Abstract
This dissertation presents studies that aim to improve and optimize the properties of wood-thermoset composites for additive manufacturing (AM) applications. Specifically, it aims to improve the mechanical properties of wood-sodium silicate (SS) composites, while considering other factors such as extrudability and cost. Short hemp fibers (HF) were first explored to improve the flexural and compressive strength of the composite. HF of lengths 1, 3, 5 mm at 2.5, 5 and 10 wt% were tested at SS at 45, 50 and 55 wt%, while 40-mesh wood fibers (WF) were kept constant in this study. The study showed that flexural and compression strengths of the composite can be improved by 31.2% and 35.6% respectively using 5% HF of 3 mm length. The study showed that longer (5 mm) and higher HF fractions (10 wt%) were difficult to process and extrude for manufacturing.
The use of hemp hurd (HH) in addition to HF was explored to further improve the mechanical properties of the composite and optimize the formulation. HH fractions of 5, 10, 15 wt% were explored, along with SS wt% of 50, 55, 60. Different types of WF were considered, (Pellet WF and unsifted WF) and compared with 40-mesh WF. A formulation of 55 wt% SS, with 10 wt% HH and pellet WFT was found to be optimum, balancing mechanical strengths, costs, processing and extrudability. Compared to the baseline (50 wt% SS, 50 wt% 40 mesh WF), the average strength was improved by 75%, and strength-to-cost ratio was improved by 29.4%.
A novel and cost-effective method of manufacturing continuous fiber-reinforced thermoset composites for screw-based AM was developed and the tensile strength of wood-SS composites (WSSC) reinforced with continuous HF were characterized. Hemp twines were treated by dipping in either water or a SS solution to improve interfacial adhesion with the WSSC matrix. The tensile strength of the composite increased from 5.52 MPa for unreinforced WSSC to 8.44 MPa for WSSC reinforced with SS treated hemp twine, representing a 53% increase.
Overall, these studies have significantly increased the tensile, flexural, and compression strength of the WSSC using short HF, HH and continuous HT reinforcement, and contributed to the advancement of sustainable AM.