Properties of thermoplastic composites with cotton and guayule biomass residues as fiber fillers

This study was conducted to evaluate the suitability of using residual plant fibers from agricultural waste streams as reinforcement in thermoplastic composites. Three groups of plant fibers evaluated included cotton burrs, sticks and linters from cotton gin waste (CGW), guayule whole plant, and guayule bagasse. The plant fibers were characterized for physical (bulk density and particle size distribution) and chemical properties (ash, lignin and cellulose contents). A laboratory experiment was designed with five fiber filler treatments, namely control (oak wood fiber as the filler - OWF), cotton burr and sticks (CBS), CBS with 2% (by weight) second cut linters (CBL), CBS with 30% (by weight) guayule whole plant (CGP), and CBS with 30% (by weight) guayule bagasse (CGB). The composite samples were manufactured with 50% of fiber filler, 40% of virgin high-density polyethylene (HDPE), and 10% other additives by weight. The samples were extruded to approximately 32 × 7 mm cross-sectional profiles, and tested for physico-mechanical properties. The CBS and CBL had considerably lower bulk density than the other fibers. Cotton linters had the highest α-cellulose (66.6%), and lowest hemicellulose (15.8%) and lignin (10.5%) of all fibers tested. Guayule whole plant had the lowest α-cellulose and highest ash content. Both CBS and guayule bagasse contained α-cellulose comparable to OWF, but slightly lower hemicellulose. Evaluation of composite samples made from the five fiber treatments indicated that fibers from cotton gin byproducts and guayule byproducts reduced the specific gravity of the composites significantly. However, the CBS and CBL samples exhibited high water absorption and thickness swelling, but the addition of guayule bagasse reduced both properties to similar levels as the wood fiber. The CGP exhibited significantly lower coefficient of thermal expansion. Composite samples with the five different fiber fillers showed similar hardness and nail holding capacity, yet oak fibers imparted superior strength and modulus under flexure and compression with the exception of the compressive modulus of CGB composites. In general, both cotton ginning and guayule processing byproducts hold great potential as fiber fillers in thermoplastic composites.     

Termite resistance of biobased composition boards made from cotton byproducts and guayule bagasse

Large quantities of cotton gin byproducts (CGB), also known as cotton gin trash or cotton gin waste, are being produced across the cotton belt of the United States annually. Similarly, guayule wastes after rubber latex production is expected to increase as this industry begins to expand. Use of these waste materials in value-added products can help the economics of the crops and aid in alleviating waste management issues and environmental problems. Conventional wood preservatives used to protect wood from insect and microbial damage are of concern to human health and the environment. Guayule bagasse (GB) has been shown to have termite control properties, and a combination of cotton gin and guayule wastes could also have such valuable properties. An initial study evaluating the physical and mechanical properties of boards produced from these two biomasses was published in 2009, this study is a continuation focusing on the termite resistance of boards produced. Thus, the objective of this research was to determine the termite resistance property of experimental composition boards made from CGB and GB. Composition boards were made from five different ratios of CGB to GB: 100:0, 75:25, 50:50, 25:75 and 0:100 (C100, C75-G25, C50-G50, C25-G75, and G100, respectively). Additionally, three-layered boards (3-layer) consisting of 25% GB (upper layer), 50% CGB (middle layer), and 25% GB (bottom layer) were made. For comparison, a commercial southern pine lumber board (SPB), a commercial oriented strandboard (OSB), and a commercial preservative treated medium density fiberboard (MDF) were included in the testing. This testing was an extension of a previous study where the mechanical properties of the CGB and GB composition boards were compared to select commercial standards. Five specimens were cut from each of the nine different board treatments and tested using Eastern subterranean termites. Weight loss, termite survival days, and visual grade of each specimen were determined according to testing standards. Results confirmed good termite control quality for boards made from GB alone. Boards containing CGB to GB ratios of 75-25 and 50-50 obtained similar termite resistance as the commercial OSB based on the total weight loss and one-week termite mortality rate. Visual grading of tested specimens revealed all six CGB and GB composition boards and the treated MDF showed better rating than the commercial OSB and pine lumber. No differences were noted among the total termite surviving days for the six CGB and GB composition boards. Overall, the biobased CGB and GB boards showed promise with the boards containing GB exhibiting improved termite resistance properties than SPB and OSB.