Thermo-physical properties of polyester fiber reinforced fumed silica/hollow glass microsphere composite core and resulted vacuum insulation panel

Abstract

In recent years, various fiber/powder hybrid core materials (HCMs) are increasingly used as VIP core. In this paper, novel HCMs from mixtures of fumed silica (FS), hollow glass microsphere (HGM), polyester chopped strand fibers, titanium dioxide and carbon black powders were successfully fabricated by the dry powder mixing method. The effect of various HGM fractions on the thermo-physical properties of the HCMs and resulted VIPs was investigated. The HCMs possessed an excellent porous structure with a high porosity of 80–90% and a fine average pore size of 19.0–181.1nm while the corresponding VIPs had a low density of 170–298kg/m3. HGM additions led to a shift in the average pore diameter of HCMs toward a finer value and more concentrated distribution but posed an increase on specific surface area of the HCMs. Both the compression and rebound ratio of the VIPs were greatly reduced by adding HGMs in FS matrix. Total thermal conductivity versus air pressure (from 0.1Pa to 1.013×105Pa) curves of the HCMs with various HGM contents and the contributions of gaseous, solid, and radiative thermal conductivity on total thermal conductivity of the HCMs were conducted, respectively. The results showed that the total thermal conductivity of VIPs increased with the HGM addition but could maintain at a low value of less than 7.2mW/(mK) when HGM content was less than 26wt.%. HCMs with 6wt.% HGM were recommended for VIPs in refrigeration while that with 26wt.% HGM were recommended for VIPs in building sectors.