Guayule is also found to be a potential source of natural polyisoprene (PI), according to a study led by Amandine Rousset ( Avignon University and GuaTecs), Ali Amor (CIRAD and CTTM), Serge Palu (CIRAD), Teerasak Punvichai (Prince of Songkla University), Sandrine Perino (Avignon University), Michel Dorget (GuaTecs and CTTM), Daniel Pioch (CIRAD), and Farid Chemat (Avignon University). However, the researchers mentioned that efforts have to be made on co-product valorisation to be competitive with currently marketed rubber and latex products.
Guayule is native to the desert of Chihuaha, located in Mexico and the US’s southern Texas. Native plants can live up to 30-40 years or more, resist temperature higher than 40°C, and withstand temperatures below -15°C.
PI and/or resin are found in different sections of the stems, branches, roots, leaves, and flowers. On average, there are 8% of PI and 10% of resin in the plant. Natural rubber is contained in thin-walled cells, the parenchyma cells, located in the bark and the pith.
There are two major types of processes for guayule’s PI extraction: processes that extract PI in a coagulated state, the aim being to obtain dry rubber (i.e. for tyres) and processes that extract PI in the emulsion form (i.e. latex for gloves). The main processes to obtain dry rubber are: flotation (aqueous process), sequential extraction (solvent process), simultaneous extraction (solvent process), and more recently supercritical-CO? (with co-solvents). To extract PI in the emulsion form, an aqueous process was developed and improved progressively.
Depending on the used process, products and co-products are different: dry rubber or latex, resin, leaves (if the plant has been defoliated) and bagasse.
However, efforts have to be made on co-product valorisation to be competitive with currently marketed rubber and latex products.