Valorisation des argiles kaoliniques des Charentes dans le caoutchouc naturel

Abstract

Unmodified kaolinitic clays have semi-reinforcement properties in natural rubber. The amount of kaolinite is favourable to reinforcement, the amounts of quartz and mica is prejudicial. Properties connected with crystallinity and consequently with fineness are the second reason why vulcanized products vary : these are best when filler is well crystallized. The properties of rubbers change also according to the processing way as a function of the geologic level the kaolinite is extracted from. Wet processing ways using sodium salts give the best results when the crystallinity decreases with the amount of potassium. Dry grinding and classification in air give the best results when the crystallinity does not depend on the amount of potassium. Vulcanisation accelerators directly incorporated in the filler increase also mechanical properties. Aminoplasts grafting leads to a product whose properties are similar to the carbon black properties. Though grafted kaolinites have weaker reinforcement properties than carbon blacks, they present two main advantages i.e. the low processing cost and the good ageing of vulcanized products.