Microorganism-derived biodegradable polymers

Biodegradable polymers are macromolecules mainly derived from renewable sources, which can be enzymatically or hydrolytically degraded into low molecular parts. These parts can be reabsorbed by microorganisms, which ideally convert them to CO2 and water heading to an environmentally closed circular flow economy between growing of nutrients, production, utilization, and material recycling (Fig. 1). 

As it was previously said, biodegradable polymers tend to consist of ester, amide, or ether bonds. In general, biodegradable polymers can be separated into two main groups based on their structure and synthesis Agro-polymers, or those derived from biomass [7] and biopolyesters, which are those derived from microorganisms or synthetically made from either naturally or synthetic monomers (Fig 24.1). 

Bionanocomposites are an ecological alternative to conventional nanocomposites based on petroleum-derived polymers, as they are based on biodegradable polymers obtained from renewable resources. Biomass is the source of agropolymers like starch and cellulose and also of monomers used to chemically synthesize polymers like polylactic acid (PLA). Other kinds of biopolymers, e.g., xanthan gum and poly (hydroxyalkanoates), are produced by microorganisms. Even though most of the bionanocomposites reported in the hterature are based on layered sihcates, the number of examples illustrating the use of fibrous clays in the preparation of new bionanocomposites is growing rapidly. 

Biodegradable polymers can be classified into three categories according to their origin (i) synthetic polymers, particularly aUphatic polyesters, such as poly (L-lactide) (PLA) [1-3], poly(e-caprolactone) (PCL) [4—6], poly(p-dioxanone) (PPDO) [7-9], and poly(butylene succinate) (PBS) [10-12] (ii) polyesters produced by microorganisms, which mainly correspond to different poly(hydroxyalkanoate)s (e.g., poly(P-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)) and (iii) polymers derived from natural resources (e.g., starch, cellulose, chitin, chitosan, lignin, and proteins). 

PHB has many physical properties in common with poly(propylene), and a PHB-PHV copolymer (BIOPOL) has recently been used to manufacture plastic shampoo bottles. PHB-PHV is of special interest because it is biodegradable. Since it is a naturally occurring polymer, it is easily degraded by enzymes produced by soil microorganisms and therefore does not persist in the environment after disposal. Other biodegradable polymers, such as polyesters derived from e-caprolactone and lactic acid, are also known and have been commercialized. Although it remains to be seen how widespread the use of biodegradable plastics will become, research and development of these materials is sure to continue as we try to deal with contemporary environmental issues. ... 

If man-made biodegradable polymers are introduced into an ecosystem nothing different from natural occurrences should happen. But consider that any shift of the population may activate certain microorganisms, which can be pathogenic to crop plants or soil animals. This should be seen as theoretical derivation as currently there is no specific literature available which deals with such effects caused by synthetic... 

Chemical modification of natural polymers such as starch, dextran, cellulose and proteins represents an attractive alternative route to totally synthetic polymers for producing biodegradable polymers. Early modification of polysaccharides resulted in hydrophobic materials such as cellulose acetate and cellulose nitrate. Both are degradable by microorganisms. Hydroxyalkylcelluloses should be of interest because of their liquid crystalline properties.The only question is whether their biodegradability is unified. Polysaccharides react with small carboxylic acids to produce derivatives that are biodegradable. " ... 

Completely biodegradable Here the polymer matrix is derived from natural sources (such as starch or microbially grown polymers), and the fiber reinforcements are produced from common crops such as flax or hemp. Microorganisms are able to consume these materials in their entirety, eventually leaving carbon dioxide and water as by-products (Katarzyna et al., 2010). 

In this chapter, alternatives to traditional polymers derived from fossil fuels are commented. Materials derived from plants and microorganisms are presented, as well as biodegradable materials obtained from fossil fuels. 

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