Exploring the Possibility of Cardanol-g-Natural Rubber As a Substitute to Aromatic Oil Plasticizer in Natural Rubber

The use of aromatic oil as a plasticizer in the rubber industry which pervades for more than a century is now limited due to its carcinogenic effect because of the presence of polycyclic aromatic hydrocarbons. Therefore, there is a need to substitute these hazardous aromatic oils. Meta-pentadecenyl phenol, popularly known as cardanol is an agricultural by-product of the cashew industry and a renewable resource. Multifunctional activity of cardanol in the rubber and polymer industries has been well established in the recent past. The present study highlights the grafting of cardanol on to natural rubber in the latex stage and studying its processing characteristics and technical properties. The grafting parameters have been optimized by using Taguchi method. Grafting of cardanol on to natural rubber is confirmed by FTIR and NMR spectroscopy. The cardanol grafted natural rubber (CGNR) is found to have lower Mooney viscosity, lower Wallace plasticity number and higher cure rate as compared to the unmodified natural rubber. The physico-mechanical properties of the CGNR vulcanizates are at par with or even better than the gum natural rubber vulcanizates. The CGNR vulcanizates show lower compression set, higher rebound resilience and higher abrasion resistance. The rheological characteristics exhibit better flow behavior as compared to oil plasticized natural rubber. Differential scanning calorimetry and dynamic mechanical analysis exhibit lowering of the glass transition temperature of the CGNR as compared to raw natural rubber. This confirms the plasticization effect of the cardanol when grafted onto the natural rubber.