Supercritical CO2 Extraction of Rubber and Resin from Guayule

Guayule (Parthenium argentatum) is a woody shrub native to the southwestern U.S. that produces rubber in its stems. In the production of guayule hard rubber for tires, two residue streams are produced: a liquid resin and a fine, dry, woody bagasse. Natural rubber is an organic poly-isoprene elastomer used for tires, seals, and many other applications. The rubber tree (Hevea brasiliensis) grown in southeastern Asia and South America accounts for 99% of the world’s natural rubber. Hevea rubber contains allergenic proteins (“latex allergy”) that guayule shrub does not.

In this study, supercritical CO2 extraction was investigated for guayule resin and rubber extraction. Conventional extraction techniques for rubber and other plant compounds have the challenges of that thermolabile compounds can decompose at the temperatures used and large volumes of organic solvents are required—two factors that decrease the feasibility of these techniques for large-scale applications. Supercritical fluid extraction (SFE) process is considerably closer to being carbon-neutral, using very little organic co-solvent (3-5% here), having fewer emissions, and using lower temperatures. The properties of CO2 can change dramatically with SFE conditions. To understand the effects of conditions on the extraction efficiency, rubber and resin need to be quantified within the guayule biomass before and after extraction. Here, sequential Soxhlet extraction with acetone and hexane was used to represent total and residual rubber and resin. Those rubber and resin contents were then compared to the weights of rubber and resin recovered from the SFE collection vessels.