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New Fabric to Harness Energy from the Sun and the Wind
newsroundup.pngSeptember 27, 2016 | The Engineer

 

Researchers from Georgia Tech have developed a new fabric that combines solar cells with triboelectric nanogenerators. These nanogenerators have the capability to harvest power from physical motion, such as that which results from the wind blowing.

 

Tunable Chitin Films Developed from an Ionic Liquid Process

September 26, 2016 | Green Chemistry

 

Films with tunable properties made from chitin, one of the world’s most abundant polymers, have been developed through a collaboration of researchers in Alabama and Canada. The researchers believe these renewables-based films will have applications in packaging materials, biomedical devices, and absorbent materials.

 

Minimizing Waste in a Sonogashira Cross-Coupling Reaction

September 23, 2016 | ACS Sustainable Chemistry & Engineering

 

Researchers in Europe have developed a copper-free, heterogeneous catalytic system for the palladium-catalyzed Sonogashira cross-coupling reaction. The palladium catalyst is attached to a silica and polystyrene support, which avoids leaching of the metal into the product.

 

A Step Closer to Using Alane in Hydrogen Fuel Cells

September 23, 2016 | Phys.org

 

A more energy-efficient and less expensive method of producing alane, or aluminum trihydride, has been discovered by researchers at the U.S. Department of Energy’s Ames Laboratory along with other partners. While the technology is not ready for commercialization, it serves as a proof of concept that alane can be produced without tremendously high pressures of hydrogen gas.

Foam Infused with Spent Coffee Grounds Cleans Contaminated Water

September 21, 2016 | Laboratory Equipment

U.S. researchers have found a way to recycle spent coffee grounds into filters. These filters are capable of removing heavy metal contaminants from ground water.

 

Biobased Carbon Fiber Produced from Sugar

September 21, 2016 | The Daily Evergreen

Researchers at Washington State University are working on a way to convert agricultural and forestry sugar feedstock to polyacrylonitrile, which is used in the production of carbon fiber. “By utilizing a bio-based form like sugar rather than a petrochemical form, the cost of carbon fiber productions goes down and less greenhouse gasses will be released through the production process,” said Jinwen Zhang, associate professor with the School of Mechanical and Materials engineering.

 

Can These Biobased Nanoparticles Help Detect Tumors?

September 20, 2016 | Labiotech

The Italian company Bio-ON has released their newest product, which uses bioplastic nanoparticles to detect tumors. Bio-ON’s plastics are produced from agricultural waste, which eliminates competition with the food industry, and are 100% biodegradable.

 

Eastman Chemical Company Develops a Safer Solvent

September 20, 2016 | Green Biz

The chemical company has developed Eastman Omnia, a new high-performance solvent for cleaning applications, after a long journey using both computational and bench chemistry to narrow down their search. They used the EPA’s guidelines for carcinogenicity, neurotoxicity, acute mammalian toxicity, reproductive and developmental toxicity, repeated-dose toxicity, and environmental fate and toxicity to develop the new solvent.

 

Alkaline Membranes for Renewable Energy Storage and Conversion

September 19, 2016 | Azo Materials

Rensselaer Polytechnic Institute recently received a $2.2 million grant from the U.S. Department of Energy's Advanced Research Projects Agency-Energy (ARPA-E). The grant will fund research to develop ion-conduction materials for alkaline membranes, which will allow the replacement of platinum with Earth-abundant metals in next-generation fuel cells.

 

Making Surfboard Manufacturing More Sustainable

September 19, 2016 | Surfline

Surfers around the world are going green by choosing certified ECO-boards over other options. Sustainable Surf's ECOBOARD program aims to reduce the environmental impact of a surfboard related to the carbon footprint and use of hazardous materials and encourages manufacturers to use recycled and plant-based materials.

 

Navy Completes Flight Tests Using Biofuel

September 19, 2016 | Biomass Magazine

The U.S. Navy is a leader in incorporating alternative fuel into operational supplies, in order to increase mission capability and flexibility. Part of this vision was realized this month when the EA-18G "Green Growler" completed flight testing of a 100-percent advanced biofuel at Naval Air Station Patuxent River, Maryland.

Turning Windows into Solar Power Generators

September 9, 2016 | Green Building Elements

Several start-ups, including Ubiquitous Energy, PolySolar, and SolarWindow Technologies, are finding ways to turn infrared and UV light from the sun into electricity using windows. They’ve designed transparent coatings that can be applied to existing glass surfaces or even flexible plastic.

 

Chemical Company is to Offer Biobased Temperature Controlled Packaging

September 12, 2016 | Packaging Europe

Croda, a specialty chemical company, has developed a biobased phase change material. The new material has applications in pharmaceutical packaging, especially for shipping temperature-sensitive pharmaceuticals.

 

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Bioscience Company Wins Award for ‘Best Ingredient Made From Recycled Materials’

September 9, 2016 | EconoTimes

Amyris, Inc. in partnership with Boticario Group has been named a Gold Winner by Cosmetics Design USA for their development of the ingredient Neossance Hemisqualane. This ingredient, which is biodegradable and non-toxic to aquatic life, has applications in skin and sun care, hair care, and makeup removal.

 

Earth Friendly Products Releases First Pet Care Products with EPA’s Safer Choice Label

September 14, 2016 | Market Wired

Earth Friendly Products, maker of ECOS environmentally friendly cleaning products, announced that they are the first company to receive this label for a line of pet care products. These hypoallergenic conditioning shampoos are made using the safest ingredients and have been tested for performance.

