DYNAMIC VISCOELASTIC PROPERTIES OF THE BIAXIALLY STRETCHED POLYPROPYLENE FILMS

Abstract

The effects of molecular orientation and crystallization on the dynamic viscoelastic properties of the biaxially stretched polypropylene films were investigated.The specimens were prepared by stretching T-die extruded films to various ratio by various methods at 145°C at a rate of 1600%/min in a circulating hot-air bath. The stretching methods of films were uniaxial under the conditions of free and/or constant width, two-way successivebly biaxial and simultaneously biaxial stretching.The temperature dependence of tanδ, dynamic modulus, E′, and dynamic loss, E″, of the stretched films were measured at 100 c. p. s. using a Viscoelastic Junior Spectrometer.The following results were obtained:(1) The stretched films by each process show characteristic dynamic viscoelastic properties due to the orientation and crystallization.(2) The peak value of tan δ in the αa-absorption region, E′ and E″ values, of the stretching direction (MD) were higher than those of transverse direction (TD) for the uniaxially stretched films. These tendency is observed in the two-way successively biaxially stretched films. These values of MD and TD are some for the simultaneously biaxially stretched films.(3) The molecular chains in the biaxially stretched films seem to be more extended than in the uniaxially stretched films.(4) The temperature of tan δmax changes with the stretching conditions. This is due to the fact that the temperature depends not only on the degree of orientation but on the orientation mode and the orientation direction.