Most people associate crops in farmers\u2019 fields with food production. What they don\u2019t realize is that those plants, or at least some parts of them, could one day be incorporated into their cars, tennis rackets or shoes.<\/p>\n
Biocomposite materials made from natural fibers and\/or bio-based resins are making inroads into markets ranging from automotive and building materials to clothing and sporting goods. According to Lucintel, the global biocomposites market should grow by 7.9 percent from 2018 through 2023, reaching an estimated $7.6 billion in value.<\/p>\n
In Europe, biocomposites made their first appearances in 1972, when Fiat introduced a 50 percent wood\/50 percent polypropylene \u201cwoodstock\u201d material into its vehicles. This material is still used successfully in different markets.<\/p>\n
Some European automotive manufacturers today use components that contain as much as 70 percent natural fibers like kenaf or hemp and only 30 percent oil-based resin. \u201cYou can have savings on the CO2 footprint and have very good technical properties, and at the same time the material is very lightweight,\u201d says Asta Partanen, who specializes in bio-based materials and composites at Germany\u2019s nova-Institute, a consulting organization with a focus on the bio and CO2-based economy.<\/p>\n
Biopolymers used in European composite production include bio-polyethylene (bio-PE), polyactic acid (PLA) and bio-based polybutylene succinate (PBS). Natural fibers are derived from many sources, including wood, cork, linen, flax, hemp, bamboo and sunflower shells.<\/p>\n
The benefits of using natural fibers for composites begin with their optical and haptic properties, according to Partanen. Natural materials allow composites to cool much sooner, reducing the cycle time in injection molding.<\/p>\n
In general, natural fibers can\u2019t achieve the strength of carbon fiber composites and they don\u2019t have the same tensile or impact strength as GFRP. \u201cBut they may have different properties that are important in the differentiation of products from standard plastic products. It\u2019s always a matter of application,\u201d says Partanen. Natural fiber composites are a better environmental choice than GFRP because they have a 20 to 50 percent lower carbon footprint.<\/p>\n
Working with Biofibers<\/p>\n
In Canada, the Composites Innovation Centre (CIC) in Winnipeg, Manitoba, helps composites manufacturers incorporate biofibers into their products. \u201cWe\u2019re trying to address some of the technology gaps and hurdles that our clients and industry are facing,\u201d says Lin-P\u2019ing Choo-Smith, vice president of CIC\u2019s biomaterials program.<\/p>\n
To minimize the adjustments that composites manufacturers must make to use natural fibers, the CIC primarily uses traditional industry resins, processes and equipment in its research. \u201cIf [manufacturers] have to change too many things, it becomes a barrier,\u201d says Choo-Smith.<\/p>\n
The first step is finding the right fibers. For composites taking on structural loads, \u201cwe want fibers on the longer side (i.e. high aspect ratio of fiber length to diameter) with good chemical properties and tensile strength,\u201d says Choo-Smith. \u201cWe tend to focus on flax and hemp because they fit these requirements, grow well in our prairie regions, and we have a good amount of it.\u201d<\/p>\n
In choosing a fiber, CIC staff look at how well a plant goes through the decortication process, which separates the fibers from the hurd (the woody or pulpy matter of the plant). Fibers with more hurd can\u2019t be used for higher end applications like textiles. CIC tests the fiber\u2019s tensile strength, its moisture uptake and its behavior with various resins. \u201cIf there is a nice affinity between resin and fiber, then there is a good chance that it will stick well to the fiber, which is known as wet-out,\u201d says Choo-Smith. \u201cIf it doesn\u2019t, we may need to treat the fiber with chemicals to change the surface properties.\u201d<\/p>\n
One benefit of biofibers is that they come from a renewable resource, but that also makes them more heterogeneous in the way that they behave. Synthetic fibers produced in a factory are very consistent. But bio-based fibers may change with growing conditions; if there\u2019s more or less rain in the summer, what happens to the quality of the product? Choo-Smith notes that winemakers have overcome a similar dilemma by blending various harvests, and the same could be done with biofibers.<\/p>\n
CIC staff hope to provide an economic boost to rural communities by making better use of the parts of crops that are otherwise composted or burned. But the conditions ideal for food production may not be the best for producing composite fibers. For example, spacing flax plants close together results in narrower stems and finer fibers, which is ideal for some end-use applications in composites. But farmers prefer wider spacing, since they produce more seed that way. If the demand for biocomposites grows and the economics are right, farmers may be willing to adjust their growing patterns to the industry\u2019s needs.<\/p>\n
