Microfibril modification

Wood has many excellent mechanical properties that result from its exceptional combination of microstructural, ultrastructural, and molecular features. The main drawback is its dimensional instability in the presence of moisture. One main reason for modifying wood chemically is to reduce this instability. Other chemical treatments of wood reach the crystalline region of cellulosic microfibrils, destroying the crystalline structure, thus eliminating most of the composite structure of wood. The resulting material does not have any of the characteristic properties of wood but it may be provided with thermoplasticity. A chemical treatment of wood as defined here excludes such radical modifications. We refer to a chemical treatment that may reduce some defects relative to wood utilization and enhance its properties while keeping the bulk of the superior mechanical properties of wood. 

The actual state of the xylans and glucomannans in the living tree is still largely unknown. Since they do not crystallize readily without some chemical modification, such as partial depolymerization or removal of side chains, or both, it would seem likely that they occur in the amorphous state in the wood. The possibility that they could form microfibrils, as does mannan B in vegetable ivory, cannot be entirely excluded.More probably, however, they occur as a powder between and around the cellulose microfibrils. Using a polarized infrared technique, Marchessault and coworkers have obtained indications that, not only the cellulose, but also the xylans and glucomannans, may be oriented in the direction of the fiber axis in wood. 

The nanofibrillated (microfibrillated) cellulose was first developed by Herrick et al. (1983) and Turbak et al. (1983) via grinding of diluted pulp suspensions in high-pressure mills. Currently, a preliminary mild chemical modification is performed before mechanical disintegration in order to minimize energy consumption. The NFC is composed of nanofibriUar bundles with a lateral size of several tens of nanometers and length of a few microns. 

Stenstad P, Andresen M, Tanem BS et al (2008) Chemical surface modifications of microfibrillated cellulose. Cellulose 15 35-45... 

A new kind of cellulose-based nanocomposite was also described in literature inspired by sea cucumbers [81], which like other echinoderms have the ability to reversibly alter the stiffness of their dermis in the presence of external stimuli. This stiffness modification is a defense mechanism of these organisms enabled by the nanocomposite structure of the tissue in which high aspect ratio collagen fibrils reinforce a viscoelastic matrix of fibrihllin microfibrils. The interaction between collagen fibrils is responsible for the stiffness change of the tissue, which is chemoregulated by soluble... 

Physical modification (influence of high tangential stress and pressure) leads to cleavage of ceUulose microfibrils and the product, with a high abiUty to bind water, is caUed microfibiillar ceUtilose. It can be used in food products as a non-calorific thickening agent and flavour carrier, in skin creams, paints and as a carrier for medicines. 

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