Bio-based and recycled materials: characterisation and hygrothermal assessment for passive relative humidity management
Action is needed for Europe to achieve the higher rates of renovation to reduce energy usage and decarbonize building stock. Bio-based materials are a solution to this problem as they combine their reusable and recyclable ability with an improved hygrothermal behaviour to save energy. However, the passive mechanisms and the hygroscopic characteristics associated to these materials is not yet understood, limiting the optimisation of bio-based products. 11 different bio-based insulation samples were tested with the intention of developing a ‘green indoor panel’ for domestic property: 4 different types of wool insulation, Hemp, Wood Wool Board, Saw Mill Residue, Wood Fibre, Straw, ICB and PET. Sample characterisation was executed via SEM imaging, thermocouples, dry and saturated thermal conductivity and density in addition to moisture buffering value (MBV) (where samples were exposed to step changes in relative humidity of 75% and 53% for 8 and 16 hours respectively). SEM imaging demonstrates the surface morphology of the sample giving an initial indication of the materials characterisation. More fibrous samples demonstrate larger air pockets, giving inherently lower thermal conductivity values in comparison to a more heterogenous sample. Furthermore, MBV is not per si a defining characteristic to decide the hygrothermal properties of a material but the shape of the final mass change graph should also be considered. On saturation of samples thermal conductivity values increase and some samples cannot exhibit an efficient water adsorb/desorption exchange. Using thermocouples, latent heat of vapourisation and condensation can be demonstrated as an indication of the stabilisation of the sample. From 11 samples, the innately best 3 samples have been selected for further experimentation: Wool 1, Wool 2 and Saw Mill Residue.