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Biopolymers

Biopolymers are biodegradable polymers which can be created from either renewable (based on agricultural plant or animal products) or synthetic material.  The four main types are outlined below:


1. Starch based polymers
Starch is a natural polymer which occurs as granules in plant tissue. It is obtained from potatoes, maize, wheat and tapioca and similar sources. Starch can be modified in such a way that it can be melted and deformed thermoplastically. The resulting material is suitable for injection moulding and extruding.

Moscardino spork [1]

Applications
Thermoplastic starch is unsuitable for packaging liquids. It can sustain only brief contact with water. It has good oxygen barrier properties.

2. Sugar based biopolymers
• The starting material for Polyhydroxibutyrate is made from sucrose or starch by a process of bacterial fermentation. Varying the nutrient composition of the bacteria produces differences in the end product. This makes it possible to tune the properties of the material, e.g. its moisture resistance. The polymer can be formed by injection, extrusion, blowing and vacuum forming.

• Polylactides (lactic acid polymers)are made from lactic acid, which is in turn made from lactose (or milk sugar) obtained from sugar beet, potatoes, wheat, maize etc. Polylactides are water resistant and can be formed by injection moulding, blowing and vacuum forming.

Applications
Polylactides decompose harmlessly in the human body and have therefore long been used for medical applications. Examples include surgical implants which do not require operative removal. Until recently, it was not feasible to use polylactides for packaging because of their high price, around US$500 per kilogram.

Polylactic acid (PLA) has been used in the manufacture of the Belu water bottle and Interface flooring.

PLA is only suitable 4 commercial composting.


3. Cellulose based biopolymers
The use of cellulose for making packaging material such as cellophane is long established. The material is transparent and has good folding properties. Whether in the form of pure cellulose or of a nitrocellulose coating, the material is wholly biodegradable and can be composted by existing waste processing plant.

Applications
Familiar applications of cellophane include packaging for CDS, confectionary and cigarettes. The material is gradually falling out of favour, however, owing to its high price (about US$6 per kilogram). Other cellulose polymer materials (e.g. cellulose film) have also been commercially available for many years but are losing market share to polymers such as polypropylene.


4. Synthetic based biopolymers
Synthetic compounds derived from petroleum can also be a starting point for biodegradable polymers, e.g. aliphatic aromatic copolyesters. These polymers have technical properties resembling those of polyethylene (LDPE). Although these polymers are produced from synthetic starting materials, they are fully biodegradable and compostable.

Applications
The relatively high price of biodegradable polymers of synthetic substances, e.g. aliphatic aromatic copolyesters has prevented them from reaching a large scale market. The best known application is for making substrate mats.

[Source: http://www.o2.org/ideas/cases/biopolymers.html, accessed Nov 2006]

[1] http://www.treehugger.com/files/2005/07/moscardino_spor_1.php, accessed September 2005

Benefits
Besides being available on a sustainable basis, biopolymers have several economic and environmental advantages. Biopolymers could also prove an asset to waste processing. For example, replacing the polyethylene used in coated papers by a biopolymer could help eliminate plastic scraps occurring in compost.

Consumers have a lively interest in biopolymers too. Conventional plastics are often seen as environmentally unfriendly. Sustainable plastics could therefore provide an image advantage.

The major advantage of biodegradable packaging is that it can be composted. But the biodegradability of raw materials does not necessarily mean that the product or package made from them (e.g. coated paper) is itself compostable.

Biopolymers can also have advantages for waste processing. Coated paper (with e.g. polyethylene) is a major problem product for composting. Although such materials are usually banned from inclusion in organic waste under separate collection schemes, some of them usually end up nonetheless in the mix. The paper decomposes but small scraps of plastic are left over in the compost. The adoption of biopolymers for this purpose would solve the problem.

[Source: http://www.o2.org/ideas/cases/biopolymers.html, accessed Nov 2006]

More information

Mater-Bi by Novamont - www.novamont.com/

Biocorp's "Bio-Grade 300" (for cutlery, etc)

Biotec products (some have similar properties to PS) - www.biotec.de/engl/index_engl.htm

Eco-Flow foam (American Excelsior Company) - www.americanexcelsior.com/solutions_environmental.php

EnPol (Polyval, UK) - www.enpol.co.uk/

Symphony Plastics - www.symphonyplastics.co.uk/ or www.degradable.net/

[Source: Sabine, O2mailing list, 23 March 2007]