The chemical crosslink density (CLD) and network structure of natural rubber ( N R ) vulcanizates, modified with phosphorylated cardanol prepolymer (PCP) , have been studied by equilibrium swelling and other chemical methods. The PCP-modified NR vulcanizates showed lower CLD, as compared to the unmodified NR samples, the decrease being lesser for the semiefficient vulcanization (SEV) system, as compared to the conventional (CV) and efficient (EV) vulcanization systems. The superior tensile characteristics of the PCPmodified vulcanizates of the SEV system is presumed to be partly due to the presence of an entangled network structure between the aliphatic segment of PCP and the isoprene chains, as evident from X-ray diffraction studies. The critical role of Zn++ ions in the crosslinking reactions, especially at higher concentrations of PCP, was evident from the increase in CLD a t 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.

China clay (kaolin) has been modified with sodium salt of rubber seed oil (SRSO). SRSO was characterized using X-ray diffraction (XRD), infrared spectroscopy (FTIR), and differential thermal analysis (DTA). XRD of the unmodified and SRSO-modified kaolins showed an increase in the d-(001) spacing of kaolin platelets from 7.15 to 14 Å . FTIR spectroscopy indicated possible grafting of the organic moiety of rubber seed oil (RSO) onto the clay surface. DTA of the SRSO-modified kaolin indicated that the SRSO is more strongly bound in a constraint environment within the lamellae of kaolin. Natural rubber (NR) mix containing 10 phr of SRSO-modified kaolin was found to cure faster than that of a similar mix containing unmodified kaolin. NR vulcanizates containing SRSO-modified kaolin showed considerable increase in tensile modulus, tensile strength, and elongation at break indicating its potential as an organomodified nanofiller.

SynopsisPhosphorylated cardanol preopolymers ( P C P ) are obtained by simultaneous phosphorylation and oligomerization of cardanol, an unsaturated pentadecylphenol extracted from the nuts of the plant Anacardiurn occidentale L. Although GPC showed the presence of only oligomeric species in the system, the high viscosity of 0.35-0.45 million cps was found to be due t o invoivement of hydrogen bonding. IR spectra of PCP gave bands a t 1030 and 1240 cm-', indicating P-0-C linkages. The decrease in iodine value and the absence of vinyl IR bands at 895 and 907 cm-' indicated oligomerization. NMR spectra of PCP showed partial loss of unsaturation. A carbonium ion initiated mechanism is indicated for the oligomerization. PCP was found to he highly reactive with aldehydes, amines, and isocyanates. Highly insoluble and infusible thermoset products could be obtained. TGA studies showed a two-stage decomposition with improved thermal stability above 500°C for PCP compared to cardanol-formaldehyde (novolac) -type resins. Completely cured PCP was highly resistant to hydrolysis by water. Studies on mechanical properties showed that the P C P cured with HMTA gave a tensile strength of 16.9-21.5 M N / m 2 and an impact strength of 1.63-2.04 J compared to 24-48 M N / m 2 and 1.35 J, respectively, for phenol formaldehyde (novolac) resin prepared under similar conditions. The lap shear strength of PCP-bonded wood pieces showed a value of 400 f 10 N/cm2 in comparison to 60 -+ 10 N/cm2 of cardanol formaldehyde (novolac) resin, indicating that phosphorylation improves the bonding characteristics. With a phosphorus content of 7.9%, PCP showed good fire-retardant properties. Vertical burning studies did not show any propagation of fire or any afterglow. PCP cured with HMTA gave a limiting oxygen index value of 35, which on bromination increased to 42.0. PCP could find application as polymeric fireretardant additive for plastics and elastomers or as filled or unfilled fire-resistant plastics/composite products.

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