore, it is understandable that the damage or loss of MS tissues significantly reduces the quality of life and limits mobility. Tissue engineering and its applications in the healthcare industry have been rapidly growing over the past few decades. Tissue engineering has made significant contributions toward developing new therapeutic strategies for the treatment of MS defects and relevant disease. Among various biomaterials used for tissue engineering, natural polymers offer superior properties that promote optimal cell interaction and desired biological function. Natural polymers have similarity with the native ECM, including enzymatic degradation, bio-resorb and non-toxic degradation products, ability to conjugate with various agents, and high chemical versatility, biocompatibility, and bioactivity that promote optimal cell interaction and desired biological functions. This review summarizes recent advances in applying natural-based scaffolds for musculoskeletal tissue engineering. Full article

YAG ceramic fiber, with its high thermal conductivity and easy to achieve limit size, provides design flexibility as a laser gain medium. Its mainstream forming method was mainly high-pressure extrusion, but there were disadvantages, such as lack of flexibility. In this work, the flexible green body of YAG ceramic fiber was prepared by melt spinning. The melting characteristics of TPU with four different Shore hardnesses were systematically investigated. The microstructure, element homogeneity of the surface and fracture SEM images of the prepared ceramic fiber were also analyzed in detail. The optimized process parameters of YAG ceramic fiber preparation were as follows: the melting temperature was 220 °C, the screw feed rate of the double-cone screw extruder was F = 15.0 mm/min and the TPU-95A# was used. The ceramic fiber with the mass ratio of TPU-95A# to ceramic powder = 4:6 had the best microstructure quality. It had good flexibility and could be knotted with a bending radius of about 2.5 mm, and the tensile strength reached approximately 20 MPa. These results are crucial for advancing YAG ceramic fiber applications. Full article

Laser Sintering (LS) was the first Powder Bed Fusion (PBF) method for polymers and it is now quite an established process for rapid prototyping and even for the production of functional parts. High Speed Sintering (HSS) is a variant of PBF which was later developed and it has the potential to be more scalable than LS. Most of the work for HSS and LS has been conducted with polyamide-12 (PA 12). This work reports the first effort to use polyethylene terephthalate (PET) in HSS. Well defined, simple and complex parts could be printed without any build failures. However, limitations were induced by current HSS machines which led to some curvature (warpage) in tensile bars after manufacturing. The reason for this was that all currently available machines for HSS are built for polymers such as polyamide 12, which means their maximum bed temperature is limited to 190 °C. This corresponds to the lower limit of processability of PET in PBF processes. The slightly curved tensile bars were straightened by heating them to 230 °C with a weight on top, and afterwards the mechanical properties were measured. The tensile modulus was similar to what was obtained with PET via LS but the strength and elongation-at-break (EAB) was lower. Microscopy showed that the reason for the lower strength and EAB was the incomplete melting of particles. This arose from the temperature limitation of the current generation of HSS machines. The porosity was established as 2.23% by helium pycnometry which is the same as for LS. The results of the thermal analysis indicated that the PET parts manufactured with HSS were semi-crystalline like the PET parts manufactured via LS. Full article

A novel drug delivery system based on chitosan nanofibers containing some steroidal derivatives was developed using an electrospinning process. Oxazolines and aziridines from the cholestane series of steroidal epoxides were successfully synthesized and characterized by elemental analysis, Fourier transforms infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹HNMR), and mass spectroscopy (MS). Steroidal-compound-loaded chitosan (ST-CH) nanofibers were fabricated using the electrospinning technique in the presence of polyvinylpyrrolidone (CH/PVP). The electrospun nanofibers were characterized by scanning electron microscopy (SEM). The swelling degree of the electrospun nanofibers and their steroidal compound release performance were studied as well. Furthermore, their antibacterial activity against gram-positive (Staphylococcus aurous) and gram-negative bacteria (Escherichia coli) was evaluated. The experimental data revealed that identical and bead-free nanofiber mats loaded with 10 Wt. % of synthesized steroidal derivatives had been obtained. The FTIR spectrum proved that no change occurred in the chitosan structure during the electrospinning process. The synthesized nanofiber mats showed a high swelling degree and a burst release of steroidal compounds after 2 h doping in phosphate buffer saline. In addition, the electrospun nanofibers containing 3β-chloro-N-amido-5α-cholestano-aziridine and those containing 3β-acetoxy-N-amido-5α-cholestano-aziridine were the most active, with activity indices of 91 and 104% in the case of S. aureus and 52% and 61% in the case of E. coli, respectively. The release mechanism by CH/PVP of the drug samples was studied based on the charge density and diffusion controlled factors. The oxazoline derivatives release mechanism from CH/PVP was evaluated by applying the suppositions of the Ritger-Peppas kinetic model and by estimating the transport exponent; the latter revealed the involvement of the solvent diffusion and chain relaxation processes. Tailored steroidal loaded-chitosan (ST-CH) nanofibers are expected to be feasible and efficient drug delivery systems. Full article