AIC's 47th Annual Meeting

In this paper we discuss the strengthening of methylcellulose (MC) with nanocrystalline cellulose (NCC) and with microfibrillated cellulose (MFC) for high relative humidity (RH). MC is the least hydrophilic cellulose ether among the water soluble ones. Its long-term stability is very high. The same is true of its purity, according to Feller and White (1990). A good tensile strength for re-adhesion of flaking paint on canvas or wood as well as for wood glueing has been proven by many conservators. Therefore the use of MC is becoming more common in the field of conservation. However, the cohesion decreases dramatically when the relative humidity is rising (Debeaufort und Voilley 1997). In the range of 22% RH to 53% RH, the difference in tensile strength was only 9%, whereas for 75% RH the decrease amounted to 46%, for 84% RH even 80%. Nanocellulose has been recently proposed as a novel consolidant for canvas and paper consolidation as well as a reinforcement for some consolidants at room temperature and 50% RH. However, most of our heritage is located in churches, castles, collections or museums without climate control systems. Often the RH is 75%, 84% or even 100%. Therefore we started to strengthen the tested methylcellulose in order to maintain a product more resistant to high RH. After drying, pure NCC and MFC are no longer water-soluble. This is not in accordance with our professional requirements regarding retreatability or reversability. However, the adhesive mixtures MC-MFC/NCC stay water soluble when mixed with methylcellulose. Consequently, mixing the components MC and MFC or NCC could lead to a water soluble yet more resistant adhesive at high RH. Hence we tested the ratio of the components, the preparation, the homogenizing methods (magnetic stirrer, dissolver, SpeedMixer, hand-held blender and ultrasonic), the application, the drying and, finally, the behaviour at high humidities (75% RH, 84% RH and 100% RH). Several analytical techniques were used for the product characterization (tensile strength tests, elasticity tests, weighing technology) as well as scanning electron microscopy (SEM) and atomic force microscope (AFM). Subsequently we analyzed the penetration into porous chalkground on wood by means of fluorescent dyed cellulose and thin sections. The mix of MC and NCC showed the smallest loss of tensile strength during high RH. The tensile strength of the mixture at 75% RH corresponded with the tensile strength of pure methylcellulose at 50% RH. We developed a final product which is substantially more resistant to high humidity than pure methylcellulose and which shows that ratio, homogenizing and application methods are crucial.