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United States Department of Agriculture

Agricultural Research Service

Research Project: Improvement and Utilization of Natural Rubber- and Castor Oil-producing Industrial Crops

Location: Crop Improvement & Utilization Research

Title: Guayule resin detection and influence on guayule rubber

Authors
item Nepomuceno, Bruna
item McMahan, Colleen

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 10, 2012
Publication Date: N/A

Technical Abstract: Guayule (Parthenium argentatum) is a natural rubber (cis-1,4-polyisoprene) producing crop, native to North America. Guayule also produces organic resins, complex mixtures of terpenes, triglycerides, guayulins, triterpenoids and other components. During natural rubber extraction, guayule resins can be co-extracted with the polymer, sometimes leading to a significant fraction of low molecular weight extractables in the rubber. Resin present in guayule rubber can affect viscosity, thermal stability and mechanical properties of rubber compounds. The objectives of this study were: 1) quantify the extractable content of guayule rubber and other polymers, 2) evaluate the use of Gel Permeation Chromatography (GPC) to characterize the resin in rubber, 3) measure the effect of the resin addition on physical properties of cast polymer films. The four polymers investigated were: 1) solvent extracted Guayule rubber (Sacaton simultaneous extraction process) 2) dried Guayule latex (aqueous process), 3) synthetic Polyisoprene (Natsyn™), 4) dried Hevea latex (RRIM 600 Campinas, Brazil). Acetone soluble extracts were quantified as function of temperature by Accelerated Solvent Extraction (ASE). GPC was used to characterize the polymers before and after extraction, and the extracts. Guayule resin (Sacaton simultaneous extraction process) was added at +5% and +10% to a solution of guayule rubber in THF, and films cast for physical property testing. The evaluations included bulk viscosity, thermal stability (by Plasticity Retention Index (PRI)), and green strength of cast polymer films. Resin addition and subtraction was readily quantified by the GPC UV detector at 254 nm and by Refractive Index; over a range of molecular weight from ~75 to ~500 g/mol. This demonstrated the potential of the GPC to measure rubber molecular weight and resin content simultaneously. The correlation between resin quantified by GPC and by ASE extractables was determined for all four polymers. Addition of Sacaton resin to guayule rubber led to decreased bulk viscosity, and softening of green tensile properties due to plasticization, in agreement with other published results. However, thermal stability (PRI) was improved, possibility due to antioxidant present in the Sacaton guayule resin.

Last Modified: 10/1/2014
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