Migration of volatile compounds from paper stacks during accelerated ageing

In order to develop improved artificial ageing methods for paper, several research projects conducted by different laboratories throughout North America have shown that paper sheets, aged in an enclosed environment or arranged in stacks, deteriorate faster than single sheets aged under the same conditions. This was found to be especially true for acidic paper. The objectives of this project are: to investigate the changes in paper properties from the top of the stack (open to environment) to the centre, to determine if they are effected by possible migration of volatile products from the paper, and to find out whether or not the diffusion of acidic compounds have the same effect on the stability of thermally aged paper and naturally aged paper. An alum-rosin sized fully bleached kraft paper was aged in stacks, at three different temperature and humidity conditions and four different intervals. The stacks were open at the top to allow diffusion of volatile products to occur. Test methods included grammage, moisture content, brightness, yellowness, L*a*b*, zero-span tensile strength, pH and the degree of polymerization. These tests showed a decrease in paper properties from the top of the stack to the centre. This indicates a diffusion effect where volatile compounds escape from the paper at the top of the stack, but remain trapped towards the centre, where more severe degradation occurs. It is not entirely clear if this diffusion effect is the same at ambient conditions as it is at the elevated temperatures used in this study. The research project was carried out in collaboration with the Canadian Conservation Institute.