Biopolymers natural poly

One of the most highly developed biopolymers is poly (lactic acid) (PLA). In the USA, PLA is manufactured by NatureWorks at a plant in Nebraska using lactic acid derived from corn. (Lactic acid can also be obtained from other natural sources such as wheat or potatoes.) Poly (lactic acid) is produced by ring opening polymerization of the lactide, as shown in Figure 8.12. 

The equilibrium properties in dilute aqueous solution of weakly ionized polysaccharides, e.g. carboxylated natural poly= saccharides, have not been so thoroughly investigated in comparison with other natural and synthetic polyelectrolytes. For instance, a detailed thermodynamic characterization of acid ionization and of counterion binding in terms of combined experimental potentiometric, calorimetric and volumetric data has not been achieved so far for the above types of polysaccharides. Such a description, however, is of obvious relevance for a better understanding of structure-conformation dependent solution properties for this important class of biopolymers. 

In general, the properties of a biosystem and a synthetic polymer as well as the nature of the biological medium dictate the degree and type of interaction between a biostructure and a polymer. The biocompatibility of synthetic polymers depends on their chemical nature, physical state, and macroscopic form, which can be modified by functionalization of the polymer skeleton. Many biopolymers, such as proteins and nucleic acids, are natural poly electrolytes. Similarly, the outer cell membrane of living cells has charged groups. The biological medium is an electrolyte with an aqueous phase. Therefore, electrostatic... 

A composite material is a two-phase or multiphase compact material with its components (phases) separated by interfaces which can be formed naturally or be manmade. One of the composite material phases is the matrix (phase I). It exists in the solid (crystalline or amorphous) state of aggregation. Within the matrix, particles are distributed discretely. This is phase II or disperse phase [23]. Biocomposites are composite materials made from natural fiber and petroleum-derived nonbiodegradable polymers like PP, PE, and epoxies or biopolymers like poly lactic acid (PLA), cellulose esters. Composite materials derived from biopolymer and synthetic fibers such as glass and carbon come under biocomposites. Biocomposites derived from plant-derived fiber (natural/biofi-ber) and crop/bioderived plastics (biopolymer/bioplastic) are likely more ecofriendly, and such biocomposites are sometimes termed green composites [24]. 

Poly(3-hydroxybutyrate) is a biopolymer produced by numerous bacteria in nature as an intercellular carbon and energy reserve and belongs to the class of poly (hydroxyalkanoate)s (PHAs). In 1925, the French microbiologist Maurice Lemoigne discovered and characterized PHB extracted from Bacillus megaterium. However, it is produced by a various number of microorganisms such as Cupriavidus necator or Ralstonia eutroph. PHAs are biodegradable polyesters with a structure as shown in Fig. 1. 

Helix-Coil Stability Constants for the Naturally Occurring Amino Acids In Water. XIV. Methionine Paramaters from Random Poly(hydroxypropylglutamine-L-methionine>" Hill, D. J. T. Cardinaux, F. Scheraga, H. A. Biopolymers 1977, IS, 2447. 

A large number of macromolecules possess a pronounced amphiphilicity in every repeat unit. Typical examples are synthetic polymers like poly(l-vinylimidazole), poly(JV-isopropylacrylamide), poly(2-ethyl acrylic acid), poly(styrene sulfonate), poly(4-vinylpyridine), methylcellulose, etc. Some of them are shown in Fig. 23. In each repeat unit of such polymers there are hydrophilic (polar) and hydrophobic (nonpolar) atomic groups, which have different affinity to water or other polar solvents. Also, many of the important biopolymers (proteins, polysaccharides, phospholipids) are typical amphiphiles. Moreover, among the synthetic polymers, polyamphiphiles are very close to biological macromolecules in nature and behavior. In principle, they may provide useful analogs of proteins and are important for modeling some fundamental properties and sophisticated functions of biopolymers such as protein folding and enzymatic activity. 

Most food systems are of a colloidal as well as a polymeric nature. The presence of a nonadsorbing polymer in a skim milk dispersion induces an effective attraction between the casein particles, called depletion interaction, resulting in phase separation at sufficiently high polymer concentration. Tuinier et al. (2003) discussed the influence of colloid-polymer size ratio, polymer concentration regime, size, poly-dispersity and charges in colloid/biopolymer mixtures, demonstrating the challenging complexity of the subject. 

Natural polymer-based networks have also been investigated. The proteins etc comprising antibodies represent the largest group [164, 166, 169, 189] but this is of course a specialised area. Poly(saccharides), in particular starch [60], dextran [161], dextrin [161] and maltohexose [161], and also natural polypeptides, mainly enzymes [162-165], embody the more accessible biopolymers. In some instances imprinting is achieved through formation of covalent bonds, with crosslinkers like cyanuric chloride or glutaraldehyde. Likewise chitin derivatives similarly crosslinked have been exploited [136]. 

A further application of time-resolved fluorescence measurements is in the study of conformational dynamics of polymer chains in solution. Fluorescence anisotropy measurements of macromolecules incorporating suitable fluorescent probes can give details of chain mobility and polymer conformation (2,14). A particular example studied in this laboratory is the conformational changes which occur in aqueous solutions of polyelectrolytes as the solution pH is varied (15,16). Poly(methacrylic acid) (PMA) is known to exist in a compact hypercoiled conformation at low pH but undergoes a transition to a more extended conformation at a degree of neutralization (a) of 0.2 to 0.3 (1 6). Similar conformational transitions are known to occur in biopolymer systems and consequently there is considerable interest in understanding the nature of the structures present in model synthetic polyelectrolyte solutions. 

Polymers derived from renewable resources (biopolymers) are broadly classified according to the method of production (1) Polymers directly extracted/ removed from natural materials (mainly plants) (e.g. polysaccharides such as starch and cellulose and proteins such as casein and wheat gluten), (2) polymers produced by "classical" chemical synthesis from renewable bio-derived monomers [e.g. poly(lactic acid), poly(glycolic acid) and their biopolyesters polymerized from lactic/glycolic acid monomers, which are produced by fermentation of carbohydrate feedstock] and (3) polymers produced by microorganisms or genetically transformed bacteria [e.g. the polyhydroxyalkanoates, mainly poly(hydroxybutyrates) and copolymers of hydroxybutyrate (HB) and hydroxyvalerate (HV)] [4]. 

Poly(4-hydroxybutyrate) [P(4HB)] is a highly ductile, flexible polymer withstanding an extension of around 1,(XX)% before breaking, compared to P(3HB), which can only extend to less than 10% before breaking. Combining these different monomers to form copolymers, as in P(3HB-co-4HB), been described as one of the most useful PHAs by Sudesh et al. [5], produces a family of materials with mechanical properties that can be tailored to specific needs. P(3HB-co-4HB) has been found to have desirable mechanical properties for applications in the medical and pharmaceutical field [11]. The biocompatibility and bioabsorbable nature of P(3HB-co-4HB) makes it the most valuable type of biopolymer among the vast number of different PHAs synthesized by microorganisms. To date, five wild-type bacteria, which can produce P(3HB-co HB), i.e. R. eutropha... 

Chitosan is a naturally occurring polymer derived from the shells of crustaceans. It is a derivative of chitin (poly-/V-acetylglucosamine), which is the second most abundant biopolymer after cellulose (Dai et al., 2011). 

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