William W. Schloman

Guayule extractables: Influence of extraction conditions on yield and composition

The yield and composition of the resin extracted from guayule will depend upon the choice of extraction medium. Water-soluble components, primarily polysaccharides, are entrained by solvent when the shrub is first deresinated with acetone (sequential extraction). Entrainment of water-soluble components does not occur when rubber and resin are both removed with a solvent such as the acetone-pentane azeotrope (simultaneous extraction). As a consequence, resin yield is substantially (68%) higher with sequential extraction. Resin from simultaneous extraction contains no detectable ash. While resin composition, including the levels of sesquiterpene esters, triterpene keto alcohols, and triglycerides, varies with the conditions of extraction, the total content of species bearing chemically reactive groups such as carbonyl shows little change (1.2–1.3 mmol g−1). This suggests that the water-soluble material in resin from sequential extraction contains components suitable for commercially valuable derivatization. Rubber yield and molecular weight are unaffected by the choice of extraction medium.

Low-molecular-weight guayule natural rubber as a feedstock for epoxidized natural rubber

Abstract The low-molecular-weight fraction of guayule rubber ( M w 2.68 × 105) can be modified to yield a low-viscosity analog of epoxidized natural rubber. A hexane or cyclohexane solution of rubber is treated at 23–63°C with peracid formed in situ from hydrogen peroxide and formic acid. The epoxidized polymer enhances the physical properties of cured rubber compositions, particularly abrasion and oil resistance properties. Low-molecular-weight natural rubbers from other temperate zone plants could be similarly modified.

Allelopathic response of vegetables to guayule residue

Abstract Water leachates from guayule processing residues or residues mixed with peat moss or soil significantly delay germination onset and decrease percentage germination for the following crops: broccoli, cantaloupe, cauliflower, cotton, guayule, lettuce, pepper, and tomato. These effects can be ascribed to p-anisic acid present in leaf resin and a variety of substituted benzoic and cinnamic acids present as carboxylate salts in leaves and bagasse.