Abstract
For the industrial production of rubber, one of the key ingredients is a processing aid. It not only facilitates the processability but also tunes the final properties of the resultant rubber. In general, for a polar rubber like acrylonitrile-butadiene rubber (NBR), the processing aids earning the most attention are synthesized from petroleum, such as dioctyl phthalate (DOP). However, due to their toxicity, many rubber chemists have tried to find alternative chemicals that are environmentally friendly and derived from a renewable resource. In this research, we investigated the effects of the soybean oil fatty acid (SBOFA), synthesized in house via hydrolysis of SBO, on the properties of NBR in comparison with DOP. Initially, it was found that the addition of SBOFA improved the flowability of the NBR compound, as indicated by the progressive decrease in the Mooney viscosity with increasing levels of SBOFA. The results from various techniques indicated that the crosslink density of the NBR vulcanizates passed through the maximum at the SBOFA loading of 4 phr. Upon loading SBOFA up to 4 phr, there was no significant deterioration in the mechanical strength of the SBOFA-plasticized NBR vulcanizates. Typically, the presence of SBOFA at 4 phr enhanced the thermal resistance of the NBR vulcanizate by shifting the thermal decomposition to a higher temperature. At a given loading, it was found that the SBOFA-plasticized NBR vulcanizate showed a comparable plasticizing efficiency and mechanical strength with the DOP-plasticized one. The result from this study shows that SBOFA is a good alternative sustainable eco-friendly processing aid to use for NBR.
Highlights
Processing aids are one of the major nonvolatile additives in the rubber industry
The soybean oil fatty acid (SBOFA) used as a processing aid for the NBR compound in this study was obtained by alkaline hydrolysis of soybean oil (SBO)
The results of this study show that SBOFA derived from a natural seed crop is a potential alternative processing aid for NBR in the rubber industry
Summary
Petroleum-based oils, including aromatic, paraffinic, and naphthenic oils, have become common processing aids, but they are nonrenewable and indestructible materials They have mostly been used as a processing aid in the rubber industry, especially in tire products, because their price is lower compared to other types of processing aids and they have a good balance of properties [3]. The polycyclic aromatic hydrocarbon (PAH) content in aromatic oils has been shown to be harmful to humans and the environment, according to the regulation (EC) No 1907/2006 of the European Parliament and of the Council Regulation Concerning the REACH legislation [6] These petroleum-based oils are good extender oils in both nonpolar (i.e., natural rubber (NR) and styrene butadiene rubber (SBR)) and polar elastomers (acrylonitrile-butadiene rubber (NBR)), due to their polarity that improves the compatibility with elastomers [5,7,8], they are classified as carcinogens. There has been intensive research to develop eco-friendly rubber processing aids to reduce the consumption of nonbiodegraded oils (or petroleum oil) in the rubber industry, while still maintaining the plasticizing efficiency while reducing the toxicity of the processing aid
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