Polymers最新文献

Transglutaminase (TGase) is an enzyme that catalyzes acyl transfer reactions by creating covalent cross-links between protein molecules and has been used to improve the physical and functional properties of protein-based foods. The objectives of this study were the extraction, purification, and biochemical characterization of TGase from sardine (Sardina pilchardus) flesh in order to provide a suitable TGase enzyme for food industry applications. The results showed a specific activity, yield, and purification fold of 357.14 U/mg protein, 36.74%, and 183.15, respectively. The enzyme exhibited maximal activity at 40 °C and pH 8.0, with a molecular weight of around 57 kDa. The effect of time on TGase thermal stability at 40 °C showed a gradual decrease in its catalytic activity during the incubation time until the enzyme was completely inactivated at 60 min. Additionally, the sardine TGase was found to be calcium-dependent. However, Mg²⁺ and Ba²⁺ ions were found to be effective in its activation to some extent and a total inhibition was shown by Zn²⁺ and Sr²⁺ ions. The TGase activity was affected markedly by NaCl and EDTA, and lost, respectively, about 80.7% and 36.49% from its activity by increasing the concentration (1.5 M NaCl and 20 mM EDTA). Based on the surface hydrophobicity and solubility results, the cross-linking of natural actomyosin mediated by TGase increased to a greater extent. The results revealed that sardine TGase possessed attractive qualities, making it a potential alternative to other TGase sources for food industry applications.

Polyamide-based glass fibre-reinforced composites are extensively used in electrical and automotive applications due to their excellent mechanical, thermal, and electrical properties. However, prolonged exposure to high temperatures can lead to significant degradation, affecting their long-term performance and reliability. This study investigates the thermal ageing behaviour of polyamide 6,6 composites containing halogenated flame retardants used for electrical applications. The objective of this research is to evaluate the extent of degradation through accelerated ageing tests and to develop an Arrhenius-type ageing model to predict the long-term performance of these materials. This study examines the effects of thermal ageing at temperatures between 160 and 210 °C on flexural properties and explores the underlying degradation mechanisms. Results indicate that short-term exposure to high temperatures can enhance flexural strength due to annealing effects, which are eventually outweighed by thermal oxidation and increased crystallinity, leading to an increase in brittleness. The derived Arrhenius model, with an activation energy of 93 kJ/mol, predicts a service life of approximately 25 years at 80 °C, but a significantly shorter one at 130 °C. These findings underscore the importance of considering thermal ageing effects in the design and application of PA66 composites in high-temperature environments.

The structural damage repair of composite material is an important issue that needs to be addressed during the service life of composite materials. To investigate the effects of a scarf structure and scarf angle on the repair quality of composite material, this paper proposes a mixed-scarf (MS) repair structure that combines ramped-scarf (RS) and stepped-scarf (SS) repair structures. The effect of the repair structure on the mechanical properties was analyzed, as well as the quality of the adhesive interface. The results show that at a scarf angle of 10°, the repair efficiency and the quality of adhesive interface are better than that of scarf angles of 20° and 30°. At a scarf angle of 10°, the recovery degree of the flexural strength of the MS repair structure is 79.72%, which is 6.77% and 38.24% higher than that of the RS and SS repair structures, respectively. However, in terms of flexural modulus, regardless of repair structure, the flexural modulus is highest at a scarf angle of 20°. Furthermore, the impact strength of the MS repair structure is approximately 87.60% that of the RS repair structure; additionally, it exhibits an increase of 45.83% compared to the SS repair structure. Overall, the quality of the adhesive interface for the RS and MS repair structures is similar and better than that of the SS repair structure. In conclusion, the MS repair structure is well suited for small-angle scarf repairs, whereas the RS repair structure is more appropriate for large-angle repairs; in contrast, the SS repair structure demonstrates the least effective performance in terms of repair outcomes.

