Graft Copolymerization of Acrylonitrile onto Sodium Salt of Partially Carboxymethylated Tamarind Kernel Powder Using Ceric Ammonium Nitrate as a Photo‐Initiator in an Aqueous Medium Under Ultraviolet‐Radiation

Abstract

Ultraviolet (UV) radiation-induced graft copolymerization of acrylonitrile (AN) onto sodium salt of partially carboxymethylated tamarind kernel powder (Na-PCMTKP, DS = 0.15) has been carried out using ceric ammonium nitrate (CAN) as a photo-initiator. The optimal UV-radiation-induced grafting conditions have been established with Na-PCMTKP = 0.5 g (dry basis), [HNO 3 ] = 0.2 mol L −1 , [AN] = 0.295 mol L −1 , [CAN] = 6.0 × 10 −3 mol L −1 , time = 6 h, temperature = 30°C, volume of water = 144.58 mL, and total volume = 150 mL. The maximum percentage of grafting (%G) and percentage grafting efficiency (%GE) achieved under these established optimum reaction conditions are 361.16% and 89.33%, respectively. The various reaction conditions have been varied with a view to study their influence on the grafting yields (%G and %GE). A plausible mechanism to explain initiation, propagation, and termination of UV-radiation-initiated graft copolymerization has also been suggested. The influence of the efficiency of the photo-initiator on the grafting yields has been investigated. Fourier transform infrared, thermogravimetric analysis, differential scanning calorimeter (DSC), and scanning electron microscopy techniques have been successfully used to provide the evidence of grafting of polyacrylonitrile onto Na-PCMTKP. The kinetics of thermal decomposition of the graft copolymer, Na-PCMTKP-g-PAN, has also been investigated with the help of the DSC curves obtained at different heating rates. The Ozawa and the Kissinger methods have been utilized for the evaluation of the kinetic parameters for the thermal decomposition of the graft copolymer sample. The synthesized graft copolymer after saponification may be used as a superabsorbent hydrogel for potential applications.