Will Guayule rubber compete with Hevea?
The rising costs of Hevea-based and synthetic rubbers are putting pressure on manufacturers to raise prices or face lower margins. Tyre companies including Bridgestone, Michelin, and Goodyear, have raised prices by 5-15% in 2010/2011 with more increases to come. Due to increasing financial pressures, manufacturers are looking for alternative sources of rubber. Guayule rubber has been emerging as an attractive and sustainable alternative to both natural rubber and synthetic rubber.
Guayule
A shrub growing in the Arizona desert may bring big changes to the global rubber industry. Liquid extracted from the root of the Guayule (pronounced - why-u-lee) plant is used to create natural latex and rubber and with the expected worldwide inconsistency in rubber supply in the coming years, some believe the plant is the next generation of rubber.
Yulex Corporation
Arizona-based Yulex Corporation has been working with the plant for years to develop it into a global industrial crop and a source for a wide variety of products including natural rubber and energy. Guayule rubber is transformed into medical products - like latex-free medical gloves - that the company says are safer for the environment and people - especially those with latex allergies. Yulex Corporation’s new production facility, set to open in January 2012, is located within the Lone Butte Industrial Park in Chandler, Arizona, and is part of the Gila River Indian Communitya perennial that thrives in an arid desert environment, guayule is native to the Chihuahuan desert. It grows and is harvested much like cotton, so to grow the vast amounts of guayule Yulex needs, the company is turning to Arizona’s cotton farmers and asking them to grow guayule instead cotton. Yulex officials hope that eventually, guayule replaces cotton as the most commonly grown crop in southern Arizona.
Experts say that guayule is a better crop for farmers to grow as it is a modest water user compared to other crops commonly grown in Arizona, including cotton, corn and alfalfa. It is also a stable crop and not subject to the same market forces as traditionally grown crops.
Background
Although it is expected to transform the global rubber industry, guayule is not a new discovery. It was first harvested during the pre-columbian era. In the early 1900s, it was commercially produced in Mexico and imported into the United States, accounting for 24 percent of total rubber market in the United States, according to Yulex. But over production of the shrub caused a halt in guayule rubber production by 1912. It was rediscovered again during World War II when rubber imports from Southeast Asia became difficult to acquire. It was abandoned again, after the war, when cheap imports overtook the market, but guayule received a boon in the 1980s when a need for latex-free medical products, because the plant does not contain the proteins often associated with latex and rubber allergies. Today, guayule rubber is used to make medical supplies, latex-free gloves and other items.
After the rubber-making liquid has been extracted from the plant, the remaining plant material is used to make a clean-burning biofuel
Hevea and guayule
Over 2,000 rubber producing species are known, however, only two, Hevea brasiliensis (A. Juss.) Muell.-arg. and guayule (Parthenium argentatum Gray), have been exploited as commercial sources of natural rubber. Today, Hevea is essentially the sole source of natural rubber, nevertheless, active research and development programs are underway to commercialize guayule. Guayule is envisioned as a new or alternative crop for arid and semiarid areas of the southwestern United States, north central Mexico, and regions with similar climates around the world.although Hevea is the dominant rubber crop today, Hevea and guayule have had parallel histories of development. In both, commercialization began with the harvest of wild stands before the establishment of plantations and the initiation of cultural studies. Variability within stands and lowered yields per unit area were problems in both species. These problems continued through the early attempts at cultivation since the populations were very heterogeneous genetically due to their establishment from open-pollinated seed.annual yields have been increased dramatically in both, from 400 to over 2,500 kg/ha for Hevea , and from 300 to 1,000 kg/ ha for guayule . The differences in development between the two crops can be associated with the initiation of the Rubber Research Institutes in Asia. The Rubber Research Institutes have been responsible for over 100 years of continuous increases in Hevea yields and the production of a uniform and reliable industrial product . Guayule, on the other hand, has suffered from intermittent research efforts, which have in many cases been under mined by periods of neglect. Guayule researchers have found themselves more than once in the position of “reinventing the wheel.”
Cultural practices
. Guayule is adapted to hot desert environments, and sites with well-drained calcareous soils and relatively low concentrations of nutrients. Sandy-loam soil are most suitable since root diseases, which are exacerbated by standing water, are one of the few problems encountered in guayule cultivation . Fertility treatments have been shown to have little effect on growth, and guayule is only slightly tolerant to soil salinity.
