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 alternative of petroleum-based plastics due to its high tensile strength and biodegradability. However, the low impact strength limits its extensive application in the engineering field. In this work, a supertough binary PLA blend was fabricated through pre-stretching above the glass transition temperature to a certain pre-strain. The biodegradable and biocompatible poly(ε-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 increase in pre-strain. The highest notched Izod impact strength reached 251 kJ/m2 at the pre-strain of 400%, nearly 132 times of that for neat PLA (1.9 kJ/m2). To our knowledge, such fabulous impact toughness has not been referred in literature. Even at the pre-strain of 150%, the blend exhibited a sufficiently high notched Izod impact strength of 149 kJ/m2. Small-angle X-ray scattering demonstrated a typical structural feature of combination of PLA shish-kebabs and oriented PCL lamellar stacks due to strain-induced crystallization. The wide-angle X-ray diffraction indicated that PLA crystals had high orientation at the pre-strain of 200% and above. The crystallinity of the PLA matrix increased with the increase in pre-strain, which was consistent with the increasing trend of impact strength. The high orientation of shish-kebabs and increased crystallinity of PLA matrix were the key factors for drastically toughening PLA. This work provides a feasible and effective method to manufacture competitive PLA materials, which can be extended to improve impact toughness of other brittle glassy polymers.