Compósitos de nanocristais e nanofibrilas de celulose: preparação, caracterização e potenciais aplicações em processos de restauração de documentos e obras de arte sobre papel

Abstract

Cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) extracted from Eucalyptus pulp were used for developing nanocomposites (casting method) with promising applications as an innovative restoration method, especially as a material for filling paper losses in documents and artworks. CNCs and CNFs were used as high content reinforcing material (66% wt) in several compositions which were elaborated with cellulose ether as polymeric matrix and sizing agent (methylcellulose or tylose), a plasticizer (propylene glycol or polyethylene glycol), inorganic filler (CaCO3), and a pigment (TiO2, BaSO4 or ZnO). Aiming at comparing the traditional method applied by restorers, equally made paper composites were formulated with cellulose fibers from bleached eucalyptus pulp. Same materials were applied, except for the plasticizer. 45 samples were prepared (17 CNCs-based composite samples, 17 CNFs-based samples, 9 EUC-based samples, 1 commercial paper and 1 wood paper sample). Therefore, preliminary visual and tactile analyses were developed, as well as tests to measure chemical stability (pH, XRD, FT-IR, TGA), physical stability (water activity, water content and water vapor isotherms), and analyses of mechanical (stress-strain curves) and optical behavior (UV-Vis Spectroscopy), and surface morphology (MEV). Moreover, simulated reintegration procedures were carried out. Most of the testing was executed before and after accelerated artificial aging test. CNCs-based composites were more chemically stable (neutral pH and not variable, higher crystallinity index), as well as they were physically stable (compatible hysteresis with traditional paper samples) and presented good tensile strength and yielding limit. They were more chromatically stable and had a uniform surface (there were CNCs along the entire nanocomposite surface). Thus, they presented an excellent applicability as reintegration material. CNFs-based composites, on the other hand, presented great results in stress-strain behavior field (tensile strength was up to 3 times bigger than that of traditional paper, and they have higher strain, resilience and toughness). Therefore, they had been considered promising materials in the cultural heritage field. However, the applicability in reintegration procedures was not verified due to the high physical deformation it suffers after casting. Both CNCs and CNFs nanocomposites presented enhanced properties. Therefore, they are favorable innovative techniques which are able to improve the cultural heritage preservation.