| The guayule (pronounced, 'why-YOO-lee') plant is a woody perennial shrub that is native to areas of the southwestern United States and northern Mexico, and is a well-documented source of high-quality natural rubber. The U.S. needs a domestic source of natural rubber to allay concerns about its future availability. Cultivation of guayule in North America has been attempted many times since the late 19th century, and companies, including major tire manufacturers, are again investing in guayule research. However, full-scale commercialization of guayule rubber needs established markets for the two basic by-products of guayule rubber extraction: the plant resins (primarily non-rubber compounds) and the bagasse (fibrous residue).;The research objective was to investigate guayule resin for use as a binder modifier in flexible (asphalt) pavement mixtures (FPMs). The bulk of the work occurred from 2006 through 2014 in collaboration with the USDA Agricultural Research Service and the Yulex Corporation. Yulex produced hypoallergenic guayule latex for healthcare applications using a water-based extraction method. Of the many guayule-based materials investigated, an acetone-extractable, residual resin in the dried latex was shown to be an effective recycling agent for FPMs with high contents of reclaimed binder.;Beginning in 2013, the endeavor transitioned to collaborating with Bridgestone Americas and PanAridus. These companies used solvent-based extraction methods for producing tire-quality guayule rubber, thus generating resins as process by-products. The Bridgestone and PanAridus resins, compositionally different from each other, were subjected to limited laboratory evaluations and show promise as binder modifiers. |
