W.W. Schloman

Characterization and Performance Testing of Guayule Latex

Abstract Physical and biological properties were determined for a preliminary production run of low-ammonia latex from guayule (GR latex). GR latex, and dipped films produced from compounded GR latex, contain none of the Hevea allergens known to elicit Type I systemic allergic reactions. The polymer phase of GR latex has a lower bulk viscosity and a higher resin content than that of NR. In addition, GR latex serum and rubber lack the activating components present in NR latex. As a result, GR latex cures more slowly and reaches a lower state of cure. The aged stress-strain properties of cured GR films are nonetheless similar to those of NR films.

Anti-termitic efficacy of the resin and rubber in fractionator overheads from a guayule extraction process

Abstract Antitermitic properties were evaluated for a mixture of resin and rubber obtained by solvent extraction of guayule. Pine (Pinus strobus L.) sapwood was impregnated with fractionator overheads consisting of resin and low-molecular-weight rubber. The impregnated wood was exposed for 71 months at two sites in the Panama rain forest and for 67 months at a site in the Arizona desert. None of the treated wood sustained any termite damage at either site, whereas untreated baitwood was routinely destroyed. The impregnant mixture acted as a termite antifeedant rather than a repellant. Almost no loss of resin or rubber was sustained by specimens exposed in Arizona, whereas significant losses occurred at both sites in Panama. Environmental factors, including microbiological activity, may have contributed to the loss of both resin and rubber in the rain forest environment. Enough impregnant did remain in the wood to protect it from termite attack throughout the exposure period.

The leachability of guayule resin from treated wood

Abstract Field evaluation has shown that guayule resin has potential as a protectant for wood against damage by terrestrial wood-destroying organisms. When used in this capacity, it is essential to know whether the resin migrates from the wood, as a contaminant, into the natural environment. Thus, a study was made to determine the loss of resin from treated wood via leaching under optimum laboratory conditions. After 193 days of continuous exposure to recirculating synthetic seawater, there was no loss of resin from the treated wood caused by leaching nor was there any chemical change in composition of the recovered resin. These results support the use of guayule resin as an environmentally-safe, long term protectant against damage by terrestrial wood-destroyers.

Protein Levels Affect the Cure Efficiency and Allergenic Potential of Polyisoprene Latices

Abstract Commercial NR latex has a higher total protein content than guayule (GR) latex. Some NR proteins are allergens bound to the rubber particle surface. Washing NR latex with a non-ionic surfactant displaced these particle-bound proteins and reduced allergens by more than 95%. The cost of such deproteination was reduced vulcanization efficiency, as determined by crosslink density. The extent of vulcanization correlated well with both total protein and allergen levels. Compared with films prepared from untreated NR latex, films from both surfactant-treated NR latex and GR latex had lower states of cure. Where particle-bound proteins were still present, as they are in GR latex, crosslink development could be completed by heat aging. In contrast, crosslink development in the film from surfactant-treated NR was complete after dipping and drying. The resulting films yielded high levels of extractable protein allergens.

Reduction of resin in polyisoprene latices by lipase-catalyzed hydrolysis of triglycerides

Abstract Resin components act as diluents and plasticizers that can degrade the stress–strain properties of cured rubber compositions prepared from natural polyisoprene latices. Lipase-catalyzed hydrolysis is an effective means of reducing the resin content of latex. By using a commercial lipase that is active at the pH of ammoniated latex, the resin contents of Hevea and guayule latices were reduced by about 7 and 33%, respectively. Maximum conversions of the latex resin triglycerides were obtained within about 12 h at 37°C. The recovery and recycle of lipase were easily effected.

Semisynthetic guayule latex with reduced allergenicity

Abstract Semisynthetic latices were prepared batchwise using solvent-swollen rubber extracted from guayule ( Parthenium argentatum ). Emulsification of the extracted rubber with anionic surfactants followed by vacuum desolventization yielded stable, low-resin products. The swollen guayule rubber had a low protein content (2.3 μ g/g dry rubber). As a consequence, the semisynthetic latices had protein contents (11–20 μ g/g dry rubber) significantly lower than that of native guayule latex (129 μ g/g dry rubber) isolated directly from the shrub. More importantly, these semisynthetic latices and the dipped films prepared from compounded latices contained none of the protein allergens associated with either Hevea brasiliensis latex or native guayule latex.