Cationic cyclization of deproteinized natural rubber latex using sulfuric acid

An increase in the plasticity of natural rubber (NR) to be a thermoplastic elastomer was carried out by cyclization reaction. The cyclized (NR) was obtained from deproteinized (NR) latex as a raw material, sulfuric acid as a catalyst, and Terric 320 as a nonionic surfactant. Various reaction times, dry rubber contents, concentrations of catalyst and temperatures affecting the degree of cyclization in (NR) were investigated. The resulting material was subjected to characterization by FT-IR, ¹H-NMR, solid-state ¹³C-NMR and DSC as well as the investigation of the gel content of the cyclezed NR. A method of determining the degree of cyclization of NR was also developed. The sufficient condition to prepare the cyclized NR was found to be 54% (w/w) concentrated sulfuric acid at 90°C for 3 h. The higher degree of cyclization in the product was accompanied with a higher gel content and glass transition temperature of cyclized rubber. In addition, the microstructure of the cyclized (NR) was also investigated.