Radiation induced grafting of acrylic acid onto cellulose: an iterative procedure

In this study, we have designed, developed and fabricated filter paper discs for the detection of chromium (Cr) in ground water. This was accomplished by radiation induced grafting of acrylic acid onto the surface of filter paper. Radiation induced grafting is a validated and versatile technique for imparting functionality to a polymer substrate thereby broadening its applications. However, there is an upper limit to the extent of grafting that can be achieved, mainly dictated by the monomer concentration, radiation dose, competing polymerization, additives like Mohr's salt, mineral acids etc. Irrespective of the substrate and composition of the grafting solution, after some irradiation dose, a saturation point of grafting is reached. Preliminary investigations revealed that the intensity of colour developed on the paper disc is proportional to the extent of acrylic acid grafting, therefore higher degree of grafting was required which was not achievable by the conventional method. We could find a solution to this; we could get higher degree of grafting by employing an iteration of the conventional grafting process. This acid functionalized paper was further treated with a colour reagent, which forms a coordination complex with Cr and the paper subsequently develops colour. Unlike other substrates, the use of extraneous mineral acids is not necessary for our substrate and therefore, the problems associated with acid handling can be circumvented. The colour and its intensity produced on the paper were discernible and distinguishable to the naked eye, even at a very low concentration of 1 ppm. (author)