Alkali-extracted tree bark for efficient bio-based thermal insulation

•Utilization of bark as a renewable thermal insulation material.•Alkaline extraction treatment and lyophilisation to modify properties of poplar bark.•Thermal conductivity results can be compared with current natural thermal insulation materials. Efficient bio-based thermal insulation materials are capable of providing a significant contribution to green building. As natural barrier material, tree bark is potentially suitable for thermal insulation purposes. However, since the natural thermal insulation performance of tree bark is only modest, procedures for improving insulation e.g. by reducing density, may be of interest. In the present study it is shown that by means of a mild alkaline extraction up to 50% of the mass of tree bark can be removed, resulting in density less than a third of untreated bark. After lyophilisation, a thermal conductivity of bark treated with this procedure of approx. 0.045 W(mK)−1 compared to 0.065 W(mK)−1 for untreated bark was determined. Thus it is demonstrated that underutilised and widely available bark residues from forest resources present a potential alternative raw material for efficient bio-based thermal insulation, given that remaining technological challenges such as circumventing the necessity of lyophilisation are solved.