Biaxially stretched in comparison with conventionally blown coextruded composite plastic films

Abstract

Multilayer composite films consisting of polyolefins, either polypropylene, linear low density or medium density polyethylene, a thin adhesive layer, and a polyamide in various ratios were prepared using two basically different processes. The first, a conventional blown film process in which the extrudate is stretched while in the molten state; and the second, a two‐stage process in which the quenched extrudate is stretched at a temperature below the polymers' melting point. The films so prepared, having identical composition and similar extents of stretching, were compared on the basis of their tensile properties, thermoelastic shrinkage, oxygen transmission rate, and thermal behavior. The effects of stretching temperature, rate, and extent on the behavior of the composite films and control single layer films were investigated. The stretching temperature was found to be the dominating single process parameter in determining the films' behavior. The overall performance including tensile properties, barrier, and shrink properties of the “cold” stretched films was found markedly superior to that of the conventionally blown films. The stretched composite films possess physical properties that cannot be attained by the conventional process.

Molecularly Oriented Films for Space Applications

“…In this study, molecular orientation and cryogenic treatment have been utilized to potentially enhance material properties of space durable polyimides useful for these space applications. Polymer film properties influenced by stretching include, but are not limited to [12][13][14][15][16][17][18][19][20][21][22][23]: (a) mechanical properties such as tensile strength, modulus and elongation; (b) structural properties such as orientation, crystallinity and birefringence, and (c) other properties such as electrical conductivity, coefficient of thermal expansion, creep and surface roughness. Some general trends observed when films are oriented include: (a) tensile strength and modulus increase with increased stretch ratio, (b) elongation and creep strain decrease with increased stretch ratio, (c) crystallinity increases with increased stretch ratio and stretching rate, and (d) birefringence increases with increased stretching rate and stretch ratio but decreases with increased stretching temperature.…”

Partially miscible EVOH/copolyamide-6/6.9 blends: The effect of stretching on the structure

“…The Δ n 12 values strongly depended on the composition of the EVOH‐rich blends but varied just slightly in the COPA‐rich blends. As previously described for stretched films,35 the ratio of molecular orientation, which is partially relaxing, and unrecoverable viscous flow depends on the stretching temperature; the lower the temperature is in the T g to T m region, the higher the orientation is. Because the stretching temperature was 80 °C for all compositions, the EVOH‐38 phase was expected to be much more oriented than the COPA phase (the melting temperatures of EVOH‐38 and COPA were 174 °C and 133 °C, respectively, and their T g values were 58 and 30 °C, respectively13).…”