Seeds of change: the growing trend of producing biodegradable polymers from oilseed crops.
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What is important for us to realize, is that by clever exploitation of our impressive infrastructure in the oil and gas and petrochemical industries, and our immense agricultural industry, we can begin to address issues of dwindling fossil resources, environmental impact, and economic sustainability. These are large, grandiose times, when the future, not just environmentally, but economically, may be written by the choices we make now.
A not-so-small subset of the changes that can be made to our economic and environmental benefit is the production of plastics from renewable agricultural sources. Almost all of the plastics currently produced are from fossil fuel derived feedstock. Clearly, as oil and gas reserves dwindle, the cost and availability of such feed stock will be severely affected. Furthermore, a very large percentage of the plastics produced from fossil fuel feedstock are non-biodegradable. Many potential plastics from agricultural feedstock have much more improved biodegradability properties.
Consequently, much attention has been focused lately on the use of agricultural feedstock to produce plastics and other industrial materials. Perhaps the most visible of many efforts in this direction has been the Dow-Cargill joint venture to produce biodegradable plastics from Poly Lactic Acid (PLA). However, there has been a steady, growing increase in the amount of research and commercialization activities related to the production of industrial materials from vegetable oils. Given the space allocated for this short article, it is not possible to cover the use of oilseed fibres in industrial materials.
It is important to realize that at the heart of energy and materials utilization by humans, is the humble carbon-carbon bond. The substitution of agricultural and forestry biomass for petroleum products is simply a difference of the amount of time the carbon-carbon bonds, generated ultimately out of photosynthesis, are stored ... and some clever applications of physics and biotechnology, and chemistry.
Production of Agricultural Biomass
Of the daily energy from sun of approximately 1.5 x [10.sup.22] J, only 4 x [10.sup.18] J are used to build up biomass. Only approximately 7 percent of the biomass is used by mankind. Furthermore, the buildup of biomass worldwide (~ 200 billion tons) is approximately 1000 larger than the amount of plastics produced worldwide (~ 180 million tons). Accepting that this biomass is renewable if sustainable agricultural methods are used, there exists an opportunity to substitute agricultural feedstock for that derived from petroleum, from an availability perspective. The research challenge becomes the need to match both functionality and price targets set by petroleum-derived plastics. Of the farmed biomass, starch sources are by far the most utilized currently for the production of plastics. However, an exciting development that has occurred over the past few years is the rising utilization of oilseeds as a source for plastics. Figure 2 shows the average production of vegetable oils worldwide, and that projected for the near future. It is clear that vegetable oil production is on the increase.
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The exploitation of soybean oil for new industrial purposes has by far outstripped the similar utilization of canola and flaxseed oils (the majority of flaxseed oil that is processed in Canada goes towards industrial usage, particularly as a drying oil in paints, varnishes, etc.). However, this article also reports on work with canola and flaxseed oils that is taking place at the University of Alberta. More on these efforts appear below.
Canola is Canada's predominant oilseed crop. Saskatchewan produces approximately 50 percent of Canada's canola production, with Alberta and Manitoba also being major production regions. Canada produces approximately 20 percent of the world's edible oil supply. Net revenues per acre is the single largest factor in determining the amount of canola grown in Canada's western provinces, and canola prices are at the mercy of a marketplace which is governed by world oilseed prices. Major increases in soybean oil production in Brazil and China, as well as similar increases in palm oil production in Malaysia, have depressed overall price levels. Consequently, the relative profitability of canola production in Western Canada has been adversely affected, resulting in significant reduction in canola production acreage since 2000. In a report prepared by the Alberta BioPlastics Network, an analysis of the 2002 canola area grown relative to the highest number of hectares grown within the previous 10 years suggests that Western Canada could easily produce an additional 3.987 million metric tonnes. Alberta alone could produce an additional 1.835 million metric tonnes.
Flaxseed is the first oilseed to be widely grown in Western Canada. An ancient crop with a wide variety of uses, flax production is small compared to canola in Western Canada, with 20 percent of the area devoted to growing canola being devoted to growing flax. In addition, although in Europe a major use of Flax is in the utilization of its fibres, in Western Canada, the varieties normally grown are the short fibre oilseed varieties. Manitoba and Saskatchewan are by far the largest producers of flaxseed in Canada, with Alberta being a very minor producer. In the same report prepared by the Alberta BioPlastics Network, the 10 year production history of flax in Western Canada illustrates that the current cropping system is capable of considerably more production than what was the case in 2002. If flax cultivation return to peak historical levels, the total additional capacity relative to 2002 production is an additional 345,005 tonnes.
