Biodegradable polymers, disposal

While this book is focused on drug delivery, the value of biodegradable polymers is not limited to this field. Biodegradable polymers will be useful in other areas of medical therapeutics, such as sutures and bone plates and other types of prostheses. The polymers will also be useful in nonmedical fields, for disposable plastics, bottles, diapers and many other entities. 

In view of the necessity for getting waste disposal under control coupled with the limited fossil raw material resources, biodegradable polymer and in particular polymers from renewable resources will gain importance in the future. In the most sensitive application area, food contact materials and articles, it is possible initially to use these materials in very limited amounts. The easy decomposition of these packaging materials is in opposition with the inertness needed to protect packaged food. These polymers are particularly sensitive to moisture. By finishing operations such as surface treatments, one could improve the inertness of these polymers. However, the degradability would be diminished by such processes. 

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. 

In September 2004, Novamont acquired the Eastar Bio technology of Eastman Chemical for an undisclosed sum. The deal includes all patents and technology rights but not production facilities or distribution channels. Eastman introduced its biodegradable polymer in 1997 and since then has invested more than 75m in the project. The resin is used commercially for single-trip disposable packaging, as well as for barrier films and waste-bin liners. Eastman has a 15,000 tonnes per annum production plant at Hartlepool in the UK, which was started up in 1999, for production of Eastar Bio products. 

DuPont offers a family of biodegradable polymers based on polyethylene terephthalate (PET) technology known commercially as Biomax. Proprietary monomers are incorporated into the polymer, creating sites that are susceptible to hydrolysis. At elevated temperatures, the large polymer molecules are cleaved by moisture into smaller molecules, which are then consumed by naturally occurring microbes and converted to carbon dioxide, water and biomass. Biomax can be recycled, incinerated or landfilled, but is designed specifically for disposal by composting. 

Coated or laminated paper products represent a significant potential market for biodegradable polymers. At present, packaging such as hamburger wrapping and disposable cups, are extrusion coated with low density polyethylene film that is resistant to biodegradation. This also restricts the biodegradation of the paper substrate since it acts as an impervious barrier. 

Serviceware made with biodegradable polymers such as PLA is particularly valued at outdoor events such as sports stadiums, concerts, universities, amusement parks, shopping malls and other venues that benefit from the disposal options available with biodegradable polymers. Over the next five years, biopolymers are expected to make further inroads into these markets. 

Vertex is actively involved in the commercialisation of biodegradable polymers and uses Nature Works PLA material. The company initiated a development project to ascertain the technical and commercial viability of PLA in 2003, which has resulted in a decision to supply various stock products made from PLA. These include disposable cups, fresh food containers including deli containers and salad bowls, bakery containers including sandwich wedges, bottles, food trays and extruded sheet for further processing. 

The most fundamental classification of polymers is whether they are naturally occurring or synthetic. Common natural polymers (often referred to as biopolymers) include macromolecules such as polysaccharides e.g., starches, sugars, cellulose, gums, etc.), proteins e.g., enzymes), fibers e.g., wool, silk, cotton), polyisoprenes e.g., natural rubber), and nucleic acids e.g., RNA, DNA). The synthesis of biodegradable polymers from natural biopolymer sources is an area of increasing interest, due to dwindling world petroleum supplies and disposal concerns. 

Synthetic polymers are arguably the most important materials made by chemists and used in modem society. Chapter 30 Synthetic Polymers expands on the foundations of polymers discussed in earlier Chapters 15 and 22. Of significance is emphasis on the environmental impact of polymer synthesis and use, discussed in sections on Green Polymer Synthesis (30.8), Polymer Recycling and Disposal (Section 30.9A), and Biodegradable Polymers (Section 30.9B). 

During the search for efficient and ecologically justified waste-management concepts, the use of biodegradable polymer materials was repeatedly made a political demand. Next to the arguments of a partial solution to the waste-disposal problem by natural degradation, the conservation of the petrochemical resources, the reduction of C02-emission, and the use of renewable resources are a point of discussion. 

Biodegradable biopolymers (BDP) are an alternative to petroleum-based polymers (traditional plastics). It will be important to find durable plastic substitutes, especially in short-term packaging and disposable applications. The continuously growing public concern concerning this problem has stimulated research interest in biodegradable polymers as alternatives to conventional non-degradable polymers such as polyethylene and polystyrene, etc. The economic value of renewable raw materials will increase to a significant extent [1] and induce new industrial activities [2,3]. 

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