Mechanical properties of moulding material made from crop stalks and modified UF resin

Abstract: Due to advantages in being lightweight, inexpensive, biodegradable, and an easy process, composite materials with plant fiber filler have been widely applied in industry, agriculture, national defense, and other fields. In this study, flowerpots in a friendly environment were moulding-prepared through the procedure of mixing and hot-pressing in an oil hydraulic machine. The flowerpots were made of rice husk, rice husk power, and modified urea-formaldehyde resin. The rice husk or husk power components were added as reinforcing agents, while the resin component was added as a matrix material. The purpose of this paper is to discuss the influence of the dosage of urea-formaldehyde resin (UF), modified urea-formaldehyde resin (SUF), ratio of rice husk and rice husk power, and the wet cycle treatment on the mechanical property of the flowerpots. Thermal stability and microstructure of the flowerpots treated with the rewetting method were analyzed by Thermo-gravimetric Analysis (TGA) and a Scanning electronic microscope (SEM). The results showed that the mechanical properties of the flowerpots could be improved by applying modified urea-formaldehyde resin or adding rice husk power. With the dosage of modified UF, modulus of rupture, modulus of elasticity, and tensile strength of the straw flowerpot all improved. The modulus of rupture, modulus of elasticity, and tensile strength were 75.48 MPa, 16.06 GPa, and 17.44 MPa, respectively, when the ratio of reinforcing agent and matrix material was 1:0.5 (w/w) and the ratio of unbroken rice husk and rice husk power was 3:7 (w/w). Wet cycle treatment led mechanical parameter values of all formula specimens to decline in different degrees, with tensile strength and maximum bending deformation of SUF-pot specimens dropping most significantly. Using rice husk as the reinforcing agent (RH) in the wet cycle treatment resulted in the modulus of rupture, modulus of elasticity, and tensile strength of UF/RH to drop to 21.97%、24.91%、and 15.09%, while SUF/RH dropped 9.92%、15.37%, and 30.10%, respectively. TGA analysis showed that the pyrolysis rate and mode of the straw flowerpot materials by wet cycle treatment had been slightly changed; namely materials mass loss rate was reduced and maximum thermal decomposition temperature increased. The SEM graphs of the composites fractured surface showed that the surface of the flowerpots treated by wet cycling had become rough. Some pieces of rice husk divorced from modified urea formaldehyde resin were clearly visible. Obviously, the interface between rice hull and SUF had become weak. This test showed that the straw flowerpots prepared with SUF resin were less stable than those prepared with UF resin, which implied that the former was liable to degrade. In regard to the production costs, the straw flowerpots are more than 10% lower than the plastic flowerpots. Substitution of plastic flowerpots with straw flowerpots would not only be beneficial in reducing white pollution from the use of plastic products, but also in promoting comprehensive utilization of the crop straw. Therefore, there will be an excellent market prospect of straw flowerpots.