Solubility behavior of SIR 3CV natural rubber and its response to grafting with maleic anhydride

Beside the rubber, natural rubber also contains protein, lipid, carbohydrate, and salts. Natural rubber undergoes gel formation and hardening during storage, as a consequence of the interaction between the non-rubber components. SIR 3CV is a natural rubber grade processed with particular methods to prevent storage hardening. Dissolution of SIR 3CV in toluene followed by coagulation with acetone yield two phases of the material, i.e., the quick-coagulating phase (SIR 3CV-A) and the slow-coagulating one (SIR 3CV-B). The two phases differ in color, with the slow-coagulating appears light yellow, while the other appears brownish. ATR-FTIR spectra of the two rubbers indicate that SIR 3CV-B contained protein and the residue of phospholipid treatment with hydroxylamine. This phase is more polar than the other; therefore, it was more difficult to coagulate after acetone was added to the solution. After reaction with maleic anhydride, SIR 3CV-B produced 4.14 wt.% of grafted maleic anhydride, while the other one generated only 1.76 wt.% of the grafted group. The more polar phase can receive a higher amount of maleic anhydride grafted to its molecule, presumably because of its better affinity with maleic anhydride. These results suggest that partial coagulation with solvents having different polarities may be used to tailor the amount of maleic anhydride grafted into the rubber.