The Development of Composites with Negative Thermal Expansion Properties Using High Performance Fibers

Almost all solid materials exhibit positive thermal expansivity. However, in many engineering designs, materials with negative thermal expansivity are desirable. The characteristics of high performance fibers, such as high strength, exceptional thermal conductivity and electrical insulation may also include negative thermal expansivity. Therefore, it should be possible to develop fiber reinforced composites with negative thermal expansivity by using an optimum combination of particular fiber reinforcements and a polymer matrix. This paper describes the development of such high performance fiber reinforced composites with negative or low thermal expansivity using four high strength fibers — polyethylene fiber (Dyneema), poly-p-phenylenebenzobisoxazole fiber (Zylon), aramid fiber (Technora) and carbon fiber (Torayca). The results showed that the newly developed Dyneema fiber and Zylon fiber composites exhibited significant negative thermal expansivity. Structural products of a stable size over a wide temperature range can be obtained by this method of controlling the coefficient of thermal expansion.