The effect of wheat straw bleaching on some mechanical properties of wheat straw/LDPE biocomposites

Abstract

Using biocomposites containing wheat straw (WS) and synthetic polymers like polyethylene (PE) has gained tremendous popularity, but its application in the packaging industry is not substantial. Due to the prevalence of raw WS color which manifests itself in the WS/LDPE biocomposite, the present investigation is dedicated to fabricate a bleached WS/LDPE composite. Thus, raw WS and the pulp of WS were treated with three levels of xylanase, five concentrations of hydrogen peroxide and five levels of sodium dithionite. The bleached raw WS and its pulp were used to fabricate WS/LDPE composites and their colorimetric properties were measured using L*, a*, and b* coordinates. The results indicated that "bleached raw WS with 4% H2O2" and "bleached WS pulp with 10 units of xylanase and by addition of 1% H2O2" demonstrate the highest degree of lightness based on L* value. Then, 40% of above mentioned treatments were blended with LDPE to develop a biocomposite using a twin screw extruder. Further, lightness index and the mechanical properties of the final composites were measured. Results indicated that the composites containing unbleached raw WS had the lowest and the bleached WS pulp with 10 unites of xylanase and 1% H2O2 had the highest L value amongst all treatments. Also the raw WS/LDPE and the bleached raw WS/LDPE composites had the highest and the lowest tensile strength, respectively. It needs to be mentioned that the flexural strength of all treatments was higher than the control, whereas the impact resistance of them was lower than the control.