Modification of natural polymers

G. John, Chemical Modification of Natural Polymers, Ph.D thesis. Regional Research Laboratory, Trivandrum and Kerala University, Trivandrum, India (1992). 

Above we have shown the attractiveness of the so-called green nanocomposites, although the research on these materials can still be considered to be in an embryonic phase. It can be expected that diverse nano- or micro-particles of silica, silicates, LDHs and carbonates could be used as ecological and low cost nanofillers that can be assembled with polysaccharides and other biopolymers. The controlled modification of natural polymers can alter the nature of the interactions between components, affording new formulations that could lead to bioplastics with improved mechanical and barrier properties. 

Table 4 Summary of studies focused on the chemical modification of natural polymers using ozone as activator...

Tyrosinase (polyphenol oxidase, a copper-containing monooxygenation enzyme) was used as catalyst for the modification of natural polymers. Phenol moiety-incorporated chitosan derivatives were subjected to tyrosinase-catalyzed cross-linking, yielding stable and self-sustaining gels.90 Tyrosinase also catalyzed the hybrid production between the modified chitosan and proteins. 

While the relatively young polymer industry was learning much from the modification of natural polymers, production figures were small. As the purely synthetic polymers came on stream, the range of valuable applications for plastic materials rapidly increased. Today, the annual mass of polymeric... 

WILLIAM M. DOANE received his PhD in Biochemistry from Purdue University in 1962. Since that time he has conducted and led research in isolation, characterization, and modification of natural polymers, principally starch. Currently he is Research Leader of Derivatives and Polymer Exploration Research at USDA s Northern Regional Research Center. 

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. 

B.S. Kaith, and A.S. Singha, "Modification of natural polymers-VII Ceric ion induced grafting of methylacrylate onto Flax fibre" International Congress of Chemistry and Environment, 2001. 

Shalaby, S. W. and Shah, K. R., Chemical Modifications of Natural Polymers and Their Technological Relevance, in Water Soluble Polymers, Vol. 467, ACS Symposium Series, American Chemical Society, Washington, DC, 1991, chap. 4. 

Considerable interest has been shown on chemical modification of natural polymers by means of graft copolymerization of vinyl monomers onto natural polysaccharides. By the process of grafting, physical and chemical properties of synthetic monomers are superimposed onto the properties of different natural polymers using redox system [36, 37]. In this case, the reaction can take place between two polymers or a polymer and a second monomer and they are based on classical organic chemistry (Scheme 7.7). Kennedy reviewed many of the possibilities of further reactions after polymerization, and distinguished between grafting onto and from [38]. 

Modifications of Natural Polymers Imanishi, Y., Ed. CRC Press Boca Raton, FL, 1992 ppl5-84. 

The progress of chemistry, associated with the industrial revolution, created a new scope for the preparation of novel polymeric materials based on renewable resources, first through the chemical modification of natural polymers from the mid-nineteenth century, which gave rise to the first commercial thermoplastic materials, like cellulose acetate and nitrate and the first elastomers, through the vulcanization of natural rubber. Later, these processes were complemented by approaches based on the controlled polymerization of a variety of natural monomers and oligomers, including terpenes, polyphenols and rosins. A further development called upon chemical technologies which transformed renewable resources to produce novel monomeric species like furfuryl alcohol. 

McCormick C.L., Lichatowich D.K., Pelezo J.A., Anderson K.W., Homogeneous solirtion reactions of cellulose, chitin, and other polysaccharides, Modification of Natural Polymers, ACS Symposiitm Series No. 121, 1980, pp. 371-380. 

All natural polymers are considered to be biodegradable or at least not harmful to the environment. However, modification of natural polymers either by grafting synthetic polymers or by chemical conversions such as oxidation and esterification, changes their properties and biodegradation characteristics significantly. Therefore, polymers produced by any of these modifications must be evaluated for biodegradability in the same manner as purely synthetic polymers. 

Modification of natural polymers such as starch, cellulose, and proteins is a way of capitalizing on the well-accepted biodegradability of the base material with... 

It was shown in Chapter 1 that life is supported by many natural polymers or macromolecules. Natural polymers have been used for centuries, e.g. natural rubber. Modification of natural polymers permitted new useful goods to be made, but sometimes not very well adapted to everyday life, e.g. the highly flammable celluloid. 

Starch in its native or modified form, has been subjected to extensive study over the past 50 years. Early interest in starch was associated with the food and paper industry, textile manufacture, and pharmacolog) . With the increased interest of biomedical and pharmaceutical research in biodegradable polymers as matrices for controlled drug delivery systems, impressive activities on the modification of natural polymers to meet growing needs have been reported (Hag et al, 1990 Kost and Shefer, 1990 Shefer et al, 1992 Trimnell et al, 1982 Vandenbossche et al, 1992 Visavarungroj et al, 1990). 

While vulcanization of NR and GP was the first purposeful modification of natural polymers, the first man-made polymer was nitrocellulose, NC, discovered by Braconnot in 1833 (see Appendix I). Several commercial products followed, e.g., Collodion (lacquers based on alcohol-ether solution), Parkesine (the first thermoplastic material hot rolled and formable into variety of shapes), Ivorite (used as a substitute for ivory). Celluloid (camphor plasticized NC). Cellulose acetate, CA, was introduced in 1869 by Schutzenberger. Casein crosslinking by formaldehyde resulted in a 1885-patent hy Kritsche and Spitteler for what later became known as Galalith, a horn-like material quite successfully used even today as an imitation of ivory and porcelain [Seymour, 1982 1989]. 

Staudinger s studies of polymer structure and Carothers achievements in polymer synthesis accelerated the development of polymer chemistry, especially its shift from chemical modification of natural polymers to the design and synthesis of new materials. Thousands of synthetic polymers are now known some mimic the properties of natural materials, others have superior properties and have replaced natural materials. 

V. K. Thakur, A. S. Singha, and M. K. Thakur, Surface modification of natural polymers to impart low water absorbency. Int. J. Polym. Anal. Charact. 17,133-143 (2012). 

PPO was used as catalyst for modification of natural polymers. The enzymatic treatment of a chitosan film in fhe presence of PPO and phenol derivatives produced a new material of chitosan derivatives [ 55]. During the reaction, unstable o-quinones were formed, which then reacted with chitosan to yield modified chitosans. In the enzymatic treatment of p-cresol with a low concentration of chitosan (< 1%), the reaction solution was converted into a gel [56]. 

---