Polyhydroxybutyrate-valerate copolymers PHBV

This is a copolymer consisting of hydroxybutyrate and hydroxyvalerate units incorporated randomly along the chain. The hydroxyvalerate content may be varied by adding controlled amounts of a simple organic acid. 

While stable under normal conditions of storage and use, the polymer degrades when deposited in microbially active environments. 

At the present time there are two causes of variation between grades  

as might be expected, the use of plasticiser has a similar effect to that of increasing the hydroxyvalerate content. It also has a more marked effect on depressing the glass transition temperature and therefore improves properties such as impact strength and ductility at lower temperatures. 

As with most polyesters, the polymers have quite good resistance to oils, particularly hydrocarbons, but are hydrolysed by acids and bases. 

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A more recent biodegradable polymer is polyhydroxybutyrate-valerate copolymer (PHBV) from ICI Americas Inc.. These copolymers are produced through biochanical means. In fact, these natural thermoplastics are derived from bacteria. They are fully degradable in many microbial environments. Other biodegradable polymers include Konjac, a water-soluble polysaccharide produced by FMC Chitin, another polysaccharide that is insoluble in water and Chitosan, which is soluble in water. 

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-... 

Metabolix s PHBV (polyhydroxybutyrate valerate) was initially developed by ICI. PHBV and related copolymers are made in a pilot plant using different bacteria to create compositions with up to 70% crystallinity. Elongation can be manipulated from 5% to 100%, and melting points range between 135 and 185 °C (275-365 °F). 

Another important family of biobased polyesters is the polyhydroxyalkanoates (PHAs) the most common members of this family are polyhydroxybutyrate (PHB) and its copolymer, polyhydroxybutyrate-valerate (PHBV). 

One of the early truly biodegradable polymers was polyhydroxybu-tyrate/valerate (PHBV). This is a member of the polyester family which is produced by certain types of bacteria when they have a diet which is carbon-rich but poor in some essential nutrient. Under these conditions, they produce polyhydroxybutyrate (PHB) as a food store to be called upon when carbon sources are less available. With manipulation of the diet, the bacteria can be induced to form a copolymer, PHBV, which has more useful properties than PHB. 

The two most common PHAs are polyhydroxybutyrate (PHB) and a copolymer of polyhy-droxybutyrate and polyhydroxy valerate (PHBV). PHAs can be used as films, fibers, and coatings for hot beverage cups made of paper. 

PHA constitute a whole class of microbially synthesized polyesters [33], of which polyhydroxybutyrate (PHB) and the copolymer with valerate (PHBV) have attracted much attention as possible replacements of oil-based thermoplastics. To serve as a useful injection moldable plastic with reasonable ductility, PHA... 

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