Use of a hydrotalcite isopropanol dispersion for deacidification and preservation of cellulose cultural heritage objects - Preliminary study

Preservation of cellulose cultural objects, particularly books, is a field of research with about 100 years of history. The most dangerous in terms of their lifespan is the use of acidic wood-based paper which represents a problem in both quality and durability. Acid hydrolysis of polymeric cellulose chains is a key factor responsible for loss of visual appearance quality and mechanical strength. Sulphate and aluminium ions together with generated formic, acetic, and other higher carboxylic acids accelerate the rate of degradation catalytically as well as autocatalytically. Alkaline species (alkali and alkali earth hydrogen carbonates, oxides, organocompounds, and amines) suppress the degradation processes. This paper refers to the utilisation of hydrotalcites (HT, MgxAl2(OH)2x+4CO3, x > 6) as deacidifying agents in a non-halogenated low toxic carrier – isopropanol. Preparation of an HT dispersion, its characterisation, and application to (acidic) test paper are described. Due to its ion exchange and neutralization capabilities, HT increased pH of test papers from about 4 to at least 6. Similarly to the action of HT as antacids, it is possible to suppose the neutralizing capability in deacidifying of aged-acid papers, even at pH lower than 7. A higher increase of pH was achieved only with extremely high loadings of HT; 16 g / m2 allowed to reach a surface pH value equal to 7.8. Both the optical properties and mechanical strength of treated samples were improved at loadings up to 3 g / m2.