By Scott Kriner, Green Metal Consulting
There is growing interest in using green chemistry to avoid hazardous chemicals of concern. This was a theme in a recent webinar series conducted by the Green Science Policy organization. Green Science can be defined as “the design of chemical products and processes that reduce or eliminate the use and/or generation of hazardous substances”. According to the Green Science Policy organization, the 12 principles of Green Chemistry are as follows:
1) Prevent waste
2) Maximize atom economy
3) Design less hazardous chemical syntheses
4) Design safer chemicals and products
5) Use safer solvents and reaction conditions
6) Increase energy efficiency
7) Use renewable feedstocks
8) Avoid chemical derivatives
9) Use catalysts, not stoichiometric reagents
10) Design chemicals and products that degrade after use
11) Analyze in real time to prevent pollution
12) Minimize the potential for accidents
In the webinar series we were reminded that humans have sometimes advanced themselves at the expense of nature. For example, we have harnessed the energy of the atom, created molecules that never existed in nature, and discovered how to use petroleum for energy and for many types of products used every day. So it was no surprise to hear in each of the webinars, the question as to whether we really need to use certain chemical compounds, substances and metals in the products that we manufacture.
One example cited was based on the solvents, resins and other components in paint systems. The images of a peacock tail feather were used to point out how nature creates color without chemicals. The vivid colors of a peacock feather are not the result of chemicals or pigments. Instead, it is the unique structure of the feather which includes barbules which are strap-like twigs growing off the branches of the feather. The structure of the barbule arrays in the feather is measurably different for the different colored regions. According to research in Shanghai, these barbules contain nanoscale photonic lattices which create iridescence. English scientists Robert Hooke and Isaac Newton first observed this phenomenon of Structural Coloration and wave interference. Their discovery was further explained by Thomas Young a century later. Young correctly described iridescence as the result of interference between reflections from two (or more) surfaces of thin films. Those reflections are also combined with refraction as light enters and leaves such films. The geometry and the angles of the light are responsible for the different colors of the peacock’s tail feathers. This same effect is responsible for the iridescence seen on butterfly wings and in some plants.
Some articles suggest that the use of this type of structural coloration could have potential uses for industrial, commercial and military applications. Examples include surfaces that could provide brilliant colors, adaptive camouflage, efficient optical switches and low-reflectance glass. The webinar series challenged paint manufacturers to consider concepts like structural coloration to replace some conventional liquid paint ingredients.
This point in the webinar reminds us of the power of biomimicry. Biomimicry is “the imitation of the models, systems and elements of nature for the purpose of solving complex human problems”. We must remember that in nature there is no waste. The science of looking to nature for answers to mankind’s problems is nothing new.
So let’s look at some fun examples of how biomimicry has led us to new materials and products.
If you ever wondered how a Gecko holds on to surfaces, you only have to look at his foot pads and see how nature can make things sticky without applying chemical adhesives. A gecko has over 500,000 setae on each foot pad, and each setae is tipped with 100-1000 spatulae. The gecko can stick to surfaces through the use of van der Waal forces between the finely divided setae and a surface. This technology has already been used in the carpet industry.
Sharkskin has inspired new types of materials used in swimsuits. These materials were first introduced during the 2008 Summer Olympics. Scientists have found that sharkskin is made up of thousands of overlapping scales called dermal denticles (or "little skin teeth"). The denticles display grooves that are aligned with the flow of water over their surface. These grooves disrupt the formation of eddies, or turbulent swirls, which allows the water to pass by faster. Scientists also believe the roughness of these denticles can also discourage the growth of algae or barnacles.
Scientists have been able to replicate the shape and micro-roughness of dermal denticles in swimsuit material and also on the hull of boats. The improved efficiency in boats or ships is significant for cargo and container shipping where slight increases in efficiency can mean significant savings in fuel. Scientists are also applying the sharkskin technique in hospitals to create surfaces that can resist bacterial growth.
Scientists studying large termite dens have discovered that they are very comfortable places to live despite the harsh desert environment in which they are often found. Even with extreme swings in day and nighttime temperatures, the inside of a termite den often remains steady at 87 degrees. The explanation is the use of a natural cooling chimney and tunnels. Using those aspects in the dens, an architect in Harare, Zimbabwe applied the concepts to the 333,000 square-foot Eastgate Centre, which uses 90% less energy to heat and cool than traditional buildings. The building uses large chimneys that naturally draw in cool air at night to lower the temperature of the floor slabs. During the day, the slabs remain cool which reduces the air conditioning load.
