Cardanol grafted natural rubber, prepared at room temperature, is a potential green substitute for carcinogenic aromatic oil plasticized natural rubber.

Cardanol, an agricultural byproduct of the cashew industry, is a cheap and abundantly available renewable resource. The multifunctional activity of cardanol in the rubber and polymer industries has been well-established in recent years. The present study highlights the chemical grafting of cardanol onto natural rubber in the latex stage. The cardanol grafted natural rubber is characterized by FTIR and NMR spectroscopies. The grafting parameters have been optimized for maximum yield in terms of percent grafting and grafting efficiency by the Taguchi method. Four control factors, i.e., initiator concentration, cardanol concentration, reaction temperature, and reaction time, are chosen at three different levels. The optimum parameter combination is found to be the initiator concentration 2 phr, cardanol concentration 10 phr, reaction temperature 65 °C, and reaction time 6 h. The analysis of variance method is used to evaluate the percentage contributions of the different control factors on the percent grafting and grafting efficiency.

Natural rubber (NR) usage is wide‐spread from pencil erasers to aero tyres. Carbon black and silica are the most common reinforcing fillers in the rubber industries. Carbon black enhances the mechanical properties, while silica reduces the rolling resistance and enhances the wet grip characteristics. However, the dispersion of polar silica fillers in the nonpolar hydrocarbon rubbers like natural rubber is a serious issue to be resolved. In recent years, cardanol, an agricultural by‐product of the cashew industry is already established as a multifunctional additive in the rubber. The present study focuses on dispersion of silica filler in natural rubber grafted with cardanol (CGNR) and determination of its technical properties. The optimum cure time reduces and the cure rate increases for the CGNR vulcanizates as compared to that of the NR vulcanizates at all loadings of silica varying from 30 to 60 phr. The interaction between the phenolic moiety of cardanol and the siloxane as well as silanol functional groups present on the silica surface enhances the rubber–filler interaction which leads to better reinforcement. The crosslink density and bound rubber content are found to be higher for the silica reinforced CGNR vulcanizates. The physico‐mechanical properties of the silica reinforced CGNR vulcanizates are superior to those of the NR vulcanizates. The CGNR vulcanizates show lower compression set and lower abrasion loss. The dynamic‐mechanical properties exhibit less Payne effect for silica reinforced CGNR vulcanizates as compared to the NR vulcanizates. The transmission electron photomicrographs show uniform dispersion of silica filler in the CGNR matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43057.

Carbon black is advantageous for rubber as a reinforcing filler. Carbon blacks at higher loadings require process aids for easier processing and improved filler dispersion. Aromatic oils have been used so far in the rubber industry as plasticizer and process aids. The presence of polycyclic aromatic hydrocarbons in these oils has raised concerns, and they have been banned. Rubber industries are looking for alternate sources of process aids from renewable resources. Cardanol (m-pentadecenyl phenol), an agricultural by-product of the cashew industry, is cheap and abundantly available. It was proved recently to be a plasticizer and a multifunctional additive. The dispersion of carbon black in natural rubber (NR) grafted chemically with cardanol (CGNR) is investigated and compared with that of oil plasticized natural rubber. The physico-mechanical properties of the carbon black–filled CGNR vulcanizates are better than that of the aromatic oil plasticized NR vulcanizates. The cross-link density and bound rubber content are higher and the Payne effect is lower for the carbon black–filled CGNR vulcanizates as compared with oil plasticized NR vulcanizates. Dispersion of carbon black in the CGNR matrix is uniform and better than the aromatic oil plasticized NR.

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