FRACTURE-BEHAVIOR OF POLY(VINYL CHLORIDE) METHYL-METHACRYLATE BUTADIENE STYRENE POLYMER BLENDS

The fracture mode of poly(vinyl chloride)/methyl methacrylate/butadien e/styrene (PVC/MBS) polymer blends can change from ductile to brittle in accordance with the changes in shape of the test specimen or test c onditions. Therefore. the mechanisms of impact energy absorption and t he main cause of stress whitening are complicated. The following resul ts on PVC/MBS blends were obtained by carrying out fracture experiment s at different test speeds and temperatures: 1) The ductile/brittle fr acture mode of the PVC and PVC/MBS blends can be explained by sigma(c) (the craze initiation stress)/sigma(y) (the shear yield initiation st ress), which depends on the strain rates and temperature. 2) The fract ure behavior of the PVC/MBS blends can be classified into the followin g types from the standpoints of fracture mode and whitening degree: Fr acture I: ductile fracture without whitening: Fracture II: ductile fra cture with whitening: and Fracture III: brittle fracture without white ning. 3) The following concepts can be estimated from the measurements of yield stress, specific gravity and SEM, TEM and visual observation s. In Fracture I, shear yield occurs mainly. In Fracture II, both shea r yield and crazing occur. In Fracture III. deformation of the rubber and local crazing occur. 4) The main cause of stress whitening in PVC/ /MBS blends is light scattering by cavities in the rubber particles. 5 ) In Fracture II. at first. crazes with cavities in the rubber particl es occur. Then. shear yield occurs. Finally, crazes are healed by the heat, and only the cavities in the rubber remain.