 

NSF Awards Research Grant for Plant-Based Indigo Dye Production

September 14, 2016 | Newswise

Stony Creek Colors, which manufactures biobased textile dyes, and the Donald Danforth Plant Science Center, a not-for-profit institute, have received a grant to improve genetic resources for plant-based indigo dye production. The goal of the research is to make the manufacturing of blue jeans more sustainable.

 

Chemistry Professor at UCLA Wants to Improve Safety Culture

September 15, 2016 | Lab Manager

UCLA chemistry professor Craig Merlic was recently spotlighted for his activities as the head of the UC Center for Laboratory Safety. He teaches a safety course for all of the chemistry and biochemistry graduate students, and hopes the center’s work will become the “gold standard in laboratory safety in the United States.”

 

5 Great Videos on Biomimicry

September 15, 2016 | Green Biz

Green Biz highlights five videos about biomimcry—the idea that humans should try to mimic natural systems when making decisions about product design, architecture, engineering, energy systems, carbon capture, city planning, and more.

 

Renmatix Receives Investment for Commercialization of Plantrose ® Process

September 15, 2016 | Renmatix

Renmatix, a leader in affordable cellulosic sugars, received a $14 million investment from Bill Gates and Total, the global energy major. The investment will drive the building of Plantrose-enabled biorefineries, facilitating further market development in downstream bioproduct applications.

 

 

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Contributed by David Constable, Ph.D., Director, ACS Green Chemistry Institute®

 

It’s hard to believe that three weeks have passed since we were at the 252nd ACS National Meeting in Philadelphia. The ACS National Meetings are usually a whirlwind of activity and it’s a bit overwhelming to keep up with all the concurrent activities. We once again had the pleasure of several Pharma RT member company representatives, Leanna Schuster from GSK and Mike Kopack of Lilly, join us at our booth to talk to attendees about green chemistry and what they are doing in their respective companies to implement green chemistry. We also partnered with our LAUNCH colleagues to promote the 2016 LAUNCH Chemistry Challenge.

 

In case you had not heard, this year’s LAUNCH challenge is “…a global call for innovators, entrepreneurs, companies and organizations to enable predictive chemical design through innovative applications of data in chemistry. “ There are 4 focus areas: Data Generation, Data Access, Data Integration, and Data Analysis and Application. I would invite you to investigate this and see if you have a part to play.

 

One of the highlights of the week was the opportunity to hear Senator Chris Coons speak at the Hero’s of Chemistry Awards Ceremony. Senator Coons is a strong and articulate supporter of sustainable chemistry. We are extremely grateful for his persistent advocacy in the Senate to progress some form of legislation promoting greater Federal Agency attention to sustainable chemistry. He and Senator Collins have asked the U.S. General Accounting office to do a technology assessment around sustainable chemistry implementation in the U.S., and we are looking forward to a report sometime next year.

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The ACS GCI continues to progress the 21st Annual Green Chemistry and Engineering Conference under the able leadership of Jenny MacKellar, Dawn Holt and Jane Day. The Advisory Committee and Technical Program Chairs continue to map out the details of the conference and planning for all the various parts of the Conference are well in hand. We are looking forward to the Technical Session Submissions and I would ask you to remember that the closing date for that is the 7th of October. This is going to be another great conference, and I hope you are making plans to be a part!

 

We continue our work on the education roadmap with a variety of stakeholders, once again under the able leadership of Jenny MacKellar and our Leadership Team Jim Hutchinson, Mary Kirchoff and Eric Beckman. It’s challenging work to integrate green chemistry concepts into what is normally taught in chemistry curriculum. One bridge we’re building is the idea of systems thinking; a concept familiar in biology and engineering, but not so much in chemistry. But, to truly address some of the major sustainable and green chemistry challenges we face, we need to think more about all the systems involved in making the world more sustainable and where to integrate green chemistry thinking and practice. These opportunities need to be recognized and understood by educators so they may be taught within routine chemistry education.

 

As always, please do let me know what you think.

 

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Contributed by Mark Dorfman, Biomimicry Chemist, Biomimicry 3.8

 

Nature, the oldest and wisest chemist, is by necessity, a green chemist. By “nature”, I’m referring to the living natural world. Unlike inanimate rocks and minerals, organisms are constrained by the need to survive, thrive and nurture their young in the same place they make, use and manage chemistry. For example, minerals achieve brilliant colors using lead, mercury or cadmium, but over billions of years of R&D, organisms have figured out how to achieve a dazzling array of show-stopping displays without relying on the incorporation of heavy metals.

 

Color is only the tip of the iceberg. We would be hard-pressed to find a functional challenge faced by commercial chemicals and materials that organisms haven’t faced in varied environments. The list includes functions such as lubrication, self-cleaning, oxygen management, coatings, surface slipperiness, adhesion, water/ice resistance, conductance, fragrance, flavor, structural strength and flexibility, impact resistance, protection from predators, responsiveness to environmental cues, biodegradability, and signal sending/receiving.

 

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Not only do organisms not pollute their environment or themselves, in the course of meeting these functional challenges through chemistry, they create conditions conducive to life. For example, oxygen is a by-product of the energy-generating and chemical-synthesizing photosynthetic system; mollusks filter their watery surroundings; and falling leaves decompose into nutrients that feed the host tree and nourish the surrounding soil.