The green transition trend in the wood-based panel industry aims to reduce environmental impact and waste production, and it is a viable approach to meet the increasing global demand for wood and wood-based materials as roundwood availability decreases, necessitating the development of composite products as alternatives to non-wood lignocellulosic raw materials. As a result, the purpose of this study is to examine and assess the physical, mechanical, and acoustic properties of particleboard manufactured from non-wood lignocellulosic biomass. The core layer was composed of non-wood lignocelluloses (banana stem, rice straw, coconut fiber, sugarcane bagasse, and fibrous vascular bundles (FVB) from snakefruit fronds), whereas the surface was made of belangke bamboo (Gigantochloa pruriens) and wood. The chemical characteristics, fiber dimensions and derivatives, and contact angles of non-wood lignocellulosic materials were investigated. The contact angle, which ranged from 44.57 to 62.37 degrees, was measured to determine the wettability of these materials toward adhesives. Hybrid particleboard (HPb) or sandwich particleboard (SPb) samples of 25 cm × 25 cm with a target density of 0.75 g/cm³ and a thickness of 1 cm were manufactured using 7% isocyanate adhesive (based on raw material oven dry weight). The physical parameters of the particleboard, including density, water content, water absorption (WA), and thickness swelling (TS), ranged from 0.47 to 0.79 g/cm³, 6.57 to 13.78%, 16.46 to 103.51%, and 3.38 to 39.91%, respectively. Furthermore, the mechanical properties of the particleboard, including the modulus of elasticity (MOE), bending strength (MOR), and internal bond strength (IB), varied from 0.39 to 7.34 GPa, 6.52 to 87.79 MPa, and 0.03 to 0.69 MPa, respectively. On the basis of these findings, the use of non-wood lignocellulosic raw materials represents a viable alternative for the production of high-performance particleboard.

This in vitro study investigates the impact of the chemical modification of resin composite surfaces on repair bond strength of micro-hybrid resin composite material. First, 7 mm circular × 3 mm thick resin composite disks were prepared using teflon molds. Then, 50 specimens out of 100 were allocated for stimulated aging using a thermo-cycling (10,000 cycles) device. Both the 24 h and 1-year-aged composite discs were embedded in epoxy resin using a 2.5 cm wide × 1.5 cm thick circular mold. The surfaces were treated with Clearfil S3 bond alone or with the additional application of silane or porcelain primer. The other two groups were bonded with CRB bond with or without a porcelain primer. Using a teflon mold, a 2 mm circular and 3 mm high repair composite cylinder was built on the treated surfaces. The specimens were then stressed to de-bond by applying shear force to measure repair bond strength, and they were observed under the microscope to determine the failure pattern. The data were analyzed using SPSS26.0. Univariate analysis showed a significant effect (p = 0.013) of the bonding protocol on the repair bond strength; however, the effect of aging was insignificant (p = 0.170). The S3 bond with additional silane and the CRB bond showed the significantly higher repair bond strength of the 1-year-aged micro-hybrid composite. However, in case of 24 h aged specimens, the repair bond strength was statistically insignificant among the tested groups (p = 0.340). Chemical surface modification with silane has the potential to improve the repair bond strength of micro-hybrid resin composite materials.

Continuous loading on asphalt pavements induces fatigue damage at the interface between the asphalt binder and aggregate or within the binder itself. The understanding of asphalt's fatigue response is considered crucial for the prolongation of pavement service life. Variable stress fatigue tests were conducted on asphalt binders, with conditions such as stress amplitude being altered to analyze fatigue performance and life. This study refines asphalt fatigue evaluation systems, introducing a variable stress time sweep test. Modulus recovery after stress changes was revealed through rheological analysis, indicating damage recovery. Fracture surface analysis showed that increased high-stress loadings resulted in reduced edge flow zone width and a flatter surface. Statistical analysis indicated an "exercise effect", enhancing fatigue life in the second stage. Stress transitions altered fatigue crack paths, surpassing Miner's linear criterion prediction. The fatigue life curve was accurately fitted using the two-stage life model, affirming its applicability in evaluating variable stress fatigue tests.

