Unique explanations are given to describe changes in the mixing torque and tensile and impact properties of poly(vinyl chloride) (PVC) /wood sawdust composites affected by various types and concentrations of silane coupling agents. Concentrations of 0.5-1.0 and 1.5 wt % coupling agent are recommended for the optimization of the tensile and impact properties of the composites, respectively. Changes in the tensile and impact properties of the composites with a low sawdust content were more sensitive 19 to the addition of silane coupling agents than those with a high sawdust content. KBM603 was suitable for improving the tensile properties, whereas KBE603 is recommended for 1 high impact resistance of the composites. The differences in the mechanical and thermal properties of the PVC/sawdust composites were dependent on the characteristics of the functional groups in the silane coupling agents used, such as hydrophilic level, number of functional groups, self-condensation reaction, and effectiveness of the hydrolysis reaction. Silane coupling agents above 1.0 wt % resulted in an increase in polyene sequences in the PVC structure. (C) 2005 Wiley, Periodicals, Inc.