Stress relaxation of composites made of polypropylene and organo-montmorillonite modified wood flour during water immersion

Wood flour (WF) was modified with sodium-montmorillonite (Na-MMT) and didecyl dimethyl ammonium chloride (DDAC) to form an organo-montmorillonite (OMMT) inside WF at different OMMT concentrations from 0.25 to 1%. The modified WF was blended with polypropylene (PP) to produce PP/WF composites at a weight ratio of 1:1 by compression molding. The composites were immersed in water and their stress relaxation behaviors were investigated at 26, 40, and 60 degrees C, respectively. Results: (1) All composites show stress relaxation with increasing compression testing time, indicating that they have pronounced rheological properties. (2) The stress relaxation becomes more severe with increasing temperature and water immersion time. (3) OMMT improves the stiffness of the composites with slower stress relaxation, and the PP/WF 0.5% OMMT seems to perform best among all.