Swelling Characteristics of Some Natural Rubber Based Elastomers

This paper outlines the swelling behaviour of natural rubber (NR) vulcanisates. The findings are discussed with respect to the effects of various parameters on swelling behaviour of NR vulcanisates, the parameters including crosslink characteristics (crosslink density and type), penetrant characteristics (shape and size), swelling temperatures, fillers and swelling related mechanical properties. The following are noted: (i) The degree of swelling is strongly dependent on crosslink density i.e. the higher the crosslink density the less is the swelling, (ii) The degree of swelling is also dependent on flexibility and mobility of crosslinks controlled by the type of crosslinks present in the rubber compounds, (iii) The degrees of swelling and deswelling (recovery of swelling) of crosslinked natural rubbers are dependent on penetrant characteristics and swelling temperature. Penetrants with smaller size and more symmetric in shape tend to cause higher degree of swelling, this effect being more pronounced as the swelling temperature is increased, (iv) The degree of swelling of ground flexible polyurethane (PU) filled NR vulcanisates reduces as the reinforcement between the filler and the rubber increases, the reinforcement improving as the particle size and moisture content of the PU filler are reduced. The effect of PU filler added into NR vulcanisates on swelling behaviour is similar to that found in carbon black filled NR vulcanisates, (v) The mechanical properties of the vulcanisates are found to deteriorate during swelling and to recover on the complete deswelling.