Effect of Perfluoropolymers on the Anti-Wear Properties of Carbon Fiber/Polyphenylene Sulfide Composites: A Comparative Study

In this work, several perfluoropolymers (PFP), including commercial polytetrafluoroethylene (PTFE), perfluorinated ethylene-propylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and irradiated PTFE (iPTFE) were used as additives to lubricate carbon fiber (CF)-reinforced polyphenylene sulfide (PPS) composites. The tribological properties of the yielding composites were studied and correlated with the melt processability of PFPs. Although the neat FEP and PFA have higher friction coefficients when compared with neat PTFE, the composites filled with FEP and PFA additives were found to exhibit a lower friction coefficient compared to PTFE at PFP content below 10 wt %. Moreover, the iPTFE-filled composites also showed similar results as FEP or PFA filled ones, very different from PTFE at low additions. Based on the morphological investigation, we postulate that FEP, PFA, and iPTFE are melt-kneaded with PPS due to their melt processability at processing temperature, leading to the good dispersion in composites in the form of smaller deformed spheres and/or fibril bands. The well-dispersion of PFPs in composites promotes the formation and growth of the transfer film on the counterface during sliding.

The synergistic effect of polytetrafluoroethylene in-situ fibrillation and dibenzoyl sebacate hydrazide on the crystallization and foaming behavior of poly (lactic acid)

The fully degradable poly (lactic acid) foam with green environmental protection characteristics can alleviate the shortage of petroleum resources caused by the application of plastics. However, due to the inherent low melt strength and slow crystallization rate of linear PLA. It is difficult to obtain PLA microcellular foam with good morphology. In order to obtain PLA microcellular foam with ultra-high expansion ratio and small cell size, PTFE (polytetrafluoroethylene) nanofibers with excellent CO₂ adsorption rate were introduced. Self-assembled nucleator TMC-300(dibenzoyl sebacate hydrazide) was also introduced to blend with PLA to obtain small-sized cells. The results show that the PTFE entanglement network as a self-assembled template can effectively improve the early crystallization nucleation efficiency and increase the crystallinity of branched PLA (CBPLA)/TMC by 7 %. The microcellular foam with PTFE content of 0.5 wt% (CBPLA/TMC/PTFE 0.5) was successfully prepared by physical foaming agent, which had the lowest cell size (8.7 μm) And high expansion ratio (1200 %).

Effects of grafting and long-chain branching structures on rheological behavior, crystallization properties, foaming performance, and mechanical properties of polyamide 6

Polyamide 6 (PA6) was modified with ethylene maleic anhydride syndiotactic copolymer resin (ZeMac), and triglycidyl isocyanurate (TGIC) as modifiers to prepare a grafting structure and a long-chain branching structure, respectively. The effects of two modifiers on the rheological behavior, crystallization properties, foaming performance, and mechanical properties of PA6 were systematically studied by rotating rheometry, differential scanning calorimetry and scanning electron microscopy. The results showed that there were differences in crystallization properties between the two modification methods, but they significantly improved the rheological, foaming performance, and mechanical properties of PA6. In particular, PA6 with long-chain branching structure through TGIC modification showed better performance in various physicochemical characterizations. The introduction of ZeMac reduced the average diameter of bubbles in pure PA6 from 146.32 to 88.12 µm, and the density of bubbles increased from 1.69 × 105 to 5.35 × 105 cells·cm−3. The introduction of TGIC reduced the average diameter of bubbles in pure PA6 from 146.32 to 64.36 µm, and the density of bubbles increased to 1.31 × 106 cells·cm−3. Moreover, the mechanical properties of both nonfoamed and foamed samples were improved after modification.

Flexibly Controlling the Polycrystallinity and Improving the Foaming Behavior of Polylactic Acid via Three Strategies

Controlling foamability plays the central role in preparing PLA foams with high performances. To achieve this, chain extension was often used to improve the rheological property of PLA resins; however, despite the availability of this approach, it often deteriorates the biodegradability of PLA and greatly increases the processing cost and complexity. Hence, we reported a special crystallization induction method to design PLA foams with a tunable cellular structure and a high expansion ratio. A novel crystallization-promoting agent combination (D-sorbitol, CO2, and phenylphosphonic acid zinc salt) was used to induce PLA to enhance the chain interaction force and chain mobility and to provide crystallization templets. A series of PLAs with tunable stereocomplex (Sc)/α crystallinity and rapid non-isothermal crystallization ability were obtained. The effect of various crystallization properties on the foaming behavior of PLA was studied. The results demonstrated that proper crystallization conditions (a small spherulite size, a crystallinity of 6%, and rapid crystallization ability) could virtually contribute to the optimized cellular structure with the highest cell density of 4.36 × 106 cell/cm3. When the Sc crystallinity was above 10%, PLA had a superior foamability, which thereby resulted in a high foaming expansion ratio of 16.2. A variety of cellular morphologies of PLA foams could be obtained by changing the foaming temperature and the crystallization property. The proposed crystallization-induced approach provided a useful method for controlling the cellular structure and the performances of the PLA foams.

Improvement of Mechanical and Biological Properties of PLA/HNT Scaffolds Fabricated by Foam Injection Molding: Skin Layer Effect and Laser Texturing

Polylactic acid (PLA) is one of the important materials for orthopedic regenerative engineering applications due to its biodegradability and biocompatibility. Nonetheless, PLA may show insufficient mechanical strength for some bone replacement applications. Halloysite nanotube (HNT) is one of the non-toxic, biocompatible reinforcement for improving mechanical and biological properties of PLA for tissue engineering applications. In this study, PLA/HNT scaffolds were prepared by chemical foam injection molding process. Laser surface texturing was applied on the skin layer of the injection molded scaffolds to enhance the cell viability and hydrophilicity of PLA. The effects of HNT concentration on cell morphology, mechanical and thermal properties, cell viability and biodegradation profile of the scaffolds were studied. The results demonstrated that cell viability increased by 43% in PLA/HNT scaffolds compared to neat PLA. Hydrophilicity of the scaffolds that have thick skin layer was enhanced by the laser surface texturing in two different designs and consequently, cell viability increased about 16%. Surface roughness measurements and water contact angle measurements have verified this result.

Rheological behavior, crystallization properties, and foaming performance of chain-extended poly (lactic acid) by functionalized epoxy

The branched/micro-crosslinked structure formed by chain extension reaction between EGMA and PLA improved the rheological behavior and crystallization properties of PLA, which ameliorated the foaming performance of various PLA samples.