By Eloi Grignon, Ph.D. student, Member-at-Large for the GCI
Faced with a worsening climate crisis and growing food insecurity, humans have begun to produce food from the air. While you’d be forgiven for assuming this plot to be that of an Asimov story, it is, in fact, the reality that several start-ups envision for the future of agriculture. Indeed, a wave of firms have developed gas-to-protein technologies that employ bacteria to convert feed gases into an edible flour.
In truth, none of the technologies designed to date rely solely (if at all) on air. For instance, Solar Foods, a Finnish biotech company, combines carbon dioxide from the air with green (i.e. not derived from fossil fuels) hydrogen and water to feed a carefully selected bacterium. The result of this fermentation is their proprietary Solein protein, which they currently produce at a rate of 1 kg per day.1 Others in the gas-to-protein industry have developed their fermentation processes around different gases: Calysta uses methane supplied by the energy giant BP while Lanza Tech relies on the waste carbon monoxide generated by a nearby steel plant.1
The synthesized proteins are generally viewed and marketed as alternatives to other plant-based proteins, such as those derived from soy, whose cultivation is land-intensive and can come at the cost of intense deforestation.2 Here, gas-to-protein agriculture has the tantalizing potential to produce food on similar scales while requiring only a fraction of the area. A 2018 study estimated that widespread adoption (roughly 10-20% market share) of gas-to-protein could reduce farmland area by 6% and associated GHG emissions by 7%.3
Gas-to-protein agriculture may also help phase out animal-based proteins. One suitable target for replacement is fishmeal, the powder obtained from drying and grinding the bones and offal of commercial fisheries’ by-catch. Fishmeal, which is used as the primary source of protein for farm-raised fish, consumes approximately one quarter of the global wild fish catch and is strongly linked with the depletion of aquatic environments and collapse of local fisheries.1 As a more sustainable alternative, Calysta produces a bacteria-sourced protein with all the amino acids required to feed farmed fish. The potential impact is huge: Calysta’s CEO claims that the presence of a 100,000-tonne plant of synthetic protein can allow 500,000 wild fish to remain in the ocean.1
The boons of gas-to-protein agriculture are pushed to truly stupendous heights when CO2-consuming processes are employed. According to Solar Foods, the operation’s economic use of energy coupled with its inherent carbon sequestration could translate to a protein with only 1% of the carbon footprint of its plant- and animal-derived counterparts.1
Beyond the increased protection of forest and aquatic ecosystems along with huge water and energy savings, gas-to-protein agriculture has other, more intangible advantages. For instance, the liberation of food production from environmental dependence means that the protein’s annual tonnage need not be subject to environmental crises or day-to-day weather. Moreover, scaling production up or down can be achieved far more easily when no marginal land or animals come into the equation.
Although there is great promise for gas-to-protein firms to gain an established foothold, there remain several economic hurdles impeding widescale production. Chief among these is the high cost of green hydrogen – a key ingredient of many firms’ protein recipe. Green hydrogen is produced from the electrolysis of water and, as such, its price is contingent on the supply of low-cost electricity. It is hoped that the economies of scale associated with the advent of renewables will lower the price of electricity sufficiently to render gas-to-protein agriculture the economically favourable option. The balance may also be tipped in favour of gas-to-protein agriculture if alternative, non-monetary costs, such as those of land and wildlife, are factored into consumer decision-making.
The first agricultural revolution saw us take mastery of our environment and irreversibly change the course of human history. If gas-to-protein agriculture is to become a mainstay, could we now, 12 millennia later, be on the brink of witnessing an equally important turning point?
 Scott, A. (2020). Food from the air. CHEMICAL & ENGINEERING NEWS, 98(35), 18-21.
 Pikaar, I., De Vrieze, J., Rabaey, K., Herrero, M., Smith, P., & Verstraete, W. (2018). Carbon emission avoidance and capture by producing in-reactor microbial biomass based food, feed and slow release fertilizer: potentials and limitations. Science of the Total Environment, 644, 1525-1530.
It is April 2020 and you are scrolling through your endless TikTok “for you” page when you stumble across a video informing you about so-called “fast fashion”. The words “affordable” and “toxic” stick with you because they are not used to describe or advertise fashion, and yet you wonder how you have never heard of that side of the fashion industry.
Hi, my name is Hana and I will provide you with a quick perspective on what I think is one of the most overlooked environmental problems of our modern world.
What is Fast Fashion?
In the past decade, brands have taken to widening their production lines by mass-producing clothes and continuously cycling fashion trends through the use of cheap labour and cheap materials. In simpler terms, mass-production can be defined by the shipment of new styles received daily (e.g. H&M and Forever 21) or when a retailer introduces 400 styles a week on its website (e.g. Topshop). Fast fashion is mainly aimed at young women whose dependence on social media can persuade them to think that they are behind on trends as soon as they see styles being worn by influencers and celebrities. An example of a fast fashion brand boosted by social media is Shein, so trendy and yet so unbelievably cheap. The need to shop for the latest trend is facilitated by the garment’s affordability, thus catering to young people’s disposable income. One of the most alarming concerns associated with fast fashion and the rapid cycling of trends is the incredibly high yield of textile waste, which often ends up in a landfill. According to the EPA Office of Solid Waste, the average American disposes of up to 68 pounds of clothing and textiles per year.1 Want a better picture? If the population of the United States is comprised of 328 million individuals, the theoretical annual number of textile waste going to the landfill would rise to a whopping 22300 million pounds – the weight of 2 million adult elephants!
