Methyl methacrylate and ethylacrylate (MMA-co-EA) and methyl methacrylate and butylacrylate (MMA-co-BA) copolymeric processing aids were introduced into poly(vinyl chloride) (PVC)/33.3 wt % wood-sawdust composites containing 0.6 and 2.4 phr of calcium stearate lubricant. The properties of the composites were monitored in terms of processibility, rheology, thermal and structural stability, and mechanical properties. It was found that the mixing torque, wall shear stress, and extrudate swell ratio increased with increasing processing aid content because of increased PVC entanglement. MMA-co-BA (PA20) was found to be more effective than MMA-co-EA (K120 and K130), this being associated with the flexibility of the processing aids, and the dipole-dipole interactions between sawdust particles and polymeric processing aids. The shark- skin characteristic of the composite extrudate at high extrusion rate was moderated by the presence of processing aids. Adding the acrylic-based processing aids and lubricant into PVC/sawdust composites improved the thermal and structural stability of the composites, which were evidenced by an increase in glass transition and decomposition temperatures and a decrease in polyene sequences, respectively. The changes in the mechanical properties of the composites involved a composite homogeneity, which was varied by degree of entanglement and the presence of wood sawdust, and un-reacted processing aids left in the composites. (C) 2004 Wiley Periodicals, Inc.