Soluble protein-free natural rubber latex prepared using guanidine hydrochloride as a denaturant

Abstract

Purified natural rubber was successfully prepared in the presence of a denaturant named guanidine hydrochloride (GNH). In this work, fresh field natural rubber (FNR) latex was used as a starting material. The conditions of purification such as the effect of GNH concentrations, incubation time and temperature were studied. The results showed that the soluble protein-free natural rubber (SPFNR) contained undetectable extractable (EP) and antigenic (AP) protein, and very low nitrogen content, i.e. 0.013 wt% at GNH concentration of 0.1 phr, after 1-h incubation at 30 °C. These results were supported by the Fourier transform infrared (FTIR) spectroscopy, where the absorption peak of the amine functional group (proteins) disappeared substantially and the fatty acid ester functional group (lipids) decreased swiftly after purification. Transmission electron microscope (TEM) images showed that the non-rubber component matrix disappeared in the SPFNR film. Less water hydration was obtained for the SPFNR film, which was reflected by a lower water uptake percentage than the FNR film. Furthermore, the thermal property determined by a thermogravimetric analyzer (TGA) showed that FNR and SPFNR films were comparable to each other. The stress at break showed that the FNR film was superior to the SPFNR film. Interestingly, the strain at break was about similar for both films, indicating the SPFNR film has softer and more elastic characteristics.