The Starch-Based Revolution
Man was using oil at least five thousand years ago for applications such as lighting, medication and waterproofing. Although petroleum is a naturally occurring resource, it is finite and, therefore, it is predicted that starch-based and other ‘bio’ products, solar and wind energy, may take on a crucial role in the survival of our planet in the longer-term. Already, renewable energy sources in the UK generate approximately 3% of the total electricity supply, 14% of which comes from wind energy.
Starch-based packaging is a recently developed alternative to oil-based packaging, although man has already tried some alternatives in the past. Whale oil, for example, was prevalent until whale stocks were decimated and coal oil proved too costly to extract. Although oil field exploration continues in a bid to satisfy our burgeoning consumer and industry demand for the resource, the starch-based revolution is forging ahead to provide another, perhaps, more permanent and viable alternative.
Unlike its starch-based rival, oil-based plastic will not degrade. Landfill, effectively, becomes a tomb to plastic that can remain intact indefinitely. Oil polymers cannot be disposed of by incineration since they can produce toxic gases, carbon dioxide and carbon monoxide when burnt. PVC, for example, produces hydrogen chloride on burning. However, oil-based plastic can be safely disposed of through recycling and there is scope for increasing the use of recycled plastic in a range of existing and new product applications. It is likely that improved recovery levels for PET and HDPE, for example, may be necessary to exploit growth opportunities. Waste recycling of plastic packaging in 2002 is reported to be at 22.6% based on 393,665 tonnes (source: Department for Environment Food and Rural Affairs).
Since starch-based products are organic, they can be disposed of through degradation or by incineration because no harmful gases are produced on burning. In landfill soil, the oxygen that is present allows micro-organisms to break down the material until it biodegrades to carbon dioxide, water and mineral salts. The length of time that a starch-based material will take to degrade will depend upon prevailing conditions such as temperature.
Oil
Petroleum, or crude, is an oily, flammable liquid that has formed over millions of years. Plant and animal remains amassed on shallow sea floors and when the waters receded, layers of silt, sand, clay and organic material covered them. Buried deep, and in the absence of oxygen, the material could only partially decompose to form a petroleum liquid that seeped into the spaces between the earth’s rock layers. When tectonic plates moved, it collected in deposits from where it is now extracted by land wells and giant offshore platforms.
Both oil-based plastics and the starch-based alternatives are derived from molecules or polymers. A polymer is composed of many small monomers or units that are linked together in a chain. Polymers that are extracted from oil can have different molecular structures whereby the monomers can be linear, branched, or cross-linked which dictates their type of plasticity.
Well known industrial packaging such as polyethylene, polypropylene, vinyl acetate, polystyrene, teflon, perspex and nylon are manufactured from thermoplastic or thermosoftening polymers that form a long chain of carbon atoms which are held together by covalent bonds. Parts of the chain can form into small crystals and when heat is applied to the polymer, they melt and become soft enough to be poured into a mould or extruded onto a rotating drum to produce a film. As the polymers cool, new crystals form between the chains and the shape is fixed but the polymer can be reheated and remoulded if required, enabling these types of plastics to be recycled.
Starch
Starch is a degradable complex carbohydrate (polysaccharide) polymer. White and odourless, it is produced by plants during photosynthesis when it is used as to store energy. Wheat (the most widely grown crop in the world), corn, rice and potatoes all store particularly high amounts of starch. The crops are processed to extract the starch in preparation for the manufacture of alternative materials to those that are oil-based, the fundamental difference being that they will degrade.
Starch is composed of amylose and amylopectin polymers. The molecular structure, that can vary according to the plant it is extracted from, has glucose units which are linked together in chains. The chain length also depends upon the plant type. Amylose molecules have a linear structure whilst amylopectin molecules have a branched, tree-like structure and the combination of the two gives starch its granular consistency.
Leading manufacturers of environmentally-friendly plastic alternatives have developed patented processes for extracting and treating plant starch and producing starch-based pellets. For example, corn can be milled or leached in water in order to extract the starch. Plant sugar is then derived from the starch and following further processing and polymerisation, starch-based granules are produced, ready for use in the manufacture of bio-plastics and other products.
