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Abstract: Cavitation and superstructure evolution of polymers during stretching play crucial roles to influence the mechanical properties of materials. In this study, we investigated deformation-mediated superstructures and cavitation of poly (l-lactide) (PLA) as well as their dependence on stretching temperatures by in-situ small-angle X-ray (SAXS) analysis coupled with mechanical testing. It is found that the cavitation and crystalline deformation are strongly influenced by stretching stress during deformation, which significantly depends on the stretching temperature. At lower stretching temperature (70 °C), the cavitation is initiated before the yielding and then stimulates the crystallite shearing. At higher stretching temperature (90 °C), however, the crystallites shear firstly and then crystalline deformation promotes the formation of cavities orientated along the stretching direction. High stretching temperature benefits the formation of relatively perfect crystals with high orientation. The results provide the basic knowledge of how to adjust the mechanical properties of polymer materials by controlling their superstructure in the deformation process. [Copyright &y& Elsevier]

Abstract: The present work explored the structure-property correlations for the biopolymer poly(l-lactic acid) (PLA) by studying deformation-mediated molecular orientation and crystallization. The structural and morphological variations of amorphous PLA under different strain rates were investigated. The result showed that strain rate significantly influences its strain-hardening behavior. The crystallinity and orientation as well as cavitation of deformed PLA increase with the increase of strain rates. The structure evolution has been divided into three potential stages: (i) at small strains (<100%), the crystallinity of PLA increases by orientation-induced crystallization; (ii) at intermediate strains (100%–160%), the crystallinity of deformed PLA slightly decreases due to the breakage of existing crystals under stress accompanying with newly formed voids and cavities; (iii) at high strains (>160%), the increasing number of oriented chains in the amorphous regions promotes the crystallization of PLA. Our study suggests that strain rate and stretching strain play important roles on modulating the crystallization and orientation of amorphous PLA. [Copyright &y& Elsevier]