IMPACT OF NEGATIVE THERMAL EXPANSION MATERIAL ZRW_(2)O_(8) IN POLYCARBONATE COMPOSITES

摘要

Negative thermal expansion materials have the potential to offset the expansion of other materials when used as fillers in composites. For example, polycarbonate has excellent mechanical and optical properties, resulting in widespread use. However, its significant thermal expansion can lead to problems in applications. Zirconium tungstate (ZrW_(2)O_(8)) shows isotropic NTE over a wide temperature range from -272.6 deg C to 777 deg C, and can be used to reduce the expansion of NTE/PC composites. Nanosized ZrW_(2)O_(8) can be obtained via a topotactic transformation zirconium tungstate hydroxide hydrate (ZrW_(2)O_(7)(OH)_(2)(centre dot)2H_(2)O), which is accessible by a hydrothermal method. For better interaction between inorganic particles and polycarbonate, surface modifications were carried out by in situ polymerization reactions. Conditions for effective binding of oligomers on the particles surfaces were established. Free standing composite films were cast after blending modified particles and commercial polycarbonate. During this process, it is important to avoid crystallization, which alters the mechanical and optical properties of polycarbonate. As polycarbonate easily crystallizes with any additives, the extent of crystallization was determined by powder x-ray diffraction. The interaction between the filler particles and matrix was investigated using scanning electron microscopy.