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Hydroxyapatite (HA) and Halloysite nanotubes (HNTs) percentages have been optimized in Polycaprolactone (PCL) polymeric matrices to improve mechanical, thermal and biological properties of the composites, thus, to be applied in bone tissue engineering or as fixation plates. Addition of HA guarantees a proper compatibility with human bone due to its osteoconductive and osteoinductive properties, facilitating bone regeneration in tissue engineering applications. Addition of HNTs ensures the presence of tubular structures for subsequent drug loading in their lumen, of molecules such as curcumin, acting as controlled drug delivery systems. The addition of 20% of HA and different amounts of HNTs leads to a substantial improvement in mechanical properties with values of flexural strength up to 40% over raw PCL, with an increase in degradation temperature. DMA analyses showed stability in mechanical and thermal properties, having as a result a potential composite to be used as tissue engineering scaffold or resorbable fixation plate.

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In this study, poly(lactic acid) (PLA)/polytetrafluoroethylene (PTFE) composites containing different amounts of PTFE were prepared by melt blending. The mechanical, crystallization, and foaming properties of the prepared composites were investigated. Tensile test results indicated that the mechanical properties of the composite with PTFE showed significant reinforcement and toughening effects. The average elongation‐at‐break of the composite increased by 72% compared with pure PLA. Scanning electron microscopy (SEM) showed that the PTFE elongated into fibrils during blending and formed a physical network of entanglements in the melt. Differential scanning calorimetry (DSC) also showed that PTFE had a significant nucleation effect on polymer crystals and greatly increased the crystallinity of the PLA matrix. Moreover, PTFE dramatically enhanced the melt viscosity of PLA, which was investigated by rheological tests. The injection molding foaming experiments revealed that adding 1 wt% PTFE had the most notable heterogeneous nucleation effect on foamed cells, with the cell size decreasing from 81.5 μm for neat PLA to 25.2 μm, and the cell density increasing from 1.34 × 108 cells/cm3 to 2.53 × 109 cells/cm3. POLYM. ENG. SCI., 57:570–580, 2017. © 2016 Society of Plastics Engineers

Ultra‐high‐molecular weight polyethylene (UHMWPE) powder was processed using injection molding (IM) with different cavity thicknesses and injection‐compression molding (ICM). The processing parameters of feeding the powders were optimized to ensure proper dosage and avoid jeopardizing the UHMWPE molecular structure. Dynamic mechanical analysis (DMA) and Fourier‐transform infrared spectroscopy tests confirmed that the thermal and oxidative degradations of the material were avoided but crosslinking was induced during melt processing. Tensile tests and impact tests showed that the ICM samples were superior to those of IM. Increased cavity thickness and ICM were helpful for reducing the injection pressure and improving the mechanical properties due to effective packing of the material. Short shot molding showed that the UHMWPE melt did not exhibit the typical progressive and smooth melt front advancements. Due to its highly entangled polymer chains structure, it entered the cavity as an irregular porous‐like structure, as shown by short shots and micro‐computed tomography scans. A delamination skin layer (around 300‐μm thick and independent of cavity thickness) was formed on all IM sample surfaces while it was absent in the ICM samples, suggesting two different flow behaviors between IM and ICM during the packing phase. POLYM. ENG. SCI., 59:E170–E179, 2019. © 2018 Society of Plastics Engineers

Abstract:The processability of injection molding ultra-high molecular weight polyethylene (UHMWPE) was improved by introducing supercritical nitrogen (scN 2 ) or supercritical carbon dioxide (scCO 2 ) into the polymer melt, which decreased its viscosity and injection pressure while reducing the risk of degradation. When using the special full-shot option of microcellular injection molding (MIM), it was found that the required injection pressure decreased by up to 30% and 35% when scCO 2 and scN 2 were used, respectively. The mechanical properties in terms of tensile strength, Young's modulus, and elongation-at-break of the supercritical fluid (SCF)-loaded samples were examined. The thermal and rheological properties of regular and SCF-loaded samples were analyzed using differential scanning calorimetry (DSC) and parallel-plate rheometry, respectively. The results showed that the temperature dependence of UHMWPE was very low, suggesting that increasing the processing temperature is not a viable method for reducing injection pressure or improving processability. Moreover, the use of scN 2 and scCO 2 with UHMWPE and MIM retained the high molecular weight, and thus the mechanical properties, of the polymer, while regular injection molding led to signs of degradation.