Investigation of the possibility of eliminating the natural flavor (color and smell) of wheat straw/LDPE biocomposite for packaging application

Biocomposites are materials composed of plant fibers and synthetic polymers that have attracted a significant amount of attention due to their role in reducing problems caused by plastic waste management. These materials have already been used vastly in various other industries, while they have only been introduced to the packaging industry recently. Hence, a project entitled "Production of Wheat Straw/Polyethylene composite and Study of its Various Properties" was defined and implemented. The successful production and characterization of these composites and their observed defects, such as the pungent odor and the different color compared to pure polyethylene, led to the start of this investigative project. Thus, using different bleaching methods – natural and/or chemical, wheat straw was bleached. The xylanase enzyme was used in the natural method in levels of 5 , 10 , and 20 units per gram of the raw material (lignocellulosic pulp), and substances such as hydrogen peroxide and sodium ditiunat were used in the chemical method in levels of 1 , 2 , 3 , and 4 percent. The results of the different bleaching treatments showed that xylanase as a natural and friendly environment material reduced the consumption of bleaching chemical substances. Furthermore, the xylanase enzyme supplementation for prebleaching of wheat straw pulp, decreased the consumption of chemical hydrogen peroxide as a main treatment in the bleaching method. In addition, using xylanase reduced the kappa number and lignin content of pulp. It is the other benefit of xylanase enzyme supplementation before the major bleaching. Finally, the best results of the different bleaching treatments in terms of lightness (Lvalue) including "bleached wheat straw with 4% hydrogen peroxide (WS (B))", and "bleached wheat straw pulp with xylanase and followed by 1% hydrogen peroxide (Pulp (B))" were chosen as filler materials and were mixed with pure polyethylene as a matrix in ratio of 60 to 40, and MAPE (maleic anhydride polyethylene) as a compatibilizer (%10). Mechanical, thermal, and colorimetric properties of treatments were evaluated and compared to control sample (pure polyethylene). The lightness index of composites was showed that the unbleached wheat straw composite had the lowest L value, and the bleached wheat straw pulp with xylanase and hydrogen peroxide 1% had the most L value after polyethylene. The mechanical properties of composites was also showed that the tensile strength of all treatments was less than pure polyethylene. Raw wheat straw + polyethylene composite and the bleached wheat straw + polyethylene composite had the highest and the lowest tensile strength respectively among the treatments. The flexure bending strength of all treatments was better than the control treatment. Impact resistance of all treatments was lower in compared to control. The results of the thermal behavior of the composites from DSC curves showed that the melting temperature of bleached wheat straw pulp with xylanase and hydrogen peroxide1% composite was higher than pure polyethylene and the others. The maximum and the minimum decomposition temperature of the composites were belong to the unbleached wheat straw (76/424°C) and the bleached wheat straw pulp (23/354°C), respectively.