Binder less wood chip insulation panel for building use made from wood processing residues and wastes, 2: Effect of chip thickness and panel density on thermal conductivity and resistance against falling impact

A manufacturing technology using wood shavings for insulation panels for building uses was developed in this study. The wood shavings mat was cold-pressed without any binder and was wrapped with plastic film to keep it in the compressed state. In this study, panels with densities ranging from 80 to 120 cubic kg/m were manufactured by using two types of wood shavings with different thicknesses. The effect of chip thickness and panel density on thermal conductivity and resistance against falling impact was investigated. The dependence of thermal conductivity on temperature and moisture content, and changes of compressive stress with time under various humidity conditions were also investigated. Thermal conductivity showed a tendency to increase with increasing panel density. Thinner shavings provided the panel with lower thermal conductivity than thicker ones when compared at the same panel density. The thermal conductivity increased linearly with rising temperature or moisture content, and it was found that their effects were greater than on solid wood. On the other hand, better resistance against falling impact was obtained at higher panel density, and thinner shavings were superior to thicker ones when compared at the same panel density. While exposed to various humidity conditions for three months, panel compressive stress decreased up to approximately 40% under cyclic humidity conditions. At a panel density less than 100 cubic kg/m, resistance against falling impact became worse due to much reduced compressive stress. On the basis of these results, it can be concluded that the manufacturing conditions that balance better thermal insulation capacity and better resistance against falling impact can be achieved by using a panel density of 100 cubic kg/m and thinner shavings as the raw material.