CHEMICAL CROSS-LINK DENSITY AND NETWORK STRUCTURE OF NATURAL-RUBBER VULCANIZATES MODIFIED WITH PHOSPHORYLATED CARDANOL PREPOLYMER

The chemical crosslink density (CLD) and network structure of natural rubber (NR) vulcanizates, modified with phosphorylated cardanol prepol ymer (PCP), have been studied by equilibrium swelling and other chemic al methods. The PCP-modified NR vulcanizates showed lower CLD, as comp ared to the unmodified NR samples, the decrease being lesser for the s emiefficient vulcanization (SEV) system, as compared to the convention al (CV) and efficient (EV) vulcanization systems. The superior tensile characteristics of the PCP-modified vulcanizates of the SEV system is presumed to be partly due to the presence of an entangled network str ucture between the aliphatic segment of PCP and the isoprene chains, a s evident from X-ray diffraction studies. The critical role of Zn++ io ns in the crosslinking reactions, especially at higher concentrations of PCP, was evident from the increase in CLD at higher concentrations of ZnO. The reduction in the IR absorption intensity, in the presence of ZnO, indicated the probable complex formation of Zn++ ions with the phosphate groups of PCP. (C) 1994 John Wiley & Sons, Inc.