Hydroxyl Terminated Natural Rubber (HTNR) as a Binder in Solid Rocket Propellant Norfhairna Baharulrazi 1, a , Hussin Mohd Nor 2,b and Wan Khairuddin Wan Ali 3,c 1,2 Polymer Engineering Department, Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia. 3 Aeronautical Engineering Department, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia. a norfhairna@cheme.utm.my, b hussin@cheme.utm.my, c wankhai@fkm.utm.my Keywords: Hydroxyl terminated natural rubber (HTNR), oxidative degradation, liquid rubber, propellant, deproteinized natural rubber (DPNR) 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) and Gel Permeation Chromatography (GPC). 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 . Introduction About four decades ago, the development of methods for the production of TLNR was started. Essentially, oxidative chain scissions which involve controlled degradation of natural rubber (NR) backbone can be divided into two ways which are photochemical and chemical routes. Some methods that can be used to produce TLNRs have been developed and can be summarized that there are three main methods photochemical, redox, and oxidation at high pressure and temperature 1-5 . Telechelic liquid natural rubbers (TLNRs) are very useful in the synthesis of tailor made polymeric structures such as NR based elastomers, block segmented copolymers, NR based thermoplastics and interpenetrating networks 6 . Moreover, these liquid rubbers can also be used as a photocuring component and binders in rocket propellant. In recent years, productions of LNR more focus on tires, rubber gloves, wiring, tube and others. Basically, the polymeric binders used in the propellant have been transformed starting with traditional polyvinyl chloride (PVC), to polybutadiene acrylic acid acrylonitrile terpolymer (PBAN), then carboxyl terminated polybutadiene (CTPB) and lastly come out with hydroxyl terminated polybutadiene (HTPB) 7 . Many previous researchers reported about the use of HTPB as a rubber binder. Maruizumi et al., (1988) in research entitled development of HTPB binder for solid propellant reported the production of HTPB by free radical polymerization 8 . Then, they examined the characteristic of produced HTPB by studying the performance of the propellant. Muthiah et al., (1993) studied on the rheology of HTPB propellant and examined the effect of mixing speed and mixing time 9 .