Evaluation of thermal treatments to improve physical and mechanical properties of bio-composites made from cotton byproducts and other agricultural fibers

• We evaluate thermal-treating on composites made from five natural fibers.
• Maximum treatment temperature was 185 °C.
• Composites made from phenol formaldehyde resin performed best.
• Thermal treating reduced water absorption compared to untreated specimens.
• Thermal-treating had mixed results on MOR and internal bond properties.

Demand for wood products continues to grow at levels that challenge the available resources. Alternative materials are sought to sustainably supplement the wood fiber industry. Experiments were conducted on composite boards made from agricultural residues. The boards were subjected to thermal treatments to improve mechanical properties. Board construction was accomplished by pressing fibers in a 10% resin matrix with 1.5% wax at 166 °C and 3.45 MPa. Composite boards were produced using cotton carpel, cotton stalks, kenaf, flax, and southern yellow pine, and cotton carpel blended 50/50% with kenaf, cotton stalks, flax and southern yellow pine. In one thermal treatment, fiber was heated to 185 °C for 30 min before the boards were made. In the other thermal treatment, finished boards were heated to 185 °C for 30 min. Four specimens from each board were subjected to water absorption, thickness swelling, internal bond, and stress testing modulus of rupture and modulus of elasticity in accordance with methods described in the American Society for Testing and Materials (ASTM) D 1037-06a. Thermal-treating the fibers post-fabrication reduced water absorption in all boards compared to untreated specimens. Thermal-treating had mixed effects on MOE, MOR, and internal bond with some fiber composites having improved values while others had lower values. Kenaf had significantly higher water absorption and swell properties compared to the other materials. Southern yellow pine and flax had equivalent water resistance. Composite blends with cotton carpel exhibited equal or improved mechanical properties compared to non-blended treatments.