IMPACT OF NEGATIVE THERMAL EXPANSION MATERIAL ZRW_2O_8 IN POLYCARBONATE COMPOSITES

摘要

Negative thermal expansion materials have the potential to offset the expansion of othermaterials when used as fillers in composites. For example, polycarbonate has excellentmechanical and optical properties, resulting in widespread use. However, its significant thermalexpansion can lead to problems in applications. Zirconium tungstate (ZrW_2O_8) shows isotropicNTE over a wide temperature range from -272.6 °C to 777 °C, and can be used to reduce theexpansion of NTE/PC composites. Nanosized ZrW2O8 can be obtained via a topotactictransformation zirconium tungstate hydroxide hydrate (ZrW_2O_7(OH)_2·2H_2O), which isaccessible by a hydrothermal method. For better interaction between inorganic particles andpolycarbonate, surface modifications were carried out by in situ polymerization reactions.Conditions for effective binding of oligomers on the particles surfaces were established. Freestanding composite films were cast after blending modified particles and commercialpolycarbonate. During this process, it is important to avoid crystallization, which alters themechanical and optical properties of polycarbonate. As polycarbonate easily crystallizes withany additives, the extent of crystallization was determined by powder x-ray diffraction. Theinteraction between the filler particles and matrix was investigated using scanning electronmicroscopy.