 

A set of deep patterns common to the chemistries across species and environmental contexts make the living world a rich storehouse of strategies that could inspire innovative, green chemistry approaches to new commercial chemistries and materials. Perhaps the two most important deep patterns in nature’s chemistry are self-assembly and shape complementarity. In biology, chemical transformations occur when reactants fit together hand-in-glove at ambient temperatures and pressures. The 3D shape self-assembles as a result of the strategically placed functional groups that attract or repel each other in a watery environment, thereby pulling the complex structure into the required shape. Shape complementarity and self-assembly relate to multiple green chemistry principles including: waste prevention, atom economy, less hazardous chemical syntheses, safer solvents and auxiliaries, reduced derivatives, catalysis, and inherently safer chemistry for accident prevention.

 

Another important deep pattern in nature’s chemistry is maximizing the use of non-covalent bonds. This includes: hydrogen bonds, van der Waals forces, and hydrophobic, electrostatic and pi interactions relating to the green chemistry principles of reduced derivatization and designing for degradation down to reusable building blocks. Nature’s chemistry meets its functional challenges using just over two dozen elements in the periodic table in relative positions and proportions that result in effective yet safer chemicals and materials. Nature introduces toxicity only when toxicity is the desired functional challenge, such as for protection or predation.

 

Biomimicry is a methodology that systematically taps into the living natural world’s rich vein of innovative biological knowledge, including nature’s chemical intelligenceto tease out the deep patterns and principles at work across divergent species. It then uses these deep patterns and principles to inform the design of new high-performing, high-quality, and effective solutions for solving specific industrial chemical and materials challenges in a way that is, by nature, green.

 

 

“The Nexus Blog” is a sister publication of “The Nexus” newsletter. To sign up for the newsletter, please email gci@acs.org, or if you have an ACS ID, login to your email preferences and select “The Nexus” to subscribe.

 

To read other posts, go to Green Chemistry: The Nexus Blog home.

Contributed by Catherine Rawlins, Chair of the Northeastern Section American Chemical Society - Younger Chemists Committee (NSYCC)

 

Over the years of my involvement in the NSYCC, our group and our goals have grown considerably. We continuously expand activities to include more hands-on and impactful programming, and recently considered the topic of green chemistry. It is still a focus area many people are not familiar with, especially with how it can be implemented in the lab or classroom. Accordingly, we developed a 1.5-hour workshop as part of a larger green chemistry event hosted by Pfizer. The workshop will focus on green chemistry education for educators. The goal is to develop techniques to better engage their students with chemistry, human health and the environment through real-world applications in the chemical industry.

 

We were fortunate to receive a Local Section Sustainability Programming Grant from the ACS Committee on Environmental Improvement to help make this event possible.  We are also going to collaborate with Pfizer to take the event to the next level. Pfizer already has a workshop and curriculum established which covers key concepts in green chemistry as it applies to drug development. Raymond Borg, a long time board member, volunteer and green chemistry enthusiast, will co-facilitate this workshop with his advisor Dr. Jonathan Rochford and the UMass-Boston Sustainable Scientists Group. Their efforts in fostering this partnership will make for a successful event!

 

This half-day workshop will introduce participants to the pharmaceutical industry and give insight into how drugs are discovered and developed. Participants will learn how to determine greener alternatives to solvents in the lab, and work with real case studies to determine the different synthetic routes to create a drug. It will also cover biocatalysis, flow and transition metal catalysis with a discussion of how to reduce the degree of hazardous materials and streamline these processes. One of the founders of Beyond Benign, Dr. John Warner, will be speaking on the challenges and benefits of educating educators about green chemistry. The remainder of the workshop will focus on an easily implementable green chemistry lesson plans for the teachers to implement in the classroom.

 

The workshop is free and will be held on Saturday, November 5th at UMass-Boston’s brand new Integrated Science Complex building. Pfizer will provide breakfast and lunch along with helpful educational materials for attendee usage. It is our hope that we can spread this knowledge to a wide range of chemists and science educators to promote greener and cleaner methods in our field.

 

Information about the schedule of the workshop will be posted as it develops. Should you have questions, please contact Catherine at catherine.rawlins@nsycc.org, or Raymond Borg at raymondedwardborg@gmail.com

 

We hope to see you there!

 

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“The Nexus Blog” is a sister publication of “The Nexus” newsletter. To sign up for the newsletter, please email gci@acs.org, or if you have an ACS ID, login to your email preferences and select “The Nexus” to subscribe.

 

To read other posts, go to Green Chemistry: The Nexus Blog home.

Contributed By Jonathan Winfield 1, Jonathan Rossiter 2 and Ioannis Ieropoulos, Ph.D. 1, Bristol BioEnergy Centre, Bristol Robotics Laboratory 1, University of the West of England, Dept. of Engineering Mathematics, University of Bristol 2

 

Robotics is a field that is not normally associated with green technology or sustainability. Robots are generally constructed using materials that are non-biodegradable, toxic and expensive. These factors can limit the potential uses that an artificial agent might have, especially if operation is required outside and away from where humans live. Things are further complicated when considering the robot’s power supply. In most cases, batteries are used that will inevitably run out and require recharging from charging stations. Imagine then, an environmentally friendly robot, one that can safely roam a targeted area whether that is within agricultural fields, rain forests or remote jungles. Movement would not be random but with a preset purpose built-in perhaps to identify pests, clean up human-made waste and generate electricity from it, or simply monitor/sense environmental conditions.

