Growing pressure on forest resources and demand for sustainable building materials are increasing interest in valorizing tree bark, a high-volume sawmilling residue, into engineered products. This thesis investigates the feasibility of producing high-performance binderless Douglas-fir (Pseudotsuga menziesii) bark boards and establishes an integrated process-property framework. The work examines how furnish preparation, board density, and pressing severity (temperature and time) govern bonding performance, while developing a pressing-severity model for schedule design and a scalable bark board for cladding applications. In the first stage, process development evaluated mat ventilation (solid cauls vs. metal screens), pressing schedule (conventional pressure control vs. breathing and degassing), furnish type and density (particle vs. fibre furnish; 800–1050 kg/m³), and initial moisture content (1, 4, and 8%) in relation to bonding and board performance. Core gas pressure and temperature measurements showed that replacing caul plates with metal screens and introducing breathing and degassing steps effectively suppressed delamination without compromising heat transfer efficiency. Fibreboards consistently outperformed particleboards, particularly at 1050 kg/m³, while an initial moisture content of 1% maximized bonding strength and undried furnish (~8%) caused severe vapour-induced defects. The second stage focused on performance optimisation and self-bonding mechanisms for high-density fibreboards targeted for cladding applications. Four fibre types were compared to identify the optimum fibre size and pressing temperatures of 200–260 °C, and times of 6–18 min were evaluated in relation to internal bond (IB), modulus of rupture (MOR), thickness swell (TS), and water absorption (WA). Boards made with fine fibres at 1050 kg/m³ delivered the best overall performance. Under this configuration, optimum properties were achieved at 260 °C and 14 min, where IB was 2.4 times that of commercial MDF, and TS and WA outperformed the siding requirement by 75% and 57%, respectively. A semi-empirical relationship between specific IB and pressing severity factor (PSF) was established as IBₛ = 3.73 ln(PSF) − 4.58. Scalability was demonstrated by manufacturing 2 ft × 2 ft panels and a mock-up wall system, while durability was comparable to Western Red Cedar in soil decay tests and showed <5% mass loss in termite tests.
Jiawen Shen (Thu,) studied this question.