Application of Arrhenius law to DP and zero-span tensile strength measurements taken on iron gall ink impregnated papers: relevance of artificial ageing protocols

Abstract

Iron gall inks (IGI) were largely used for writing until the nineteenth century. Under certain circumstances, they provoke a substantial degradation of their cellulosic support. It was shown in a previous works that combination of oxygen and iron largely impacts cellulose chain breaking occurring in acidic conditions (pH 3–4). The present study aims to study the kinetic of this degradation. It assesses the validity of Arrhenius law between 20 and 90 °C taking advantage of the fast depolymerization of IGI impregnated papers at room temperature and using two complementary tools: DP measurements and zero-span tensile strength. The first one is sensitive enough to measure degradation at its very beginning, while the second is more appropriate for advanced stage of degradation. Similar activation energies (97 ± 2 kJ mol−1) were found via DP and zero-span measurements, and reaction rates of IGI impregnated papers were 1–2 orders of magnitude above available data related to lignin-free acidic papers. These observations suggest a dominant hydrolytic mechanism that involves directly or indirectly oxygen and iron.