Functional properties chemical modification

Over the last two decades, there has been an increasing interest in the industrial use of plant proteins for non-food applications because of their renewabiUty or biodegradability Plant proteins ve thus been used for the fabrication of materials such as films and coatings, adhesives, thermoplastics and surfactants. However, for many applications, it is necessary to confer and/or to improve some specific properties by chemical modification of the native proteins. Particularly, the esterification of their carboxyl and amide groups by a fatty alcohol (Fig 1) could lead to a protein-derivative with improved functional properties. Such modification would result into a lower water sensitivity of the protein-based products and it would therefore offer... 

I found this book very thorough in its description and analysis of HA and very well written. It covered all aspects of HA its history and discovery, its biological role and functions in the body, production and purification, structure and rheological properties, chemical modifications, application in medicine, cosmetology and aesthetic medicine. It should be taken into consideration that the manuscript was written several years ago, so the chapter about HA production could be seen as outdated. Nevertheless, we decided to leave it intact in this version, because it contains important information about HA purification for industrial needs. Additionally, it serves to allow the authors to present their significant achievement with regard to the chemical modification of HA, an accomplishment that has opened the doors to many new products. 

Mixed Ether Derivatives of HEC. Several chemical modifications of HEC are commercially available. The secondary substituent is generally of low DS (or MS), and its function is to impart a desirable property lacking in HEC. 

New elastic polymeric materials (resistance to higher stroke or air) can be obtained by using physical modification methods, but using this method, two phases (PS and rubber) in the mixture were formed. Small rubber particles spread as a PS layer and, after awhile, the relationship between the layers decreases and rubber particles gather in the upper layer of the materials. This can be the cause of the loss of resistance of the materials. These material disadvantages have stimulated the polymer synthesis to increase the PS resistance to higher physico-mechanical properties, such as higher temperature and stroke for the chemical modification of PS with various functional modifiers. 

These observations demonstrate that the different functional groups can be attached to the aromatic ring of PS with various chemical modification conditions, and it is possible to obtain different technical properties for polymer materials. 

Grafting reactions alter the physical and mechanical properties of the polymer used as a substrate. Grafting differs from normal chemical modification (e.g., functionalization of polymers) in the possibility of tailoring material properties to a specific end use. For example, cellulose derivatization improves various properties of the original cellulose, but these derivatives cannot compete with many of the petrochemically derived synthetic polymers. Thus, in order to provide a better market position for cellulose derivatives, there is little doubt that further chemical modification is required. Accordingly, grafting of vinyl monomers onto cellulose or cellulose derivatives may improve the intrinsic properties of these polymers. 

Due to the lack of a commercial supply, as well as their usually low molecular weight and poor solubility, xylans have found little industrial utility and interest in their modification has been rather low in comparison to commercially available polysaccharides such as cellulose or starch. With the aim of improving the functional properties of xylans and/or imparting new functionalities to them, various chemical modifications have been investigated during the past decade. Most of them were presented in recent reviews [3,399]. 

The early works by Muzzarelh et al. [179] showed that tyrosinase converts a wide range of phenohc substrates into electrophihc o-quinones [180]. Tyrosinase was used to convert phenols into reactive o-quinones which then underwent chemical reactions leading to grafting onto chitosan. A review article showed that in general the tyrosinase-catalyzed chitosan modifications resulted in dramatic changes in functional properties [181]. 

Owing to multi-functionahty, physical properties such as solubihty and the glass transition temperature and chemical functionahty the hyperbranched (meth) acrylates can be controlled by the chemical modification of the functional groups. The modifications of the chain architecture and chemical structure by SCV(C)P of inimers and functional monomers, which may lead to a facile, one-pot synthesis of novel functionahzed hyperbranched polymers, is another attractive feature of the process. The procedure can be regarded as a convenient approach toward the preparation of the chemically sensitive interfaces. 

The chemical modification of polymers is a post polymerization process which is used in certain situations i) to improve and optimize the chemical and mechanical properties of existing polymers or ii) to introduce desirable functional groups in a polymer. 

A good example of a reactive modifier which has been used (14) to enhance properties of polyolefins is maleic anhydride (MA). The formation of maleic adduct in polypropylene (PP), for example, can be used to effect several modifications e.g. to improving hydrophilicity, adhesion and dyeabflity. Moreover, the polymer-maleic adduct has an availabla additional functionality to effect other chemical modifications for achieving the desired material design objectives. Reactions of MA with polymers in solution are described in the patent literature (15). 

Unsaturated groups are very interesting for application development because this specific functionality opens up a broad range of possibilities for further (chemical) modification of the polymer structure, and therefore its physical and material properties. The direct microbial incorporation of other functional substituents to the polymer side chains, e.g. epoxy-, hydroxy-, aromatic-, and halogen functional groups, influences the physical and material properties of poly(HAMCL) even further [28,33,35,39-41]. This features many possibilities to produce tailor-made polymers, depending on the essential material properties that are needed for the development of a specific application. 

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