Aqueous tetrabutylammonium hydroxide, TBAH(aq), has been found to dissolve cellulose and to be a potential solvent for chemical processing or fiber spinning. In this paper, we have investigated the dissolution state of cellulose in 40 wt % TBAH(aq) solvent, and present an extensive study of rheology, combined with static light and small-angle X-ray scattering, to correlate cellulose aggregation with changes in the rheological parameters. Two cellulose molecular weights are compared. Microcrystalline cellulose (MCC), with a degree of polymerization of ca. 260, and a dissolving pulp with an approximately ten times higher molecular weight. Scattering data demonstrate that cellulose is molecularly dissolved at lower cellulose concentrations, while aggregates are present when the concentration exceeds a certain value. The onset of the aggregate formation is marked by a pronounced increase in the scattering intensity at low q, shear thinning behavior and violation of the empirical Cox-Merz rule. Additionally, the SAXS data suggest the presence of a solvation shell enriched in TBA(+) ions, compared to the bulk solvent. The results are consistent with the recent suggestion that while native cellulose I may still dissolve, solutions are, above a particular concentration, becoming supersaturated with respect to the more stable crystal form cellulose II.

Modern society is now demanding greener materials due to depleting fossil fuels and increasing environmental awareness. In the near future, industries will need to become more resource-conscious by making greater use of available renewable and sustainable raw materials. In this context, agro-forestry and related industries can indeed contribute to solve many resource challenges for society and suppliers in the near future. Thus, cellulose can be predicted to become an important resource for materials due to its abundance and versatility as a biopolymer. Cellulose is found in many different forms and applications. However, the dissolution and regeneration of cellulose are key and challenging aspects in many potential applications. This chapter is divided into two parts i achievements in the field of dissolution and regeneration of cellulose including solvents and underlying mechanisms of dissolution and ii state-of-the-art production of value-added materials and their applications including manmade textile fibers, hydrogels, aerogels, and all-cellulose composites, where the latter is given special attention.Keywords: Cellulose, dissolution and regeneration, fiber, hydrogels, all-cellulose composites . IntroductionCellulose was isolated for the first time by the French chemist "nselme Payen in [ ], who extracted it from green plants and reported its elemental composition four years later [ ].Cellulose is the main component of the cell wall in higher plants, typically combined with © 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.lignin, hemicelluloses, pectins, proteins, and water. "part from higher plants, cellulose can be synthesized by bacteria or be found in algae and tunicates. This readily available and renewable biopolymer is widely used in many applications such as paper, textiles, membranes, or packaging [ ]. Cellulose is the most abundant and studied biorenewable material with an estimated annual production of . x t [ ]. "fter more than years of research into the sugar of the plant cell wall , consumers, industries, and governments are increasingly demanding products from renewable and sustainable resources that are biodegradable, nonpetroleum based, carbon neutral, and, at the same time, generating low environmental, animal/ human health and safety risks [ ].Regarding its basic structure, cellulose is a linear syndiotactic homopolymer composed of D-anhydroglucopyranose units "GU , that are connected by -glycosidic bonds Figure [ ]. The size of the cellulose molecules can be defined by the average degree of polymerization DP . The average molecular weight is estimated from the product of the DP and the molecular mass of a single "GU. Each "GU bears three hydroxyl groups one primary and two secondary moieties that represent more than % by weight , with t...

Cellulose gelation in 2 M NaOH aqueous solution was followed by time resolved turbidity and rheology measurements. The kinetics of gelation is observed to change from several hours down to few seconds when the temperature is increased from 25 to 30 °C, consistent with earlier work. The increase of turbidity upon gelation demonstrates the formation of larger cellulose aggregates, while wide angle X-ray scattering data confirms the gradual formation of crystalline domains. This suggests that the gelation can be understood as cellulose precipitation/crystallization where an effectively cross linked network and gelation results from that cellulose chains may participate in more than one crystallite.

SUMMARY: Cellulose dissolution and regeneration is an increasingly active research field due to the direct relevance for numerous production processes and applications. The problem is not trivial since cellulose solvents are of remarkably different nature and thus the understanding of the subtle balance between the different interactions involved becomes difficult but crucial. There is a current discussion in literature on the balance between hydrogen bonding and hydrophobic interactions in controlling the solution behavior of cellulose. This treatise attempts to review recent work highlighting the marked amphiphilic characteristics of cellulose and role of hydrophobic interactions in dissolution and regeneration. Additionally, a few examples of our own research are discussed focusing on the role of different additives in cellulose solubility. The data does support the amphiphilic behavior of cellulose, which clearly should not be neglected when developing new solvents and strategies for cellulose dissolution and regeneration. ADDRESSES OF THE AUTHORS

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