Mechanical behaviour of polypropylene composites containing fine mineral filler: Effect of filler surface treatment

The inclusion of mineral fillers in thermoplastics improves some mechanical properties but reduces others, such as impact strength. However, the use of ultrafine fillers limits this degradation. The influence of two surface treatments on the mechanical propel ties of polypropylene/ultrafine-kaolin composites was studied. In the first treatment, stearic acid was used on dry powder, and the second was a cationic treatment with quaternary ammonium in suspension. An improvement in the impact strength was found when the second agent was used. This can be explained from both macroscopic and microscopic points of view. We observe a better particle dispersion in the matrix and thermal analysis indicates that the crystalline structure of these materials is finer. In addition, tensile tests carried out on matrix/agent blends show that a soft interface around each particle could act as a shock absorber during an impact test. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.