Although the extrudate swelling, melt fracture, and extrusion deformation of polymer micro-catheters in traditional extrusion molding can be eliminated via the double-layer gas-assisted extrusion (DL-GAE) method, some failure problems are generated under unreasonable process conditions. To ascertain the reasons for failure in DL-GAE molding of polymer micro-catheters, the influences of the interaction between the melt and double assisted gas on the DL-GAE molding of polymer micro-catheters were experimentally and numerically studied. Meanwhile, a DL-GAE die and experimental system were designed and constructed. We analyzed the influence laws of the melt and assisted gas on the DL-GAE molding of polymer micro-catheters, as well as reasons for the molding's failure. Our studies demonstrate that under the condition of stable DL-GAE, as the melt flow rate increases, the wall thickness and diameter of polypropylene (PP) micro-catheters increase. When the melt flow rate continuously increases, the stability of the assisted gas is destroyed, resulting in the failure of DL-GAE. In addition, under synchronized pressures of a double gas-assisted layer, the diameters of the micro-catheters increase, but their wall thickness decreases. Under an individual pressure increase of the outer gas-assisted layer, surface bump defects are generated. Under an individual pressure increase of the inner gas-assisted layer, the diameters of PP micro-catheters swell prominently until they break. Therefore, although DL-GAE can eliminate extrusion problems of polymer micro-catheters, it is suggested that reasonable process parameters for the melt and double assisted gas should be satisfied and matched. This work can provide significant technical support for the DL-GAE of polymer micro-catheters during manufacture.

Infrared thermography is a real-time and efficient method for defect detection. This study utilizes line laser scanning infrared thermography to detect cracks in manually laid-up unidirectional CFRP, 3D-printed CFRP cracks, and naturally occurring microcracks in CFRP deflectors. In manually layered unidirectional CFRP, detection performance is influenced by the layup direction, with cracks aligned to the layup exhibiting minimal hindrance to heat conduction, resulting in weaker high-frequency components in thermal images and poorer detection accuracy. In contrast, the composite structure of 3D-printed CFRP minimizes the impact of crack orientation. By analyzing the temperature characteristics of the crack center and thermal drag tail for cracks with varying opening angles, the study establishes a relationship between the crack opening angle, crack depth, and thermal features. Fitted curves of the ratio between crack opening angle and absolute temperature difference yielded an average R² of 0.9828 and MSE of 0.1287, validating the effectiveness of the proposed approach. Finally, the features of microcracks in CFRP deflector plates were effectively extracted through high-frequency filtering, which demonstrated the broad applicability and robustness of this study.

The prevalence of bacterial infections in wounds is a significant challenge to successful wound healing. This study investigates the antibacterial effect of hyaluronic acid and alginate aerogel loaded with zinc oxide nanoparticles as a potential dressing for wound healing. The aerogel composite was synthesized via supercritical gel drying and characterized by scanning electron microscope, Fourier transform infrared spectroscopy, and nitrogen porosimetry. The absorptivity of the prepared aerogel was evaluated, as well as the antibacterial activity, which was evaluated against common wound pathogens, including Staphylococcus aureus and Escherichia coli, using the agar diffusion method. The results show the effective antibacterial properties of the prepared hydrogel and aerogel. Furthermore, the results show water absorption ability of 5791 and 1585% for loaded and unloaded aerogels, respectively. The ZnO released from the aerogel exhibited a rapid release followed by a slow and sustained release. These findings highlight the potential of aerogels based on hyaluronic acid and alginate and loaded with zinc oxide nanoparticles as an innovative antibacterial wound dressing material, which is expected to improve wound healing and reduce the risk of bacterial infections.

This paper investigates the use of glass and carbon fiber-reinforced polymer composites with epoxy matrices for non-pneumatic tires (NPTs), as an alternative to conventional elastomer-based designs. A novel NPT design approach was developed in three steps: (i) a finite element model with isotropic material properties was constructed to identify suitable spoke geometries; (ii) an anisotropic parametric study quantified key parameters influencing the load-bearing capability of two selected concepts from step (i); and (iii) a preferred version was chosen from step (ii) and evaluated under multiple load cases to ensure it met all requirements. The final tire design incorporates thick spiral spokes superimposed with a cosine-like function, showcasing the strengths and limitations of non-elastomeric reinforced polymers for NPT design. This study provides innovative insights into reducing the mass of NPTs and demonstrates the potential of fiber-reinforced polymer composites to achieve more lightweight, durable, and efficient NPT designs in comparison to pneumatic ones.