Supertoughened Polylactide via the Addition of Low Content Poly(ε-caprolactone) and Tensile Deformation above the Glass Transition Temperature

Polylactide(PLA) is considered as an ideal alternativeof petroleum-basedplastics due to its high tensile strength and biodegradability. However,the low impact strength limits its extensive application in the engineeringfield. In this work, a supertough binary PLA blend was fabricatedthrough pre-stretching above the glass transition temperature to acertain pre-strain. The biodegradable and biocompatible poly(& epsilon;-caprolactone)(PCL) was used as a toughening modifier for the PLA/PCL 95/5 (wt/wt)blend. It was found that the impact strength increased with the increasein pre-strain. The highest notched Izod impact strength reached 251kJ/m(2) at the pre-strain of 400%, nearly 132 times of thatfor neat PLA (1.9 kJ/m(2)). To our knowledge, such fabulousimpact toughness has not been referred in literature. Even at thepre-strain of 150%, the blend exhibited a sufficiently high notchedIzod impact strength of 149 kJ/m(2). Small-angle X-ray scatteringdemonstrated a typical structural feature of combination of PLA shish-kebabsand oriented PCL lamellar stacks due to strain-induced crystallization.The wide-angle X-ray diffraction indicated that PLA crystals had highorientation at the pre-strain of 200% and above. The crystallinityof the PLA matrix increased with the increase in pre-strain, whichwas consistent with the increasing trend of impact strength. The highorientation of shish-kebabs and increased crystallinity of PLA matrixwere the key factors for drastically toughening PLA. This work providesa feasible and effective method to manufacture competitive PLA materials,which can be extended to improve impact toughness of other brittleglassy polymers.

Automated summary

In this study, a supertough binary PLA blend was fabricated by pre-stretching above the glass transition temperature, leading to significantly improved impact strength. Small-angle X-ray scattering and wide-angle X-ray diffraction analysis revealed that pre-stretching increased the orientation and crystallinity of PLA crystals, which greatly enhanced its toughness. This work offers a feasible and effective method to manufacture competitive PLA materials.