What seems clear, however, from an analysis of the production patterns and pressures facing the Canadian oilseed industry, is that if a lucrative industrial alternative to edible utilization is developed, there is ample oilseed acreage that will be devoted to this demand. Clearly, increases in production of edible oils are not going to be fuelled by increases in the demand for edible oil, given the production capacity of countries like Brazil, China, Malaysia, and India. Furthermore, given the use of edible oils in vegetable shortenings and margarines, and growing concerns over both trans fatty acid content as well as with high-carbohydrate diets in North America, edible uses of vegetable oils are currently being threatened.
It is interesting to contemplate what our winter holidays would have been like if suddenly all of the items made from plastic were absent. For plastics are so ubiquitous in our environment, it is nearly impossible to find a room in everyday life, much less during the holiday season, where some form of plastic is not contained. If you are like me and have small children who absolutely love having a tree and presents under it to tear apart, then a plastic-free holiday season is a significant challenge (we have 3-year-old triplets--try telling them that this year morn and dad decided plastic is not earth-friendly). If you have an artificial tree, it is made almost entirely of plastic. 99 percent of most toys are plastic. The carpet on which the tree sits is plastic. A significant percentage of the clothes we wear is plastic. Most homes are made from upwards of 75 percent plastic material, etc. In fact, the world consumes approximately 180 million tons of plastics every year. This is a staggering amount, and to put it in context of the oil reserves that are used to make this amount of plastic, it takes approximately 141 MJ/kg of energy to produce Nylon and 76 MJ/kg of energy to produce amorphous PET, so that millions of tons of fossil fuels are required to make the 180 million tons of plastic annually--and this accounts only for the primary processing of the plastic, not for the millions of tons of fossil fuel that are used to further process the plastics into toys, Christmas trees, carpets, house siding, insulation, car panels, and a host of other commonplace items that we take for granted. Primary plastic production consumes approximately 4 percent of the global production of petroleum--2 percent as feedstock for actual plastic production, and 2 percent as the energy source to fuel the process. There exists wonderful market opportunity here! If Canada is able to manufacture plastics which are competitive on a performance, price, and biodegradability basis, there is a great opportunity to marry our petrochemical expertise with our agricultural expertise to create an industry of agricultural plastics. It is important for readers to understand that despite the size of the opportunity, the state of art for producing plastics from agricultural sources is not even close to being able to replace entirely the amount and range of plastics produced from petroleum--particularly from functionality and price perspectives. It is misleading to suggest that modern science has solved the problem of replacing polyethylene, with its various forms and their wide physical functionality, as it is to suggest that we are on the verge of replacing petroleum as a source for the range of modern plastics produced and utilized. The current solutions that have been offered up by researchers which can compete on a price and functionality basis represent an extremely small percentage of the volume of plastics produced annually. However, the opportunity does exist, is growing, and is increasingly being considered an alternative by petrochemical industries. For example, Dupont has indicated that they intend to derive 25 percent of their revenue from non-depletable resources by 2010. This goal will require that they search for novel and innovative methods that will produce chemicals that consumers demand from renewable resources. In addition to DuPont's goals, other chemical companies such as Dow, Cargill, BASF have initiated programs that will improve the sustainability of the chemicals industry.
Information from the American Plastics Council indicates that the overall production and sale of plastics within North America is in the order of 45 million tonnes. This may be broadly divided in to the sales shown in Table 1 below.
The opportunities for oil-based plastics lie mostly in the polyols and polyurethane segment of the market. This does not take into consideration the use of oils as drying oils, industrial solvents, biodiesel, etc. According to a market summary published by the United Soybean Board in February 2000, vegetable oil based polyurethanes are most suited to three markets: polyurethane foams, polyurethane binders, and agricultural film (the last not necessarily being a polyurethane). The total U.S. market size for polyurethane foams is currently approximately 3,000 million pounds, and for polyurethane binders and fillers, approximately 400 million pounds, per annum. Some of the more aggressive market segments include the transportation industry (automotive bumpers, moulded plastic parts like dashboards, etc.), packaging for both the food and retail industry, moulded plastic parts for appliances (including medical devices), the construction industry (with applications in insulation as well as in anything requiring rigid moulded plastic), in carpeting (applications include flexible foam carpet backing, and binders for carpet fibres), and applications related to tanks and pipes (insulation, sealants, etc.). Interesting work being done at the University of Alberta has also shown that elastomeric polyurethanes from vegetable oils may be suitable for medical and laboratory tubing, sealants, and other uses. The estimated market is believed to be greatly understated here, as only the areas where the market entrance should be relatively easy have been discussed.
