Guayule as an Alternative to Hevea Natural Rubber in the Automotive Industry
Guayule (Parthenium argentatum Gray) is a shrub native to the southwest United States. The plant is capable of producing large amounts of cis- 1, 4-polyisoprene, the polymer of natural rubber. Attempts to diversify sources of natural rubber are being made in order to respond to price fluctuations. Producing guayule has sustainability benefits over Hevea; for instance, it can be grown domestically in otherwise unfarmed regions. The polymer guayule produces is free of proteins that trigger natural rubber allergies. The absence of these proteins increases the amount of stress the rubber can withstand before crystallizing, leading to a more flexible compound. Guayule natural rubber is compounded using automotive formulas; the resulting compounds are found to have longer elongation than compounds of Hevea. The quantity of disulfide bonds connecting chains of cis- 1, 4-polyisoprene can be increased in order to make the physical properties of guayule natural rubber compounds more closely resemble those of Hevea natural rubber compounds. Furthermore, guayule rubber naturally contains a resin composed of partially formed polymer chains called terpenes. Resin’s presence in a compound further softens it and increases its elongation. Alternate bio-fillers are also examined, as well as the performance of guayule natural rubber relative to the rubber produced by Taraxacum koksaghyz.