Mechanical and Thermal Insulation Properties of Porous Silica/Polyurethane Composites

Porous hydroxyl-terminated polybutadiene-based polyurethane (HPU) composites containing various hollow glass microspheres (HGMs) up to 75 vol.% were synthesized by one-step bulk polyaddition-type polymerization. An unfilled (non-porous) HPU sample was also prepared as a reference. The thermal conductivity of the HPU/HGM composites, which are considered as a three-phasic material composed of a bulk HPU matrix, silicate thin layer, and pores, could be predicted perfectly by the Felske model. The thermal properties, such as Tg and thermal stability, of the HPU/HGM composites were affected slightly by the addition of HGMs compared to the unfilled HPU. On the other hand, the shell thickness and volume of the HGMs played an important role in determining the mechanical properties of the composites leading to reinforcement with increasing wall thickness and content of HGMs.