Crazing Mechanism and Physical Aging of Poly(lactide) Toughened with PEO-PBO Diblock Copolymer

Poly(lactide) (PLA), a commercially available sustainable polymer, is an alternative to petroleum-based plastics. However, PLA lacks ductility and toughness limiting its applications. Small amounts of a liquid poly(ethylene oxide)-block-poly(butylene oxide) (PEO-PBO) diblock copolymer additive were blended with PLA to enhance its toughness. The incorporated PEO-PBO generated a macrophase-separated morphology with particle diameters of 0.2-0.9 μm. Adding 1.8 wt % PEO-PBO to PLA led to a 20-fold increase in elongation at break without affecting the bulk elastic modulus. The micromechanical deformation process of the PEO-PBO/PLA blend was investigated via in-situ small angle X-ray scattering during tensile testing. The volume of crazed material was proportional to the total surface area of the PEO-PBO particles and both quantities increased with PEO-PBO loading. Craze development was found to be independent of aging time. Therefore, the PEO-PBO/PLA blend was able to remain ductile compared to neat PLA. These results demonstrate that designing additives that promote deformation by crazing is an effective way to overcome the aging-induced embrittlement of glassy polymers.