 

When designing such a robot it is important to consider that the natural environment is a well-balanced and closed system where new organisms are born, live and die. The materials that make up the dead are then recycled within that same ecosystem. Could a biodegradable robot fit into such a system and be developed with the capability of consuming other robots at the end of their life? These are areas that we at the University of the West of England (UWE) and the University of Bristol have been investigating through a Leverhulme Trust funded project to develop biodegradable robots.

 

Based at the Bristol BioEnergy Centre within the Bristol Robotics Laboratory, this line of work has focused on three overlapping areas, a) the robots source of power in the form of microbial fuel cells, i.e., the robot’s stomach, (b) the robot’s mechanism for movement, i.e., artificial muscles, (c) the biodegradability of the materials. In addition we also looked at whether power could be produced from the consumption of its own parts, i.e., could a robot muscle be fed to the robot stomach!

 

Microbial fuel cells (MFCs) even when made out of conventional materials are a very promising green technology. MFCs have been described as ‘bio-batteries’ but this term is not wholly correct because batteries start life with a set amount of reactants. Once the reactants are depleted the battery will cease to operate until recharged at a human-made charging station. A fuel cell on the other hand will carry on producing power for as long as it is being fed with a fuel. For MFCs, that fuel can be any liquid containing organic matter, e.g., wastewater, urine or agricultural runoff. As with a conventional battery, a MFC consists of a negative (anode) and a positive (cathode) electrode. Bacteria grow on the anode and breakdown organic matter in the wastewater releasing electrons and protons. The movement of the electrons and protons to the cathode equates to the production of electricity. Making the technology even more attractive is that the production of electricity comes as a direct consequence of the removal of organic pollutants—the more power produced the cleaner the liquid becomes. This process is never-ending providing the bacteria are continuously fed; we have MFCs in our lab that have been running now for eight years!

 

Quite rightly there has been considerable interest in the technology from wastewater treatment companies as well, in addition to the robotics application. Before investigating biodegradable robots, Prof. Ieropoulos developed the EcoBot series of robots. Using MFCs as the sole source of power, four robots were constructed over a ten-year period. Each new embodiment moved closer to total autonomy such that EcoBot’s III and IV could move towards a food source when their ‘on-board’ bacteria were hungry and even expel waste when depleted. The EcoBots were a wonderful demonstration of utilizing bacterial power for a useful purpose, however the MFCs aboard the robots were built from conventional plastics and materials.

 

The first step in developing biodegradable MFCs was the identification of alternative and functional ‘green’ materials to replace the commonly used components. In conventional MFCs, a proton exchange membrane (PEM) is often used to separate the electrodes while allowing for the movement of protons from anode to cathode. Not only are PEMs expensive but they can inhibit microbial metabolism and more importantly for our project, they are not biodegradable. In order to find biodegradable replacements, the focus moved to porous materials, ones dense enough to isolate the electrodes but of a porosity that would enable proton transfer. A range of diverse and in some cases unconventional materials were trialed; these included paper, gelatin, alginate and even fruit (specifically kiwi fruit). Perhaps the most unusual material investigated was natural rubber from condoms!

 

The motivation for using natural rubber was that it was also proving to be a viable material for the biodegradable artificial muscles. In the early stages of the experiment the MFCs with condom membranes produced no electrical current whatsoever. This was because the material was so impermeable that even protons could not pass through, which is perhaps expected given the original purpose of the material.

 

After a number of weeks and to our surprise, the MFCs began generating a working voltage which continued to increase over the ensuing months. After almost a year the MFCs with ‘condom’ membranes were outperforming those with conventional PEMs. What was enabling the production of bio-electricity? Biodegradation. Microbes were eating into the natural rubber and creating channels and pores that enabled the flow of protons. Impressively over time, areas of the rubber were completely degraded but the accumulation of microorganisms (biofilm) formed a natural patching that ensured the electrodes remained isolated from one another. The formation of such biofilms on conventional PEMs can inhibit performance but with the rubber separators, their presence boosted performance.

 

Next we looked at developing alternative electrode materials and our list of ingredients included egg yolk, gelatin, graphite and lanolin. During all of our experiments we ensured the materials were both biodegradable and non-toxic using microbiological techniques and through composting studies at the Bristol Botanic Gardens.

 

The next step was to develop stacks or multiples of biodegradable MFCs in order to maximize power output. For the individual MFCs in the stack we used natural rubber from laboratory gloves, egg-based electrodes and 3D printed MFCs chassis using biodegradable plastic (polylactic acid). The completed MFCs are shown in Figure 1 and when fed with natural waste (e.g., urine) the stack of 40 MFCs in a series/parallel electrical configuration produced over 3 volts and a power density of 4 Watts/m3

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For the artificial muscles we focused on biodegradable electroactive polymers, materials that change in size or shape when stimulated by an electric field. In other words, these materials transduce electrical energy into mechanical energy. In general, there are two categories, i) materials that actuate through the movement of ions and, ii) those that respond to electrons. In both cases biodegradable materials were successfully used as viable replacements to the conventional versions. Natural rubber, being very compliant, proved to be an excellent dielectic elastomer actuator. Gelatin demonstrated actuation through the movement of Na+ ions in the gel and in solution, as shown in the figure below.

 

Now with moving parts and a source of power we looked at whether a biodegradable robot might be able to gain energy by consuming the parts of another. To achieve this, gelatin muscles were ‘fed’ to MFCs. Fuel cells fed with the ‘robot muscle’ exhibited a doubling in power as the bacteria consumed the material.

