Natural Polyesters

Plastics. Vehicles in offset inks for plastics (polyethylene, polystyrene, vinyl) are based on hard drying oleoresinous varnishes which sometimes are diluted with hydrocarbon solvents. Letterset inks for polystyrene employ vehicles of somewhat more polar nature. Polyester or other synthetic resins (acryhc) dissolved in glycol ethers and/or esters are used in some of the older inks. Uv inks are widely used for decoration of these preformed plastic containers. 

Beside the natural polyesters a number of synthetic aliphatic polyesters have also been shown to be biodegradable. From a commercial point of view the most important synthetic biodegradable aliphatic polyester was traditionally polycaprolactone (PCL). 

Figure 12.28. Examples of natural polyesters of bacterial origin.

The (.R)-3-hydroxy-butyrate (Fig. 19-1), which is responsible for the stereochemistry of the methyl group in the sulfone ring, can be produced by depolymerization of biopolymers, e. g. Biopol from Zeneca. This is a natural polyester produced by some microorganisms as a storage compound. 

The natural polyesters, which are produced by a wide variety of bacteria as intracellular reserve materials, are receiving increased attention for possible... 

Bonartsev, A. R et al. Biosynthesis, biodegradation, and application of poly(3-hy-droxybutyrate) and its copolymers natural polyesters produced by diazotrophic bacteria. Comm. Current Res. Educat Topics Trends Appl. Microbiol Ed. Mendez-VUas, A. Formatex, Spain 2007,1, 295-307. 

Cutin. Structural component of the outer lipophilic protective layer (cuticle) of the aerial parts of plants, especially leaves. Suberin serves similar functions in roots and bark. C. is a natural polyester, formed enzymatically from hydroxyfatty acids with 16 and 18 C atoms. o+Hydroxy- and dihydroxyfatty acids, e.g., 10,16-dihydroxypalmitic acid, as well as epoxy- and oxofatty acids, and a,o>-dicarboxylic acids are the main components of cutin. Cutinases (C.-cleaving enzymes) occur especially in pollen and in plant-pathogenic fungi, e.g., Fusarium solani (while rot in potatoes). 

The results of the present study indicate that the ESI-MS technique enables determination of the subtle structure of bio-inspired and natural polyesters. Moreover, the distribution of comonomers in the mass selected copolyester macromolecules can be shown by the ESI-MS" fragmentation experiments, thus demonstrating the utility of this technique for the analysis of individual macromolecules including their end groups and composition. 

Abiotic hydrolysis is the most important reaction for initiating the environmental degradation of synthetic polymers (Gbpferich 1997) such as PE (Gu 2(X)3), PTT (Heidary and Gordon 1994), PLA, and their copolymers (Hiltunen et al. 1997 Nakayama et al. 1996). The degradation of most synthetic plastics in nature is slower than that of natural polyesters. This process involves environmental factors, followed by the action of microorganisms in their surroundings (Albertsson et al. 1994 Cruz-Pinto et al. 1994). 

Abstract Polyhydroxyalkanoates (PHAs) are natural polyesters that accumulate in numerous microorganisms as a carbon- and energy-storage material under the nutrient-limiting condition in the presence of an excess carbon source. PHAs are considered to be one of the potential alternatives to petrochemically derived plastics owing to their versatile material properties. Over the past few decades, extensive detailed biochemical, molecular-biological, and metabolic studies related to PHA... 

As mentioned above, and despite the fact that suberin is widespread in plants [1], only two species produce suberin-rich biomass residues in amounts that justify the exploitation of this natural polyester as a renewable source of chemicals for polymer synthesis, namely, Quercus suber and Betula pendula. Betula pendula is one of the most important industrial hardwood species in Northern Europe, where it is mainly used as raw material in the pulp and paper industry, which generates considerable amounts of bark. Typically, a mill with a pulp production of 400 000 ton per year, leaves about 28000 ton per year of outer bark [37]. Considering a suberin content ranging from 32 to 59 per cent, [14], birch s outer bark has, like cork, an enormous potential as a source of suberin and suberin components. 

Some natural polyesters, such as polyhydroxybutyrate, are commercial products of micro-organisms. Outside of the cell the enzymatic synthesis of high-molecular-weight polyesters may be impractical on any sensible scale, but the synthesis of smaller blocks with a molecular weight of several thousand is practical. The ester bond is formed under conditions where water activity is low, and the concentrations of alcohol and carboxylic acids are high. The reaction (Scheme 6.28), which is a transesterification between... 

In the materials with DBDI (Fig. 2.14(b)) the overall etched texture is much flatter. The regions of chemical segregation are more or less equally attacked. The material with DBDI does not show the precipitated crystals. A more detailed SEM description on the morphology of MDI and DBDI based PUs and mixtures of them, is made in section 2.3.2.2. where the materials are characterized and compared from two perspectives (a) effect of the SS macrodiol nature (polyester or polyether) (b) effect of type, and number of diisocyanates (crystallizing or not) and their order of introduction in the reaction synthesis. 

Hefetz, A., Fales, H. M. and Batra, S. W. T. (1979c) Natural polyesters Dufour s gland macrocyclic lactones form brood cell laminesters in Colletes bees. Science, 204, 415-7. 

Since the discovery of the simple PHB homopolymer by Lemoigne in the mid-1920s, a fam-ity of over 100 different aliphatic polyesters of the same general stmcture has been discovered. PHB is onfy the parent member of a famify of natural polyesters having the same three-caibon... 

The dependence of the ambient humidity on PHBV polymers structure, even if the impact is small, can dramatically affect the thermal and mechanical properties. This changing behavior is commonly observed for natural polymers such as cellulose and starch, and for natural polyesters such as PLA and PCL. 

Bonartseva, A. P., Myshkinal, V. L., Nikolaeva, D. A., Furinal, E. K., Makhinal, T. A., Livshits, V. A., Boskhomdzhiev, A. P., Ivanov, E. A., lor-danskii, A. L., and Bonartseva, G. A. (2007). Biosynthesis, biodegradation, and application of poly(3- hydroxy butyrate) and its copolymers natural polyesters produced by diazotrophic bacteria. Current Research and Educational Topics and Trends in Applied Microbiology A. Mendez-Vilas (Ed.), p.295. 

Poly(3-hydroxya]kanoate)s (PHAs) are natural polyesters, which many organisms in the environment accumulate in the form of intracellular granules to store carbon and energy when they are subjected to stress conditions [1-3]. PHAs are produced by a fermentation process in the bacteria by means of enzymatic polymerization (PHA synthase). The type of biosynthesized polymers is determined by the substrate specificities of the PHAs synthases and depends on the carbon source. PHAs are semi-crystalline, isotactic (only the enantiomer of absolute configuration R is present in these polymers) with a hydrophobic character. Although the most well-studied PHA is poly(3-hydroxybutyrate) (PHB), over 140 constitutive monomer units [4] have been investigated. 

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