Effects of NaOH/NaCl pretreatment on water absorption behavior of rape straw powder/PVC composites

The rape straw treated with different concentrations of NaOH and NaCl were used as fillers, and rape straw powder/PVC composites were prepared by extrusion method. The water absorption behavior, degradation of mechanical properties, and wear resistance of the composites were studied. The results showed that the saturated water absorption rate of the composites treated with 7 % NaOH was the highest, and the mechanical properties and wear resistance were seriously degraded, the composites treated with 7 % NaCl showed excellent water resistance and property stability. The hydrophilic component in the fibers was removed by NaCl treatment, the diffusion rate of water was effectively suppressed. The structure of the fibers was excessively destroyed by high concentration NaOH, providing channels for water molecules. The numerical simulation revealed that water molecules diffused along the directions of width and thickness of the composites in a step-like manner, gradually penetrating into the surface and interior of the composites, finally reaching the three-dimensional diffusion equilibrium state. NaCl treatment significantly enhanced the water resistance of composites compared with NaOH treatment, which provided an important theoretical basis for improving the durability of WPCs in water environment. • The effect of pretreatment on water absorption of composites was revealed. • The composites treated with NaOH absorbed more water than those treated with NaCl. • The water absorption of the composites was revealed by the finite element method. • The properties of NaOH treated composites deteriorated seriously after immersing. • The composites treated with NaCl maintained good properties after immersing.