 

There is clearly more work to be done before biodegradable robots are a thing of the present, but our preliminary findings suggest that it may not be long before such robots are helping protect the environment. They could be sent to remote or sensitive areas to collect data, even tapping into natural resources to obtain their energy, e.g., muddy puddles, sediments or pests like flies or mosquitos. As long as this fuel is continuously supplied the robots will be able to keep working and therefore accruing data. We envisage a built-in mechanism that initiates biodegradation once the robot’s ‘time has come’ or its mission is complete. For example, the release from an internal compartment of a specific microorganism to consume the robot or an inert chemical that renders the robot chassis consumable. In comparison to drones, the biodegradable ground robots, while not covering as much area, could continue operating for longer. Perhaps further down the line, biodegradable drones may even be achievable!

figure2.JPGAnother role is deployment in areas where human-made waste has accrued such as oil spills or nuclear waste. There have been reports of bacteria that can eat up crude oil in spills and even nuclear waste. Imagine then sending robots to infected areas, loaded with these bacteria that clean the problem as the robot glides over the surface until the area is uncontaminated. Once the all-clear has been broadcast, there need not be any further human intervention, i.e., to remove the device, because the robot can be left to degrade harmlessly into the environment.

 

 

 

“The Nexus Blog” is a sister publication of “The Nexus” newsletter. To sign up for the newsletter, please email gci@acs.org, or if you have an ACS ID, login to your email preferences and select “The Nexus” to subscribe.

 

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Contributed by Jeffery A. Byers, Ph.D., Assistant Professor of Chemistry, Boston College

 

It is particularly challenging to find an application where synthetic plastics have not become important. From disposable bags, cutlery and cups, lightweight automobile parts, vibrant paints and robust coatings, sticky adhesives, flexible textiles, and even devices designed to deliver drugs, the usefulness of synthetic polymers have arguably made them the most important discovery of the twentieth century. However, as we get firmly entrenched in the twenty-first century, our society is faced with the challenge of continuing to produce synthetic polymers that have properties suitable for all of these applications (and more) but without the environmental disadvantages that have plagued many synthetic polymers derived from non-renewable resources. In order to achieve this goal, access to synthetic polymers that are degradable and derived from renewable resources is an ongoing effort for chemists and engineers. Unlike the synthetic polymers developed previously, these new materials must meet the materials properties requirements and have degradable properties that are in line with the intended application: plastic bags should last months and car bumpers should last years, not vice versa.

 

As part of this ongoing effort, our research group has targeted versatile catalyst systems that can incorporate multiple building blocks (i.e., different monomers), control three-dimensional structure (e.g., stereochemistry) and control polymer architecture (e.g., linear versus cross-linked polymer). A catalyst system that has been particularly versatile has been the iron-based complex shown below that, when combined with an alcohol initiator, is active for the ring opening polymerization of lactide (a byers1.jpgcyclic dimer of lactic acid) to give the industry leading biodegradable polymer, poly(lactic acid). The catalyst was extremely well behaved resulting in nearly uniform molecular weight distributions and a linear relationship between molecular weight and conversion, both characteristics of a living polymerization reaction.[1] However, what distinguished this complex as a particularly versatile catalyst was the ability to control three dimensional structure by changing the identity of the initiators and the ability to change the reactivity of the complex by altering its oxidation state (e.g., iron(II) vs. iron(III)). These properties have been utilized to synthesize polymers that contain the biologically-derived poly(lactic acid) in a way that is expected to diversify its physical and mechanical properties as well as tailor its degradation rates.

 

An interesting and useful property of lactic acid is that it is a chiral molecule. Chiral molecules, like hands, are molecules whose mirror image is not superimposable. When these lactic acid units are assembled in a polymer, the two different possible chiral lactic acid units, or stereoisomers, can assemble in regular or irregular ways. Previously it has been shown that the physical properties[2] and degradation rates[3] of poly(lactic acid) can be profoundly affected by how the stereoisomers are distributed (e.g., alternating versus homogeneous distribution) and how regularly they are distributed. For example, polymers that have a random distribution of lactic acid stereoisomers are amorphous materials that degrade relatively quickly while those with uniform distribution are crystalline materials with high melting points and slower degradation rates. Thus, the ability to synthesize poly(lactic acid) with the stereoisomers distributed in different ways provides access to materials with a broad array of physical properties and degradation profiles.

 

Historically, carefully designed, and (often) chiral catalysts have been utilized to synthesize poly(lactic acid) in a stereoregular fashion. However, this approach can be synthetically laborious if the synthesis of poly(lactic acids) with different degrees of stereoregularity is desired. Alternatively, the iron-based catalysts that we have developed are capable of producing a range of stereoregular poly(lactic acids) from a single iron catalyst precursor.[4] The key to the success of this method was the discovery that stereoselectivity in the polymerization reaction could be affected by the identity of additives used as initiators. Whereas alcohol initiators led to stereoirregular poly(lactic acid), silanol initiators led to stereoregular poly(lactic acid). Not only did the different additives change the selectivity of the reaction, the regularity of this stereoselectivity (also known as tacticity) could be controlled by altering the identity of the silanol initiator and the stereoisomer of the lactide (see graph where higher Ps indicate more stereoregular polymer and Ps = 50 is stereorandom polymer). Since the silanol initiators were used as additives in the reaction, a variety of stereoregular poly(lactic acid) was obtainable without the need to synthesize a library of metal precursors. Mechanistic studies revealed that the origin of the stereoselectivity in these reactions was a consequence of the silanol additive converting the achiral iron complexes into chiral catalysts during the course of the reaction. Since the three dimensional structure of the catalyst was partially defined by the silanol additive, the degree of stereoselectivity could be altered by changing the identity of the silanol additive.