Resins from Plants<\/p>\n
Dixie Chemical of Pasadena, Texas, has been working with bio-based materials for their resins since 2011. Alejandrina Campanella, the company\u2019s thermoset and bio-based material platform leader, says it\u2019s easier to work with plant oils, which are fairly consistent in their performance, than with biofibers, which can vary with environmental conditions.<\/p>\n
Dixie currently produces two lines of bioresins; MAESO, derived from soybean oil, and MAELO, from linseed oil feedstocks. Like typical unsaturated polyester resins, they contain a reactive diluent such as styrene or vinyl toluene. However, Dixie also makes a methacrylated fatty acid (MFA) derived from palm, coconut and soybean oils, which can be used to replace all or some of the styrene or vinyl toluene. Using MFA reduces emissions and odors in the manufacturing process, and the MFA resins are tougher and less brittle than those made with styrene.<\/p>\n
\u201cWe\u2019re also working on a toughener made with soybean oil, which can be used for epoxies, vinyl ester and polyester resins. When we\u2019ve compared it to products that are currently available in the market, it appears to have similar properties. This could have a really big impact,\u201d says Campanella.<\/p>\n
In most cases the processes for manufacturing bio-based composites are no different than those for oil-based composites. \u201cYou may have to optimize your formulation, but that also happens if you\u2019re using a resin made from oil,\u201d says Campanella. Dixie generally sticks with palm oil, soybean oil and linseed oil or their fatty acids because of their pricing and availability.<\/p>\n
Much of the interest in bio-based composites comes from the transportation industry, says Campanella. Ford, BMW, Mercedes Benz and Jaguar all have interior products made with biocomposites, ranging from seat backs and door panels to carpeting and insulation. There are biocomposites in many sporting goods, including tennis rackets, snowboards and bicycles. In the construction industry, windows, doors, insulation and other building products have all been made with bioresins and\/or natural fibers.<\/p>\n
Recycling Potential<\/p>\n
Megan Robertson, associate professor in the department of chemical and biomolecular engineering at the University of Houston, is researching several aspects of bio-based resins. Her research group initially tried replacing Bisphenol A (BPA) in epoxy resins with readily-available vegetable oils, but the resulting composites did not have the necessary strength or thermal properties.<\/p>\n
They then tried bio-based phenolic acids derived from fruits and vegetables. \u201cThey have very similar functionality and similar chemical structures to BPA, which can impart desirable physical properties to the resin,\u201d says Robertson. The problem is that bio-based phenolic acids aren\u2019t currently obtainable in large volumes. More recently the researchers have focused on epoxies made from the more widely available lignin-based feedstocks. Resins made with lignin-derived molecules could have commercial potential in the shorter term.<\/p>\n
Robertson is also researching bioresins and composite recyclability. Current recycling processes, based primarily on thermally treating the materials, work only with thermoplastics. Recent advances in the chemical recycling of polymers, which breaks the plastic down into monomers so the materials can be repolymerized, hold some promise for thermosets.<\/p>\n
Since the esters in bio-based resins can undergo chemical degradation reactions like hydrolysis, \u201cour hypothesis was that if we can distribute those ester linkages throughout the epoxy resin network, we can make a network that can be degraded under the right conditions,\u201d says Robertson.<\/p>\n
Researchers tested two epoxy resins \u2013 one a soybean oil-based and the other made with BPA \u2013 in a solution with a very high pH, which accelerates hydrolytic degradation. \u201cWe found that if we put a traditional epoxy resin through this process, even after three months we found no noticeable change in the mass,\u201d explains Robertson.<\/p>\n
The test with the bio-based resin was more promising. \u201cThe soybean-oil based epoxy resin degraded within two weeks; the solid mass completely disappeared,\u201d she adds. Other bio-based epoxies, which also contain high concentrations of esters, have reacted to the solution the same way. The challenge will be to make a thermoset that could maintain the desired properties in applications, but that could be broken down after it reaches the end of its useful life.<\/p>\n
The Case for Bio<\/p>\n
Deborah Mielewski, Ford\u2019s senior technical leader for materials sustainability, has worked for decades trying to get more bio and recycled materials into the company\u2019s vehicles. One of her first victories came in 2008, when Ford introduced seats for its Mustang that contained foam made from soybean oil. A few years later the company added composite storage bins made with wheat stalk fibers into its Flex SUV, reducing its annual petroleum usage by 20,000 pounds and CO2 emissions by 30,000 pounds.<\/p>\n
