As the quest for sustainability continues, researchers are finding ever more obscure starting materials from which to make plastics. Lou Reade reports.
Polymers made from renewable resources like sugar and starch - rather than oil - are on the increase: a recent report from Freedonia estimates that demand for bioplastics will swell by 30 per cent in the next five years - reaching 1 billion tonnes.
This is only a tiny fraction - around 1 per cent - of global plastics production, but it shows a new direction for materials research. Major end users such as Ford, Procter & Gamble and Coca-Cola are all pouring large fortunes into the search for bio-based materials, which will help them live up to their sustainability commitments.
Until now, commercial production of bioplastics has been limited to a few starting materials: polylactic acid (PLA) is a biodegradable polymer derived from corn; others, such as PHA and PHB, are made from starch; there has also been a recent surge in polyamides made from castor oil, and polyethylene derived from 'bio ethanol' (which in turn comes from sugar cane).
But the real challenge for the future is to avoid 'food' crops and use either non-food crops - or food waste - so as not to avoid inflating food prices.
Researchers have already uncovered a range of surprising - and occasionally bizarre - raw materials that could be used as polymer precursors. Instead of sugar and starch, think eggshells, mushroom compost and meat proteins. Other potential sources include algae, cellulose and food industry waste such as shells and husks.[Page Break]
Researchers in New Zealand have developed a way of turning blood meal - a waste product from meat processing - into a bioplastic.
The technology, developed from research led by Waikato University senior lecturer Johan Verbeek and since spun out into a commercial company called Novatein, which will attempt to take the idea to market. It expects to have developed a commercial product within the next few years.
The plastic made in the process has similar mechanical properties to low density polyethylene (LDPE), and is made using a 'scalable process'.
Around 1.5kg of bioplastic can be made from 1kg of blood meal. New Zealand's meat industry produces around 80,000 tonnes/year of bovine blood.
Similar research at Clemson University in the US has also identified the potential to make plastic from blood. In a paper presented at last year's 'Antec' plastics technical conference in the US, researchers Sam Lukubira and Amod Ogale, of the department of chemical and biomolecular engineering, told delegates how they had used meat- and bone-meal (MBM) to produce bioplastic sheets, for potential use in sheets for geo-structural applications.
When the relative humidity of the MBM powder was above 55 per cent, excessive denaturation occurred, producing a dark, glue-like material. Glycerol was used as a plasticiser (in quantities of around 30 per cent by weight), and the pressed sheets were tested for mechanical properties. Those made with finely ground particles (less than 250 microns) were twice as strong as those made from larger particles.[Page Break]
Walking on eggshells
Scientists at the University of Leicester are looking to create new types of plastics from egg shells.
A research team is led by Andy Abbott, professor of physical chemistry and head of the chemistry department at the university, is investigating how it might make starch-based plastics from the egg shells.
Food producers need to pay to dispose of egg shells in landfill: Leicester-based Just Egg, for example, uses 1.3 million eggs per week, and spends £30,000 a year to send 480 tonnes of shells to landfill.
The company's managing director, Pankaj Pancholi, said: "It would be great if the egg shells could be recycled into the plastic packaging that we use for egg products."
The project aims to develop a way to convert the egg shells into a range of starch-based plastics, and test the mechanical properties such as strength. The researchers also intend to identify ways to use the egg shells as fillers that could 'bulk up' different grades of plastic. Potential applications include ready meal food trays and shop fittings - though the ultimate goal is to produce packaging that protects egg products.
The team will also try to extract proteins called glycosaminoglycans (GAGs), for possible use by the pharmaceutical industry.[Page Break]
Plant waste materials is another potentially fertile source that could be used to make bioplastics.
The Oil Palm Biomass Consortium (OPBC), coordinated by Netherlands-based TU Delft, and the innovation unit of the Malaysian Prime Minister's office, will look at the use of palm waste as a raw material for the chemical industry. Malaysia is one of the world's largest exporters of palm oil, but current production processes use only the palm fruit.
"The waste of the palm plant, such as the stem, leaves and the processed palm fruits, can form an important source of biomass for bio-fuels, bio-plastics and other products," said Luuk van der Wielen, professor of bioseparation technology at TU Delft. "The use of such organic materials as palm waste is becoming much more attractive as a more sustainable source of raw materials for the production of chemicals. By this collaboration Dutch chemical companies can gain access to this resource as well."
But these natural materials are not always used as chemical precursors. In some cases, they can be used as 'fibre providers', adding reinforcement to conventional polymers.
An example is Curran, a cellulose material extracted from carrot waste by Scottish company Cellucomp. It can be blended with a range of conventional resins - including polyurethane, polyester and epoxy - to create composites with high stiffness, strength and toughness.
Cellucomp is working with Dutch farm cooperative Royal Cosun to commercialise the material. Curran, combined with carbon fibres, was used to make the Reactor fishing rod, while sheets of the material have been used to produce a skateboard.
The material is currently made in a pilot plant, but is expected to be commercially available next year.
Biowert of Germany is using grass from local farmers to create a range of products, including a bioplastic.
AgriPlast granules comprise 40-75 per cent cellulose fibres from meadow grass (which is produced during the process of crop rotation) and 25-60 per cent recycled polypropylene (PP) or polyethylene (PE). It says that parts made from its AgriPlastic are around 20 per cent lighter than those made from PP or PE.
The granules are free-flowing and can be injection moulded into components such as spoons, brackets, machine cases, and protective caps. Biowert says the material has high flow, which ensures fast cycle times during production.[Page Break]
The automotive industry is also looking for new sources of material. It is the leading consumer of rubber - so the leading tyre manufacturers are actively seeking alternative sources of the material.
Continental is pinning its hopes on dandelions - due to a fungal infection that is threatening rubber trees worldwide. Researchers at the University of Münster and the Fraunhofer Institute for Molecular Biology and Applied Ecology (IME) have identified an enzyme that controls polymerisation of the plant's latex. By switching off the enzyme, the latex can flow freely - and be used industrially.
Dirk Prüfer, of the Institute for Institute of Plant Biology and Biotechnology at the university, says: "The first results show that Russian dandelions produce a high-quality natural rubber. Its physical and chemical properties match up well with those of the Brazilian rubber tree."
The dandelions would need to be 'farmed' on a huge scale, but could be established quickly in response to increased demand for rubber.
At the same time, Goodyear is looking to avoid the fluctuating price and availability of petroleum-derived isoprene through a deal with biotechnology company Genencor. The deal gives Goodyear a sustainable source of isoprene (the monomer from which synthetic rubber is made). Isoprene is traditionally sourced from crude oil, but Genencor has uses special enzymes to 'ferment' it from starch. It expects to begin commercial production in the US next year.
Whether it is rubber, engineering plastics or commodity resins, the search for alternative feedstocks is accelerating. But while today's alternatives are invariably 'food' crops, those of the future will be waste products.
Just as the ancient alchemists dreamed of turning base metals into gold, so today's chemicals producers are looking to use biotechnology and sophisticated catalysts to turn muck into money - or, at the very least, plants into plastic.