Evolution of Filament-Shaped Porous Structure in Polycarbonate by Stretching under Carbon Dioxide

Abstract

Abstract:We found that a filament-shaped porous structure with periodic distance was obtained in polycarbonate for optical disk grade (OD-PC) film by stretching under compressed carbon dioxide (CO 2 ). The evolution of the characteristic porous structure was investigated by in situ observation during the stretching under compressed CO 2 and the optical microscopic observation of the stretched specimen. The voids were obtained under high CO 2 pressure as in the case of elevated temperature, suggesting that the evolution of the voids was caused by crazing due to chain disentanglement by accelerated molecular motion owing to the plasticization effect of CO 2 . The filament-shaped voids were initiated at around the yielding point and increased continuously by nucleation in the matrix around the surface of the pre-existing voids. The shape of the voids did not change to an ellipsoidal one during stretching due to suppression of the craze opening by the hydrostatic pressure effect. The stretching of the CO 2 -absorbed depressurized OD-PC revealed that the initiation of the voids was not only caused by the plasticization effect, but the hydrostatic pressure effect was also required.

Structural Evolution of Two-Phase Blends of Polycarbonate and PMMA by Simultaneous Biaxial Stretching

“…On the other hand, poly(methyl methacrylate) (PMMA) has poor toughness, but exhibits high scratch-resistance due to high surface hardness; its pencil hardness is 4H. The tensile property of glassy PMMA changes from brittle to ductile with increasing temperature [41], while that of glassy PC changes from ductile to brittle when the molecular weight is low [42,43]. Fracture toughness of PMMA and PC abruptly increases at very high loading rates [44].…”