Development of binderless bark boards as a high-performance exterior building product

With exterior cladding as the target application, this study developed an optimized refining and pressing strategy for converting Douglas-fir bark, which is rich in lignin and extractives, into high-performance binderless boards. Board structure development was first examined by comparing particle and fibre furnish at target densities of 800, 925, and 1050 kg/m³ , followed by evaluation of coarse and fine fibre, press temperatures (200–260°C) and times (6–18 min). Internal bond, modulus of rupture, thickness swelling, and water absorption were tested, together with termite and soil-decay resistance to assess durability-related performance. Thermal and spectroscopic analyses were used to better understand the mechanisms contributing to bond development and durability. Board integrity was best with fine fibre pressed to 1050 kg/m³ , and optimum properties achieved by pressing at 260°C for 14 min, meeting North American standard requirements for cladding. Bark boards had superior bonding and water resistance compared to representative wood-based panel benchmarks, and termite and soil-decay tests indicated promising biological durability. The successful fabrication of larger 600 × 600 mm panels for a prototype demonstration supports process scalability. This work demonstrates a durable bio-based cladding product from bark that could reduce reliance on petrochemical adhesives while creating higher-value uses for forestry residues.