Quasi‐brittle to ductile transition in impact‐modified PVC

The toughness of impact‐modified poly(vinyl chloride) (PVC) compounds was examined by using a modified Charpy test. Increasing impact speed resulted in a quasi‐brittle to ductile transition in all PVC compounds. In the quasi‐brittle region, a PVC of 56,000 M_w fractured through a craze‐like damage zone that could be described by a modified Dugdale model. Furthermore, the same molecular‐weight PVC modified with either 10 pph (parts per hundred parts by weight) of chlorinated polyethylene (CPE) or 10 pph of methylmethacrylate‐butadiene‐styrene (MBS) impact modifier also conformed to the Dugdale model with the craze‐like damage zone. The CPE effectively improved the impact performance of PVC by shifting the quasi‐brittle to ductile transition to a higher loading rate. Compared to CPE, MBS was a better impact modifier, and its use resulted in a higher quasi‐brittle to ductile transition loading rate in the same PVC matrix. Fracture initiation toughness of all the materials was described by the Hayes‐Williams modification of the Dugdale model. The intrinsic brittle fracture energy obtained by extrapolation to zero craze length was determined only by the PVC matrix and was independent of the impact modifier. However, the kinetics of craze growth, and hence the response to rapid loading, depended on the impact modifier. Increasing the molecular weight of the PVC resin resulted in a more complex damage zone that was not amendable to the Dugdale analysis. J. Vinyl Addit. Technol. 10:11–16, 2004. © 2004 Society of Plastics Engineers.