The double-edged sword of democratization
As journalist Lucy Siegle puts it, “fast fashion isn’t free. Someone somewhere is paying.”3 Siegle is not wrong: Chinese workers make as little as 12-18 cents per hour, according to figures from the U.S. Labour Committee. With the increasing competition between emerging economies, these workers will be receiving lower wages and will start working in even poorer conditions, resulting in a net decrease in production costs. Fast fashion brands hold their manufacturing factories in low to middle-income countries which significantly lowers production costs. As a result, low to middle-income countries produce 90% of the world’s clothing.1
A bit of the chemistry explained
As a materials science student, I find that a big part of this problem lies in the chemistry of the textiles used. On one hand, antibacterial agents that are added to textiles can lead to antibiotic resistance in humans, according to a Swedish Chemicals agency. On the other hand, dyes contain toxic chemicals that bio-accumulate, causing the spread of diseases and increase the risk of cancer among individuals in various communities (and that is not considering these chemicals’ effects on factory workers)!4 Brian Tsui, a fellow GCI member, further discusses the chemical aspect of this problem in his blog post titled, “Textiles True Colours: How Sustainable are they?” I would highly recommend giving it a read if you wish to know more about the fashion industry’s use of chemicals in dyes.5 Although there are numerous ways to approach this, a good way to start would be ensuring that the materials safety data sheets of industrial chemicals be more comprehensive and catered to the non-chemist so that the general public, as well as manufacturers, have a better understanding of the chemicals and textiles used. More importantly, meaningful communication between materials chemists, governments, and retail giants should be practiced to ensure strict and uncompromising regulations for textile production.6
What is slow fashion?
This concept is likely intuitive now after I explained fast fashion; but to reiterate, slow fashion is the decrease in clothing consumption as a consequence of an increase in garment lifetime. You might be asking yourself whether the solution lies in the hands of luxury brands since we can check off the aspect of an increase in garment lifetime. Surprisingly, this not the case! Luxury retailers have very similar shortcomings to other fast fashion chains, where some manufacturers are based in low to middle-income countries and labourers work under questionable environments. Some luxury retailers also hold large unsold inventories that go to (you guessed it!) landfills. The advantageous side of shopping luxury brands, however, is that they typically provide longer-lasting items by using higher quality fabrics, second-hand sales, and viable repair services.8
So, what can you do?
When I was first researching this topic, I was quite overwhelmed by how deeply entrenched consumerist patterns are in our societies. I have noticed, though, that the solution to the problem of fast fashion really does lie within the hands of a more environmentally conscious consumer. If this weren’t the case, Patagonia would not have switched to recycling plastics bottles to use them in fabrics and Versace would not have used corn by-products to make Ingeo, a more sustainable fabric.1 I have compiled a list of small and easy steps we could all take towards building a more sustainable wardrobe:
Buy less! A rule of thumb is to ask yourself if you are head-over-heels in love with the clothing item you are contemplating buying. If you are, great! Now ask yourself if you will have the opportunity to wear it on a biweekly basis!
Wash your clothing items less That is not to say that you should not wash a dirty clothing item! Wash garments only when needed and according to their clothing label. Not only will this allow your clothes to last longer, but it will also reduce your carbon footprint.
Shop second-hand! I cannot stress this enough. I always take my friends thrift-shopping whenever possible. Thrifting saves clothes from landfills and reduces your carbon footprint. If you are concerned with its trendiness, you can rest assured that thrifting gives you timeless elegance (fashion trends also do cycle, as I mentioned earlier!).
Shop local Many have been preaching supporting local businesses due to the COVID-19 pandemic and you are probably sick of it, but try to give it a shot! Most local businesses actually sell sustainable clothing items that do not take advantage of cheap labour and do not rely on heavily manufactured dyes. Not only is this an easy way to prevent your local family-owned business from closing down, but you would also be saving the environment.
Shop luxury brands for “essentials” Seems counterintuitive but splurging on that one designer piece that would last you 10-20 years is definitely more worthwhile than spending on a garment you would be paying more money to replace every few years.
Donate/ Sell your clothes! By donating, you are increasing the lifetime of your garment and allowing someone else to flaunt a unique garment with its very own pre-loved charm. Selling your clothes is also a great way to start your own business by selling your more expensive clothing items. A great way to start selling clothes is through apps like Depop where you can list your clothing items and price them as you want.
If you have read through my blog post thus far, thank you and I trust that you have learned something new! I also hope you realize that it is now your responsibility to carry this message forward by practicing sustainable consumption and spreading awareness about sustainable fashion in your community.
Claudio, L. Waste Couture: Environmental Impact of the Clothing Industry. Environmental Health Perspectives2007, 115(9).
Wang, Z.; Cousins, I. T.; Scheringer, M.; Hungerbühler, K. Fluorinated Alternatives to Long-Chain Perfluoroalkyl Carboxylic Acids (PFCAs), Perfluoroalkane Sulfonic Acids (PFSAs) and Their Potential Precursors. Environment International2013, 60, 242–248.