Velcro is a widely known example of how biomimicry can use nature to solve problems. Velcro was invented by Swiss engineer George de Mestral in 1941. After a walk with his dog that took them through a burr patch, he returned and started the process of removing the burrs from the dog’s fur. In the process he examined the burs and noticed the small hooks on the end of the burr needles. From that discovery he created Velcro to hold things together.
Any traveler dreads the thought of bedbugs in their hotel room. Scientists have found a way to mimic a natural way to get rid of the bugs through their understanding of kidney bean leaves. The remedy has been used in Europe for centuries. Kidney bean leaves are strewn on the floor next to beds and they seem to snare the bed bugs in the evening. The bug-infested leaves are then removed and burned the next morning.
Researchers at the University of Kentucky found that the bedbugs are snared within seconds of walking on a kidney bean leaf. The scientists found that the leaf contains microscopic trichomes that impale the bedbugs by hooking their legs as they walk over the surface. Based on this finding scientists formulated a material that has similar microscopic features as the kidney bean leaves, in a similar fashion to the way Velcro mimics the hooks on burrs. This work could lead to a pesticide-free method to get the bugs before they get us while we sleep.
Whales power their movement in the water with their fins and a tail. In 2004, scientists at Duke University, West Chester University and the U.S. Naval Academy discovered that the bumps on the front edge of a whale fin greatly increase its efficiency by reducing drag by 32% and increasing lift by 8 %. With this information in hand, we are seeing wind turbine blade designers using the same type of profile on the leading edge of the blades. The result has been increases in the efficiency of turbines. The same discovery is helping cooling fans, airplane wings and propellers to change their conventional designs in order to boost efficiency.
The lotus flower has a micro-rough surface that naturally repels dust and dirt particles, keeping its petals clean. When viewed under a microscope the lotus leaves contain hundreds of tiny nail-like protuberances that tend to repel specks of dust. When water flows over a lotus leaf, it collects anything on the surface, leaving a clean surface behind. Ispo, a German company, spent four years researching this phenomenon and used the lessons from nature to develop a paint with similar properties. The micro-rough surface of the painted layer pushes away dust and dirt, diminishing the need to wash the surface. This has implications for maintenance of painted surfaces.
The Stenocara beetle lives in a harsh, dry desert environment and survives because of the unique design of its shell. The Stenocara's back is covered in small, smooth bumps that serve as collection points for condensed water or fog. The entire shell is covered in a slick wax and is channeled so that condensed water from morning fog is funneled into the beetle's mouth. Researchers at MIT have been able to use this type of design to develop a material that collects water from the air more efficiently than existing designs. Could this help in moisture management in the building envelope where we now struggle with the proper placement of air, water and vapor barriers to keep moisture out of buildings?
This bug’s larvae spin silk under water to create tubes for shelter. The silk remains sticky when wet, which is a rare quality for any type of adhesive. There is potential for this finding in the medical profession. Researchers believe that the silk could help to develop new medical adhesives that are able to stick to wet tissue or even glue together broken bones.
This bird’s nest is composed of mud fortified by sticks and fur. Scientists have observed the bird vibrating the mud as it dries, which apparently helps it cling to the other materials in the nest. As scientists were reviewing other construction materials, they felt that the use of vibration may be helpful to improve the features of quick-set concrete and other building construction materials.
If this insect explores areas for food but finds none it emits a chemical substance that signals to other ants that there is no reason to look in that same area. This concept has caught the attention of the agricultural industry. Scientists are suggesting that rather using pesticides on crops, a healthier and safer method may be to naturally steer pests away from food sources.
It is fascinating and fun to think about the potential of so many other products being inspired by nature and possibly manufactured using green chemistry. That thinking is behind the Biomimicry Institute that focuses on the advancement of nature-inspired products and systems. We are reminded that everything in nature is cycled and recycled through the ecosystem. Humans, however, too often use natural resources with a ‘cradle to grave’ rather than a 'cradle to cradle' mentality. Our waste often ends up in landfills or waterways. If we can find ways to use more natural resources in a more efficient manner and focus on the total life cycle of products, we can minimize our impact to the environment.