Effect of Microstructure and Loading-Rate on the Mode I Fracture Behavior of Poly (lactic acid).

Abstract

Poly (lactic acid) was molded under four different kinds of condition to obtain samples with different microstructures. A single crystal was not observed in the specimen molded at 0°C. The size of spherulites became larger with increase of molding temperature. The density of spherulites increased with increase of molding time. Mode I fracture toughness, KIC was measured at a static (1 mm/min) and an impact loading rate (1 m/s). KIC became lower with increase of degree of crystallization at the static loading rate. This is mainly due to suppression of craze formation in the vicinity of crack-tip. On the other hand, at the impact loading rate, KIC increased with increase of degree of crystallization. Thus, the results showed that crystallization has significant influence on KIC, and its effect on the static KIC was different from that on the impact one. Relationship between fracture toughness and fracture micromechanism was discussed on the basis of the results of fracture tests and microscopies.