Niinimäki, K.; Peters, G.; Dahlbo, H.; Perry, P.; Rissanen, T.; Gwilt, A. The Environmental Price of Fast Fashion. Nature Reviews Earth & Environment2020, 1 (4), 189–200.
An efficient way to administer pharmaceutical drugs to a patient is through a tablet. The drugs are measured and coated in a plastic that is broken down when the drugs are injected into the person, and the drug is absorbed into the bloodstream and transported to the tissue it acts upon. The traditional processes of packaging drugs in these plastics, however, often require the usage of high temperatures and solvents that can be harmful. For example, many volatile organic compounds like benzene and chloroform are used. There is the potential for some of the solvent to remain as a residual impurity after the manufacturing process and can be toxic to the patient or the environment. These materials also need specific management to prevent them from escaping into the atmosphere. Even more, the process of coating the drugs sometimes reduces the efficiency of the dose; for instance, high temperatures and volatile solvents can cause up to a 50% drop in efficacy (1).
At the University of Nottingham, Professor Steve Howdle and his team have used green chemistry techniques to design a plastic coating that does not decrease drug efficacy. The plastic degrades in the body at a controlled rate, releasing the drug into the patient over a specific period.
Professor Howdle uses supercritical fluids (Figure 1), specifically supercritical carbon dioxide (sc-CO2), instead of the conventional benzene and chloroform solvents typically used (1). A supercritical fluid has properties of both liquids and gases at a certain pressure and at around room temperature. Using sc-CO2, conventional solvents are not required and biodegradable plastics can be used to make polymers that coat the drugs before being administered to the individual. Furthermore, it has been demonstrated that using sc-CO2 allows for the plasticization of these polymers near room temperature, which means that the drug activity is unaffected. At room temperature, the plastics are solid but when exposed to high pressure (i.e. the critical pressure of sc-CO2), they liquify and allow for the drugs to be mixed in. Once in the blood, the polymers degrade slowly over days, allowing for a steady release of the drug into the patient. This maximizes the effect of the medicine and reduces the duration of the patient’s treatment regime. Polymers can degrade at different rates and the rate of degradation can be matched with the administered drug that best suits the patient’s needs.
These techniques can allow patients to receive medications that were previously unavailable due to the drugs being too delicate or too reactive to withstand the traditional methods of coating. Because proteins are so sensitive, they are not able to withstand elevated temperatures or strong solvents; with Dr. Howdle’s techniques, however, patients will soon have access to these treatments. Furthermore, because these processes do not include volatile organic solvents, there are no residues that could potentially be harmful to the patients or the environment.
By Nina-Francesca Farac, Ph.D. student, Social Media Coordinator and Blog Coordinator for the GCI
As chemists and material scientists strive to create a sustainable chemical industry, chemical building blocks derived from renewable resources have become a research necessity1. In 2004, the U.S. Department of Energy reported 12 building blocks attainable from biomass which have high potential for high-value chemicals or materials.2–4 One of the listed biorenewable building blocks is itaconic acid (IA). IA is an inexpensive, non-toxic, and readily available compound produced by the fermentation of glucose or other biomass sources such as corn, rice, or lignocellulosic feedstock.1,2 Importantly, IA is produced through an industrially scaled glucose fermentation process with an estimated global production of 80,000 tons/year and a price of around 2 USD/kg.5 Given this compound’s potential to become economically competitive with petroleum-based sources, its manufacturing capacity is expected to grow at a rate of 5.5% each year between 2016 and 2023.5,6
IA or methylene succinic acid has a trifunctional structure with two carboxylic acid groups and an α,β-unsaturated double bond in the backbone (1, Figure 1). These functional groups make IA a promising monomer for a variety of polymeric reactions.5,7,8 The polymerization of IA and its derivatives has been extensively studied to access a wide range of new and renewable advanced materials.
Most attention has been focused on radical polymerization of IA (Figure 2a) and its various alkyl esters such as dimethyl itaconate (2) and dibutyl itaconate (3) due to their structural similarities to the traditional monomers for poly(meth)acrylates, acrylic acid (4) and methacrylic acid (5). More recently, the step-growth polymerizations of itaconate derivatives have been investigated for the synthesis of numerous polyesters (Figure 2b).5,9
Several other chemical transformations have been explored to generate interesting materials from IA-derived polymers, such as thermoplastics and thermosets. Nonetheless, researchers argue that a significant amount of chemical space remains unexplored for the synthesis of high-value materials from IA.1 Moreover, several IA-derived polymers tend to have high glass-transition temperatures (Tgs) that limit their application.
In effect, Trotta et al.1 set out to design new polymers from IA and to expand the library of IA-derived renewable materials. Published in ACS Sustainable Chemistry & Engineering in December 2018, Trotta & colleagues were able to synthesize and characterize bio-sourced thermosets and thermoplastics that are almost completely derived from IA and whose mechanical properties are tunable. The authors developed scalable and efficient syntheses of three step-growth monomers from an IA derivative (Figure 3a). These monomers were then used to access functional polyesters that can be used for making thermosets and thermoplastics that are both mechanically and thermally stable (Figure 3b).
