Synthesis, characterization and evaluation of vinyl acetate alcohol resin (VAAR) as a multipurpose binder for advanced energetic composites

VAAR containing different molar ratios of vinyl acetate (Ac) and vinyl alcohol (OH) were obtained by partial alkali hydrolysis of commercial polyvinyl acetate. As the hydrolysis progressed, VAAR exhibited gradual increase in the intensity of IR bands at 3456 cm(-1) and 3544 cm-1 (OH) as well as at 838 cm(-1) (CH2) corresponding to CH2-OH and decrease in the intensity of band at 798 cm(-1) assigned to OCO-CH3. IR patterns could be co-related with the -OH content of product. Elemental analysis of VAAR was also undertaken to monitor the progress of hydrolysis. The hydroxyl content of VAAR was determined by chemical technique and relationship between reaction time and degree of hydrolysis was established to obtain VAAR of the desired Ac/OH ratio. ESCA was done to confirm the chemical structure and association between acetate and OH groups within the polymer. Substantial increase in the tensile strength of polymer was observed on initial replecement of acetate groups by hydroxyl groups, and after a threshold limit a decrease in tensile strength was observed. Energetic formulations based on promising thermoplastic copolymer with Ac/OH ratio of 90/10 was selected as a binder for plastic bonded explosive (PBX), low vulnerable ammunition (LOVA) propellant and extruded composite propellants (ECP) in view of optimum mechanical properties. PBX sheets prepared by hot calendering of VAAP filled with 85% fine RDX delivered VOD of 7680 m/s and ECP obtained by hot extrusion of copolymer filled with 67% fine ammonium perchlorate AP and 20% Al exhibited burning rates of the order of 14.4-20.4 mm/s (in pressure range 3.5-7 MPa). These results were superior to corresponding estane-based formulations. Similarly, higher energy in terms of force constant was delivered by gun propellant obtained by hot extrusion of VAAR copolymer-based formulation containing 85% fine RDX compared to that reported for conventional M-30 propellant. Thermal studies revealed that cleavage of acetyl group is predominant during decomposition of VAAR while RDX plays a prominent role during decomposition of RDX-VAAR formulations.