 

While control over stereochemistry is a powerful advantage for tailoring the properties of poly(lactic acid), the iron-based catalysts proved to be even more versatile. Unlike most catalysts used for lactide polymerization, the iron-based catalysts can be reversibly oxidized by sequential exposure to chemical oxidants and reductants. Inspired by previous reports that demonstrated that lactide polymerization rates could be altered by changing the oxidation state of a catalyst,[5],[6],[7] we were pleased to find that our iron-based catalyst system could be deactivated upon exposure to oxidants and then later reactivated upon exposure to reductants (see blue trace in graph below). The switching capabilities of the catalyst system rendered it useful for the diversification of poly(lactic acid) when we discovered that complementary reactivity was observed when epoxides were used as monomers.[8] In other words, the iron-based catalyst could be switched on and off for epoxide ring opening polymerization much like it could for lactide polymerization, but this time the oxidized form of the catalyst was active for polymerization whereas the reduced form of the catalyst was inactive for polymerization (see red trace in graph below).

 

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We next capitalized on the complementary reactivity of the catalyst towards polymerization of epoxides and lactide by carrying out redox switchable copolymerization reactions starting from a mixture of an epoxide and lactide (see top of Scheme below).[8] Polyester-polyether diblock copolymers could be synthesized by starting with the catalyst in its reduced state resulting in the selective polymerization of lactide followed by chemical oxidation resulting in the selective polymerization of the epoxide. The alternative diblock copolymer starting with epoxide polymerization first followed by lactide polymerization could also be synthesized by starting with the catalyst in its oxidized state followed by chemical reduction. These results were exciting because they provide access to copolymers that are difficult to synthesize in one step, and they also suggested that multi-block copolymers of various polyester/polyether composition could be synthesized from the same reaction feed by altering the oxidation of the catalyst and the time between redox events. Such copolymers are expected to exhibit physical properties and degradation rates that differ significantly compared to poly(lactic acid).

 

In addition to synthesizing block copolymers using the iron-based polymerization catalysts, we have applied the redox-switching capabilities of the catalyst to create a redox-triggered crosslinking reaction (see bottom of the Scheme below).[9] Cross-linked polymers are linear polymers that have been chemically bonded to one another. Cross-linked polymers are tough materials that often demonstrate superior properties compared to linear polymers, but they are commonly difficult to process. As a result, triggered crosslinking reactions are desirable because they allow one to process the linear polymer prior to its crosslinking. Although many external stimuli have been used to trigger crosslinking reactions (e.g., heat, light, acid, etc.), to the best of our knowledge the only example of redox-triggered crosslinking reactions that has been reported to date have been for the reversible formation of disulfide bonds (i.e., RS—SR).[10] The development of a redox-triggered crosslinking reaction would complement the established methods. Moreover, while cross-linked poly(lactic acid) has been achieved through high energy light[11],[12] or electron beam irradiation,[13] the effect that crosslinking has on the physical, mechanical, and degradation properties of the polymer have largely been unexplored.

 

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To utilize the redox-switchable, iron-based complexes for crosslinking applications, we synthesized a monomer that incorporated both a lactide-like cyclic diester and an epoxide (see bottom of the Scheme below). Exposing this monomer to the reduced form of the complex resulted in the formation of a linear polyester that contained epoxide functional groups as side chains. Catalyst oxidation and concentration of the reaction mixture led to the rapid intermolecular reaction between the epoxide side chains, which resulted in crosslinking of the polymer. This material demonstrated significantly different thermal and swelling properties compared to linear poly(lactic acid). Furthermore, copolymerizing the epoxide functionalized cyclic diester with lactide using the reduced form of the catalyst followed by oxidation resulted in crosslinked poly(lactic acid) with variable crosslinking densities. This capability led to the production of a series of polymers derived from lactic acid that possessed different thermal properties. It is expected that future exploration of the polymer's mechanical properties and degradation rates will lead to polymers with significantly different properties compared to poly(lactic acid).

 

While investigation of the thermal, mechanical and degradation properties of the polymers that we have synthesized are still in its infancy, access to a wide variety of polymers with varying composition, stereoregularity, and three dimensional structure has been made possible by utilizing the iron-based catalysts developed in our lab. It is expected that the synergism between catalyst structure and polymer properties will continue to pervade with the ultimate goal of developing degradable polymers derived from renewable resources that can be used for a wider variety of applications.

 

 

REFERENCES

 

[1] Biernesser, Ashley B.; Li, Bo; Byers, Jeffery A.* “The redox controllable polymerization of lactide catalyzed by bis(imino)pyridine iron bis-alkoxide complexes” Journal of the American Chemical Society, 2013, 135(44), 16553-16560, DOI:10.1021/ja407920d.

 

[2] Auras, Rafael A.; Lim, Loong-Tak; Selke, Susan E. M.; Tsuji, Hideto Poly(lactic acid): Synthesis, Structures, Properties, Processing, and Applications; John Wiley & Sons, Inc.: Hoboken, NJ, 2011, ISBN:978-0-470-29366-9.