1. Synthesis & Characterization of Step-Growth Monomers from IA
First, a saturated diester (MS), a saturated diol (MB), and an unsaturated diester (CS) step-growth monomers were efficiently synthesized from commercially available dimethyl itaconate (DMI), an IA derivative (Figure 3a). The DMI-to-CS transformation was motivated by the instability of DMI itself in step-growth polymerization with diols. A scalable Diels-Alder reaction was carried out to circumvent this issue. The diene of choice was isoprene since it was recently demonstrated that isoprene can be derived from IA10, allowing for the synthesis of a stable monomer (CS) that is made completely from IA.
Next, binary (i.e. two-monomer) and ternary (i.e. three-monomer) step-growth polycondensations were carried out to make various amorphous polymers with low Tgs (e.g. -31 to -9 °C) and relatively high molar masses (>10 kg/mol). The low Tgs suggest easier processability and a wider range of applications for these polyesters. Thermogravimetric analysis confirms the relative stability of these polymers, particularly PMBCS (Figure 4) whereby no retro-Diels Alder reaction was observed along the polymer backbone at temperatures above 200 °C.
3. IA-Derived Thermosets
By controlling the feed ratio of the CS monomer, the authors producedternary polyesters with tunable amounts of unsaturation along the polymer backbone. This gave rise to polyesters that can be efficiently cross-linked using thiol-ene click chemistry to generate thermosets.
To continue with the theme of bio-sourced materials, the authors used a potentially renewable tetrathiol cross-linker (highlighted in purple, Figure 5b), to cross-link the ternary polymer, PMBCSx–stat-PMBMS1-x (Figure 5c).
The authors characterized both the thermal and mechanical properties of the synthesized thermosets. The cross-linking reaction afforded thermosets with slightly higher Tgs than their respective prepolymers, suggesting decreased flexibility of the polymer backbone due to cross-linking. The Young’s modulus (E), which is a measure of a material’s elasticity, was the largest for thermosets with the highest cross-linking densities. It was also observed that these mechanical properties are tunable by varying the molar mass between cross-links.
4. IA-Derived Thermoplastics
Finally, the authors prepared well-defined triblock polymer thermoplastics that can be prepared from IA-derived α-methylene-γ-butyrolactone (MBL)11 (Figure 6), giving thermoplastics that are almost completely derived from IA.
Tensile testing data indicate that the MBL chain-extended triblock polymer is indeed thermoplastic. The triblock polymer exhibits ductile tensile properties with a Young’s Modulus and tensile strength far exceeding those of the IA-derived thermosets.
5. Green Metrics
A sustainable chemical industry not only requires the use of bio-sourced/biorenewable substrates but also relies on safe and energy-efficient synthetic processes that do not generate any additional waste streams. In effect, the authors evaluated the small molecule transformations and polymerizations disclosed above using green metrics12 – measures to quantify the efficiency and/or environmental performance of a chemical process as it relates to the principles of green chemistry.13,14 Isolated yields, atom economies (AEs)15, and process mass intensities (PMIs)16 were reported for select reactions as listed in Table 1.
Most of the small molecule transformations and polycondensations are high yielding with a few exceptions. The low yield of 60% for PMBCS in reaction 4 is attributed to low polymer recovery during the purification by precipitation step.1 For reactions 2 and 3, yields >90% are achievable but on smaller scales; however, the authors desired scalable syntheses, making yields of 82% and 67% acceptable for these purposes.
The AE for addition reactions like reactions 1 and 3 is 100% whereas reactions with undesired byproducts have lower AE. Trotta et al. propose alternative synthetic routes that would result in increased AE for reactions 2, 4, 5, & 6 but these were not explored. Besides, a higher AE does not guarantee a high yielding and low PMI process and such suggestions require further investigation. On the other hand, this emphasizes the challenge scientists are faced when attempting to develop a sustainable process; it is generally difficult to implement all criteria outlined by the principles of green chemistry without having a trade-off somewhere within the process.
The PMI metric nicely showcases the impact of solvent on process efficiency. PMI values closer to 1 indicate a smaller mass of material required to synthesize 1 kg of product.1,16 PMI is low for most reactions listed in Table 1, reflecting little to no use of solvents (i.e. neat conditions) or other reagents during the reaction, workup, and/or purification steps. Comparing reactions 1 through 3, the synthesis of CS has an increased PMI of 12 due to the use of solvent during workup. Similarly, there is a sharp rise in PMI for polymers that are purified by dissolving and precipitating them from solution (reactions 4 and 5). In contrast, polymers that don’t require purification have a significantly lower PMI (reaction 6).
Overall, this paper is one of many that demonstrate the growing potential of itaconic acid as a multifunctional and renewable monomer for a wide range of polymerizations. The authors were largely successful in producing new bio-sourced and mechanically (as well as thermally) stable thermosets and thermoplastics from IA-derived materials.
Although the green metric evaluations identify several sustainable features of the reactions developed by Trotta et al., one aspect that puts into question how ‘green’ the reactions are is the type of catalyst used. Each small molecule transformation (reactions 1 – 3 in Table 1) uses either a platinum group metal or a rare earth metal – both of which are considered critical/endangered elements that are essential for use but subject to supply risk.14 It is noted that the catalyst loading for these reactions is low with amounts below 5 mol% or 5 wt%; however, it is not enough to reduce catalyst use. Complete catalyst recyclability is another factor that should be implemented. On this basis, the authors did show that the Sc(OTf)3 catalyst used in the synthesis of CS can be recovered at a 97% yield prior to distillation of the crude polymer product. The ability to recycle the other catalysts were not mentioned.
