Application of gamma radiation induced graft copolymerization for paper conservation in Sri Lanka

Paper, which contains cellulose and lignin as major constituents, is susceptible to deterioration by acid catalyzed hydrolysis, microbial and insect attacks over the time, resulting the material to be unstable and fragile. In order to preserve the archaeological and cultural value as well as the exquisite content, various conservation techniques have been utilized and gamma radiation induced graft copolymerization has gained attention due to its ability to restore the structural integrity and to act as a preventive measure, along with simultaneous disinfestation. The present study is focused on the restoration of the strength of the deteriorated paper material and prevention of further disintegration into fragments by creating interlinkages within the paper matrix. Chemical formulations containing mixtures with variable concentrations of alkyd resin and methyl methacrylate (MMA) and mixtures with variable concentrations of alkyd resin and styrene were applied to naturally aged paper and irradiated with a gamma radiation dose of 15 kGy at a dose rate of 0.33 kGy/hr. Alkyd resin was analysed and characterized to determine its chemical and physical properties. Polymer deposition yield was determined by the percentage weight gained (per unit area) and samples were characterized by Scanning Electron Microscopy (SEM) and evaluated for their physical properties such as tensile strength (ISO 1924-2: 2008) and tearing resistance (ISO 1974: 2012). Polymer deposition yield progressively increased with the concentration of alkyd resin and alteration of appearance of paper was observed for higher resin concentrations (30% and 40%). Hence, resin concentration of 20% was adopted for evaluation of physical properties based on the preliminary observations. In comparison to the control, significant improvement of tensile strength was detected for paper treated with 20% of alkyd resin in MMA, while change in tearing resistance was not significant. Tests for microbial resistance, aging, water absorbency, and folding endurance are in progress to further access the conservation properties. (author)