Influence of nonrubber components on properties of unvulcanized natural rubber

Low-protein natural rubber (LPNR) and acetone-extracted natural rubber (AENR) were prepared in solid form by alkaline treatment and acetone extraction to remove proteins and lipids. The content of proteins and lipids along with gel content were characterized by Fourier-transform infrared spectroscopy (FTIR) and size exclusion chromatography with multiangle light scattering (SEC-MALS) analysis. It was found that natural rubber (NR) treatment by alkaline hydrolysis or acetone extraction decreased proteins or lipids along with gel content. Also, having less proteins and lipids changed the network structure from macroaggregates to microaggregates. This resulted in inferior plasticity and poor mechanical, rheological, and dynamic properties. Furthermore, decreased strain-induced crystallization and storage hardening were confirmed by temperature scanning stress relaxation (TSSR), after removal of proteins and lipids. Therefore, protein and lipid contents together with gel content play essential roles in controlling various properties of unvulcanized NR.