Natural polymers cellulosics

Rayon is unique among the mass produced man-made fibers because it is the only one to use a natural polymer (cellulose) directly. Polyesters, nylons, polyolefins, and acryflcs all come indirectly from vegetation they come from the polymerization of monomers obtained from reserves of fossil fuels, which in turn were formed by the incomplete biodegradation of vegetation that grew millions of years ago. The extraction of these nonrenewable reserves and the resulting return to the atmosphere of the carbon dioxide from which they were made is one of the most important environmental issues of current times. CeUulosic fibers therefore have much to recommend them provided that the processes used to make them have minimal environmental impact. 

Usually, synthetic polymers crystallize11 j15 from a melt or a solution in form of folded lamellae. Under specific circumstances it is sometimes also possible to obtain extended chain crystals which is the preferred arrangement in the crystallites of many natural polymers (cellulose, silk). Recently it has been found33 31 that in some cases another crystalline modification can be obtained, the so-called shish-kebabs, which are a sort of hybrid between folded lamellae and extended chain crystals. These shish-kebabs are obtained by shear-induced crystallization, a process in which the polymer crystallizes from solution under the influence of an elongated flow. 

Much of our technology has been developed by observing and imitating the natural world. Synthetic polymers, such as those you just encountered, were developed by imitating natural polymers. For example, the natural polymer cellulose provides most of the structure of plants. Wood, paper, cotton, and flax, are all composed of cellulose fibres. Figure 2.15 shows part of a cellulose polymer. 

The most relevant property of stereoregular polymers is their ability to crystallize. This fact became evident through the work of Natta and his school, as the result of the simultaneous development of new synthetic methods and of extensive stractural investigations. Previously, the presence of crystalline order had been ascertained only in a few natural polymers (cellulose, natural rubber, bal-ata, etc.) and in synthetic polymers devoid of stereogenic centers (polyethylene, polytetrafluoroethylene, polyamids, polyesters, etc.). After the pioneering work of Meyer and Mark (70), important theoretical and experimental contributions to the study of crystalline polymers were made by Bunn (159-161), who predicted the most probable chain conformation of linear polymers and determined the crystalline structure of several macromolecular compounds. 

CELLULOSE ESTER PLASTICS (Organic). The cellulosics are unique among the plastics in that the basic materials used in theiv manufacture are not synthetic polymers. Rather, they are derivatives of a natural polymer, cellulose. Sec also Cellulose. The preparation of an organic cellulose ester plastic involves the formation of a suitable cellulose derivative, fallowed by processing steps that convert the cellulose derivative into a plastic. 

Highly purified cellulose wood pulp (greater than 95% alpha cellulose) is the basic raw material for making cellulose acetate. The natural polymer, cellulose, in wood pulp has a degree of polymerization of 500 to 1000, the basic repeating unit of which is cellubiose ... 

Rayon, the first of the manufactured fibers produced in large volume, is based on the natural polymer cellulose, a repeat unit of which is shown below ... 

The first man-made plastic was nitrocellulose, made in 1862 by nitrating the natural polymer, cellulose. Nitrocellulose, when mixed with a plasticizer such as camphor to make it more workable, was originally used as a replacement for ivory in billiard balls and piano keys and to make Celluloid collars. This material, from which the first movie film was made, is notoriously flammable. 

Many important fibers, including cotton and wool, are naturally occurring polymers. The first commercially successful synthetic polymers were made not by polymerization reactions but through the chemical regeneration of the natural polymer cellulose, a condensation polymer of the sugar glucose that is made by plants ... 

Cellulose is the most abundant natural polymer. Cellulose and its derivatives (cellulosics) have played an important role in developing and establishing the current concepts and industrial applications of polymer science. Current interests are based on their versatile properties, biodegradability, and status as a renewable resource (Fig. 1). 

The first man-made fiber was prepared by the manipulation of a natural polymer, cellulose, which was made soluble through nitration. These fibers, which were highly flammable, represented an impractical but pioneering step in a promising direction. 

The first plastics were actually developed during the last half of the 19th century. Paper is composed to a significant extent of the natural polymer cellulose and closely related substances. Treatment of paper with nitric acid produced the first (semi-) artificial polymer, nitrocellulose. Dissolution of nitrocellulose in alcohol/ether gave a viscous solution (collodion) which forms a hard film upon solvent evaporation. The polymer thus formed was quite flammable. An improved product based on nitrocellulose, termed celluloid, was molded into... 

Hydroxypropyl methylcellulose is a synthetic modification of the natural polymer, cellulose, fibrous or granular, free-flowing powder, odorless, and tasteless. The representation of the molecular structure of hydroxypropyl methylcellulose can be seen in Figure 31.3. 

Natural polymers Cellulose Cellulose acetate trimellitate (CAT)... 

Natural polymers Cellulose, starch, chitin, collagen and fibrin - - = - ... 

Yoshikawa M, Ooi T, Izumi J. Alternative molecularly imprinted membranes from a derivative of natural polymer, cellulose acetate. J Appl Polym Sci 1999 72 493-499. 

Thermodynamic characteristics and physical-chemical properties of natural polymers (cellulose, starch, agar, chitin, pectin and inulin), their water mixtures and some biologically active substances extracted from vegetable substances using carbon dioxide in a supercritical state are reviewed. In addition, several aspects of practical application of thermodynamic characteristics of biologically active substances are demonstrated. 

It is well known that the natural polymer cellulose and its derivatives have the ability to separate a racemate into enantiomersConsequently, further work was carried out on the selective sorption of various D, L-amino acids by chemically modified chitosan gels. 

If we step back to the nineteenth eentury, another natural polymer, cellulose, in addition to rubber, impaeted everyday life. The invention of cellulose plastics, also known as Celluloid, Parkesine, Xylonite, or Ivoride, has been attributed to three people the Swiss professor Christian Schonbein, the English inventor Alexander Parkes, and the American entrepreneur John Wesley Hyatt. 

Amorphous (PVC/Polycarbonates/Polystyrenes) Natural polymers (Cellulose-based/Protein-based)... 

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