Abstract
This dissertation consists of three projects that aim at evaluating phenolic based thermoset resins for use in extrudable wood composites. The goal of this dissertation is to use biobased resin system and nanocellulose reinforcement to create high-performance, sustainable wood-based composites for extrusion-based additive manufacturing (AM). To create extrusion-grade composites with pseudoplastic behavior and successful extrusion into continuous rods with good mechanical performance after curing, a partially biobased novolac resin was created by substituting 50% phenol with wood-derived pyrolysis oil and compounded with wood flour. Smaller particle sized wood composite enhanced thermal stability and interfacial interactions, while the addition of wood raised the curing peak temperature and decreased reaction enthalpy.
To build on this, phenol resorcinol formaldehyde (PRF) systems were mixed with 1–3 wt% of nanocellulose (cellulose nanocrystals (CNC), bleached and unbleached nanofibers (BNF, UBNF)) to enhance the curing, rheological, and mechanical properties. The influence of resin aging was also investigated. Nanocellulose raised the curing temperatures and slowed down gelation. 1 wt% made the material stiffer and stronger, but 3 wt% caused it to aggregate and reduce performance. Fresh PRF showed better properties than aged resin.
These findings were then used to create extrusion-processable wood-PRF composites as feedstocks for additive manufacturing, where nanocellulose enabled a tunable rheology, including improved yield stress and shear-thinning behavior required for printability. All formulations were effectively extruded into continuous rods, CNC increased stiffness, nanofibers increased strength, and water absorption decreased, indicating increased durability in wood composites.
Overall, this work shows that sustainable, high-performance composites with customized rheology and mechanical properties may be manufactured using biobased resin systems and nanocellulose reinforcement. These advancements highlight the significance of AM in promoting sustainable construction by supporting the wider benefits of extrusion-based AM, such as decreased material waste, lower greenhouse gas emissions, increased construction efficiency, and the capacity to address labor shortages through automation.