Imagine you are sitting on a nice comfortable sofa. It is padded with biodegradable polymer foam reinforced with waste coffee grounds. You might be eyeing up the latest cars in a magazine that sports a model with the super-shiny finish. That is made from trees and the dashboard from recycled potato peelings. Or, you might be watching an environmentally friendly TV, whose case is made from recycled waste from the food industry that was originally destined for a landfill somewhere near your home.
A recycling nightmare? Nothing so ugly, this is the ultimate world of natural products that might be coming soon. Thanks to chemists round the world, we are finding ways that might help us use the megatons of organic waste we generate every year. Biomass becomes the raw materials for chemical reactions for making tough new biodegradable plastics and polymer composites. This last word in recycling might help reduce the burden on landfills everywhere as well as providing industry with a cheap and renewable resource to replace oil and petroleum, the usual suspects in plastics manufacture. Moreover, these natural plastic products will be biodegradable, so when their useful life is over, they too can be readily recycled - either by manufacturer or microbe.
Hyoe Hatakeyama of Fukui University of Technology is reported in January's Chemical & Engineering News as being something of a recycling pioneer. He and his team are using two of the most commonly wasted biomass sources as their starting materials for making polymer foams and composite materi als, that might be used in countless consumer products. The first unlikely material they are using is coffee grounds. Several million tons a year are produced as the by-product of making instant coffee, which are simply dumped. The second natural material is molasses, another waste product this time of the sugar industry. Some molasses is used in agriculture, the rest is disposed of at sea.
The Japanese team first converted their molasses into a plastic form by reacting it with polyethylene glycol, which strings the sugary molasses molecules - sucrose, glucose and fructose - along thousands of sub-microscopic polymer chains. Then, they simply add coffee grounds, some activating agent and a catalyst, and the materials bind together to form a tough and durable composite material. If they carry out a similar reaction scheme but missing out the coffee grounds ingredient, they end up with a new version of flexible polyurethane foam. One of the advantages of these strange hybrid products is that they are more environmentally benign than conventional oil-based plastics, since they are readily biodegradable.
Kitchen sponges made from such waste materials are already on sale in Japan, C&EN reports. In the US, the efforts of Brian Seiler and his colleagues at Eastman Chemical in Kingsport, Tennessee, have taken inspiration from some of the earliest plastics and brought them right up to date. Before synthetic polymers, such as nylon and PVC, were invented there was cellulose. Cellulose is a natural polymer composed of thousands of sugar molecules strung together forming the fibrous parts of plants and trees. A century ago, it was used as the raw material for making semi-natural plastics, such as celluloid, famous as the transparent "film" of movie fame. Today, cellulose is still commonly used to make the materials for cigarette filters, suit linings and specialist photographic films. While the family of esters of cellulose with carboxylic acids ('cellulose esters') has been known for more than 100 years, the family continues to grow, as does its influence, says Seiler.
But Seiler and his colleagues did not want to make simple celluloid, they wanted a high- tech polymer that could be made from waste cellulose. The manufacture of synthetic polymers generally relies on building up the long polymer chain from chemical units called monomers. Seiler and his team reasoned that they could start with the natural cellulose polymer and simply modify it using chemistry to endow it with new physical properties.
He and his colleagues have now developed a variation on the cellulose polymer for use in car body finishes. The material, called carboxy methylcellulose acetate butyrate, can be dispersed in water, so it does away with the need for a toxic organic solvent. Moreover, it not only dries faster but also helps the paint form a much smoother, shinier finish.
Food and wood waste too are finding application in making new polymers. Nobuo Shiraishi of Kyoto University is working on methods of converting one of the biggest sources of biomass waste - wood shavings and food industry waste, such as potato and other vegetable scraps - into plastics. He and his team have developed techniques to produce both thermoset and mouldable plastics from biomass. They can make thermoset plastics, for instance, by gently heating their biomass starting material with alcoholic organic compounds with sulphuric or phosphoric acid for just an hour or two.
The team has already made materials with what Shiraishi describes as "fine plasticities, physical properties and biodegradability". The resulting plastics could be used as glues, foams, and mouldings for less environmentally damaging packaging and consumer products from TV cases to mobile phone covers.
In a similar vein, Shiraishi and his colleagues are also looking at how recycled newspaper, magazine, and box paper might be used as a cheap source of cellulose. They believe this is perfect for conversion into mouldable cellulose acetate and the fabrication of composites. Such an application would not only reduce the strain on the oil industry of using reserves for manufacturing but also provide a more environment friendly route for the disposal of waste paper destined for landfill.
We currently utilise only about 7% of the biomass we produce, mostly as wood fuel in the developing world, rather than as consumer products. But, in the West, we simply dispose of millions upon millions of tons of organic molecules in the form of waste wood materials, literally junk food and other garbage.
These materials are based on renewable and sustainable resources and have biodegradability that can be tuned and triggered by the producer and end-users.
With a little chemical ingenuity, we could avoid squandering this valuable resource and bring a little nature back into our lives. These are the perfect 21st century materials.
• David Bradley is a freelance science writer at www.sciencebase.com
