Light fibre diet

A biodegradable composite developed in the US is promising to save landfill space and reduce carcinogens in homes and at work.

The composite, made from plant fibre and a resin derived from soy protein, may soon be found in products ranging from office furniture to skateboards.

Behind the idea is Prof Anil Netravali of Cornell University's fibre science and apparel design department, who recently helped found E2e Materials to offer greener alternative materials to industry. The company makes its products from soy protein resin and mostly flax and bamboo fibres grown in New York state.

The company's first product will be a replacement for particle board. Currently this contains resins based on formaldehyde, which is carcinogenic, so industry is scrambling for a replacement resin. The biodegradable product promises to be seven times stronger than current board, and it can be made as a partially hollow sandwich, greatly reducing weight and shipping costs.

Netravali said traditional boards are made by crushing timber into tiny pieces. 'It cannot get high strength since it is made using small particles,' he said. 'Since we use longer fibres we can get much higher strength in our boards. The higher strength means we can use less material to get the same properties.'

Netravali's group has been studying advanced composites using high-strength fibres such as graphite, aramid and ultra-high molecular weight polyethylene fibres for a number of decades. But in the early 1990s he started working on green alternatives, since most of the petroleum-based composites end up in landfills at the end of their life.

Throughout his years of research on green composites, Netravali tried to gain a better understanding of the interaction of fibre and soy protein. He learnt that the interaction is an important element. 'Mechanical properties are enhanced when there is good interaction or bonding between the two,' he said. 'Cellulose fibres and soy protein have compatible chemistry, and so it works much better.'

Most of the green composites E2e Materials makes have equal or better properties compared to wood. 'However, these composites can be easily engineered to obtain required properties wood cannot,' he said. 'Some of our latest composites which we call "advanced green composites" have strength comparable to the strongest steels.' He added that on a per-weight basis, the advanced green composites are around six times stronger than steel, and may be used for structural applications.

Netravali's composites use a variety of resins based on two modified grades of commercially available soy protein. Through various chemical processes he was able to change the mechanical properties of the grades.

For example, one grade called soy protein isolate (SPI), which contains 90 per cent protein, was modified by adding stearic acid. This made the protein more than 2.5 times stiffer, gave it improved thermal stability and decreased moisture absorption — this latter property improved the mechanical properties of the resin as the composites will swell less.

Still, Netravali said there is room for tweaking the resin formula. 'As we develop different chemistry we'll need to carry out experiments to find out how the fibre/resin interaction changes with modification, and what can be done to improve it or control it depending on the application.'

The fibres used in the composites are also subject to change depending on the application. While E2e Materials is using flax and bamboo, Netravali said his group has successfully used fibres such as ramie, kenaf, sisal, pineapple, banana and hemp.

Also, he added, the fibres can be used in various forms such as yarns, fabrics and non-woven mats. 'It will depend on the composite properties,' he said.