Deterioration of ancient cellulose paper, Hanji: evaluation of paper permanence

Hanji paper, the paper material traditionally used in Korea, is in the focus of the present aging and mechanistic study. As raw materials and historic recipes for paper making are still available for Hanji today, specimen resembling historical material at the point of production can be prepared. While from that starting point, historical material had taken the path of natural aging, newly prepared samples—prepared according to both historic and current recipes—were artificially aged, and both aging modes can be compared. For the first time, an in-depth chemical and mathematical analysis of the aging processes for Hanji is presented. The aging of Hanji paper, resulting in hydrolysis and oxidation processes, was addressed by means of selective fluorescene labeling of oxidized groups in combination with gel permeation chromatography, providing profiles of carbonyl and carboxyl groups relative to the molar mass distribution. Starting Hanji showed the highest molecular weight (>1,400 kDa) ever reported for paper. We have defined two critical parameters for comparison of the paper samples: half-life DP (the time until every chain is split once on average) and life expectancy (the time until an average DP of failure is reached and no further mechanical stress can be tolerated). The two values were determined to be approximately 500 and 4,000 years, respectively, for the Hanji samples, provided there is no UV radiation. The rate of cellulose chain scission under accelerated aging (80 °C, RH 65 %), was about 600 times faster than under natural conditions. In addition, cellulose degradation of Hanji paper under accelerated aging condition was about 2–3 times slower than that of historical rag paper as those used in medieval Europe.