Introduction

Archives, libraries and similar institutions store written and printed documents which they are obliged to retain on a permanent basis for cultural reasons and, in some cases, in order to meet legal requirements.

Often, the condition of these documents is endangered for a number of reasons. One of these is related to the manufacturing process used for more modern types of paper.

In the industrial age, paper-making processes underwent significant changes. One of the processes affected was sizing, which, in industrial processes, was achieved by mixing additives into the fibre suspension before shaping the sheets. These additives included acidic substances like aluminium sulfate. The reaction of the sizing agent eventually leads to formation of free acids. The acids act as a catalyst for the hydrolysis of cellulose, making the material brittle. Climatic influences aggravate this process, air pollution and cellulose degradation processes are a further source of acid in paper.

Another factor for paper stability is the raw material itself. For centuries, paper was made of textile fibres like linen, hemp or cotton rags which rather deliver stable, long-chain cellulose. The search for a more abundant raw material led to the invention to produce pulp out of wood by a grinding process. The resulting ground wood paper still contains most of the lignin and hemicelluloses, in addition to cellulose. The low pulp purity and the mechanical process causing a partial cutting of fibres lead to a much weaker paper. Compared to the older rag papers, ground wood paper is also less stable on the long run.

The problem of paper degradation due to acid has developed into a tremendous problem for archives and libraries. In addition to the processes for deacidifying single sheets, such processes having been used in conservation for a long time, the past few decades have seen new developments in technical processes which can be used on a large scale to retard the further decay of cultural assets as bound volumes and single sheets (“mass deacidification”).

The aim of deacidification is to appreciably improve the life expectancy of paper. This is achieved by adding an alkaline substance to neutralize existing acid and slow down future acidic degradation for at least some time (buffering, alkaline reserve). Deacidification cannot improve the actual physical properties of the paper, but in combination with proper storage, it can slow down further decay.

Without validated analytical methods, it is not possible to assess whether a paper has been deacidified, or to what degree deacidification has been successful. This Technical Specification compiles the suitable measurements.

PD ISO/TS 18344:2016

Effectiveness of paper deacidification processes

Current, Under Review

Published:

29 Feb 2016