ARS | Publication request: Evaluation of various heat treatments to improve physical and mechanical properties of composites made from cotton burs, cotton stalks, kenaf, flax, and southern pine blends

Submitted to: Association for the Advancement of Industrial Crops Conference
Publication Type: Abstract Only
Publication Acceptance Date: October 15, 2012
Publication Date: November 12, 2012
Citation: Holt, G.A., Chow, P., Wedegaertner, T.C. 2012. Evaluation of various heat treatments to improve physical and mechanical properties of composites made from cotton burs, cotton stalks, kenaf, flax, and southern pine blends. Proceedings of The Association for the Advancement of Industrial Crops 24th Annual Meeting. November 12-15, 2012, Sonoma, CA. p. 45.

Technical Abstract: Previous studies evaluating physical and mechanical properties of composites produced from blends of cotton carpel (burs), cotton stalks, kenaf, and southern yellow pine indicated water absorption and thickness swell properties higher than composites made from 100% southern yellow pine. In the previous studies, Urea-Melamine-Formaldehyde (UMF) was the resin. As a continuation of the previous studies, this study evaluated composites produced from blends of cotton burs (B), cotton stalks (S), kenaf (K), flax, (F), and southern yellow pine (P) using two resins, UMF and Phenol-Fomaldehyde (PF). The objective of this study was to assess the impact of select heat treatments (pre and post) on the physical and mechanical properties of composites produced from various blends of B, S, K, F, and P, using two resins, compared to composites (heat treated and untreated) produced from 100% P and 100% commercial hardwood fibers (H). Experiments were conducted on 10 composite board blends. All fibers were processed through a hammermill and a shaker table so particles were within 0.42 to 4mm. All fibers were dried to less than 5% moisture content and blended with one of two binding agents comprised of either 10% UMF or 8% PF adhesive with 1.5% wax emulsion. Heat treatments consisted of heating fibers either pre- or post-board fabrication using an oven at 185C for 30 min. Board construction was accomplished using a 91-Mg capacity oil-heated hydraulic press. Composite boards, 0.635 cm by 40.6cm by 43.2cm, were produced using the following blend of fibers: 100% B, 50B/50K, 50B/50S, 50B/50F, 50B/50P, 100P, 100H, 100F, 100S, and 100K. Three specimens from each board were subjected to water absorption, thickness swelling, internal bond, and static bending stresses (modulus of rupture [MOR] and modulus of elasticity [MOE]). The testing was performed in accordance with methods described in Part B of the American Society for Testing and Materials (ASTM) D 1037-06a. Results indicate heat treating the fibers post-fabrication improved water absorption in all boards compared to untreated specimens. Heat treating had mixed effects on MOE, MOR, and internal bond with some fiber composites having improved values, while others had lower values. Composites with flax fibers exhibited water resistance equivalent to the 100% P and H composites. Composites made with PF resin were more dimensionally stable than those made with UMF.