Furthermore, it would have been beneficial if the authors quantified the biorenewable content of their synthesized thermosets and thermoplastics instead of using general statements such as “almost completely derived from IA”. Other studies investigating the synthesis of polymeric materials from renewable sugar-derived precursors typically state the percentage of biobased content within their resulting materials (e.g. wt% in biorenewable content). For instance, a 2015 study17 described the biobased content of thermosets derived from IA-based polyesterss in the ranges of 78 and 88 wt%. The quantification of biorenewable content would unambiguously validate the work of Trotta et al. and better gauge their impact within the literature.
(1) Trotta, J. T.; Watts, A.; Wong, A. R.; Lapointe, A. M.; Hillmyer, M. A.; Fors, B. P. Renewable Thermosets and Thermoplastics from Itaconic Acid. ACS Sustain. Chem. Eng.2019, 7 (2), 2691–2701.
(2) Noordzij, G. J.; Van Den Boomen, Y. J. G.; Gilbert, C.; Van Elk, D. J. P.; Roy, M.; Wilsens, C. H. R. M.; Rastogi, S. The Aza-Michael Reaction: Towards Semi-Crystalline Polymers from Renewable Itaconic Acid and Diamines. Polym. Chem.2019, 10 (29), 4049–4058.
(3) Werpy, T.; Petersen, G. Top Value Added Chemicals from Biomass Volume I – Results of Screening for Potential Candidates from Sugars and Synthesis Gas; 2004.
(4) Bozell, J. J.; Petersen, G. R. Technology Development for the Production of Biobased Products from Biorefinery Carbohydrates—the US Department of Energy’s “Top 10” Revisited. Green Chem.2010, 12 (4), 539–555.
(5) Robert, T.; Friebel, S. Itaconic Acid – a Versatile Building Block for Renewable Polyesters with Enhanced Functionality. Green Chem.2016, 18 (10), 2922–2934.
(7) Geilen, F. M. A.; Engendahl, B.; Harwardt, A.; Marquardt, W.; Klankermayer, J.; Leitner, W. Selective and Flexible Transformation of Biomass-Derived Platform Chemicals by a Multifunctional Catalytic System. Angew. Chemie – Int. Ed.2010, 49 (32), 5510–5514.
(8) Medway, A. M.; Sperry, J. Heterocycle Construction Using the Biomass-Derived Building Block Itaconic Acid. Green Chem.2014, 16 (4), 2084–2101.
(9) Kumar, S.; Krishnan, S.; Samal, S. K.; Mohanty, S.; Nayak, S. K. Itaconic Acid Used as a Versatile Building Block for the Synthesis of Renewable Resource-Based Resins and Polyesters for Future Prospective: A Review. Polym. Int.2017, 66 (10), 1349–1363.
(10) Abdelrahman, O. A.; Park, D. S.; Vinter, K. P.; Spanjers, C. S.; Ren, L.; Cho, H. J.; Zhang, K.; Fan, W.; Tsapatsis, M.; Dauenhauer, P. J. Renewable Isoprene by Sequential Hydrogenation of Itaconic Acid and Dehydra-Decyclization of 3-Methyl-Tetrahydrofuran. ACS Catal.2017, 7 (2), 1428–1431.
(11) Trotta, J. T.; Jin, M.; Stawiasz, K. J.; Michaudel, Q.; Chen, W. L.; Fors, B. P. Synthesis of Methylene Butyrolactone Polymers from Itaconic Acid. J. Polym. Sci. Part A Polym. Chem.2017, 55 (17), 2730–2737.
(12) Tobiszewski, M.; Marć, M.; Gałuszka, A.; Namies̈nik, J. Green Chemistry Metrics with Special Reference to Green Analytical Chemistry. Molecules2015, 20 (6), 10928–10946.
(13) Tang, S. L. Y.; Smith, R. L.; Poliakoff, M. Principles of Green Chemistry: Productively. Green Chem.2005, 7 (11), 761–762.
(14) Dubé, M. A.; Salehpour, S. Applying the Principles of Green Chemistry to Polymer Production Technology. Macromol. React. Eng.2014, 8 (1), 7–28.
(15) Jiménez-González, C.; Constable, D. J. C.; Ponder, C. S. Evaluating the “Greenness” of Chemical Processes and Products in the Pharmaceutical Industry—a Green Metrics Primer. Chem. Soc. Rev.2012, 41 (4), 1485–1498.
(16) Jiménez-González, C.; Ponder, C. S.; Broxterman, Q. B.; Manley, J. B. Using the Right Green Yardstick: Why Process Mass Intensity Is Used in the Pharmaceutical Industry to Drive More Sustainable Processes. Org. Process Res. Dev.2011, 15 (4), 912–917.
(17) Dai, J.; Ma, S.; Wu, Y.; Han, L.; Zhang, L.; Zhu, J.; Liu, X. Polyesters Derived from Itaconic Acid for the Properties and Bio-Based Content Enhancement of Soybean Oil-Based Thermosets. Green Chem.2015, 17 (4), 2383–2392.
