Effect of cooling conditions on the mechanical properties of crystalline poly(lactic acid)

Appropriate cooling conditions in melt processing were found to provide crystalline poly(lactic acid) (PLA) with greater mechanical toughness in tensile tests. PLA films cooled near its glass transition temperature T-g showed ductile behavior, whereas those obtained by a quenching process exhibited brittle fracture. The content of gauche-gauche (gg) conformer, which leads to low critical onset stress for shear yielding, increased in the films cooled near T-g. The crystallinity of the films hardly affected their mechanical toughness and proportion of gg conformer except for that with a high degree of crystallinity (> 50%). (C) 2017 Wiley Periodicals, Inc.