Kinetics of Graft Copolymerization of Acrylic Acid onto Cannabis indica Fibre

Natural fibres have received vast attention because of their combustible, non-toxic, low cost, hydrophilic and biodegradable properties. In this study, functionalization of cannabis indica fibre has been carried out by its grafting with acrylic acid (AAc) using a Ce3+-HNO3 redox initiator in an aqueous medium. Different reaction parameters such as reaction time, pH, reaction temperature, concentrations of initiator, monomer and nitric acid were optimized to achieve the maximum percentage of grafting (21.08%). The low graft yield obtained with acrylic acid was because of itshigh affinity towards water. A suitable mechanism to explain initiation, propagation and termination of graft copolymerization has also been proposed. The kinetics of the graft copolymerization of acrylic acid onto cannabis indica fibre has also been studied. It has been found that the rate expression for graft polymerization is (Rg) = k[I]0.63[AAc]1.22. The overall activation energy for the graft copolymerization of AAc onto cannabis indica fibre was found to be 15.25 kJ/mol within the temperature range of 25-45°C. Besides kinetic study the grafted samples were also evaluated for their physicochemical properties such as swelling behaviour in different polar and non-polar solvents along with resistance towards acid and base. Graft copolymerized samples have been found to show less resistance towards chemicals as compared to the raw fibre. Furthermore, the grafted samples were characterized by different techniques such as Fourier transform infrared (FTIR), scanning electron microscope (SEM), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) studies. Thermal stability of the fibre has been found to decrease after graft copolymerization which is also supported byactivation energy (Ea) values calculated both for raw and grafted fibres.