Turning unwanted straw into valuable products for industry

Common or garden straw could be a rich source of raw materials for a range of industries, from the health foods and cosmetics sectors to packaging and fabrics.

Researchers at the University of Wales, Bangor are developing environmentally friendly ways of processing wheat and other cereal straws to extract valuable products for industry.

The work is being carried out through the Government’s LINK scheme, with funding from the Swindon based Engineering and Physical Sciences Research Council, the Government’s department for rural affairs and several industrial partners.

“Some 10 million tonnes of wheat straw is produced annually in the UK, for which there is a market for about 20 per cent,” says Dr Jeremy Tomkinson, who is leading the research. “In the past the unwanted straw was burned, but since that was outlawed it is now generally chopped up by the harvesting machine and ploughed back into the land.” While some types of soil can assimilate the straw easily in this way, heavier, clay-based soils do not rot it down so well, raising doubts about the long-term sustainability of the practice.

However, The Bangor researchers believe that straw could become a source of chemical feedstock for industry.

Broadly there are four main components of straw; the waxy outer layer, cellulose, hemicellulose and lignin.

• The purified wax has potential as a base for cosmetics such as lipsticks and contains substances called phytosterols, which are currently used in cholesterol-reducing spreads.
• Cellulose is used to manufacture viscose, which in turn is converted to cellophane and rayon.
• Hemicellulose – can produce polymers of many different sizes for use in a range of industrial applications e.g. paints and coatings.
• Lignin has some small, specialised applications but its high calorific value could make it suitable to be burned in combined heat and power plants.

“The key to abstracting maximum value from the straw is to remove the various products sequentially whilst leaving the remaining ones intact,” says Dr Tomkinson.

“The emphasis is on environmentally benign processes that are as straightforward as possible,” says Dr Tomkinson. “If there is too much rocket science involved business people will not be interested because it is too risky. But you do have to design the process carefully so that you obtain the products you want. We are working closely with our industrial partners so that at every stage we know what industry requires and we can tailor the processes to meet those demands.”