By Eloi Grignon, Ph.D. student, Member-at-Large for the GCI
Since their commercialization in 1991, lithium-ion batteries (LIBs) have gradually come to pervade our daily lives. Their ubiquity is achieved through our phones and laptops (you are likely reading these words via energy supplied by a LIB), where they are used to power not only our communication with one another, but also the myriad other tasks that we have come to delegate to our devices. Increasingly, LIBs are powering how we move, too, as is evidenced by the several million battery electric vehicles already on the road.1 With the production of electric vehicles set to skyrocket – the British and French governments have already pledged to ban sales of fossil-powered vehicles by 2040 – and the possibility of using LIBs for storage of grid electricity, it is clear that LIBs are not going anywhere, either.2 Indeed, spent batteries are expected to be generated at a rate of 2 million metric tons per year by 2030.3
And yet, there is no clear idea of what is to happen to these batteries once they’ve served their purpose. Currently, fewer than 5% of LIBs in the US and Europe are recycled while the rest end up in landfills.3
Since a LIB is densely comprised of several costly metals (Figure 1), it is fair to liken used batteries to enriched ore.3 It follows, then, that complete disposal of millions of metric tons of such a material represents a tremendous waste.
Figure 1. Breakdown of LIB constituents. From Ref .
Recycling could curb the waste by salvaging this ‘ore’ and supplying it to LIB manufacturers at a cheaper price than that of virgin materials, thereby reducing LIB cost. Moreover, less of the material would have to be mined and treated in the first place. This is especially important when considering the impacts of both processes: mining has obvious environmental consequences while ore treatment is typically energy-intensive and can release harmful gases such as SOx.4 Furthermore, 10-25% of global cobalt production is mined by ‘artisanal’ workers in the DRC, many of whom lack proper wages and equipment. The UNICEF estimated in 2012 that 40,000 children were employed in such mines.5 From this perspective, LIB landfilling has a heavy economic, environmental, and moral opportunity cost attached.
In addition to wastefulness, landfilling LIBs also has direct negative consequences. Over time, the toxic constituents of the LIBs tend to flow into the soil, eventually leaching into the groundwater and accumulating in various organisms. These toxins can make their way up to humans, thus extending the health hazard to people. The harm imposed by discarded LIBs on the environment is not without some degree of irony, as LIBs have long been celebrated as a key cog in the establishment of a greener future. Evidently, this detrimental end-of-life scenario presents an incongruity.
Given the benefits of LIB recycling, it is clear that technical and economic barriers, rather than lack of purpose, are responsible for the poor recycling rates.
One such barrier results from the complicated composition within LIBs, which renders separation and recovery of all components difficult. For instance, smelting can effectively recover the heavy metals nickel, cobalt, and copper but fails to salvage lithium and the electrolyte. While hydrometallurgical (chemical leaching) methods can recover more components, they necessitate acids, hydrogen peroxide, and 7 m3 of water per ton of LIB.6 Needless to say, this is not ideal.
Another technical issue is the great variability between LIBs – different manufacturers tend to use different components and so there is no one universal composition (this pertains mainly to vehicles). As such, a recycling firm is at the mercy of its feedstock – for an input collected from many sources, there is no guarantee that 1 ton of batteries will yield a given amount of, say, cobalt.
These issues appear blatant when considering as a counterexample the success story of lead-acid battery recycling, whose simple and standardized composition – about 60% lead – enables an easy recycling process that claims nearly all (99%!) of used batteries.4
The low recycling rates are also due to economic factors. The end-to-end recycling process is energy-intensive and requires many steps, thus increasing costs. A firm operating such a process must carefully assess whether their repurposing protocol is cheap enough to supply materials that are price-competitive with mined materials. Due to the lack of LIB standardization and high volatility of constituent prices, this assessment is far from trivial and the business represents a clear risk. This risk is further exacerbated by the uncertainty of what the future of energy storage may resemble. In the arms race for higher energy density, new technologies arise frequently, thus threatening to render state-of-the-art materials (and so, recycling processes) obsolete.
While the above paragraphs appear rather pessimistic, it should be noted that we are only at the onset of the LIB boom. Indeed, the field of LIB recycling is still gaining traction and it is expected that serious investments will aid in the development of more efficient recycling techniques. To this end, the US DoE (through the $15 million ReCell Center) and the UK-based ReLib project have pledged to fund and support R&D in LIB recycling.3
There is also a clear interest from the private sector as is evidenced by the numerous startup firms currently designing their own protocols, including the Toronto-based company Li-Cycle.7
Another approach to sustainable energy storage is to circumvent the need for recycling breakthroughs altogether by designing the LIB differently from the start. For instance, the use of organic materials that are easily recyclable is increasingly explored for use in devices.1 Not only are these materials favourable in the end-of-life stage, but their production is also cheap, accessible, and environmentally benign.
In any case, scientists, engineers, and policymakers must come together to address the issues caused by LIB landfilling. And quickly, too, because the storm is coming (Figure 2).
Figure 2. A possible scenario for the growth of electric vehicle sales in the next decade. PLDVs = passenger light duty vehicles; LCVs = light commercial vehicles; BEVs = battery electric vehicles; PHEV = plug-in hybrid electric vehicles. From Ref .
Poizot, P.; Gaubicher, J.; Renault, S.; Dubois, L.; Liang, Y.; Yao, Y. J. C. R., Opportunities and Challenges for Organic Electrodes in Electrochemical Energy Storage. 2020.
