Thermal and oxidative degradation mechanism of hydroxyl terminated natural rubber for solid rocket propellant binders
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Date
2015
Authors
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Publisher
Universiti Teknologi Malaysia
Abstract
Controlled oxidative degradation of deproteinized natural rubber (DPNR) in toluene at 60 °C by cobalt bis(acetyl acetonate) (CAA) in different percentage in the presence of various alcohols (i.e. methanol, ethanol, propanol and hexanol) at various reaction times, followed by reduction with sodium borohydride (NaBH4) was studied. The structure of hydroxyl terminated liquid natural rubbers (HTNRs) obtained were analysed using Fourier Transform Infrared (FTIR) and Gel Permeation Chromatography (GPC). Controlled degradation in the presence of ethanol showed a more favourable route than other alcohols in producing number average molecular weights (Mn) comparable to hydroxyl terminated polybutadiene (HTPB). Controlled degradation in the presence of ethanol at 60 °C suggested that one hour reaction time produced the lowest Mn and slightly increased up to eight-hour reaction time. FTIR indicated that the synthesised HTNR contained hydroxyl end groups similar to that of HTPB. The study showed that the optimum percentage of CAA was 5% w/w which produced the lowest molecular weight. In this work, 5CAA-E1 (5% CAA in the presence of ethanol at one hour reaction time) with Mn of 6691 g/mol and hydroxyl end groups was chosen for scale-up experiment. An optimisation of scale-up HTNR production was obtained by increasing the reaction temperature up to 80 °C resulting in Mn of 7708 g/mol with polydispersity index (PDI) of 3.23, comparable to HTPB with Mn of 7068 g/mol with PDI of 3.47. A probable mechanism leading to the formation of HTNR was proposed based on the Nuclear Magnetic Resonance (NMR) data. The composite solid propellant was fabricated by using scale-up HTNR (Mn of 7708 g/mol) and a comparative study of HTNR-based propellant and HTPB-based propellant was made for their effect on burning rate. The value of burning rate obtained from HTNR-based propellant was 2.79 mm/s and the value is equivalent to HTPB-based propellant which is 2.95 mm/s. In order to increase the burning rate, ethylene glycol was added to HTNR and the result showed an increment of burning rate value to 3.39 mm/s. In conclusion, HTNR shows a potential as a propellant binder and comparable to HTPB rubber binder.
Description
Thesis (PhD. (Polymer Engineering))
Keywords
Solid propellants, Solid propellant rockets, Solid propellant rockets—Design and construction