Biodegradable polymers polysaccharides

Chitosan is a water-insoluble, nontoxic, edible, biodegradable polymer (polysaccharide) that is obtained commercially from chitin by alkaline deacetylation [103]. Chitosan is the second most abundant biopolymer in nature after cellulose. Since chitosan is a polycationic polymer, its high sensitivity to moisture limits its applications. One way to overcome this drawback is to blend the material with humidity resistant polymers such has PLA. Suyatma et al. [104] combined hydrophilic chitosan with hydrophobic PLA (92% L-lactide and 8% mesolactide, Mw = 49,000 Da) by solution and film mixing, resulting in improved water barrier properties and decreased water sensitivity of the chitosan films. However, testing of mechanical and thermal properties revealed that chitosan and PLA blends are incompatible. 

A special group of carrier-linked prodrugs are the site-specific chemical delivery systems [23], Macromolecular prodrugs are synthetic conjugates of drugs covalently bound (either directly or via a spacer) to proteins, polypeptides, polysaccharides, and other biodegradable polymers [24],... 

Biodegradable polymers, both synthetic and natural, have gained more attention as carriers because of their biocompatibility and biodegradability and therewith the low impact on the environment. Examples of biodegradable polymers are synthetic polymers, such as polyesters, poly(orfho-esters), polyanhydrides and polyphosphazenes, and natural polymers, like polysaccharides such as chitosan, hyaluronic acid and alginates. 

In addition to synthetic biodegradable polymers discussed so far, naturally occurring biopolymers have also been used for fabricating implantable dmg delivery systems. Examples of natural biopolymers are proteins (e.g. albumin, casein, collagen, and gelatin) and polysaccharides (e.g. cellulose derivatives, chitin derivatives, dextran, hyaluronic acids, inulin, and starch). 

Chitosan Chitosan is a nontoxic, biodegradable polymer obtained by hydrolysis of chitin, a natural polysaccharide that is a chief component of the crustacean exoskeleton. Unmodified chitosan is soluble in acidic media and has significant muco-adhesive properties. 

The most fundamental classification of polymers is whether they are naturally occurring or synthetic. Common natural polymers (often referred to as biopolymers) include macromolecules such as polysaccharides e.g., starches, sugars, cellulose, gums, etc.), proteins e.g., enzymes), fibers e.g., wool, silk, cotton), polyisoprenes e.g., natural rubber), and nucleic acids e.g., RNA, DNA). The synthesis of biodegradable polymers from natural biopolymer sources is an area of increasing interest, due to dwindling world petroleum supplies and disposal concerns. 

This chapter deals with polymers synthesized from oilseed sources. However, to provide the reader with an appreciation of the area of renewable, biodegradable polymers and the place within this area that polymers from oil seeds occupy in terms of functionality, price, and acceptability, some other polymers from major renewable sources are also discussed. The most well-known and widely used renewable biodegradable polymers are those from polysaccharides. The principal polysaccharides of interest to polymer chemists are starches and cellulose, both of which are polymers of glucose. In addition to these, fibers, polylactic acid (PLA), and triacylglycerols of oils are of particular interest for the development of biodegradable industrial polymers. 

In recent years starch, the polysaccharide of cereals, legumes and tubers, has acquired relevance as a biodegradable polymer and is becoming increasingly important as an industrial material (Fritz Aichholzer, 1995). Starch is a thermoplastic polymer and it can therefore be extruded or injection moulded (Balta Calleja et al, 1999). It can also be processed by application of pressure and heat. Starch has been used successfully as a matrix in composites of natural fibres (flax, jute, etc.). The use of starch in these composites could be of value in applications such as automobile interiors. An advantage of this biopolymer is that its preparation as well as its destruction do not act negatively upon the environment. A further advantage of starch is its low price as compared with conventional synthetic thermoplastics (PE, PP). 

During the last years a large number of monographs and publications [1-7] have been published which cover biodegradable polymers of the different material groups (e.g., polysaccharides, polypeptides, polyesters, and polyisoprenoides), as well as their copolymers and blends. 

There are many kinds of natural biodegradable polymers. They are classified into three types according to their chemical structures, i.e., polysaccharides, polypeptides/proteins and polynucleotides/nucleic acids. Among them, polysaccharides, such as cellulose, chitin/chitosan, hyaluronic acid and starch, and proteins, such as silk, wool, poly( y-glutamic acid), and poly(e-lysin), are well known and particularly important industrial polymeric materials. 

In this chapter, solid-state structure and properties relative to the morphologies of several chemically and bacterially synthesized biodegradable polymeric materials are described based mainly on the results obtained for bacterially synthesized polyesters by high resolution solid-state NMR spectroscopy. This chapter briefly discusses polymer blends, which also includes polysaccharides and proteins, since more details are given in other chapters of this book. Several books on biodegradable polymers have been published [1,2], and many review articles on structure and properties of bacterially synthesized polyesters have also been published elsewhere [7-10, 19-22]. 

There are several kinds of natural biodegradable polymers in addition to bacterial PHAs, such as proteins, nucleic acids and polysaccharides. Among them, particulary important polymers such as industrial materials are polysaccharides, such as starch, cellulose, chitin and chitosan. The solid-state structure and properties of starch and amylose [127], cellulose [128] and chitin... 

Interactions between surfactants and polymers is now an important field of interest in colloid science.1 Many aqueous solutions used in industrial applications contain mixtures of surfactants and polymers, in particular polyelectrolytes, which are widely used in water based formulations such as paints, drilling muds, etc. An interesting class of natural and biodegradable polymers are the polysaccharides found in plants. Among them, polyelectrolytes with rigid... 

The natural biodegradable polymers that are most frequently used are polysaccharides, of which starch and cellulose derivatives are preferred. Starch is an inexpensive product available, e.g., from corn. It is biodegradable in a variety of environments. 

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