Impact. of Environmental Conditions on Fiberglass-reinforced Polyurethane Foam Composites

Abstract

Incorporating reinforcement within a polymer (i.e. composite) can obtain substantial performance increases. However, composites may he susceptible to conditions that could have a significant impact on their performance. The objective of this study was to characterize SpaceAge Synthetics (SAS) fiberglass-reinforced rigid, closed-cell polyurethane foam (PU) after subjected to various environmental conditions. SAS composites were characterized as a function of material composition after conditioned to extreme temperatures, moisture, ultraviolet irradiation (UV), or a combination thereof. The experimental process involved accelerated conditioning to further induce property changes and assure long-term integrity. Empirical expressions for SAS composites were generated to represent performance changes for different environmental conditions. Increasing temperature 93 °C from ambient showed an 18% decrease in strength and 24% decrease in stiffness for a 450 kg/m3 foam density reinforced with 7.6% fiber volume fraction. This performance loss resulted from the ductility of the polymer increasing with temperature. Decreasing temperature 68 °C from ambient showed a 56% increase in strength and 26% increase in stiffness. When SAS composites were subjected to moisture at room temperature, no statistical difference was observed after being exposed to l 00% RH for 72 h duration. These mechanical performance analyses included varying material parameters such as: foam density, fiber content, void content, and thickness. The addition of heat to the l 00% RH moisture drastically reduced mechanical performance up to 33% in strength and 22% in stiffness. Ultraviolet irradiation caused chemical changes within the SAS composites, which was first noted by the pronounced color shift within the yellowness index (YI). Additional reinforcement near the surface created a 269% lower shift in YI. It was observed that initially cross-linking occurred while at the same time chain scission was occurring at a larger rate. Fourier Transform Infrared Spectroscopy proved that UV penetrated 0.25 mm within the surface, showing the effects occur mainly on the surface. Finally, SAS composites exhibited a 31 % increase in strength and a 12% increase in stiffness with a post cure process. Post curing for 4 h at 100 °C raised the glass transition temperature from 119 °C to 128 °C. The performance increase was attributed from the post cure process inducing additional cross-linking within polymer chains.