Biocomposites
Green composites: The coming New Age www.human.cornell.edu/bio.cfm?netid=ann2
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ast few decades have seen significant growth in the use of high strength fiber reinforced composites fabricated using carbon, aramid and glass fibers and reins such as expoxy, unsaturated polyester or polyurethanes. However, both fibers and resins used in these composites are made using petroleum, a non-sustainable raw material. In addition, most commercial composites are also non-degradable. This poses a serious disposal problem. While there are some efforts to solve the disposability issues through incineration (to recover energy), recycling (grinding into powder for use as filler) or reclaiming fibers (for secondary applications), we are still far away from having an eco-friendly end-of-life solution. Over 90% of the composites, at present, end up in landfills after their intended life. With ever-growing use of composites the end-of-life issue is only expected to get bigger and increasingly difficult and expensive.
Greener Composites Significant research conducted in greening of plastics and composites has led to the development of new generations of plastics and composites that are not only derived from sustainable plant-based resources but are fully biodegradable. As a result, many plant-based fibers such as ramie, sisal, hemp, flax, jute, bamboo, sugarcane bagasse and others are increasingly being used with non-degradable resins such as polypropylene (PP), nylons, polyesters, etc., to form composites that may be called greener composites.
Green Composites Research is also being conducted to develop fully green composites that combine biodegradable fibers and sustainably derived resins such as polylactic acid (PLA), polyhydroxyalkanoates (PHAs) and their copolymers, polybutylene succinate (PBS), etc., as well as those derived from plant-based starches, proteins and lipids or oils. Composites based on crosslinked oils (non-degradable), being inexpensive, have hit the markets, e.g. for parts of John Deere tractors.
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bioplastics MAGAZINE [04/14] Vol. 9
John Deere 6M Series Tractors (Photo: Courtesy John Deere)
Advanced Green Composites A new process to produce high strength liquid crystalline cellulose (LCC) fibers developed at the Groningen University (The Netherlands) has opened up the possibility to make high strength green composites by combining them with biodegradable resins. The LCC fibers have high stiffness (over 40 GPa) and strength (over 1.7 GPa). Being in continuous form conventional fiber placing machines can be easily used for these fibers. Composites made using the LCC fibers and soy protein based resins have been shown to possess excellent strength and toughness to be termed as ‘Advanced Green Composites’. LCC fibers treated by KOH (potassium hydroxide) solution, a process similar to mercerization used for cotton fibers, under tension have shown to significantly improve their strength and modulus by increasing fiber molecular orientation and crystallinity and thus increasing the composite properties further. For example, composites of LCC fibers (41.5% by wt) made with soy protein based resins resulted in strength of over 625 MPa. With fiber volume of 65%, which is common for most composites, the estimated strength of these advanced green composites was over 1 GPa. Interestingly the toughness of such composites was comparable to those based on Kevlar® fibers which are commonly used for ballistic applications. We can expect many such new developments which are at the research stage to come to market in the near future. These fully sustainable green composites, while easily protected during their use, can be biodegraded or composted at the end of their life and hence nothing has to go to the landfills. In fact, when composted, these composites can complete the nature’s intended carbon cycle. Sustainability, green chemistry, cradle-to-cradle design, industrial ecology, etc. are not just newly coined words but have become the guiding principles for the development of new generation of green materials. Composites are no exception to this new paradigm. As major manufacturers embrace these developments, the green composites can only be expected to play a major role in greening the future products. MT