Manufacturers, biodegradable polymers

Certain bacterial species produce polymers of y-hydroxybutyric acid and other hydroxyalkanoic acids as storage polymers. These are biodegradable polymers with some desirable properties for manufacture of biodegradable packaging materials, and considerable effort is being devoted by ICI Ltd. and others to the development of bacterial fermentation processes to produce these polymers at a high molecular weight (66). 

Most of the plastics and synthetic polymers that are used worldwide are produced from petrochemicals. Replacing petroleum-based feedstocks with materials derived from renewable resources is an attractive prospect for manufacturers of polymers and plastics, since the production of such polymers does not depend on the limited supply of fossil fuels [16]. Furthermore, synthetic materials are very persistent in the environment long after their intended use, and as a result their total volume in landfills is giving rise to serious waste management problems. In 1992,20% of the volume and 8% of the weight of landfills in the US were plastic materials, while the annual disposal of plastics both in the US and EC has risen to over 10 million tons [17]. Because of the biodegradability of PHAs, they would be mostly composted and as such would be very valuable in reducing the amount of plastic waste. 

The biodegradable polymer available in the market today in largest amounts is PEA. PEA is a melt-processible thermoplastic polymer based completely on renewable resources. The manufacture of PEA includes one fermentation step followed by several chemical transformations. The typical annually renewable raw material source is com starch, which is broken down to unrefined dextrose. This sugar is then subjected to a fermentative transformation to lactic acid (LA). Direct polycondensation of LA is possible, but usually LA is first chemically converted to lactide, a cyclic dimer of LA, via a PLA prepolymer. Finally, after purification, lactide is subjected to a ring-opening polymerization to yield PLA [13-17]. 

In the current industrial process, nisin is manufactured by fermentation of L. lactis subsp. lactis in a milk-based medium. Biosynthesis of nisin is coupled with the growth of lactic acid bacteria and the production of a significant amount of lactic acid (7). Lactic acid is an important chemical for food processing. It can also be used as a raw material in the production of the biodegradable polymer poly(lactic) acid (12). Unfortunately, lactic acid is not recovered in the current nisin process. 

In order to decrease human consumption of petroleum, chemists have investigated methods for producing polymers from renewable resources such as biomass. Nature Works polylactic acid (PLA) is a polymer of naturally occurring lactic acid (LA), and LA can be produced from the fermentation of corn. The goal is to eventually manufacture this polymer from waste biomass. Another advantage of PLA is that, unlike most synthetic polymers which litter the landscape and pack landfills, it is biodegradable. PLA can also be easily recycled by conversion back into LA. It can replace many petroleum-based polymers in products such as carpets, bags, cups, and textile fibers. 

Product development and improvement has a crucial role to play in the further development of the biodegradable polymers market. These include development of more reliable and lower cost raw materials for manufacture of biodegradable polymers, improvement in performance properties vis-a-vis standard thermoplastics, improvement in processing performance and development of new polymers and blends. 

New types of renewable feedstock such as palm oil for manufacture of starch-based biodegradable polymers. 

Other leading starch-based biodegradable polymer manufacturers are Biotec and BIOP Biopolymers. 

Most biodegradable polymers can be used for making injection moulded articles. Starch-based polymers are used to manufacture a wide range of items such as pencil sharpeners, rulers, cartridges, combs and toys, plant pots and bones. 

In terms of biodegradable polymers, PLA is finding growing use for manufacture of thermoformed articles such as single-use disposable cups and trays, particularly for outdoor events. Starch-based biodegradable polymers can also be thermoformed for production of trays and containers for packaging fresh food and convenience food. 

Similarly, PLA biodegradable polymer prices have fallen sharply over the last five years since the polymers were first commercialised. NatureWorks PLA is now available at prices between 1.37-2.75 per kg compared to a price range of 3.0-3.5 per kg three years ago. NatureWorks PLA has been price competitive with PET for example over the last twelve months as PLA manufacturing scale has increased and process improvements were made alongside the recent sustained higher levels of PET pricing. 

Starch-based biopolymers are lower cost materials than some other biodegradable polymer types such as synthetic co-polyesters and PLA. They are produced from relatively cheap agricultural feedstock and have simpler manufacturing processes compared with synthetic biopolymers. 

Wilkinson Industries Inc. became the first US company to manufacture thermoformed food containers and trays made from biodegradable polymers. The NaturesPLAstic product range is based on NatureWorks PLA polymers. 

NatureWorks currently offers two biodegradable polymer brands for packaging and fibre applications. NatureWorks PLA is used for manufacture of food packaging and serviceware. Ingeo PLA is used for manufacture of nonwoven textile fibres. 

Automotive is one of the largest markets for thermoplastics, but to date few applications have been developed for biodegradable polymers. This situation is expected to change over the next five years as more auto manufacturers examine the possibilities offered by biodegradable polymers to replace petrochemical-based polymers. 

Nvyro was established to produce cassava (tapioca) starch based packaging solutions. Tapioca is one of the cheapest sources of raw materials for manufacture of starch based biodegradable polymers. 

Polyvinyl alcohol is a vinyl polymer with a carbon-carbon backbone similar to other polymers such as polyethylene and polystyrene and is widely used as a water-soluble biodegradable polymer in the manufacture of delivery systems for fertilizers, pesticides and herbicides and is also used to manufacture containers and films. To date, only bacteria have been described as causing biodegradation of polyvinyl alcohols with some causing complete degradation of the polymer (see Shimao, 2001 for review). 

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