Water Resistance of Fully Bio-Based Particleboard Intended for Building Façade Application

Ventilated façades are increasingly used in building renovations, often containing non-renewable and CO2-emissions-intensive cement-based materials. Renewable biomass-based materials offer a more sustainable alternative with a high amount of sequestered CO2. However, water uptake is a critical factor in exterior applications. This study investigates the water resistance of high-density particleboards made of wheat straw (WS), grey alder (GA), and softwood (SW) for façade-related exterior applications. Two general board types were produced from each biomass using (1) steam explosion (SE) treatment and (2) the addition of birch-bark-derived suberinic acids (SAs) as the bio-based binder. In addition, the influence of conventional and mold hot pressing was investigated. The particleboards were coated with four types of innovative finishes, comprising (1) purified SA, (2) SA + chitosan (SH), (3) SA + earth pigment (SP), and (4) SHP. The water resistance of the particleboards was evaluated using an internal bonding (IB) test after 2 h of boiling and by measuring the water drop contact angle. FTIR analysis was performed to identify differences between the board varieties and to explain the obtained results. Only two board varieties (GASA and SWSA) fulfilled the Type P5 EN 312 water resistance requirement (0.15 N/mm2), achieving IB values of 0.81 ± 0.23 N/mm2 and 0.22± 0.07 N/mm2, respectively. In turn, the coatings used did not significantly increase the static contact angle compared to the reference board. Although the results of this study confirm the inherent moisture sensitivity of engineered particleboards, two board varieties demonstrate promising potential for façade-related exterior applications.