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The aim of this study was to improve the mechanical performance of biodegradable poly(L‐lactic acid) through equal channel angular extrusion (ECAE). Changes in morphology induced by the ECAE shear deformation in poly(lactic acid) (PLA) were investigated. Differential scanning calorimeter results suggested a significant improvement in crystallinity of ECAE‐deformed PLA depending on its thermal condition and deformation force. Two‐dimensional wide angle X‐ray diffraction measurement and polarized FTIR spectroscopies of ECAE‐deformed PLA revealed a structural network in the crystalline region, and the taut tie molecules (TTMs) connecting lamellae also stretched. Scanning electron microscope results showed that the macro‐fibrils were generated, and the oriented structures were arranged along the nominal shear direction at a certain angle. Both the inclined macro‐fibrils structure and the oriented TTMs within fibrils were beneficial in improving mechanical performance. Finally, the mechanical property tests showed that the mechanical properties of PLA were improved overall. The tensile strength, elongation, impact strength, and bending strength increased by 28%, 123.8%, 224.3%, and 47.6%, respectively. Meantime, a transition from brittle fracture to ductile fracture was observed from the original PLA billet to ECAE‐deformed one. Therefore, the ECAE process represents a promising approach for comprehensively reinforced PLA. [ABSTRACT FROM AUTHOR]

An investigation specifically focusing on the relationship among processing parameters, structure, and mechanical properties of solid two‐stage die‐drawn polypropylene (PP) has been done in this study, which aimed at providing a reliable reference in the choose of appropriate conditions that can be able to meet a specific processing requirement. PP sheets were drawn through a self‐design solid two‐stage die‐drawing apparatus to various drawing ratios (DRs) at different speeds and with different die‐exit thicknesses. The results showed that tensile strength, modulus, and the degree of orientation significantly increased with the nominal DR and could be further improved by increasing the drawing speed. While the crystallinity increased prior and decreased to near a constant value when the drawing speed was over 150 mm/min in the researched scope. Larger the die‐exit thickness was, lower the orientation degree was but higher the crystallinity could be obtained. Compared with crystallinity, orientation degree plays a leading role in the final product properties during a two‐stage solid die‐drawing process. POLYM. ENG. SCI., 59:2347–2355, 2019. © 2019 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the effects of extra oscillatory shear field on morphology and mechanical properties of β-nucleated isotactic polypropylene by using a homemade vibration-assisted extrusion apparatus, in which oscillatory shear field was introduced into the extrusion head driven by crank and link mechanism. The results show that the extra oscillatory shear filed induces a significantly enhanced orientation of β-crystal besides causing a better homogeneous dispersion of β-nucleant, and the oriented β-crystal has a high ratio of daughter lamellae to parent lamellae orientation, which was rarely reported in other literatures. The vibration increased the overall crystallinity and changed the relative content of β-crystal. For the higher level nucleation agent content iPP(0.4 wt%), the relative contents of β-crystal just changed a little or basically unchanged after vibration. However, for iPP contenting 0.2 wt% nucleation agent, the content of β-crystal decreased. All the changes in the morphology, crystallinity, dispersion of β-nucleant and β-crystal content had a great influence on the mechanical properties, and that result was the improvement of yield stress and decrement of the elongation at break. POLYM. ENG. SCI., 57:838-845, 2017. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]