Effects of initial morphology and molecular weight on the deformability of poly(ethylene terephthalate)

Abstract

AbstractSolution‐grown crystal (SGC) mats and solution‐cast (SC) films of poly(ethylene terephthalate) (PET) were drawn by solid‐state coextrusion followed by tensile drawing of the coextrudates. Drawabilities and properties of the drawn films, such as mechanical and thermal properties, were investigated as functions of molecular weight, initial morphology, and drawing conditions. The initial morphology and molecular weight have a marked effect on the drawability and tensile properties of the resultant drawn films. The attainable maximum draw ratio increases with increasing molecular weight, and the highest draw ratio of 11.5 can be achieved by two‐stage drawing of SC films prepared from pellets with an intrinsic viscosity of 1.43 dl/g. Such highly drawn films exhibit a tensile modulus of 17.5 GPa and strength at break of 400 MPa. These values are comparable to those obtained in conventional spinning of standard grade PET. At a given draw ratio, the tensile strength of the drawn films increases with increasing molecular weight, but the molecular weight dependence is not so marked in the tensile modulus as in the tensile strength. At a given molecular weight, the drawability of SGC mats is lower than that for SC films; however, the efficiency of drawing is higher for the former than for the latter. The difference may arise from the difference in crystallinity and/or crystal perfection of predrawn samples.