Crystallization of cellulose

Lamellar, single crystals of cellulose triacetate, precipitated from nitromethane with butyl alcohol, were studied by X-ray and electron diffraction. Only the crystals containing the mother liquor, or moistened with nitromethane, showed rich diffraction details. From stretched and annealed fibers, it was found that the unit cell is tetragonal, with a = fe = 21.15A (2.115 nm), and c = 41.36 A (4.136 nm). 

Polymer chains generally form a helix in the crystal and are aligned in parallel with each other. Let us consider a crystal of cellulose, for example. 

Single crystals of cellulose II have been obtained by controlled saponification of cellulose triacetate. They have a lamellar structure and give rise to the x-ray diagram of cellulose II. The chain molecules are oriented at 90° to the plane of the lamellae, and, since their length considerably exceeds the thickness of the lamellae, it is thought that chain folding must take place. Similar folding has been proposed in the case of synthetic polymers and native cellulose. ... 

Cellulose Crystallization. For crystallization below 100 C, the solutions were poured into petri dishes and positioned inside a closed vessel containing an excess of water. The vessel was then fitted into a temperature controlled oil bath and brought to the crystallization temperature. Crystallization of cellulose resulted from the diffusion of water into the solution. Crystallization was complete within a few minutes at 90 C whereas several days were necessary at room temperature. For crystallization between 100 C and 120 C, a similar principle was used except that a thick-wall sealed glass vessel was used to prevent water vapor from escaping. 

Figure 2. Electron micrographs of crystals of cellulose II prepared at 50 C, after shadowing with W/Ta. 2h Sample from microcrystalline cellulose (DP 34) solution. Sample from cotton cellulose (DP 2000) solution. 2C X-ray dic gram, identical for either scunples.

Figure 4. Electron micrographs of crystals of cellulose prepared at 90 C after shadowing with W/Ta. 4A from Avicel (DP 120) cellulose solution the structure consists of rod-like elements together with granular aggregates (arrows). Insert corresponding X-ray diagram. from microcrystalline cellulose (DP 34)solution. Insert corresponding electron diffraction diagram.

Dong, X.M., Revol, J.F., Gray, D.G. Effect of microcrystallite preparation conditions on the formation of colloid crystals of cellulose. Cellulose 5, 19-32 (1998)... 

Dong XM, Revol J-F, Gray DG (1998) Effect of microcrystallite preparation conditions on the formation of colloid crystals of cellulose. Cellulose 5 19-32 Dubief D, Samain E, Dufresne A (1999) Polysaccharide microcrystals reinforced amorphous poly (beta-hydroxyoctanoate) nanocomposite materials. Macromolecules 32 5765-5771 Dufresne A (2000) Dynamic mechanical analysis of the interphase in bacterial polyester/cellulose whiskers natural composites. Compos Interfaces 7 53-67 Dufresne A (2006) Comparing the mechanical properties of high performance polymer nanocomposites from biological sources. J Nanosci Nanotechnol 6 322-330 Dufresne A, Vignon MR (1998) Improvement of starch film performances using cellulose microfibrils. Macromolecules 31 2693-2696... 

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CeHulosc.—Cellulose acetate in dilute aqueous solutions has been deacetylated and thus precipitated in order to grow single crystals of cellulose 11. The crystals had a ribbon-like lamellar appearance. Best results were obtained using methylamine as the deac lating agent. 

Pure crystals of cellulose IV have been prepared by deacetylation and precipitation of cellulose acetate of a low degree of polymerization at ISO— 160 C. At temperatures between 90 and 150 °C, hybrid crystals are obtained having cellulose II and cellulose IV, domains cocrystallizing in syntaxy. When a solution leading to cellulose IV was seeded with native cellulose fibrils, a shish-kebab structure of microfibi s with cellulose II lamellae was obtained. 

Manley St., R.J. 1960. Crystallization of cellulose triacetate from solution. J Poly Sci 47 509-512. 

The effect of heating on structural transitions and crystallization of cellulose acetates, butyrates, and valerates has been investigated. The glass transition... 

Using self-assembly of a chiral nematic phase in a biopolymer liquid crystal of cellulose nanociystals, a well-controlled technique has been developed to create solid helicoidal architectures for structural colour and for further functionalisation. This section describes the self-assembly process and the control parameters of tuneable helicoidal cellulose films, and the prospects for future development. 

Crystallization of cis—1,4-polyisoprene from solution at -65 C has been carried out it is therefore possible that block copolymer preparation by epoxidation, bromination or some other reaction could be accomplished with lamellas of this polymer. Lamellar crystallization of cellulose, of amylose and of polyacrylic acid have been reported substitution reactions such as acetylation or ether formation with the hydroxyl groups and esterfication of the acid groups are possible reactions to carry out with lamellas of those polymers. The use of nonaqueous systems may be better suited to prevent swelling, and therefore, attack of the crystalline regions. It should also be possible to react poly(vinylalcohol) lamellas in suspension with acids or anhydrides to form vinyl-alcohol-vinyl ester block copolymers or with phosgene to obtain chloroformate groups which can undergo further reactions. 

CNCs two-stage thermal decomposition behavior is due to the incorporation of the sulfate groups with the crystals of cellulose [77],... 

Crystallization of cellulose acetates (d.s. 2.2—3.0) has been achieved by annealation in the presence of either nitromethane or nitromethane-n-butanol in overcooled dilute solutions. Cellulose acetate I crystallized over the whole range of compositions when annealed above the glass temperature thermal treatment of cellulose acetate II brought about crystallization of samples of d.s. 2.6, whereas heating in the presence of polar liquids resulted in crystallization over the whole range of compositions. Cellulose acetate I was converted into cellulose acetate II on heating in ethanol, and cellulose acetate II crystallized spontaneously from acetone at room temperature. A comparison of the crystalline forms obtained from cellulose acetates of different d.s. was also made. 

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