Submitted to: Trade Journal Publication
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2009
Publication Date: 10/15/2009
Citation: Bajwa, S., Bajwa, D., Holt, G.A. 2009. Optimal substitution of cotton burr and linters in thermoplastic composites. Forest Products Journal. 59(10):40-46. Interpretive Summary: Fully utilizing agricultural waste materials into value-added products has found renewed interest in recent years. In particular, finding a use for cotton gin byproducts that can be implemented across the cotton belt has been problematic. One application that has shown promise for utilizing the 2 to 3 million tons of product produced across the cotton belt each year is thermoplastic composites. In this study, two fiber fillers comprised of cotton burs and cotton burs with 2% second cut linters were evaluated for use in thermoplastic composites. The two fiber fillers were used in varying percentages ranging from 25 to 100 with the remaining fraction being oak wood flour. The various cotton bur (CB), cotton bur with 2% second cut linters (CBL), and wood flour (WF) blends were extruded into sample boards that were evaluated for physical an mechanical properties compared to a sample board made of 100% wood flour (the control sample). Results indicate some properties were equal to wood while others were adversely different than wood. For example, nail withdrawl force for all fiber filler samples were equal to the 100% wood samples while the water absorption and thickness swell properties were higher than the wood sample for some of the CB and CBL blends. Overall, the CB 25% blend performed the best. The higher percentages of CBL blends had problems due to “balling up” of the lint in the samples which caused imperfections in the mixing and blending of the materials and created weak spots in the boards. If the fibers could have been oriented or uniformly mixed in the blends without “balling up” the fibers may have performed differently. Currently, a commercial evaluation of the 25% CB and wood blend will be undertaken based on results from this study.
Technical Abstract: A study was conducted to evaluate various substitutions of cotton burr and linters fractions of cotton gin waste (CGW) as a natural fiber source in ligno-cellulosic polymer composites (LCPC.) Samples were fabricated with approximately 50% natural fiber, 40% of high-density polyethylene (HDPE) powder, 4% mineral filler and 6% of lubricant, by weight. The composition of the fiber filler was varied from 0, 25, 50, 75 and 100% by weight of either cotton burr (CB), or cotton burr with 2% of second cut linters (CBL), with the remaining fraction as wood flour. Samples were extruded in to rectangular profiles with a 31.7 X 6.3 mm die, and tested for physical properties such as specific gravity, water absorption and thickness swelling, and mechanical properties such as flexural strength, flexural modulus, hardness, screw withdrawal strength, and coefficients of linear thermal expansion (CLTE). Both CB and CBL improved the surface hardness of the LCPC, but deteriorated water absorption as well as strength properties such as modulus of elasticity (MOE), modulus of rupture (MOR) and compressive strength. A favorable property of CBL was its effectiveness in decreasing CLTE of LCPC.