 

[3] Gorrasi, Giuliana; Pantani, Roberto* “Effect of PLA grades and morphologies on hydrolytic degradation at composting temperature: Assessment of structural modification and kinetic parameters” Polymer Degradation and Stability, 2013, 98(5), 1006-1014, DOI:10.1016/j.polymdegradstab.2013.02.005.

 

[4] Manna, Cesar M.; Kaur, Aman; Yablon, Lauren; Haeffner, Fredrick; Li, Bo; Byers, Jeffery A.* “Stereoselective catalysis achieved through in situ desymmetrization of an achiral iron catalyst precursor” Journal of the American Chemical Society, 2015, 137(45), 14232-14235, DOI:10.1021/jacs.5b09966.

 

[5] Gregson, Charlotte K. A.; Gibson, Vernon C.*; Long, Nicholas J.; Marshall, Edward L.; Oxford, Phillip J.; White, Andrew J. P. “Redox Control with Single-Site Polymerization Catalysts” Journal of the American Chemical Society, 2006, 128(23), 7410-7411, DOI:10.1021/ja061398n.

 

[6] Broderick, Erin M.; Guo, Neng; Vogel, Carola S.; Xu, Culling; Sutter, Jorg; Miller, Jeffrey T.; Meyer, Karsten; Mehrkhodavandi, Parisa; Diaconescu, Paula L.* “Redox Control of a Ring-Opening Polymerization Catalyst” Journal of the American Chemical Society, 2011, 133(24), 9278-9281, DOI:10.1021/ja2036089.

 

[7] Wang, Xinke; Thevenon, Arnaud; Brosmer, Jonathan L.; Yu, Insun; Khan, Sneed I.; Mehrkhodavandi, Parisa; Diaconescu, Paula L.* “Redox Control of Group 4 Metal Ring-Opening Polymerization Activity toward L-Lactide and ∈-Caprolactone” Journal of the American Chemical Society, 2014, 136(32), 11264-11267, DOI:10.1021/ja505883u.

 

[8] Biernesser, Ashley B.; Delle Chiaie, Kayla; Curley, Julia B.; Byers, Jeffery A.* “Block Copolymerization of Epoxides with Lactide Facilitated by Redox Switchable Iron Polymerization Catalysis” Angewandte Chemie, International Edition, 2016, 55, 5251-5254, DOI:10.1002/anie.201511793.

 

[9] Delle Chiaie, Kayla; Yablon, Lauren L.; Biernesser, Ashley B.; Michalowski, Gregory R.; Sudyn, Alexander W.; Byers, Jeffery A.* “Redox-Triggered Crosslinking Reactions” Polymer Chemistry, 2016, 7, 4675-4681, DOI:10.1039/C6PY00975A.

 

[10] Chan, Nicky; Yee, N.; An, So Y.; Oh, Jung K. “Tuning Amphiphilicity/Temperature-Induced Self-Assembly and In-Situ Disulfide Crosslinking of Reduction-Responsive Block Copolymers” Journal of Polymer Science Part A, Polymer Chemistry, 2014, 52, 2057-2067, DOI:10.1002/pola.27216.

 

[11] Yang, Sen-lin; Wu, Zhi-Hua; Yang, Wei; Yang, Ming-Bo “Thermal and Mechanical Properties of Chemical Crosslinked Polylactide (PLA)” Polymer Testing, 2008, 27, 957-963, DOI:10.1016/j.polymertesting.2008.08.009.

 

[12] Quynh, Tran M.; Mitomo, H.; Nagasawa, N.; Wada, Y.; Yoshii, F.; Tamada, M.* “Properties of Crosslinked Polylactides (PLLA & PDLA) by Radiation and its Biodegradability” European Polymer Journal, 2007, 43(5), 1779-1785, DOI:10.1016/j.eurpolymj.2007.03.007.

 

[13] Phong, Lester; Han, Ernest S. C.; Xiong, Sijing; Pan, Jie; Loo, Say C. J.*, “Properties and Hydrolysis of PLGA and PLLA Cross-Linked with Electron Beam Radiation” Polymer Degradation and Stability, 2010, 95(5), 771-777, DOI:10.1016/j.polymdegradstab.2010.02.012.

 

 

 

“The Nexus Blog” is a sister publication of “The Nexus” newsletter. To sign up for the newsletter, please email gci@acs.org, or if you have an ACS ID, login to your email preferences and select “The Nexus” to subscribe.

 

To read other posts, go to Green Chemistry: The Nexus Blog home.

Ikea and Neste to Partner on Production of Sustainable and Bio-based Polymers

September 7, 2016 | Plastics Today

Neste, a company from Finland that specializes in oil refining and renewable solutions, and Ikea of Sweden have announced a joint initiative to develop and produce renewable, bio-based plastic materials. They would like to release their first proof-of-concept during 2017.

 

Beckham, Gong, and Sneddon are First Winners of the ACS Sustainable Chemistry and Engineering Lectureship Award

September 6, 2016 | ACS Sustainable Chemistry & Engineering

The awards, which recognize early career investigators’ research contributions to green chemistry, green engineering, and sustainability in the chemical enterprise, were given to Dr. Gregg Beckham of NREL, Prof. Jinlong Gong of Tianjian University, and Dr. Helen Sneddon of GlaxoSmithKline.

