GREENER PLASTICS – BIOPLASTICS
Thermoplastic materials are almost entirely derived from oil, a dwindling natural resource. After years of investigation some viable alternatives are starting to come to fruition. However, out of 245 million tonnes of plastics produced worldwide only 0.36 million tonnes (0.15%) are currently bio-based plastics. Growth over the next decade is predicted to be about 20% per annum although by 2020 this will still represent only a small share of the total (3.5 million tonnes, 1.4%). Potentially, 90% of all polymers could be replaced by bio-based equivalents.
Bioplastics, as they are known, are derived from non-fossil sources, either partially or fully. Many bioplastics are biodegradable and these are generally derived from plant starch, but more grades are becoming available which are not biodegradable and are therefore suited to more widespread applications.
Nylons manufactured from castor oil have been around for a number of years but in the past have been too expensive. Rising oil prices and concerns about global warming have led to renewed interest; castor oil based nylons reducing global warming potential by 30%-40%.
A polyethylene derived from ethanol from sugar cane is currently at an advanced stage of development.
THE CURRENT SITUATION
DuPont has undertaken a great deal of research and development in this field in an attempt to produce high performance thermoplastics from renewable sources. DuPont uses corn sugar to produce Cerenol using a patented fermentation process.
The world’s largest aerobic fermentation plant has been built in Tennessee and is a joint venture between DuPont and Tate & Lyle Bioproducts. The processes involved in the production of Cerenol use approximately 40% less energy than its petrochemical based counterpart. It is estimated that this will save the equivalent of 10 million gallons of petrol per year in producing 45,000 tonnes of Bio-PDO. This is then used in Polyesters and TPU’s, Sorona and Hytrel respectively.
Sorona is similar in performance to PBT offering good strength and stiffness with improved surface appearance and gloss.
Hytrel is already well known as a polymer. The grades made with renewable resources show improvements in temperature range and elastic recovery when compared to current Hytrel.
DuPont are by no means the only polymer producer developing in this field but they are one of the largest.
Concerns have been expressed about growing plants specifically for these sorts of applications. Although it is a renewable source there is a fear that land previously used for growing food will be turned over to more profitable production for fuels and polymers. Also, it could lead to more forests being destroyed to provide more land for cultivation.
With this in mind, thought has been given to other sources. US scientists have discovered a way to make plastics using orange peel and carbon dioxide. This process offers hope that harmful greenhouse gases could be harvested to be used in polymer production instead of pumping it into the atmosphere. Orange peel contains limonene which is a carbon based compound. It was a derivative of this oil –limonene oxide, which was used in the process. The resulting polymer was very similar in character to polystyrene.
British Airways is also investigating the possibility of an aviation fuel manufactured from waste. A plant would be built in east London by Solena Group to take waste from the area to produce the fuel. The ideal source material for the plant is waste matter that has a high carbon content. The waste is fed into a high temperature “gasifier” to produce BioSynGas. A chemical process called Fischer Tropsch is then used to convert the gas into biofuel.
Waste products from the process can be used to power the plant as well as supply 20MW of electricity to the national grid. A solid waste product can be used as an aggregate in construction.
Another by-product would be naptha which could be used for the manufacture of bio-based polymers.
Although there is a greater awareness of green issues and efforts are being made to develop new sources of base chemicals for polymers, it can be seen that there is still a long way to go.
However, as more alternatives to oil and petrol are developed so the need to find new sources of base chemicals to produce polymers will also need to be found. Also, as more biofuel processes are developed, as with the BA/Solena proposal, then more sources of suitable base chemicals for polymer production could become available.
This is an area that is developing fast and any predictions made today could well be revised considerably in just a few months time.