Cellulose shapes cellulosic polymers

Polymer forming began with the chemical modification of natural polymers such as natural rubber vulcanization and cellulose acetylation. The first efforts to shape natural polymers and early synthetic ones into useful products such as textile fibers and films for packaging date from the middle of the 19 century. 

In its natural state, cellulose is highly crystalline in structure. It is a polydisperse linear stiff-chain homopolymer composed of the glucose building blocks which form hydrogen-bonded supramolecular structures. These strong hydrogen bonds are responsible for the stiff, linear shape of the cellulose polymer chains [18]. 

Some natural polymers also form lyotropic systems. These include cellulose derivatives, cellulose being a stiff molecule but not entirely rod-shaped. Another polymer is the polypeptide poly(y-benzyl L-glutamate) (8,9),... 

Keywords Polyurethane, nanocellulose, cellulose whiskers, nanofibrillated cellulose, shape-memory polymers, waterborne polyurethanes... 

Kobayashi, H., Kazuyuki, Hayashi, N. (1992), Woven Fabric Made of Shape Memory Polymer. Available from http //www.google.com/patents id=5r8iAAAAEBAJ print sec=abstract zoom=4 v=onepage q f=false Lee, M., Wakida, T, Tokuyama, T., Doi, C., Lim, Y. J., Jeon, S. K. (2005), Liquid ammonia treatment of regenerated cellulosic fabrics. Textile Res. J., 75(1), 13-18. 

The book first focuses on commonly used industrial polymers, including polypropylenes, low- and high-density polyethylenes, and poly(vinyl chloride), as well as less widely used polymer types, such as acrylics, ether polymers, cellulosics, sulfide polymers, silicones, polysulfones, polyether ether ketones, and polybenzimidazoles. It then explores polymer derivatives and polymeric combinations that play special and often critical roles in diverse fields of human activities. The polymers covered include liquid crystal, electroactive, ionic, and shape memory polymers hydrogels and nanocomposites. The book concludes with a comprehensive overview of new developments in the use of polymers in a variety of areas. 

Many other natural cellulose fibers form bundles. For example, short flax fibers (27-36 mm) overlap each other and are held together by a mixtirre of non-cellulosic polymers, including hemicellulose, lignin, and pectins (Figure 5.7). The resultant fiber bundles have irregular shapes and contain multiple lumens. Individual flax fibers have an average diameter of around 20 / m, but the bundle... 

Multifunctional initiators based on, for example, cyclotriphosphazine [106], silesquioxane [107], porphyrin [108] and bipyridine metal complex [109, 110] cores were also successfully used for the living cationic ring-opening (co)polymerization of 2-oxazolines, resulting in star-shaped (co)polymers. The use of polymeric initiators also allowed the construction of well-defined complex macro molecular architectures, such as triblock copolymers with a non-poly(2-oxazo-line) middle block that is used to initiate the 2-oxazoHne polymerization after functionalization with tosylate end-groups [111-113]. In addition, poly(2-oxazoline) graft copolymers can be prepared by the inihation of the CROP from, for example, poly(chloromethylstyrene) [114, 115] or tosylated cellulose [116]. 

At one level, life can be regarded as a collection of hugely complex reactions taking place between organic compounds in oddly shaped containers. Many of these organic compounds are polymers, including the cellulose of wood, natural fibers such as cotton and silk, the proteins and carbohydrates in our food, and the nucleic acids of our genes. 

An erodible insert developed as a potential ocular drug-delivery system is marketed as a prescription drug for the lubricant properties of the polymer base. Lacrisert is a sterile ophthalmic insert used in the treatment of moderate to severe dry eye syndrome and is usually recommended for patients unable to obtain symptomatic relief with artificial tear solutions. The insert is composed of 5 mg of hydroxypropylcellulose in a rod-shaped form about 1.27 mm diameter by about 3.5 mm long. No preservative is used, since it is essentially anhydrous. The quite rigid cellulose rod is placed in the lower conjunctival sac and first imbibes water from the tears and after several hours forms a... 

In the present work, we extend the method to compensate for the hydrogen bonds present in carbohydrates. The hydroxylated character of carbohydrate polymers influences between-chain interactions through networks of hydrogen bonds that occur during crystallization. Frequently, several possible attractive interactions exist that lead to different packing arrangements, and several allomorphic crystalline forms have been observed for polysaccharides such as cellulose, chitin, mannan and amylose. The situation is even more complex when water or other guest molecules are present in the crystalline domains. Another complication is that polysaccharide polymorphism includes different helix shapes as well. 

Since Robinson [1] discovered cholesteric liquid-crystal phases in concentrated a-helical polypeptide solutions, lyotropic liquid crystallinity has been reported for such polymers as aromatic polyamides, heterocyclic polymers, DNA, cellulose and its derivatives, and some helical polysaccharides. These polymers have a structural feature in common, which is elongated (or asymmetric) shape or chain stiffness characterized by a relatively large persistence length. The minimum persistence length required for lyotropic liquid crystallinity is several nanometers1. 

A high molecular weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit, the monomer (e.g., polyethylene, isoprene and cellulose). Synthetic polymers are formed by the addition or condensation polymerization of monomers. If two or more different monomers are involved, a copolymer is obtained. Some polymers can be rubbers and some can be plastics. Plastics which are also high polymers can include both natural, or synthetic products but exclude rubber whether natural or synthetic. At some stage in its manufacture every plastic is capable of flowing under heat and pressure into the desired final shape. 

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