The wheat straw bin, developed by the Ontario BioCar project, helped focus Mielewski\u2019s team on the benefits of incorporating agricultural waste fibers into composites. \u201cThey are lighter in weight than the glass fiber and the talc that we currently put in. So, if we\u2019re worried about fuel economy, here\u2019s a way to lightweight and use something that you would otherwise burn or landfill,\u201d says Mielewski.<\/p>\n
A good example of this approach is the incorporation of pulp from Weyerhaeuser\u2019s lumber operations into the Lincoln MKX\u2019s composite armrest. \u201cThe pulp industry is struggling in this country because China is producing paper at a very low cost. So, putting pulp in a high-end composite was very attractive to Weyerhaeuser,\u201d says Mielewski.<\/p>\n
She\u2019s grown used to skepticism when she proposes using natural fibers for various vehicle components. \u201cPeople said, \u2018You can\u2019t put soy oil in and make a good foam.\u2019 Well, you couldn\u2019t just drop it in and make a good foam; it took some work,\u201d she explains. \u201cBut the chemistry can be rebalanced, and you can incorporate hydroxylated soy bean oil into the foam. We do it in every single North American-built vehicle now, and many other industries do it, too.\u201d<\/p>\n
One problem is that people don\u2019t think of green solutions as technical solutions. \u201cThey put biofiber materials in the green box, and they\u2019re only in the green box,\u201d she says. \u201cWhen you say lightweight, everyone goes directly to carbon fibers.\u201d While there is more weight savings with carbon fiber, natural fibers offer both the environmental benefits and the opportunity to work with other industries to provide a revenue stream for them.<\/p>\n
Another benefit to natural fibers is that unlike glass fibers they don\u2019t break during injection molding. \u201cNatural fibers tend to flow and bend and fill all the cracks and crevices where glass fiber does not make its way,\u201d Mielewski says. In addition, glass fibers are less conducive to anisotropy (orientation in all directions) than natural fibers.<\/p>\n
\u201cIf our engineers got used to designing with natural fibers they would love it, because they wouldn\u2019t have to worry about all the directional shrinkage and directional reinforcement,\u201d Mielewski explains.<\/p>\n
Ford is currently developing a console for the Lincoln MKX that will incorporate both pulp and glass fibers into the composite, and Mielewski hopes that designers will use more biofibers as they learn more about them.<\/p>\n
Mielewski\u2019s group is currently studying bamboo for composite fibers and algae oil for resins. They\u2019re also working with Mexican tequila producer Jose Cuervo to develop applications for composites made with fibers from agave, which is used in tequila production. Since Ford has three assembly plants in Mexico, this research fits well with the company\u2019s efforts to convert local waste streams into sources of revenue for residents.<\/p>\n
The challenge is developing the supply chain to deliver a steady stream of the agave material. Someone must be willing to harvest the fiber, dry it, chop it and compound it into plastics so that it\u2019s commercially available to use for vehicles. The problems involved in setting up such supply chains have been an important part of the learning curve in working with biocomposites, admits Mielewski.<\/p>\n
Encouraging Adoption<\/p>\n
Building a supply chain is just one barrier to biocomposites going mainstream. When oil prices are relatively low, as they are today, there\u2019s less economic incentive for companies to use biomaterials. In addition, companies happy with their current composites may be reluctant to make formulation changes and go through the rigorous testing procedures required to make the switch, observes Campanella.
\nFord-armrest<\/p>\n
The armrest in Ford\u2019s Lincoln MKX is made from cellulose tree fibers, which were used to replace glass-filled plastic. The biofiber armrest weighs about 10 percent less than the earlier version and is produced 30 percent faster. Photo Credit: Ford Motor Company<\/p>\n
At Ford, Mielewski hopes to overcome this reluctance by working with upper management on a company-wide policy that requires the use of biomaterials and recycled materials. Partanen thinks the outlook for biomaterials would improve if they received the same kind of government support that biofuels have been given.<\/p>\n
Nevertheless, Campanella remains optimistic about the long-term outlook for biocomposites. \u201cWe think there will be a lot of opportunity in a few years, and we have to be prepared,\u201d she says.<\/p>\n
\u201cWe cannot depend upon a continuous stream of petroleum. No matter how you slice it, that is a limited resource,\u201d adds Mielewski. It\u2019s time to give robust, high-performance biocomposites the attention they deserve. \u201cThey are lighter, better for the planet, they produce less pollution and less landfill,\u201d she says. \u201cThey have a lot of really positive aspects to them.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"
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