Cellulosic nanomaterials include polymer matrix nanocomposites, aerogels, hydrogels, plant fiber assemblies such as networks or pressed films, or even wood structures where the nanostructure is tailored or specifically exploited. The large bulk of synthetic polymers used in packaging or in textiles, are not biodegradable, and this provides opportunity for new cellulosic materials. Materials based on native cellulose are preferable, since enzymes in nature can degrade cellulose whereas chemically modified cellulose may not be biodegradable. Combination of cellulose with other biological polymers, such as starch, hemicelluloses or chitosan results in preserved biodegradability and may additionally provide high optical transmittance. Earlier work on nanocellulose composites with chitosan, starch and hemicellulose matrices will be briefly reviewed. Physical aspects of light absorption and scattering will also be discussed, as well as suitable measurement techniques.<br/><br/>Wood sticks were prepared and subjected to delignification by different means. Peracetic acid treatment was found to be a suitable method for preparation of delignified wood fibers, termed holocellulose fibers. High-density films were prepared from the delignified wood fibers. The ultimate strength and modulus of the films were remarkably high, approaching those of nanocellulose films. The high molar mass of the cellulose, high fiber lengths and strong fiber-fiber bonding due to hemicellulose effects, are reasons for this observation. The intrinsic strength of the individual wood fibers was measured as a function of cellulose microfibril angle, and the strongest fibers (with low microfibril angle) approached 1 GPa in strength.<br/><br/>Films were also prepared from oriented wood fibers. Strength and modulus increased further compared with the materials with random-in-the-plane fiber orientation. Finally, ramie fibers were also delignified and subjected to high pressure compression under wet conditions and elevated temperature. Even higher strength and modulus was observed compared with the wood fiber materials. In addition, the optical transmittance was quite high. Routes towards improved optical transmittance, new optical functionalities are discussed.

Design of biodegradable cellulosic nanomaterials combining mechanical strength and optical transmittance

256th National Meeting (2018)

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