While there are a number of efforts underway exploring the use of sustainable, natural rubber alternatives for use in tires (earlier post, earlier post, earlier post), cars use a great deal of rubber for non-tire applications as well; the Ford Fiesta, for example, contains about 3 kg of the material, excluding the tires.
Ford Motor Company is thus investigating alternative sustainable sources of rubber for automotive use in these non-tire applications. The company is working closely with The Ohio State University’s Ohio Agricultural Research and Development Center’s (OARDC’s) Program of Excellence in Natural Rubber Alternatives (PENRA) on researching the use of latex from guayule and Russian dandelion root in applications such as the car’s interior (cup holders), floormats, suspension bushings, engine mounts and so on, said Janice Tardiff, Elastomer Technical Expert at Ford.
Rubber (cis-1,4-polyisoprene) is one of the most important polymers naturally produced by plants because it is a strategic raw material used in more than 40,000 products, including more than 400 medical devices. The sole commercial source, at present, is natural rubber harvested from the Brazilian rubber tree, Hevea brasiliensis.
Primarily due to its molecular structure and high molecular weight (>1 million daltons) this rubber has high performance properties that cannot easily be mimicked by artificially produced polymers, such as those derived from, e.g., bacterial poly-hydroxy-alkanoates (PHAs). These high performance properties include resilience, elasticity, abrasion resistance, efficient heat dispersion (minimizing heat build-up under friction), and impact resistance.—Mooibroek and Cornish (2000)
Almost all natural rubber is harvested by tapping tropical rubber trees (Hevea brasiliensis). The current global natural rubber market is 9.7 million tons and US $20 billion. The US imports about 1.5 million metric tons (3,306,000,000 lbs) annually, according to PENRA.
Demand for rubber is growing, especially as southeast Asia, India, China and Brazil expand and develop their economies. Due to extreme price fluctuations characterizing natural rubber, ranging from $1 to $4 per pound, the monetary and environmental cost of shipping the rubber internationally, and a desire to lower each vehicle’s environmental footprint, Ford is searching for a more sustainable domestic rubber source. PENRA, for its part, was created to integrate and accelerate the incubation, demonstration, market entry, and growth of a domestic natural rubber industry.
PENRA has been focusing on Russian dandelion (Taraxacum kok-saghyz); guayule (Parthenium agentatum), a shrub grown in Arizona, is another promising alternatives, as it is already being used in high-performance gear like wetsuits, medical gloves and more. Guayule produces natural rubber in its bark parenchyma cells and the shrub is processed to extract the latex. Guayule rubber is comparable in quality to Hevea natural rubber and the residual, non-latex guayule plant material can be transformed into valuable co-products, such as bioenergy.
A new study (Rasutis et al.) explores the sustainability implications of guayule rubber commercialization related to the three pillars of sustainability, including environmental impacts of rubber production, economic barriers and advantages, and social implications. The authors found that guayule rubber provides an opportunity to lower the environmental impacts of a major commodity, to develop an industry to support the local US economy, and to reduce US dependence on non-renewable petroleum sources and rubber imports.
There are a number of considerations in developing an alternative source, PENRA notes:
Domestication and germplasm improvement: Seed acquisition, seed biology, selection, propagation, breeding and biotechnological enhancement result in high rubber yields and crop adaptability.
Production systems development: Understanding of crop physiology, cultural inputs, integrated pest and crop management practices, harvesting equipment and post-harvest conditions and enhanced natural rubber yields and seed production in improved germplasm.
BioProcessing optimization: Processing strategies that optimize the extraction and purification of rubber and associated co-products, at bench and pilot scale, and inform commercial scale designs. Guayule and dandelion root require different processing techniques, for example, each with their own challenges. For example, the processing of dandelion is still at the craft development stage, Tardiff said.
Byproduct processing: Utilization of carbohydrate by-products for high grade dietary fiber and fermentation to biofuels and platform chemicals to maximize profitability.
Rubber validation and utilization: Characterization and successful incorporation into a full spectrum product as an alternate rubber replacement.
Although additional research must be conducted to determine how much rubber could be conserved by switching to an alternative source such as guayule, Ford estimates that it could be as much as 50%, depending on the part of the car.
We are formulating rubber compounds using guayule and dandelion root to see if they perform similarly. We are very encouraged; we have not identified yet a significant difference between the two in applications. This is a multi-year project; we anticipate having prototypes within a year and commercial implementations in 5 years or less.—Janice Tardiff
Although in terms of sheer volume, tires would be a much larger application of alternative natural rubber than interior parts, success with the non-tire applications could assist the commercialization of alternive rubbers for tires, Tardiff suggested.
Production [of alternative rubber] is not yet at the level of being able to supply the tire industry. If we generate demand for guayule rubber, that’s going to help for the tire side.—Janice Tardiff
Daina Rasutis, Kullapa Soratana, Colleen McMahan, Amy E. Landis (2015) “A sustainability review of domestic rubber from the guayule plant” Industrial Crops and Products, 70 383-394 doi: 10.1016/j.indcrop.2015.03.042
H. Mooibroek, K. Cornish (2000) “Alternative sources of natural rubber” Applied Microbiology and Biotechnology Volume 53, Issue 4, pp 355-365 doi: 10.1007/s002530051627
Deborah J. Siler, Marta Goodrich-Tanrikulu, Katrina Cornish, Allan E. Stafford and Thomas A. McKeon (1997) “Composition of rubber particles of Hevea brasiliensis, Parthenium argentatum, Ficus elastica, and Euphorbia lactiflua indicates unconventional surface structure.” Plant Physiol. Biochem. 35 (11) 881-889