Tree waste based advanced thermal insulation - Vacuum insulation panels - For application at up to 70 C

Vacuum Insulation Panels (VIPs), despite being the best performing thermal insulation, face the challenges of high cost and environmental concerns associated with the core material, which typically consists of fumed silica (FS) or glass fibres. This study experimentally assessed the suitability of two novel core materials, which were generated from waste tree-based natural fibres (TNF), as potential substitutes for the expensive and widely used fumed silica. A series of composite samples were developed by mechanically mixing TNFs with FS and compressed to manufacture cores (150 mm x 150 mm). Samples were investigated for their radiative, gaseous and solid conductivities using extensive experimental techniques to identify the most cost-effective core composite for VIPs exposed to temperatures up to 70 degrees C. The spectral extinction coefficient of TNFs was determined by the use of Fourier Transform Infrared Spectroscopy and results indicated that TNFs exhibited a greater spectral extinction coefficient compared to fumed silica within the short infrared wavelength range of 2.5-7.5 mu m. The radiative conductivity of fumed silica at a temperature of 70 degrees C was determined to be 3.33 mWm- 1K-1, whereas the radiative conductivity of TNF composites varied between 0.53 mWm- 1K-1and 0.39 mWm- 1K-1. The VIP sample, which consisted of 100% FS material, had a thermal conductivity 7.84 mWm- 1K-1 when measured at an average temperature of 20 degrees C. The observed value exhibited a substantial increase with the rise in temperature, reaching 11.58 mWm- 1K-1 at a temperature of 70 degrees C. VIP containing 30 % tree-based natural fibre had the lowest thermal conductivity of 6.75 mWm- 1K-1 and 8.28 mWm- 1K-1 at 20 degrees C and 70 degrees C, respectively, among all composites studied. For this sample, VIP core material cost decreased from 3.46 pound kg -1 per R-value (100% FS) to 2.19 pound kg - 1 per R-value at 20 degrees C. The study has concluded that a content of 30% of TNF is optimum for FS cores to deliver the most cost-effective VIP.