UK team gives straw an industrial makeover

Millions of tonnes of discarded straw could be turned into raw materials for industry, with applications as wide ranging as power station fuel and polymers for paints and coatings.

Scientists at Bangor University are working on an environmentally friendly and cost-effective means of recovering the straw’s waxy outer layer and separating the rest into cellulose, hemicellulose and lignin.

Cellulose is used to make viscose, which is a constituent of cellophane and rayon. Hemicellulose can produce polymers of many different sizes for use in paints and coatings. Lignin has a high calorific value that could make it suitable for burning in combined heat and power plants.

The purified wax also has potential as a base for cosmetics such as lipsticks, and contains phytosterols, which are used in cholesterol-reducing spreads.

About 10 million tonnes of wheat straw are produced annually in the UK. In the past any waste was burned in the fields, but since stubble burning was outlawed the straw has been ploughed back into the land.

Project leader Dr Jeremy Tomkinson estimates that some two million tonnes of straw could be converted for industrial purposes using a simple chemical process.

His team chopped the straw into short pieces and then washed it in an organic solvent to strip away the wax. The next step was to bleach the straw pulp, without chlorine-based chemicals, and separate the hemicellulose and cellulose. The hemicellulose was dissolved in an alkaline water source, while the cellulose remained as a solid, enabling the two components to be separated. The remaining lignin and cellulose were then obtained by using a pH-adjusted solution. The lignin comes out of solution as a gritty, sandy material.

Dr Tomkinson said it was important to develop a process that was economically viable. ‘If there is too much rocket science involved business people will not be interested because it is too risky. The emphasis is on environmentally benign processes that are as straightforward as possible.’

The Engineering and Physical Sciences Research Council, the Department for Rural Affairs and several industrial partners have provided £300,000 of funding for the project.

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