Studies on the Biaxial Stretching of Films, (part 24). Molecular Orientation and Mechanical Properties of Uniaxial and Biaxial Stretched Poly(methyl methacrylate) Films.

Abstract

The relationship between molecular orientation and mechanical properties of poly (methyl methacrylate) films prepared by various types of stretching was investigated. The specimens were prepared by stretching the hot-pressed films to various ratios under two rates of 50 or 100%/min at 110-120°C in a circulating hot air bath. The Stretching methods were two types of uniaxial strechting with free and constant width, and simultaneous biaxial stretching. For the estimation of molecular orientation, the birefringence were measured using a tilting technique. Mechanical properties are discussed in terms of stress-strain curves.The following results were obtained:(1) The molecular orientation in the films uniaxially stretched with free width was uniaxial with cylindrical symmetry around the stretching axis, and the anisotropy of mechnical properties in the machine direction is greater than that of the other samples.(2) The uniaxially stretched films with constant width showed a uniplanar-axial orientation, in which the direction of molecular chain was parallel to the stretching axis and the film surface, Thus, Young's module were nearly equal in both the machine and transverse directions.(3) For the simultaneousbiaxially stretched films, the molecular chain showed a uniplanar orientation, which was a random orientation within the film along with parallel to film surface, at all stretch ratios. Mechanical properties of balanced films were isotropic in the film plane regardlless of the stretch ratio, and increased with stretching ratio.(4) On the transmittance of film for ultraviolet-visible radiation, all stretched films were slightly transparent than that of the unstretched film.