Gardiner, J. J. T. G., The rise of electric cars could leave us with a big battery waste problem. 2017,10.
It’s time to recycle lithium-ion batteries. C&EN Global Enterprise 2019,97 (28), 29-32.
Gaines, L. J. S. M.; Technologies, The future of automotive lithium-ion battery recycling: Charting a sustainable course. 2014,1, 2-7.
Frankel, T. C.; Chavez, M. R.; Ribas, J. J. T. W. P., The cobalt pipeline. Tracing the path from deadly hand-dug mines in Congo to consumers’ phones and laptops. 2016,30.
Larcher, D.; Tarascon, J.-M. J. N. c., Towards greener and more sustainable batteries for electrical energy storage. 2015,7 (1), 19-29.
By Nour Tanbouza (twitter @Nour_Tanbouza), PhD student, Laval University
Flow chemistry is a synthetic technique that enables chemical reactions to take place in a continuously flowing manner as opposed to running a reaction in a flask, sometimes termed batch chemistry. It has become incredibly mainstream and has been adopted by many chemical industries as a means to increase efficiency of large-scale reactions in highly controlled setups.1 What is flow chemistry, and why is it important? Furthermore, the main question, how does it contribute to sustainability?
Let us start by putting on a lab coat and safety goggles and strolling through a modern synthetic chemistry lab. Now, have a look around. What you will absolutely recognize and remember is a vast space of fume hoods and benches with different apparatus lying around like round bottom flasks, chromatography columns, stirrers, hot plates, etc. After that, take a browse through images of those same types of laboratories from the 1900s or even from the 1700s. Surely you will notice some improved safety features but what will strike you the most is how similar they are in terms of the equipment used then and now. We indeed currently have better stirring and heating equipment etc., but we still do reactions in round bottom flasks as batches.
In 2005, the catastrophic T2 laboratories explosion occurred after a thermal runaway and high-pressure build-up of their 2,500-gallon batch reactor producing MMT (methylcyclopentadienyl manganese tricarbonyl).2 These types of accidents pose a huge risk to human life and the environment in addition to the legal and financial troubles that the company could face. Thus, there is an exigent need for safe and practical technologies that enable an efficient scale up of chemical reactions. These pursuits explain the recent uptake of flow chemistry by many manufacturing companies, especially those in the pharmaceutical industry.
Figure 2. Aerial view of T2 Laboratories explosion
Flow chemistry can be thought of as a bench chemist’s very own cherry tree. The raw material is fed into the roots (pumps). Roots are the heart of the tree, and the same holds for the pumps of a flow system, so it is pivotal that they are well taken care of and are in perfect shape. Those nice healthy roots then flow the raw material over a large surface area up into the stems and leaves where reaction conditions are highly controlled and in perfect balance to elute the desired product continuously. Thus, whether targeting a few milligrams or multi-kilograms of product, it is dependent on how much feed material is flowed into the reactor. A flow reactor can be as small as a chip and still produce the needed amount of product. In 2019, flow chemistry was announced by the IUPAC (International Union of Pure and Applied Chemistry) as one of the ten chemical innovations that will change our world.3 There has been a significant paradigm shift by many industries, especially the pharmaceutical industry, to adopt flow chemistry. It is a technology that promises on-demand drug production, which is vital primarily for developing countries to access drugs in a decentralized manner.1
Figure 3. An academic flow system (equipped with a photoreactor)
Green chemistry principles and a chemical industry’s agenda align when it comes to large scale reactions. Thus, it is not so surprising to see a significant uptake of flow chemistry by many companies. This kind of endorsement has helped spark research in continuous flow which is beginning to become a dominating area of study. Among the UN Sustainability Goals is responsibility for consumption and production, which is achieved in flow because it minimizes the amount of material needed for screening and allows reactions to take place in highly concentrated media. Reaction conditions being highly controlled (such as temperatures, pressure, mixing, etc.), allow reactions to be more selective and thus decreases any by-products and increases productivity.4 Also, hazardous chemicals can be safely manipulated in flow because there is no significant build-up at any given time. It is very versatile and modular where multiple reactions can be installed in sequence to consume any reactive intermediates in situ, and purification systems can be added directly as well. A reaction can be run at extremely high temperatures that go above boiling points which can enable reactions to proceed faster while being inherently safer and consuming significantly less energy when compared to a batch reactor.
Figure 4. Illustration of a flow chemistry setup
This type of “thinking outside the flask” means stepping outside of a long-standing comfort zone which is not always trivial. However, this type of venture and side-by-side work of engineers and chemists is what made flow chemistry possible, and it is changing our world. Flow chemistry is still in its early stages, yet so much innovation has already been introduced. Give it a few years, and when you walk back into that synthetic chemistry lab, prepare to be flabbergasted by a space that resembles nothing of the past.
Malet-Sanz, L.; Susanne, F., Continuous flow synthesis. A pharma perspective. J. Med. Chem. 2012,55, 4062-4098.
