Polyesters bacteria-produced

The aim of this research was to create novel composites for bulk applications using cellulose as reinforcement. We intented to improve properties of polymer composites reinforced with cellulose by pretreating fibers with maleic anhydride modified polypropylene (MAPP). The effect of hydrolytical treatment of cellulose on the dispersibility of fibers in polymers was also investigated. Novel materials based on bacteria-produced polyesters and cellulose were manufactured and their properties evaluated. 

A more recent biodegradable polymer is polyhydroxybutyrate-valerate copolymer (PHBV). These copolymers differ from many of the typical plastic materials in that they are produced through biochemical means. It is produced commercially by ICI using the bacteria Alcaligenes eutrophus, which is fed a carbohydrate. The bacteria produce polyesters, which are harvested at the end of the process. When the bacteria are fed glucose, the pure polyhydroxybutyrate polymer is formed, while a mixed feed of glucose and propionic acid will produce the copolymers. Different grades are commercially available that vary in the amount of hydroxyvalerate units and the presence of plasticizers. The pure hy-... 

All these polyesters are produced by bacteria in some stressed conditions in which they are deprived of some essential component for thek normal metabohc processes. Under normal conditions of balanced growth the bacteria utilizes any substrate for energy and growth, whereas under stressed conditions bacteria utilize any suitable substrate to produce polyesters as reserve material. When the bacteria can no longer subsist on the organic substrate as a result of depletion, they consume the reserve for energy and food for survival or upon removal of the stress, the reserve is consumed and normal activities resumed. This cycle is utilized to produce the polymers which are harvested at maximum cell yield. This process has been treated in more detail in a paper (71) on the mechanism of biosynthesis of poly(hydroxyaIkanoate)s. 

In fact, it is now known that many species of bacteria produce a range of polyesters, some with fairly long side chains (29). These copolymers are all 100% biodegradable, since they are natural products. 

Polyesters are known to be produced by many bacteria as intracellular reserve materials for use as a food source during periods of environmental stress. They have received a great deal of attention since the 1970s because they are biodegradable, can be processed as plastic materials, are produced from renewable resources, and can be produced by many bacteria in a range of compositions. The thermoplastic polymers have properties that vary from soft elastomers to rigid brittie plastics in accordance with the stmcture of the pendent side-chain of the polyester. The general stmcture of this class of compounds is shown by (3), where R = CH3, n = >100, and m = 0-8. 

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. 

Another interesting example of lactones are the p-hydroxyalkanoates, whose ROP affords poly(p-hydroxyalkanoate)s (PHAs), a class of aliphatic polyesters naturally produced by bacteria (Fig. 3) [12, 13]. Poly(3-(R)-hydroxybutyrate) (PHB) is a typical example. PHB is a stiff thermoplastic material with relatively poor impact strength, but the incorporation of other monomers can improve the mechanical properties. 

Polyhydroxyalkanoates (PHAs) are biological polyesters that are produced by a wide variety of bacteria as osmotically inert carbon- and energy-storage compounds that accumulate in the form of granules (see Fig. 1). 

---