A preliminary study of chemical methods for stabilizing lignin in groundwood paper

Abstract

Plexiglas 201® Transparent polymethyl methacrylate sheet incorporating an ultraviolet stabilizer. An ultraviolet spectrum of Plexiglas 201® confirmed that it absorbed more than 99070 of radiation between 295 and 380nm. The thickness of sheet was 2.25mm. The spectrum was obtained using a Pye Unicam SP1800 Ultraviolet Spectrophotometer with a Unicam A R25 linear recorder. 2 EXPERIMENTAL 2.1 Materials Papers New newsprint was obtained as an end roll from a local newspaper office. The 1953newspaper, which had been stored under a variety of conditions, was a discarded bound volume from the National Library's collection. The fibre composition of both papers, determined by analysis, i~given in Table 1. phenolic component of lignin to coloured quinonoid compounds [4]. Work aimed at stabilizing the colour of groundwood paper by chemically altering the composition of lignin has shown that etherification or esterification of the free phenolic hydroxy groups of lignin retards the rate of discoloration [2, 6, 7]. The aim of the present study was to find a method of bleaching discoloured groundwood paper and treating the bleached paper in such a way that its future rate of discoloration would be reduced. Initially, naturally aged paper was unavailable, so the first experiments were carried out using new newsprint which had been artificially yellowed by exposure to ultraviolet light. The bleaching agents investigated were hydrogen peroxide and potassium borohydride. Bleached papers were acetylated using acetic anhydride [2]. An additional series of experiments was conducted in which treated papers were deacidified using magnesium bicarbonate solution. To examine the effectiveness of treatments in preventing light-induced yellowing all treated papers were exposed to ultraviolet light. The reduction in the rate of yellowing produced by covering samples with ultraviolet-absorbing plastic sheeting during exposure to ultraviolet light was also investigated. The results indicated that the method which best prevented colour reversion was bleaching with potassium borohydride followed by alkali-catalyzed acetylation using acetic anhydride. This method was then used in the second part of the study in which a naturally aged 1953 printed newspaper was examined. A vapour phase adaptation of the acetylation reaction was also investigated. The success of treatments was assessed by exposure of samples to ultraviolet light. Heataging studies were carried out to investigate the possibility that the heat produced by the ultraviolet light source had influenced the rate of yellowing. Future investigations will be aimed at examining the effect of bleaching and acetylation on the rate of embrittlement of groundwood papers.