This “Topic of the Month” with the title “Plastics made from vegetable oil” marks the beginning of a series of articles that highlight the use of renewable raw materials, with particular emphasis on the production of polymer materials. We will, however, also be taking a look at cases where it appears to be sensible and far-sighted not to use plastics, e.g. in favour of renewable resources: plastic is simply too valuable to add it to a product with only a short useful life that will soon be thrown into the dustbin or end up littering the environment in an uncontrolled fashion. The process of rethinking this involves is producing results in many different areas and is leading to the adoption of a “back to the roots” approach, which means that preference is being given to renewable materials in certain cases – for the first time or, perhaps surprisingly, once again.
Kessler and his colleagues are convinced that vegetable oils enable materials to be produced with greater flexibility, a wider range of stiffness properties and more varied design options. They report that vegetable oils are proving to be inexpensive, easily available and renewable. And, last but not least, it is apparently possible to make genetic modifications.
One aspect that is important – because it is more sustainable and more sensible in the long term – is to opt for renewable resources in plastic production instead of oil or gas. Although there is nothing new about doing this, it is not common enough in the opinion of many champions of the use of biobased plastics. Crops – or rather the products made from them, which are in this case vegetable oils – form the area in which a group of scientists headed by Professor Michael Kessler, Director of the Mechanical and Materials Engineering Faculty at Washington State University in Washington, USA, is carrying out research. Kessler and his colleagues report that they have succeeded in making polyurethane (PU) in a completely new way from olive and linseed oil.
According to Professor Kessler, about 14 million tonnes of polyurethane were manufactured in 2010; Washington State University predicts that global production will be increasing to more than 18 million tonnes per year by 2016.
Polyurethane is an extremely resistant, hard-wearing and corrosion-resistant plastic that is used in the production of foam plastics, car tyres, hoses and sealing materials. Most PU has been manufactured from mineral oil up to now.
The idea of producing polyurethane on a vegetable basis is not by any means new. The research group headed by Michael Kessler has, however, entered virgin territory – as Kessler puts it – with its method and the use of vegetable oil:
Kessler and his colleagues are convinced that vegetable oils enable materials to be produced with greater flexibility, a wider range of stiffness properties and more varied design options. They report that vegetable oils are proving to be inexpensive, easily available and renewable. And, last but not least, it is apparently possible to make genetic modifications.men.
The research scientists have produced polyurethane on the basis of olive, rapeseed, grapeseed, linseed and castor oil in the course of their study. While it is reported that mineral oil-based solvents have to be used in the conventional production of PU, the scientists from Washington State University have, it seems, succeeded in dispensing with solvents and catalysts entirely in their co-operation with colleagues from Iowa State and Cairo University.
An outline of the fundamental part of PU production: two different chemical compounds are combined in a reaction in polyurethane production. One of them is a polyol. Polyols include organic compounds that contain several hydroxy groups (-OH); what is involved here is a functional group that has a major impact on the reactive character of the compounds.
The number of hydroxy groups in a chemical compound is identified by the word ending: if a compound has one, two or three hydroxy groups, it is given the ending “-ol”, “-diol” or “-triol”; those with four or more hydroxy groups are generally referred to as polyols. Polyols of the kind required in the plastic industry can be manufactured petrochemically, i.e. on the basis of mineral oil, or oleochemically, in this case on the basis of vegetable oil. By the way: Oleochemistry is the study of vegetable oils and animal oils and fats, and oleochemicals derived from these fats and oils or from petrochemical feedstocks through physico-chemical modifications or transformation. First used in the making of soaps, oleochemistry is now part of our daily lives where it is found in a wide variety of sectors like food, cosmetics, pharmaceutical and industrial.
The plastic is given its property profile in the course of polymerisation. The individual polyols are combined to form a three-dimensional network in this process. How complex this network is and what characteristics the subsequent plastic has depend to a decisive extent on the reactive points in the molecule: some oils – linseed oil, for example – have five to six reactive points; the macromolecular structures produced tend to be on the stiff side; other oils – olive oil, for instance – in turn have fewer reactive points, which leads to a lower degree of cross-linking after polymerisation, although this makes the material more flexible.
Professor Kessler explains that the special feature of the procedure they chose is the way the polyols are manufactured, without going into the chemical details. The scientist does, however, reveal that the production process can be compared to the Lego construction principle: “The compounds in this chemical group are simply connected together and produce new compounds”. The scientists describe the way Kessler and his colleagues produce polyurethane as a new kind of chemistry that is based on a combination of castor fatty acids and modified vegetable oils.
As the Director of the Center for Bioplastics and Biocomposites, which co-ordinates the joint research activities of Washington State University and Iowa State University with the industrial community in the development of biobased plastics, Professor Kessler is hoping that their new method will attract the interest of the plastic industry. The close attention that the project is being given indicates that it appears to be considered very impressive: it was launched in early 2015 with financial support from the National Science Foundation, the US governmental authority for the funding of research and education, as well as from partners in the scientific and industrial communities. A total of 24 companies have joined in the research project. n.