Water absorption behavior of wood polymer composites fabricated using stereolithography

The impact of environmental conditions on the performance of wood polymer composites (WPCs) is an important consideration due to their various applications including construction and automobiles. Water absorption behavior of WPCs is particularly important because of the hydrophilic nature of wood fibers. This study examined the water absorption and cyclic water absorption behavior of Maple-Oak polymer composites fabricated using stereolithography and tested their mechanical performance. Results in this study showed that the moisture absorption rate increased with higher wood content, due to the hydrophilic wood flour. The cyclic moisture absorption test showed variation in absorption behavior, a reduction in sample mass was observed due to degradation in the water after long term aging. The tensile strength decreased from 19.63 MPa in the dry 15 wt% wood flour composite to 5.13 MPa following water absorption at the same filler loading. In contrast, cyclic water absorption resulted in a more moderate reduction of 23%, with tensile strength decreasing to 14.94 MPa relative to the dry 15 wt% sample. The Young’s modulus experienced similar declines between the dry samples, and the water absorbed samples while the cyclic water absorbed samples performed better across all wood flour ratios. At 15 wt%, the compressive strength increased by 5% from 23.83 MPa in dry samples to 25.15 MPa following water absorption but subsequently decreased by 3.8% to 24.78 MPa after cyclic water absorption, relative to the dry control. This change was attributed to the plasticizing effect and stress redistribution borne by fiber swelling. Impact and hardness testing was performed with observed increases in hardness in dry samples but a gradual decrease in hardness in the water-absorbed samples, though these changes were not significant. Understanding the water absorption behavior of 3D printed WPCs provides a better benchmark for understanding their durability, dimensional stability, and long-term performance in moisture-prone environments, and expanding the capacity of 3D printed components for critical use.