Stiffening and Toughening Rigid Polymers Through Controllable Stress Concertation Induced by Hard–Hard Dual Nanophases

Rigid polymers generally face the rigidity-extensibility trade-off due to the contradictory requirements for chain-segment movability. Herein, both the rigidity and extensibility of rigid poly(lactic acid) PLA are obviously improved based on the controllable stress concentration induced by hard-hard dual nanophases, overcoming the long-standing trade-off. Based on masterbatch method and short-term low-temperature annealing, nanodispersed CNTs and nanoscale PLA crystals are constructed in PLA to serve as rigid stress concentrators with small size and high quantity. With the designed hard-hard dual nanophases, the Young's modulus, elongation at break, and toughness of PLA are improved by 32%, 644%, and 776% respectively. The combined high improvement in rigidity and extensibility is unprecedented for PLA. The toughening mechanism is revealed to be that hard-hard dual nanophases can initiate plentiful small-sized microcracks and suppress the development of microcracks during continuous deformation. Besides, the high rigidity of hard-hard dual nanophases imparts PLA with a significantly improved rigidity. Moreover, dual-nanophase PLA also shows improved heat resistance and electrical conductivity. We envision that this work will enrich the theory of polymer toughening and contribute to the industrial preparation of polymers with excellent comprehensive performances.