Effect of the Water Sorption on the Mechanical Response of Microcrystalline Cellulose-Based Composites for Art Protection and Restoration Annalisa Cataldi, Andrea Dorigato, Flavio Deflorian, Alessandro Pegoretti Department of Industrial Engineering and INSTM Research Unit, University of Trento, 38123 Trento, Italy Correspondence to: A. Cataldi (E - mail: annalisa.cataldi@ing.unitn.it) ABSTRACT: Thermoplastic composites based on a commercial acrylic matrix widely used in the field of art protection and restoration (Paraloid B72) and various concentrations (up to 30 wt %) of microcrystalline cellulose powder (MCC) were prepared by melt- compounding and compression molding. The mechanical behavior of the resulting materials conditioned at a temperature of 23  C and a relative humidity level of 55% was compared to that of the corresponding dried materials. Even though the moisture absorption of the filler was lower than the neat matrix, the maximum moisture content increased with the MCC amount, probably due to the preferential water diffusion path through the microvoids and/or the filler-matrix interface. Although the increase of moisture content for filled sam- ples, DMTA analysis evidenced a stabilization upon MCC introduction, with an increase of the storage modulus and a decrease of the thermal expansion coefficient proportional to the filler loading. A similar trend was displayed by the corresponding dried materials. The tensile elastic modulus and the ultimate properties such as the stress at break and the tensile energy to break (TEB) of conditioned sam- ples increased proportionally to the filler amount. On the contrary, the failure properties of dried composites were negatively affected by the presence of the microcellulose. It is worthwhile to report that a significant improvement of the creep stability was induced by MCC introduction both for dried and conditioned samples. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40741. KEYWORDS: adsorption; composites; mechanical properties Received 13 February 2014; accepted 21 March 2014 DOI: 10.1002/app.40741 INTRODUCTION Acrylic resins are commonly used in the field of cultural herit- age restoration for the treatment of artworks. Among thermo- plastic polymers, Paraloid B72 V R , a methyl-acrylate/ethylene methyl-acrylate (MA/EMA) copolymer, is one of the most used. Thanks to its good optical features and the possibility to be eas- ily removed in case of need, this resin is applied as a protective layer for compact surfaces, as a consolidant of porous materials, and as an adhesive. 1–4 Generally speaking, the long-term efficiency of polymers used in conservation treatments is strictly related to their durability in terms of chemical and photo-thermal oxidation stability, yellow- ing resistance, preservation of mechanical properties, water resistance and gas permeability. The synergistic action of sun- light, atmospheric pollution, temperature, and moisture may induce a certain degradation of the polymer structure with a reduction of the consolidative/protective capabilities of the art- work preservative materials. 5,6 Moreover, if the artwork is sub- jected to chemical, biological, and/or physical attack, the degradation reactions are strongly promoted by the presence of water inside materials. If compared to commonly used acrylics resins for art conservation, Paraloid B72 presents a lower tend- ency to water sorption and a good chemical and photo-thermal oxidation stability. 7–9 Because of its low density, high specific strength and elevated stiffness, 10 microcrystalline cellulose (MCC) is an interesting reinforcing filler for polymeric matrices. 11,12 Due to the produc- tion process based on the reaction of cellulose with a water solution of strong mineral acids at boiling temperature, these natural fibers present a high degree of crystallinity. In fact, the hydrolysis reaction destroys the amorphous fraction and reduces the degree of polymerization of the cellulose chains. 13 Therefore, microcrystalline cellulose has a good water swelling resistance and thermochemical stability. 14,15 Moreover, microcrystalline cellulose is non-toxic, biodegradable and recyclable. In a previous work of this group, 16 the improvements of the thermomechanical properties of Paraloid B72 through the intro- duction of various amounts of a commercial microcrystalline cellulose powder have been investigated. In that work both the matrix and the filler were dried under vacuum, and the V C 2014 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2014, DOI: 10.1002/APP.40741 40741 (1 of 6)