G.A. Holt

Optimal Substitution of Cotton Burr and Linters in Thermoplastic Composites

A study was conducted to evaluate various substitutions of cotton burr and linters from cotton gin waste (CGW) as natural fiber reinforcements in ligno-cellulosic polymer composites (LCPC). Samples were fabricated with approximately 50 percent natural fiber, 40 percent high-density polyethylene, 4 percent mineral filler, and 6 percent lubricant, by weight. The experiment included substituting wood fiber in LCPC with 25, 50, 75, and 100 percent (by weight) cotton burr (CB) and cotton burr mixed with 2 percent (by weight) second-cut linters (CBL), respectively, with the remaining fraction as wood fiber and comparing it against the control (100% wood). Samples were extruded into rectangular profiles and tested for physical and mechanical properties such as specific gravity (SG), water absorption, thickness swelling, coefficients of linear thermal expansion (CLTE), flexural strength and modulus, compressive strength, hardness, and nail withdrawal force (NWF). The CB and CBL treatments exhibited SG, CLTE, hardness, and NWF comparable to the control. However, the water absorption and thickness swelling, flexural strength and modulus, and compressive strength all deteriorated at high substitution rates of CB and CBL. The favorable properties of cotton burr included its tendency to decrease CLTE and increase hardness of LCPC.

Commercial-scale evaluation of two agricultural waste products, cotton burr/stem and module wraps, in thermoplastic composites and its comparison with laboratory-scale results

Laboratory-scale research had shown the potential of using cotton burr/stem (CBS) as fiber filler in thermoplastic composites. This study evaluates the potential of using waste materials from cotton harvesting/ginning operations, CBS and cotton module wraps (CMWs), as a filler and substrate in thermoplastic composites at commercial scale. The study also compares the effect of scale-up from laboratory to commercial scale on the properties of the thermoplastic composite materials. Two separate commercial trials were conducted to manufacture thermoplastic composite boards with (a) 0, 12.5, 25 and 37.5% by weight of CBS and (b) up to 30% by weight of CMW. Testing of these samples showed that commercial-scale samples with 12.5% CBS had all properties comparable to those made with wood filler. At higher substitution rates, CBS tended to increase water absorption and coefficient of thermal expansion, and increase nail-holding capacity (NHC) and hardness in commercial-scale samples. This study also showed that CMW can be substituted by up to 30% by weight without deterioration of properties in comparison with a commercially available product. Scaling of the process had significant influence on all properties tested, expect NHC. In general, all commercial-scale samples exhibited physicomechanical properties within the range of properties reported for commercially available wood–plastic composite decking materials.