When does plastic stop being plastic? Ezio Manzini, a sustainable design strategist, likens the rapid evolution of materials and trying to define these materials as ‘like trying to capture a family photograph when the whole family is in constant motion.’ On this basis, at what point does the definition of plastic, as a substance derived from petroleum, no longer fit with the ever-increasing range of alternative starting points and ingredients that are being developed? How far will this definition stretch when in the near future plastic may be derived from any number of raw materials, which currently range from starch to chicken feathers and now castor oil?
As the world looks beyond petrochemicals to create plastic products, one of the sources it is looking to is castor oil, a substance that in popular knowledge is thought of as a laxative. Castor oil is a viscous liquid extracted from the seeds of the castor plant and is one of the most widely used vegetable oils. It was not so long ago that bioplastics were associated with flimsy, throwaway items like disposable cutlery and packaging, but renewable plastics have a come a long way in a short time. The sunglasses shown here, from Smith Optics, use Rilsan® Clear Renew, a high-performance, optical-grade plastic from the French supplier Arkema. They are made entirely with biodegradable and renewable castor oil but with the properties of nylon, meaning that it is tough with good impact resistance.
Image: Evolve sunglasses by Smith Optics
•Tough
•High strength
•Low friction
•Good resistance to wear and tear
•Drought resistant
•Easy to grow
•Transparent grades available
•Limited chemical resistance
•Compelling consumer story
Sources
Apart from the popular use as an ornament, the castor plant is common in tropical climates such as Brazil and India.
Cost
Castor oil commands a higher price than other similar seed oils such as sunflower and canola.
Sustainability issues
The wide usage of castor oil conflicts with the castor plant’s toxicity, which includes alkaloids, glycosides, various resins and volatile oils and is therefore dangerous for crop workers. Some cities and states in the USA are even trying to ban the ornamental use of castor bean plants. As if those concerns aren’t bad enough, the plant is also used to produce ricin, a toxic ingredient that is used for chemical and biological weapons. In terms of its use as a biofuel, castor oil is fairly unusual in that it does not need heat to convert into biodiesel, therefore it is less energy intensive.
Production
This renewable polyamide – Nylon – is easy to process using conventional thermoplastic techniques, including injection moulding, blow moulding, rotational moulding and extrusion. It can also be enhanced with countless fillers, such as glass and various colourants. It can also be extruded into a tough fibre for textile applications.
Typical applications
Apart from its common association as a laxative and its other healing properties, castor oil has more than 700 derivatives and uses ranging from lubricants to cosmetics for making soaps, and now, of course, as a source for the plastic industry. As with many polyamides, the main application area of this renewable form is in engineering, or other demanding applications that require enhanced mechanical properties in comparison to commodity plastics.
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–Versatile production –Strong –Good resistance to wear and tear –Low friction |
–Can be environmentally hazardous to grow and manufacture –Poor chemical resistance |