Position: Jean & Douglas McLean Professor in Fiber Science & Apparel Design
Institution: Cornell University
Further information:
We have many sustainable energy resources in solar, wind, geothermal, and hydro. But what sustainable sources do we have for materials other than plants, asks pioneer of green composites Anil N. Netravali?
Polymers and plastics occupy every part of our lives; so much so that we cannot live without them. Reinforcing these materials with fibers creates composites with a range of excellent properties such as high strength and light weight, which can be engineered into three-dimensions components for many applications from aerospace to sports gear, and automotive parts to building materials. But producing plastic-based reinforced composites from sustainable resources that can be disposed of at the end of their useful life without harming the environment remains a challenge.
Netravali has been researching alternative ‘fully green’ composites for nearly 20 years at Cornell University. His interest was sparked while working on fibers at Cornell, following his PhD at North Carolina State University.
Anil Netravali talked to Materials Today/Reinforced Plastics about his current research and the future of green composites.
What are the major themes of your current research?
The major part of my current research relates to developing green materials and technologies/processes. Within the ‘materials’ category, one particular area is the development of fully sustainable plant-based green resins and composites. At the end of their life, these materials can be easily composted without harming the environment. We have developed various ways to improve the properties of green resins and composites so they can replace petroleum-based conventional polymers and composites that are prevalent today in many applications. We have made good progress in making high-strength composites that we call ‘advanced green composites’. We have also developed fire-resistant, protein-based green composites. At present, we are working on self-healing green composites that can extend their useful life.
We are also looking at green technologies for other applications. For example, we have developed a green technology that produces hydrophobic and ultra-hydrophobic cellulose fibers and fabrics (which are inherently hydrophilic). The same technology can be used to surface-modify cellulose nano-fibrils or bacterial cellulose to ease dispersion in plastics such as PLA, which these fibers are used for reinforcement. Such nanocomposites can also be transparent and potentially suitable as replacement for heavier glass. We have also developed other green technologies for making anti-wrinkle cotton and stronger wool fibers.
How and why did you come to work in these areas?
My PhD consisted of two projects. One, supported by NASA, studied the effects of high-energy radiation, while the other Navy-supported project looked at the long-term effects of water exposure on carbon/epoxy composites. Because of my strong interest, I continued the research on composites and fiber/resin interfaces when I joined Cornell University in 1984 as an assistant professor of fiber science.
In around 1992-93, however, I started thinking ‘What happens to all these composites at the end of their life?’ The answer was simple… Most end up in landfills. Unfortunately, we still do not have an environment-friendly solution for this problem. Furthermore, most conventional polymers are derived from petroleum, which we all know will not last forever. These composites also use many chemicals that are toxic to humans. These issues motivated me to start researching ‘fully green’ composites that use both resins and fibers derived from sustainable plants and can be easily disposed of or composted at the end of their life. I do not recall anyone, that I was aware of, working in this area at that time. Fortunately, the scenario has changed dramatically in the last two decades. Now we have many groups worldwide working in this area. In fact, ‘green’ and ‘sustainability’ have become buzzwords! I am, of course, very pleased about this change.
What do you think has been your most influential work to date?
Our development of advanced green composites with high strength and toughness is perhaps at the top of my list. For these composites, we used liquid crystalline cellulose (LCC) fibers (developed at Groningen University) that have excellent strength. However, we have been able to enhance the tensile properties of LCC fibers significantly using chemical, mechanical, and thermal treatments that increase both crystallinity and molecular orientation of the fibers. After treatment, the strength of these fibers is close to 2 GPa, which is the highest for any cellulose fibers. High-strength advanced green composites made using enhanced LCC fibers and soy protein or starch-based resins are suitable for use in primary structural applications.
We are also able to orient bacterial cellulose (BC) nanofibers, which have excellent tensile properties, using templates that restrict movement of the bacteria. If these fibers can be fully oriented, which we continuing our efforts to achieve, it should result in excellent composite properties… comparable to those based on Kevlar®.
What is the relevance of your research to fiber-reinforced composites?
Green composites made using plant-based fibers, such as jute and kenaf, with plant protein and starch-based resins are already being made. These composites can be 5-6 times stronger than wood-based products such as particleboard and plywood. At Cornell, we have built shelving, cabinetry, and doors from green composites made using our technology. LCC fibers used in advanced green composites are yet to be commercially manufactured, however, but once they are I see many applications including lightweight automobile parts. At the end of their life, these composites do not have to go into landfill but can be composted.
What have been the most major developments in this field over the past decade in your opinion?
We started our research into green composites over two decades ago. Our efforts to improve the properties of protein- and starch-based resins have developed various green technologies for crosslinking. In the past decade, we have diversified our research by using some of these technologies for other applications. For example, we have used green technology to obtain ultrahydrophobic as well as anti-wrinkle cellulose (cotton, viscose, etc.), for which many applications can be envisaged. We also our use green crosslinker technology for hair stabilizing, which could make a significant impact on hair straightening treatments that currently rely on formaldehyde. Our green crosslinker could be a much healthier solution for those working in salons breathing formaldehyde for many hours a day, which can cause major pulmonary and other health issues.
Where do you see this area of research going in the future?
