Molecularly Oriented Films for Space Applications

Abstract

Because of their inherent toughness and flexibility, low density, thermal stability, radiation resistance and mechanical strength, aromatic polyimides have excellent potential for use as advanced materials on large space structures. Polyimides were uniaxially and biaxially oriented to further enhance their dimensional stability, stiffness, elongation and strength. Both unoriented and oriented polymeric thin films were also cryogenically treated to temperatures below -184 °C to show their stability in cold environments. Successful stretching depended on film quality, film thickness, soak time, grip pressure, stretching rate and stretching temperature. In-plane birefringence increased with increased stretch ratios as expected. Coefficients of thermal expansion (CTEs) decreased with increased stretch ratio by as much as 31%. Tensile strengths increased by up to 85% with increasing stretch ratio. Elongations increased by as much as 95% with stretching. Significant improvements in elongation were obtained with only a 2× uniaxial orientation. Moduli did not change significantly with stretching. Mechanical properties increased more with uniaxial stretching than biaxial stretching. Cryogenic treatment increased the tensile strength of some stretched samples by a maximum of 10–20%. Properties such as modulus and CTE did not change significantly after the films had been slow cooled to cryogenic temperatures.