Enhancement of Hygrothermal Properties of Bio-based Thermal Insulation Materials via Sol-gel Technology

Abstract

This study involves the modification of a bio-based aggregate, hemp shiv, using functionalised silica-based coatings. This is the first time sol-gel technology is used in the treatment of hemp shiv to develop sustainable thermal insulation building materials with enhanced hygrothermal properties. Bio-based materials such as hemp shiv have a tendency to absorb large amounts of water due to their hydrophilic nature and highly porous structure. In contrast, the high porosity of hemp shiv provides excellent moisture buffering and thermal insulating properties. In this work, the hydrophilicity of the hemp shiv was reduced without compromising its moisture buffering ability. A detailed investigation into the physical and chemical properties, surface roughness, porosity and microstructure of hemp shiv is presented. Application of coatings on hemp shiv was found to alter the properties of hemp shiv. The focus of this work was to particularly enhance the water-resistance of hemp shiv without significantly altering the morphology and microstructure of hemp shiv. The coatings were formulated by the cohydrolysis and polycondensation of tetraethoxyorthosilicate (TEOS). The effect of methytriethoxysilane (MTES) and hexadecyltrimethoxysilane (HDTMS) as functionalising agents in the coating was evaluated. The impact of precursors and their concentration in the coating formulation showed varying results on the hydrophobicity and roughness of hemp shiv. Furthermore, the porosity of hemp shiv was affected by the number of coating layers thereby blocking the pores responsible for the moisture buffering behaviour of hemp shiv. The selected coating formulation was found to increase the hydrophobicity of hemp shiv providing water contact angles up to 118° and reducing the water absorption rates by 250% without showing a significant reduction in the moisture absorption capacity. Novel thermal insulation building composites were developed using the coated hemp shiv in both a silica and a starch-based matrix. The composites were characterised for their hygrothermal, physical and mechanical properties where it was found that the sol-gel coating reduced water absorption capacity without affecting the moisture buffering ability of the composites. The newly designed light weight high performance composites have potential as sustainable thermal insulators and can establish innovative concepts for global application.

Date of Award	22 Nov 2018
Original language	English
Awarding Institution	University of Bath
Supervisor	Robert Lawrence (Supervisor) & Juliana Calabria-Holley (Supervisor)