There is great research going on around the world in green materials and technologies. Perhaps because it has become obvious that we have no alternative! Companies have realized that petroleum is not going to last long and they must develop sustainable sources to survive. Brazilian petrochemical company Braskem, for example, has already developed plant-derived polyethylene and polypropylene.
I expect research to accelerate in the coming years and decades to develop materials from plants that will completely replace the petroleum-based materials of today. This will be a paradigm shift away from the ‘petroleum refinery’ towards the ‘biorefinery’. I expect many commercial products will come onto the market in the next 10-20 years.
I believe the first effort should be to develop green composites, with properties better than wood, made from inexpensive waste sources to make commercialization easier. In the next 5 years or so I would like to get green composites fully commercialized.
What specific questions or problems do you hope to tackle in the future?
We are currently developing self-healing green composites, but much work needs to be done. In addition, our transparent green composites based on nanocellulose or BC on could be used in place of glass in automobile and housing applications in the future.
Our other efforts are devoted to utilizing various plant and food processing wastes to develop value-added resins and composites. This would also serve to reduce the amount of waste going to landfill. We have also begun research to use a combination of cellulose materials to obtain ‘greener’ cement with improved strength and toughness.
What factors do you believe will be key to the success of the field in the future?
More research funding will always be useful and would increase the success rate of green composites.
Stricter government regulations to encourage the use of biobased, sustainable products and reduce pollution would help accelerate research towards greener solutions. For example, California is banning the use of formaldehyde-based wood products such as particleboard, plywood, and MDF. Green composites would get boost from such actions.
Commercialization can also be a problem. One example of this, from my work, is LCC fibers that could have many applications, not just in automobiles, aviation, and sports but also in high-quality apparel. But, perhaps because these fibers are expensive to make, they have not been commercially exploited yet. Universities that license their technologies could set a timeline for the licensee to commercialize the products. Government, for their part, could direct funding agencies to incentivize grant-holders, universities and research centers, to commercialize the outcomes of their research.
But I believe industry is searching for green solutions. Most companies look at the cutting-edge research being conducted at universities and research centers. However, developing products that are not just green but are also inexpensive is key for success.
How do you believe research could impact on real-life applications in the future?
Research can be broadly defined as ‘looking for or developing new and novel materials that do not exist now’. Developing plant-based green and sustainable polymers to replace the entire range of conventional polymers would be wonderful.
I find younger generation very much interested in such transformation. I have seen a sea change between undergraduate and graduate students 20 years ago and now. Students are more informed about sustainability issues and are very keen to get involved in research related to green materials.
Wouldn’t it be nice to have a Boeing or Airbus aircraft made from green materials? Small experimental aircraft have already been manufactured using natural fibers. So that day may not be too far away! Overall, I am very hopeful that research in green materials is making big strides and will continue to develop at faster pace in the coming years.
Key publications
- N. Netravali, (Ed.), Advanced Green Composites, Scrivener Publishing, Beverly, MA jointly with Wiley, Hoboken, NJ (2018).
- N. Netravali and K. L. Mittal, (Eds.), Interface/Interphase in Polymer Nanocomposites, Scrivener Publishing, Beverly, MA jointly with Wiley, Hoboken, NJ (2017).
- M. M. Rahman, A. N. Netravali. Advanced Green Composites using Liquid Crystalline Cellulose Fibers and Waxy Maize Starch Based Resin. Composites Science & Technology (2018), DOI: 10.1016/j.compscitech.2018.04.023. https://doi.org/10.1016/j.compscitech.2018.04.023
- J. R. Kim, A. N. Netravali. Self-Healing Properties of Protein Resin with Soy Protein Isolate-Loaded Poly(D,L-lactide-co-glycolide) Microcapsules. Advanced Functional Materials 26 (2016) 4786-4796. https://doi.org/10.1002/adfm.201600465
- N. V. Patil, A. N. Netravali. Microfibrillated Cellulose reinforced Non-Edible Starch-based Thermoset Biocomposites. J. Appl. Polym. Sci. 133 (2016) 1-12. https://doi.org/10.1002/app.43803
- Y. Zhong, A. N. Netravali. Green Surface Treatment for Water Repellant Cotton Fabrics. Surface Innovations 4 (2016) 3-13. https://doi.org/10.1680/jsuin.15.00022
- J. Hoiby, A. N. Netravali. Can we build with plants? Cabin construction with Green Composites. Journal of Renewable Materials 3 (2015) 244-258. https://doi.org/10.7569/JRM.2015.634110
- M. M. Rahman, A. N. Netravali, B. Tiimob, V. K. Rangari. Bio-derived ‘green’ composite from soy protein and eggshell nanopowder. ACS Sustainable Chemistry and Engineering 2 (2014) 2329–2337. https://doi.org/10.1021/sc5003193
- T. Ghosh-Dastidar, A. N. Netravali. Novel Thermosetting Resin from Soy Flour Crosslinked using Green Technology. Green Chemistry 15 (2013) 3243-3251. https://doi.org/10.1039/C3GC40887F
- R. Nakamura, A. N. Netravali, A. B. Morgan, M. R. Nyden, J. W. Gilman. Effect of Halloysite Nanotubes on Mechanical Properties and Flammability of Soy Protein based Green Composites. Fire and Materials 90 (2013) 75–90. https://doi.org/10.1002/fam.2113
