Submitted to: Industrial Crops and Products
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/15/2011
Publication Date: 2/16/2011
Citation: Bajwa, S., Bajwa, D., Holt, G.A., Nakayama, F., Coffelt, T.A. 2011. Properties of thermoplastic composites with cotton and guayule biomass residues as fiber fillers. Industrial Crops and Products. 33(3):747-755. Interpretive Summary: Utilization of cotton gin byproducts, gin waste/trash, has been a topic of research for decades. Recent studies have been focused on the areas of energy, erosion control products, or as a substrate/filler in composite boards. This study reports on using cotton gin byproducts as a potential replacement filler in composite boards. In this study, several blends of cotton gin byproducts and guayule bagasse, plant residue from the extraction of resin from the guayule plant, were evaluated and compared to oak wood fiber in the manufacture of thermoplastic composite boards. Several mechanical and physical properties were evaluated from each of the test specimens. The test specimens from blending cotton gin byproducts, guayule bagasse, and guayule (whole plant) showed promise as replacement filler in most mechanical properties except thickness swelling (water absorption). The addition of the guayule bagasse material helped reduce the thickness swelling of the cotton gin byproduct material. Overall, cotton gin byproducts are more readily available than guayule currently is and could be a viable source of material to supplement wood fiber, but the blends need to be optimized to minimize the water absorption capabilities of the gin byproducts.
Technical Abstract: 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 32x7 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 alpha-cellulose (66.6%), and lowest hemicellulose (15.8%) and lignin (10.5%) of all fibers tested. Guayule whole plant had the lowest alpha-cellulose and highest ash content. Both CBS and guayule bagasse contained alpha-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. The composite samples with the four different fiber combinations of CBS, CBL, CGP, and CGB showed hardness and nail holding capacity similar to that of composite made from wood fiber, yet their strength and modulus under flexure and compression were slightly less than that of OWF composite except for the compressive modulus of CGB composites. In general, both cotton ginning and guayule processing byproducts hold great potential as fiber fillers in thermoplastic composites.