Halloysite nanotubes filled with MgO for paper reinforcement and deacidification

A novel material for the deacidification and protection of paper has been designed by using MgO filled halloysite nanotubes (Hal). The ability of MgO loaded nanotubes to control the acidic conditions was evaluated by pH measurements in aqueous solvent. Afterwards, paper was impregnated into hydroxypropyl cellulose dispersions containing the consolidating material. A simulation of strong acidic conditions allowed us to evaluate the deacidification effect of the composite material on the samples. In particular, the paper reaches a pH of 7.7 after 1 h exposition to HNO3 vapours when MgO-Hal nanoparticles are added to the impregnation mixture at a concentration of 10 wt% and it remains still neutral after 12 h. Dynamic mechanical analysis showed that the tensile strength of the consolidated paper is improved, since the stress at breaking increase of ca. 8% for the samples treated with MgO-Hal compared to the untreated paper. Due to the presence of halloysite loaded with the alkaline reservoir, the acidic degradation of cellulose is neutralized as suggested by the stored energy which is similar to the pristine paper without any chemical attack. Therefore, the mechanical performances of the paper are preserved during the aging together with its macroscopic aspect, as suggested by colorimetric analysis. The proposed consolidation protocol represents a further step for the self-healing and long-term protection of cellulose based artworks.