Vegetable oil polyurethanes can also be used as a binder in fibre-reinforced composites. Utilization of fibre-reinforced, thermoset and thermoplastic, composites was 3.5 billion pounds in 1997. Vegetable oil derived binders would be suitable for thermoset resins, with major end markets in automotive panels and other moulded parts, deck planking and other construction uses such as laminates, etc.
Currently, agricultural film consists mainly of low-density polyethylene. The total world demand for agricultural film is approximately 1.3 billion pounds per annum. This is an area where biodegradability is very important: it has been estimated that the removal and disposal of agricultural film can be as much as $125 per acre.
In cases where, as in agricultural films, biodegradability is important, it is difficult to use traditional plastics derived from petroleum, although plastics such as polycaprolactone are biodegradable. It is often misconstrued, however, that plastics from renewable sources are always biodegradable. This is certainly not the case, and in many instances, the end use demands that the plastic is not naturally biodegradable. Automotive panelling or construction materials are end uses which require the materials not to naturally biodegrade. In fact, the biodegradable plastics market is relatively small, and many of the opportunities for plastics from renewable sources are in the non-biodegradable plastics sector.
In a report by the Alberta Bioplastics Network, the North American demand for biodegradable plastics in 2000 was estimated at 25 million pounds, and was forecasted to increase to 35 million pounds by 2005. The different market segments were loose fill packaging, compost bags, agricultural films, hygiene products, paper coatings, etc. In the same report, the medical plastics markets were estimated at 2 billion pounds in 2000, and was projected to increase at an annual rate of 6 percent to an estimated 2.6 billion pounds by the year 2006. It should be noted that in the case of the medical industry, in those instances where the plastic product must be discarded, biodegradability is required, but only on a "triggered" basis--that is, one does not want ones medical tubing to begin deteriorating while it is in use. In instances like these, polyurethanes from vegetable oils are well suited as an ingredient, for they are biodegradable once they are "triggered."
The use of vegetable oils such as linseed (flaxseed), tung, lunaria, lesquerella, crambe, rapeseed, castor, veronia, etc., to produce polymers is not new. Plastics are created from these oils by exploiting naturally-occurring epoxide, hydroxyl, and double bond functionality. In cases where hydroxyl and epoxide functionality is required, the double bond has been exploited as a reactive site for chemical reactions to produce such functional groups.
Among the oils that are exploited as drying oils due to their carbon-carbon double bond functionality, linseed and tung are the most significant. These oils are used mostly in paints and coatings, as well as in inks and resins. They have iodine values greater than or equal to 150. Soybean oil, sunflower oil and canola oil are semi-drying oils with iodine values between 110 and 150. The major constituents of linseed oil are linolenic acid, linoleic acid and oleic acid. The major constituent of tung oil is eleostearic acid, oleic acid, and linoleic acid. The structures of these major fatty acids of tung and linseed oils are shown in Figure 3.
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The drying power of these oils are directly related to the chemical reactivity conferred on the triglyceride molecules by the carbon-carbon double bonds of the unsaturated acids, which allows them to react with atmospheric oxygen, thus leading to the process of polymerization to form a network. Linseed oil is a non-conjugated oil, rich in polyunsaturated fatty acids (approximate linolenic acid content of 60 percent). These polyunsaturated fatty acids contain double bonds separated by at least two single bonds. These oils dry via a process of autoxidation followed by polymerization. A summary of this is shown in Figure 4.
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For tung oil, with mostly conjugated double bonds from eleostearic acid (~ 77-82 percent eleostearic acid), the rate of autoxidation is much higher than that observed in linolenic acid, due to the conjugation. As a result, the polymerization products from tung oil are highly resistant to water and alkalis, and it dries so rapidly that often a highly wrinkled surface is developed in a short amount of time. Figure 5 shows the relative rate of the drying process for non-conjugated oils.