 

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September 6, 2016 | Edmonton Journal

The University of Alberta received funding from the Canada First Excellence Research Fund for the Future Energy Systems Research Institute. The institute will bring together researchers from multiple disciplines to work together on a holistic approach to reduce the environmental impacts of fossil fuels and develop low-carbon energy strategies.

 

Superatom Crystals of Fullerenes May Have Potential in Sustainable Energy Generation and Storage

September 6, 2016 | EurekAlert

Researchers at Carnegie Mellon University and Columbia University found that superatom crystals of fullerenes have distinct thermal conductivity properties that are related to the crystals’ rotational disorder. They believe they could one day make up a new material that could change from being a thermal conductor to an insulator, acting as a kind of thermal switch.

 

New Catalyst for Renewable Energy Production Requires Less Iridium

September 2, 2016 | Phys.org

Researchers at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have developed a new catalyst, a thin film of iridium oxide layered on top of strontium iridium oxide. This new catalyst is 100 times faster, works better as time goes on, and is more stable under acidic conditions than other similar catalysts.

 

New Fabric a Creative Substitute for Air Conditioning

September 2, 2016 | Cosmos

A new kind of fabric, which reflects sunlight from the body and allows for heat radiating from our skin to escape, has been developed by researchers at Stanford University. The researchers hope that the material can be developed commercially, eventually helping to reduce greenhouse gas emissions.

 

Boston University Incorporates Sustainability Ambassadors into Orientation

September 2, 2016 | BU Today

Sustainability ambassadors were a new addition to Boston University’s freshman orientation this year. They provided an engaging way for new students and their families to learn about the sustainability initiatives at the university.

 

Clean Energy from Enzymes?

September 1, 2016 | Science Daily

Hydrogenases are a group of enzymes that produce and split hydrogen, and thus have potential in the search for sustainable energy. Oxygen degrades their active sites, so a team of researchers set out to understand the mechanism of hydrogenases better in hopes to find a way to avoid this drawback.

 

 

 

“The Nexus Blog” is a sister publication of “The Nexus” newsletter. To sign up for the newsletter, please email gci@acs.org, or if you have an ACS ID, login to your email preferences and select “The Nexus” to subscribe.

 

To read other posts, go to Green Chemistry: The Nexus Blog home.

Incorporating Single Fluorine Atoms into Chiral Pharmaceuticals

September 2, 2016 | Pharmaceutical Technology

At GlaxoSmithKline, researchers discovered a greener way to incorporate a single fluorine atom at a chiral center. Their method, which utilizes fluorine gas and a copper catalyst, was found to have a process mass intensity (PMI) more than four times lower than their original method.

 

Solar Cell Technology Start-Up Awarded $2M from DOEROUNDUP.jpg

August 31, 2016 | University of Arkansas

Picasolar Inc., a start-up company out of the University of Arkansas, was awarded $2 million from the U.S. Department of Energy to advance a pilot manufacturing program. They have a goal of producing 1,000 solar panels that utilize their technology, which requires less silver than solar panels already on the market.

 

Notre Dame Research Could Have Application in Solar Cell Generation and Radiation Detection

August 30, 2016 | University of Notre Dame

Plasmonic nanoparticles have the ability to absorb light from the sun, and this research group at the University of Notre Dame is trying to harness that absorbed energy. The group also discovered that these nanoparticles can be used to detect radioactive actinides for use in nuclear forensics.

 

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August 30, 2016 | Plastic News

The Society of the Plastics Industry presented the award to Club Coffee LP for their innovative compostable coffee pod, which utilizes bioplastic in its design. Club Coffee’s pods break down fully in typical municipal and industrial composting facilities in as little as five weeks.

 

Global Green and Bio-based Solvents Market May Grow to $13.74 Billion by 2024

August 30, 2016 | Sci/Tech Nation

A recent report published by Grand View Research, Inc. predicts the market size of green and bio-based solvents to grow to $13.74 billion by the year 2024. The group attributes this projection to the strict regulations imposed on the chemical industry by the EPA and other governmental agencies.

 

Seventh Generation Incorporates Bioplastic in Laundry Detergent Bottle

August 30, 2016 | Greener Package

Seventh Generation’s 100-oz. laundry detergent bottle has received an upgrade—it’s now made from recycled HDPE and bio-based polyethylene. This takes Seventh Generation one step closer to its vision of having all of its bottles made completely from recycled or bio-based materials by 2020.

 

The Triple Bottom Line: People, Planet, Profit

August 30, 2016 | Earth 911

These 7 companies are adapting their methods to meet the triple bottom line and be more environmentally conscious.

 

Research Project in the Netherlands May Extend Battery Life of Streetlamps and Electric Cars

August 29, 2016 | Horizon

Though lithium-ion batteries last longer than lead-acid batteries, they are not utilized in streetlamps because they cannot withstand cold temperatures. This research group from the Netherlands has designed a solution—a solar-powered heater.

 

Excellence in Teaching Sustainability Award Received by Professor at Fort Hays State University

August 29, 2016 | Fort Hays State University

News Dr. Gregory Weisenborn received the Excellence in Teaching Sustainability Award from the Institute of Industrial and Systems Engineers (IISE) for teaching his students a broad and holistic approach to operations and systems engineering.

 

 

 

“The Nexus Blog” is a sister publication of “The Nexus” newsletter. To sign up for the newsletter, please email gci@acs.org, or if you have an ACS ID, login to your email preferences and select “The Nexus” to subscribe.

 

To read other posts, go to Green Chemistry: The Nexus Blog home.

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