Tunicate cellulose

Key Laboratory of Rubber-Plastics Ministry of Education, School of Polymer Science and Engineering, 

Cellulose is one of the most important natural polymers, a key source of sustainable materials on industry, and an almost inexhaustible raw material. Natural cellulose based materials have been used by our society for thousands of years and their use continues today. The first example was the fabrication of regenerated cellulose filaments by spinning a solution of cellulose in a mixture of copper hydroxide and aqueous ammonia [1]. The chemical modification of cellulose on an industrial scale led to a broad range of products based on cellulose. Since then the isolation, characterization, and search for applications of novel 

Handbook of Sustainable Polymers Processing and Applications Edited by Vijay Kumar Thakur and Manju Kumari Thakur Copyright 2016 Pan Stanford Publishing Pte. Ltd. 

There are several polymorphs of crystalline cellulose-I, II, III, and IV. Each has been extensively studied [4]. Crystalline cellulose that is naturally produced by a variety of organisms, it is sometimes referred to as natural cellulose. Cellulose-I has two polymorphs, a triclinic structure [ ) and a monoclinic structure [I ], which coexist in various proportions depending on the cellulose source. The Iq structure is the dominate polymorph for most algae and bacteria, whereas is the dominant polymorph for higher plant cell wall cellulose and in tunicates [5-7]. Allomorph ratios are species specific, and this gives rise to natural structural variations in cellulose crystals. However, the mechanisms contributing to crystal formation remain unknown [8]. 

Tunicates, the only animals known to produce cellulose, are a family of sea animals that have a mantle consisting of cellulose microfibrils embedded in a protein matrix [Fig. 13.2). The thick leathery mantle in their mature phase is used as a new source of cellulose. Most research has used a class of tunicates that are commonly known as sea squirts [Ascldlacea), marine invertebrate filter feeders [9]. The structure and properties of tunicate cellulose [TC) are expected to be comparable between species, but there may be small differences in the cellulose microfibril formation process [10]. 

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Figure 13.4 shows the XRD profile of the tunicate cellulose sample. The sample showed four characteristic cellulose Ip reflectlon at 14.7,16.6, 22.5 and 34.5°, respectively, corresponding to the (110], (110], (200] and (400] crystallographic planes of the cellulose lattice, this observation was correlated with other result of FT-IR [7]. The crystallinity of the tunicate cellulose is higher than 90%. 

Van den Ber et al. [166] has prepared nanocomposites of semi conducting polymers reinforced with tunicate cellulose whiskers with a typical diameter or around 20 nm. The results showed that the nanocomposites synergistically combine the electronic characteristic of the conjugated polymers with the improved mechanical properties of the cellulose scaffold. Other studies suggest that cellulose whisker can be used for electrical applications such as the creation of circuitry in a special kind of smart paper [167]. 

Sturcova, A., Davies, G.R., Eichhorn, S.J. Elastic modulus and stress-transfer properties of tunicate cellulose whiskers. Biomacromolecules 6, 1055 (2005)... 

Studies on the biogenesis of cellulose microfibrils in the tunicates have focused mainly on the tunic of ascidians. Results from studies with various species of ascidians have suggested that the epidermal cell is the most probable site for synthesis of tunic cellulose in the majority of ascidians (Millar 1951 Deck et al. 1966 Dilly 1969 Cloney and Grimm 1970 Smith 1970 Terakado 1970 Wardrop 1970 Stievenart 1971 Katow and Watanabe 1978 Torrence and Cloney 1981 Cloney and Cavey 1982 Robinson et al. 1983). However, these early studies did not show the details of the mechanism and the exact site of synthesis of cellulose in the epidermal cell of ascidians. 

Figure 1.7 TEM micrographs of nanocrystals obtained by sulfuric acid hydrolysis of (a) cotton (b) avicel and (c-e) tunicate cellulose. The insets of (a) and (b) provide higher resolution images of some characteristic particles. Reprinted with permission from [47, 53]. Copyright 2010 John Wiley and 2008 American Chemical Society.

Berg, O., Capadona, J.R., Weder, C., 2007. Preparation of homogeneous dispersions of tunicate cellulose whiskers in organic solvents. Biomacromolecules 8, 1353—1357. 

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