Polyhydroxybutyrate-valerate biodegradability

Polyhydroxybutyrate-valerate copolymer Biodegradable polyester used in degradable plastic... 

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-... 

If the homopolymer decomposes at the fabrication temperature another approach is to make a copolymer that can be melt processed at a lower temperature. For example, polyhydroxybutyrate decomposes at the processing temperature (190°C), whereas the copolymer with valeric acid can be processed at 160°C without decomposition. These aliphatic polyesters are biodegradable and most importantly, the decomposition products are not toxic, hence their use in medical applications (e.g., sutures). 

In the presence of limited nutrients, bacteria can be induced to make polyhydroxybutyrates and valerates, which are processed into a copolymer known as BiopoP. BiopoP has properties similar to polypropylene, but it is biodegradable and obtained from nonpetroleum sources. 

Polyhydroxybutyrate (PHB) is a polyhdroxyalkmioate polymer with pl tic-like properties that is synthesized by some soil bacteria (e.g. Alcaligenes eutrophus). The genes for the pathway have been cloned and inserted into plants with successful production of PHB. Additional research is required to optimize the properties the butyrate-valerate copolymer has superior functionality but it remains more difficult to express this material in plants compared to the pure polymer (75). Improved expression levels and localization would also assist in separations and in the economic cost to produce this renewable biodegradable plastic. 

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. 

Biodegradation experiments of polymer-films in marine and soil environments indicated that, in general and depending on the environment, biodegradation rates for unblended polymers were polyhydroxybutyrate-C(9-valerate > cellophane > chitosan > polycaprolactone. Results from blends are more difficult to interpret since different biodegradation rates of the component polymers and leaching of plasticizers and additives can impact the data [216]. 

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