Effect of various alcohols and reaction time on the properties of hydroxyl terminated natural rubber synthesized via oxidative degradation

Abstract

The oxidative degradation of deproteinized natural rubber (DPNR) using cobalt bis(acetyl acetonate) in the presence of different alcohols and various reaction time; followed by reduction with sodium borohydride (NaBH4) for the synthesis of hydroxyl terminated liquid natural rubbers (HTNRs) was carried out. The synthesis of HTNRs from natural rubber is particularly important as an alternative to hydroxyl terminated polybutadiene (HTPB); one of the current leading synthetic rubber for the production of rubber binders for composite solid propellants. Four different alcohols (i.e. methanol, ethanol, propanol and hexanol) were investigated in order to achieve degraded DPNR with lowest molecular weight. The structure of the obtained HTNRs were analysed using gel permeation chromatography (GPC) and fourier transform infrared (FTIR). Based on GPC analysis, it was found that the use of ethanol at 1 h reaction time resulted in lowest molecular weight of approximately 6,690 g/mol. Analysis of chain scission of the HTNRs were consistent with the molecular weight attained. FTIR analysis, on the other hand confirmed the presence of hydroxyl functional group in the synthesized HTNRs with the highest amount of hydroxyl group presence in the HTNR prepared using ethanol. Overall, the properties of synthesized HTNRs (molecular weight and functional groups) displays a potential material for the production of propellant binder and are comparable to the properties of commercially available HTPB.