The crosslinking behaviour of cellulose in gamma irradiated paper

Abstract

The behaviour of cellulose-based materials in a relatively low gamma dose range (less than 10 kGy) is of interest for the application of ionizing radiation for the preservation of cultural heritage. Different relationships between the absorbed dose and number of scissions or degree of polymerization (DP) were established on a large dose range (over 100 kGy). The significant decrease of DP was confirmed for doses range of interest for cultural heritage preservation, for pure cellulose paper and other sorts of commercial paper. However, other physical properties of the paper have less or no change for irradiation at doses below 10 kGy.The purpose of this study is to evaluate the changes induced by gamma irradiation to the hydrogen bonds structure in cellulose, in a low dose interval, by thermal analysis and infrared spectroscopy.Our results confirm the crosslinking behaviour for Whatman paper at low irradiation doses. A similar behaviour was observed for copy paper but with reduced intensity and higher statistical errors. This behaviour can explain why mechanical resistance of irradiated paper remains unchanged below a certain dose, as previously reported in a number of studies. The carbonyl content shows a continuous increase over the tested dose range but the increase of carbonyl content in Whatman paper at doses lower than 10 kGy is lower than the initial carbonyl content of copy paper. The ionizing radiation treatment for cultural heritage is not nonintrusive in case of paper but the degradation risks are minimal for doses below 10 kGy.