Mechanisms of Photo Degradation for Layered Silicate-Polycarbonate Nanocomposites

摘要

The use of advanced lightweight materials to improve combat survivability has been of crucial interest to the U.S. Army for a number of years. Specifically, hybrid organic/inorganic polymer matrix nanocomposites show promise in providing many of the physical properties required (i.e., lightweight structure, rugged abrasion resistance, and high ballistic impact strength). However, as with any polymer system, these materials are susceptible to degradation over time when exposed to various environmental (i.e., sunlight, moisture, temperature, etc.) conditions. This structural degradation will eventually compromise the original integrity of the materials' desired properties. Polycarbonate (PC) has outstanding ballistic impact strength, good optical clarity, and high heat-distortion resistance. The Army has a continuous interest in research on PC for better chemical resistance and enhanced resistance to abrasion. The focus of this research is to exploit nanotechnology through incorporation of layered silicates for property enhancement. Typical mica-like clays consist of stacked platelets with the thickness of each individual platelet on the order of 1 nm. In this study, the effect of accelerated weathering upon newly developed PC-layered silicate nanocomposite materials was investigated. The silicate loading varied from 0 to 3.5% by weight. A fluorescent ultraviolet (UV)/condensation weatherometer was selected for the exposure study. The materials were characterized by UV/VIS spectroscopy and Fourier transform infrared spectroscopy. The results reveal that the carbonate linkages undergo a scission reaction upon UV exposure, thereby compromising the original properties of the material. Furthermore, these scissions produce a yellowing of the polymer matrix that can inhibit its use where optical clarity in important.