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Some vegetable oils contain naturally occurring specialized functional groups, such as epoxy and hydroxyl groups, which make them candidates for cross-linking with various chemical cross-linkers, to form polymeric networks. Castor oil and lesquerella oil (also called pop weed) contain hydroxyl groups in addition to double bonds. Veronia oil contains naturally occurring epoxide functional groups. The structures of the dominant fatty acids of castor, lesquerella, and veronia are shown in Figure 6. Triacylglycerides of ricinoleic and lesquerellic acid both contain three hydroxyl functional groups, and are therefore referred to as triols. The presence of these hydroxyl groups permits cross-linking with such chemical cross-linkers as sebacic acid to form polyesters, or with diisocyanates to form polyurethanes. The epoxide functional group in veronia oil is typically cross-linked with such dibasic acids as sebacic acid, to form crosslinked polyesters. These groups can also be reacted with various acrylic acids in the presence of a tertiary amine, to create a variety of acrylates, the resulting ester being highly UV active, and therefore easily polymerized through acrylate vinyl moieties.
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In cases where hydroxyl and epoxide functionality do not naturally exist, but are desired, these functional groups can be created by exploiting the existence of double bond functionality. The double bonds can easily be epoxidized, and if hydroxyl groups are required, the epoxidation procedure is usually followed by alcoholysis to form the polyols. Alternatively, the double bonds can be first converted to aldehydes by hydroformylation with either rhodium or cobalt as the catalyst, followed by hydrogenation to hydroxyl groups by hydrogenation with nickel. An example of the double bonds in a soybean oil triacylglyceride being converted to hydroxyl groups is shown in Figure 7.
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Research conducted at the University of Alberta has produced a number of elastomer and flexible, semi-rigid and rigid foams from canola and flaxseed oils. This research was performed by the Alberta BioPlastics Network ,and significant efforts are currently underway to commercialize the technology that has been created.
Table 1 Resin Millions of tonnes sold in 2001 PP (Polypropylene) 7.5 PVC (Polyvinyl Chloride) 6.7 HDPE (High Density Polyethylene) 5.1 LLPDE (Linear Low Density Polyethylene) 4.9 LDPE (Low Density Polyethylene) 3.5 Total Thermosets: 3.4 Thermoplastic Polyester 3.2 Other Styrenics, Nylon, Polysuphone 4.4 All others (includes polyurethanes, 5.8 polyols, isocyanates) Total 44.6
The author would like to thank AVAC Ltd., the Alberta Crop Industry Development Fund, the Alberta Agricultural Research Institute, the Agriculture and Food Council, the Alberta Canola Producers Commission, and NSERC, for financial support for the Alberta BioPlastics Network's research into vegetable oil based plastics. Peter Sporns' assistance in creating the chemical structures and in proofreading this manuscript is also gratefully acknowledged.
Market Opportunity Summary, Soy-based Plastics, February 2000, United Soybean Board.
Lynn Crandall, Bioplastics: A burgeoning industry, Inform, 13, 626-628, 2003.
"Biodegradable Polymers from BASF," a presentation on November 29, 2002, by Scherzer, Freyer, and Kunkel, BASF Plant, Mannheim, Germany.
Assessment of Western oilseeds as a feedstock for a bioplastics industry, Jerry Bouma, Alberta BioPlastics Network, May 2003.
Dharma Kodali, Biobased Lubricants, Inform, 14, 121-123, 2003
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To learn more about Dupont's plans to utilize non-depletable resources, visit the discussion entitled, "Sustainability and Integrated Science for the 21st Century" at www.dupont.com/NASApp/dpuontglobal/ corp/index.jsp?page = /content/US/en_US/ news/releases/2003/nr02_17_03.html.
The Alberta BioPlastics Network (ABN) is a multi-institutional research network. Its mandate is to engage in activties to promote the use of Alberta's agricultural commodities as feedstock for the production of specialty chemicals and polymers, and significant efforts are currently underway to commercialize the technology that has been created.
The institutions that participate in the ABN are:
University of Alberta
Alberta Agriculture, Food and Rural Development
Alberta Research Council
Agriculture and Agri-Food Canada
Alberta Economic Development Environment Canada
Alberta Canola Producers Commission
For a full list of the members of the network, or for additional information, please contact business manager Rekha Singh at the Alberta Bioplastics Network, 410 Agriculture Forestry Centre, Agri-Food Materials Science Centre, University of Alberta. Edmonton, AB T6G 2P5. Or call 780-492-9081, or email@example.com.
Suresh S. Narine of the University of Alberta is the director of the Alberta Bioplastics Network and chair of the Fundamental Science focus area.
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|Comment:||Seeds of change: the growing trend of producing biodegradable polymers from oilseed crops.|
|Author:||Narine, Suresh S.|
|Publication:||Canadian Chemical News|
|Date:||Jan 1, 2004|
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