Tree bark utilization in insulating bio-aggregates: a review

This review gives an overview of recent advances in research on the role of tree bark material in bark-cement bio-composites, and their potential as building insulation materials. Suberin and other bark extractives seem to be of great importance for the insulation properties of such composites. Bark is a readily available, biological raw material with unique properties and it has revealed promising results as a bio-insulation material, either alone or in mixtures with different matrices (cement, lime, resins, polymers, etc.). The thermal, mechanical, acoustic, and hygroscopic properties of these bark-insulating composites depend on several factors, primarily the type of tree bark, the density and mechanical strength of the bark, the density of the boards produced, and the ratio of bark material to the binder material used in the board production (cement, lime, resins, polymers, etc.). The size of granules and the thickness of the board produced seem to be factors with a lower impact on the properties of the bark-cement composites. A low proportion of bark fibers or particles (0.5-1%) in bark-cement composites has proven highly beneficial to their mechanical and thermal properties and ensures higher workability of the mixture. Different modification treatments of bark material should be investigated, with the aim of decreasing the bark extractives content, to improving the cement setting, decreasing the unstable hemicellulose components and their hygroscopic nature, improving the bark particles' durability in alkaline environments, and upgrading their adherence properties. As the demand for alternative, sustainable structural materials keeps rising, the cement-bark composites will undoubtedly keep attracting the attention of the scientific and industrial world. (C) 2021 Society of Chemical Industry and John Wiley & Sons, Ltd