A Greener Route to Disperse Carbon Black in Rubbers in Absence of Process Oil

Carbon black is inevitable as reinforcing filler in the rubber industry as it enhances the mechanical and dynamic properties of the rubber products. The use of carbon black as filler at higher loadings in rubber compounds requires process oils for easier processing and for improving  filler dispersion. The use of aromatic oils as plasticizer and process aid is prevalent in the rubber industry for more than a century. But the growing concern about its carcinogenic effect on health and environment ground due to the presence of polycyclic aromatic hydrocarbons has raised questions on  its  safety when used in the rubber industry. Thus, there is an ardent need to look out for alternate sources of  process oils mostly from renewable resources. In recent years, it has been discovered that, cardanol (m-pentadecenyl phenol), an agricultural by-product of the cashew industry is a cheap, abundantly available renewable resource that act not only as a green plasticizer but also as a multifunctional additive in the rubber industries. The present study focuses on dispersion of carbon black and the technical properties of carbon black filled natural rubber vulcanizates by chemically grafting cardanol onto natural rubber (C-g-NR). This does not require additional plasticizer for processing and dispersion of carbon black in natural rubber. The optimum cure time  reduces for the C-g-NR vulcanizates  as compared to  that for the NR vulcanizates at all loadings of carbon black varying from 30 to 60 phr. The physico-mechanical properties of the carbon black reinforced C-g-NR vulcanizates  does not get effected  but becomes even better than that of the oil plasticized natural rubber vulcanizates. The C-g-NR vulcanizates show lower compression set, higher rebound resilience and better abrasion resistance. The dynamic rheology   studied with the  help  of a rubber process analyzer (RPA)  exhibits better flow properties for the carbon black filled C-g-NR. The dynamic-mechanical properties show less Payne effect  for carbon black filled C-g-NR vulcanizates as compared to that of oil plasticized NR. The transmission electron photomicrographs show uniform dispersion of carbon black in the C-g-NR matrix. Cardanol-g-natural rubber is a potential substitute for aromatic oil as the plasticizer in natural rubber.