Strengthening of paper by treatment with a suspension of alkaline nanoparticles stabilized by trimethylsilyl cellulose

Abstract

Control over the mechanical properties of cellulose-based artifacts (e.g. paper) is highly important in cultural heritage science. Especially, a non-aqueous method that does not cause swelling but can be applied to either single paper sheets or bound cellulose items (e.g., books) without any preselection is currently needed. Herein, we present a new multilayer deposition method that can simultaneously deposit alkaline reserve and improve the mechanical properties of historic wood pulp (HWP) paper, which often suffers from high fragility and brittleness. Alkaline nanoparticles (magnesium hydroxide Mg(OH)2NPs) stabilized by hydrophobic cellulose derivative i.e., trimethylsilyl cellulose (TMSC) in hexamethyldisiloxane (HMDSO) are prepared and deposited in the form of multiple layers on HWP paper by a technically effortless dip coating procedure. An enhanced and irreversible deposition of Mg(OH)2 NPs–TMSC and an alkaline reserve (AR) up to 4% (139 meq[OH−]/100g) are achieved as revealed by infrared spectroscopy and back-titration measurement. The tensile strength of uncoated HWP paper (1.6 MPa) is increased to 5.5 MPa after coating with Mg(OH)2NPs/TMSC (before aging) and then to ca 9 MP (after accelerated aging). In the latter case, the TMSC is transformed to cellulose by cleaving of O–Si bonds. The surfaces are evenly covered with thin and transparent coatings of hydrophobized nanoparticles as demonstrated by electron scanning microscopy and contact angle measurements.