Hydroxyl Terminated Natural Rubber (HTNR) as a Binder in Solid Rocket Propellant

Abstract

Controlled degradation of deproteinized natural rubber by oxidative method using cobaltous leading to the formation of telechelic liquid natural rubber (TLNR) has been the subject of study in the current work. Hydroxyl-terminated natural rubber (HTNR) having number-average molecular weights (Mn) below 10,000 gmol-1 were synthesized at temperatures 60°C using Cobalt bis (acetyl acetonate) (Co) in the presence of ethanol and Sodium borohydride. The HTNR were characterized structurally by using Fourier Transform Infrared (FTIR), Gel Permeation Chromatography (GPC) and Nuclear Magnetic Resonance (NMR) spectroscopy. From the FTIR and GPC analysis, one hour reaction showed the lowest Mn around 6691 gmol-1 comparable to Hydroxyl terminated polybutadiene (HTPB) which were 7708 gmol-1. As the reaction time increases the Mn also increase up to 8 hours of reaction. FTIR indicated that the synthesized HTNR contained hydroxyl end groups. The study showed the optimum percentage of Cobalt bis (acetyl acetonate) is 5% which produce the lowest molecular weight. Next, the HTNR underwent crosslinking reaction with isophore diisocyanate (IPDI). Then, metal fuel (aluminium powder, Al), oxidizer (ammonium perchlorate, AP) and HTNR were mixed together and went through compression process to produce solid rocket propellant. Burning rate obtained from HTNR samples were 2.78 mms-1 which were equivalent to HTPB samples which is 2.94 mms-1.