The semiarid plateau re gion of the Chihuahuan desert (1,200 to 2,100 m in elevation) in which guayule occurs naturally has a temperature range between -18 and 49.5°C. High temperature does not appear to affect growth, but temperatures below 4°C induce semi-dormancy and extended freezing temperatures can cause plant death. Areas with annual precipitation between 280 and 640 mm are preferable for guayule cultivation, but in order to achieve maximum yields, moderate to heavy applications of irrigation are necessary. Both dry matter production, and resin and rubber yields, have been shown to increase proportionally with increased water availability. In addition, irrigation can shorten the time until harvest. However, excess water is harmful to guayule plants of all ages, causing disease, reduced soil aeration, and increased weed competition. These problems are especially damaging to young plants.
Presently, stand establishment is accomplished by transplanting. Seeding transplants are produced in greenhouses and fields are established using typical commercial transplanting systems. Transplanting has been extremely successful, but is estimated to be more expensive than establishment by direct-seeding . Direct-seeding has been successful on an experimental scale, but no commercial scale plantings have been attempted.
Mechanized techniques have been developed or adapted for all aspects of guayule cultivation. For example, the cost of transplanting may be reduced by clipping instead of digging whole plants. By clipping, the branches are cut approximately 10 cm above the soil level and re-growth occurs from the root crown. Novel equipment has been developed for this purpose and breeding programs are now selecting lines with high levels and rates of regeneration.
Processing
Effective processing of rubber and nonrubber co-products is essential to a viable guayule industry. Rubber in guayule is found in the parenchyma cells, mainly in the bark, and must be released during processing. During the present effort to commercialize guayule three processing methodologies have been researched.
The first and oldest method is flotation. This is essentially the same methodology used at the turn of the century and during the Emergency Rubber Project. In this procedure, ground shrubs are placed in a large vat of dilute sodium hydroxide until the woody tissue takes-up water and sinks to the bottom and the resinous rubber floats to the top in what are called “worms.” These worms are skimmed from the top and the rubber is deresinated with acetone. Flotation was reemployed by the processing facility at Saltillo, Mexico, from which all of the guayule rubber used in test tyres was produced .
The second method is sequential extraction, in which the resin is first extracted with acetone or another polar organic solvent, and then the rubber is extracted with hexane. Sequential extraction has only been used experimentally and appears not to be an economically viable method.
The third processing method is simultaneous extraction, in which a mixture of solvents, usually acetone and hexane or pentane, are used. After the initial extraction, more acetone is added to coagulate the high molecular weight rubber. This method has been used at both of the experimental processing facilities built by Texas A&M University at College Station, Texas and at Sacaton, Arizona by the Bridgestone/ Firestone Corporation. Although this method has been successful in extracting rubber, engineering difficulties in handling the shrub have plagued both facilities
Co-products
Economic forecasts suggest that for guayule to become a crop which can compete without subsidies, rubber yields must be increased and/or commercial utilizations of processing co-products must be identified and developed. One potentially valuable co-product is the lowmolecular-weight rubber fraction, which accounts for approximately 25% of the total rubber yield. These low-molecularweight rubber compounds have high value specialty applications as non-tyre rubber. Another processing co-product, the resins, are only partially characterized, but are predominantly fatty-acid triglycerides and terpenoids. Resins have been used successfully as wood preservatives, a feedstock for specialty chemicals (coatings and rubber additives), and as a high value fuel with no ash. Unfortunately, resin composition varies with shrub line, cultivation site, harvest date, and processing history. Guayule bagasse was used to fuel the early processing plants in Mexico and unprocessed shrub was used to fuel various processes in the Mexican mining industry. Today, bagasse is still being considered as a cogeneration fuel, as well as, a feedstock for gasification, conversion to liquid hydrocarbons, as a source of fermentable sugars, and as a fiber. These applications are not unique and are typical of other types of waste lignocelluloses.
Economics
Guayule commercialization depends upon its being economically competitive with Hevea rubber. But this only considers guayule as a direct substitute for Hevea, which means that guayule rubber must either perform the same functions at a lower cost or perform better at the same cost. Guayule researchers are not looking to replace Hevea, but to enhance worldwide rubber production. Demand for natural rubber continues to grow at a rate greater than new plantings of Hevea. Guayule should be able to fill this need, especially locally in arid and semiarid environments.