Study of Transport Phenomena in Guayule Deresination

Abstract

Abstract Renewed interest in guayule as an alternative source of natural rubber has brought the processing aspect back into focus as an important determinant in the effort of guayule commercialization. To meet the current technological requirement, the quality of the guayule rubber needs to be standardized like the presently known Technically Specified Natural Rubber. In order to produce good standard quality guayule rubber, the resin constituent must be thoroughly and consistently eliminated. This condition stipulates an effective and efficient extraction process which in consequence demands a thorough understanding of the resin compounds and their behavior during extraction with acetone. The emphasis of this study is to examine the physical state of resin inclusion in the rubber and the mechanism of its removal during solvent extraction. The ultimate objective is to determine the necessary transport parameters in the deresination process of guayule latex coagulum, better known as ‘worms’ in popular terminology. Worm deresination was used in guayule processing in the U. S. during World War II, and it is currently also performed in the CIQA Pilot Plant in Saltillo, Mexico. Previous work on the subject had been carried out by Banigan and Clark of the U. S. Natural Rubber Research Station at Salinas, California in the early 1950's. Banigan had determined that the worm deresination occurred by diffusion and made experiments to determine diffusion coefficients using thin sheets of dried worms with acetone, ethanol and methylethyl ketone as solvents. He also noted the possibility of two different diffusion coefficients due to the mixed nature of guayule resin. Recent investigations at CIQA have confirmed that the resin consists of two major groups, namely the nonvolatiles and the volatiles. The nonvolatile components are mainly fatty acid triglycerides, while the volatiles are terpenoids such as α-pinene, dipentene, etc. The present study attempts to provide more detailed transport data using modem analytical techniques and the current knowledge of transport processes in polymeric materials. Since the available diffusion data are only for dried worms, whereas in reality the worms are deresinated in the wet state, the present work has used wet worms as the study material.