The rise of fast-fashion trends in our global economy has led to a booming textiles manufacturing industry. According to the Ellen MacArthur Foundation, globally the industry consumes over 98 million tonnes of non-renewable resources per year.1 The majority of these items have seen less utilization compared with early 2000s. With an increasing consumer awareness of eco-friendly and sustainable practices in manufacturing, pressures at the consumer level have led to changes to these labour-intensive processes. Of note is the dyeing process, which historically has been a wet process. The dyeing, printing, and washing steps consume large amounts of energy and generate large volumes of wastewater, which contain the excess dyes, surfactants, and salts. In 2014 alone, coloration of textiles generated over 1.5 billion tons of wastewater.1 Much of this wastewater is neither environmentally benign nor biodegradable and requires further energy investment during the remediation step. Smaller eco-conscious manufacturers such as Ikeuchi Organic, a company located in Japan, have been tackling these issues by utilizing 100% wind power for their operations.2 The smaller scale allows for easier implementation of wastewater treatment and a final product which passes Class 1 certification as set by OEKO-TEX STANDARD 100, a global leader in textiles regulations.3 The underutilization of sustainable textiles dyeing processes on a large scale, however, continues to be a problem. The search for highly competitive, as well as energy and cost-efficient processes along with bridging the gap between laboratory and industrial scales to deliver the benefits of eco-friendly manufacturing is an ongoing goal in the textile research community.
Figure 1. Growth of clothing sales and decline in clothing utilization since 2000.1
Traditionally, the dyeing process involves an interaction between a dye molecule and a fibre (adsorption). This is accompanied by the movement of the dye to the interior of the fibre (diffusion). Consider cotton, which comprises an estimated 21% of global fibre usage.4 Cellulose is the primary component of cotton fibers, totalling up to 95% by mass. The most common method for dyeing cotton involves reactive dyes. As their name suggests, a reactive dye is a high energy molecule which can react with natural cellulose and form a covalent bond. The reactive molecule is low cost, easily tuned to a variety of vibrant colors, and simple to apply.
Figure 2. Types of reactions involving reactive dye and cellulose. Top is substitution, bottom is addition.
At each step of the process, there are several factors that determine the quality of the final product.5 Temperature has a pronounced effect on increasing dye penetration and more rapid diffusion, but at the cost of increased dye hydrolysis. Tight cotton fibres require higher temperature for effective permeation of the dye into the fibre, while loose cotton fibres require lower temperatures for the same effect. The alkalinity of the solution also plays an important role, as the concentration of the cellulose anion is proportional to the pH of the solution. During the dyeing process, some alkali is consumed, and therefore the pH of the final dye solution is lower than the initial pH. Electrolytes are also important to the dyeing solution, acting to overcome the electrostatic repulsions between anionic cellulose and the anionic dye linkers. Finally, the concentration of these additives also impacts the dyeing process. There is a fine line between rate of dyeing and negative impacts on production costs and the environment. These are just some examples of challenges textiles research scientists face when developing a new dye process.
Kim et al highlighted the use of nanofibrillated cellulose (NFC) as a supplement to normal cotton cellulose.6 The large surface area of NFC resulted in an abundance of surface cellulose hydroxyls. Consequently, the salt, alkali, and water amounts could be reduced by an order of magnitude, generating significantly less wastewater. Most importantly, the dyeing process was not significantly impacted by these changes and the resulting fabric is largely indistinguishable from traditional dyeing methods. A life-cycle assessment based on the experimental data suggested that the NFC-based process would result in a significant reduction on wastewater load.
Figure 3. Comparison of various dyeing methods. a) conventional dyeing method; b) conventional dyeing method with decreased salt and alkali concentration; c) NFC-based dyeing with decreased salt and alkali concentration.
Xia et al demonstrated the use of a co-solvent, ethanol, effective for eliminating the need for electrolytes.7 The ethanol was found to impact the dyeing process in four main ways: improving the solubility of the reactive dyes, decreasing the dielectric constant and electrostatic repulsion of the solution, increased aggregation of dyes leading to enhanced dyeing kinetics, and decreasing the surface tension improving dyeing efficiency. These efforts, too, improved the clarity of the resulting waste solution compared to commercial wastewater without loss of fabric colour.
Figure 4. Comparison of fabric wastewater with ethanol-water salt-free method and traditional electrolyte-added dyeing method.
Ding et al developed a method for dyeing without the use of reactive organic dyes, instead opting for base metal nanoparticles.8 Carbon black nanoparticles are first functionalized onto cotton fibres via radiation grafting. Subsequent immobilization of iron oxide red, cobalt green, or cobalt blue for red, green, and blue colors respectively, give rise to colorized cotton fabric. Various approximate colors can be created by varying the concentration of each nanoparticle, and the colour is retained even after 20 wash cycles. Most importantly, the lack of reactive dyes results in pronounced clarity of the resulting dye solution compared to real wastewater.
Figure 5. Images of wastewater samples. W0 is real wastewater from a dyeing factory. WCB1–WCB5, WCoG1–WCoG5, WCoG1–WCoG5, WFeR1–WFeR5 are samples from various concentrations of nanoparticle dyes.
Textiles and clothing play an important part of everyday life. The current clothing manufacture system is wasteful and polluting to the environment. With material and process scientists at the forefront, a new textiles economy built from sustainable methodologies will be vital as we continue to deplete our non-renewable resources.
There is a movement to develop a new type of product life system called ‘the circular economy’ . Part of this movement aims to manufacture products from recycled or raw materials, and after its useful lifetime, re-introduce the product (now considered waste) as recycled material. The motivation for the introduction of the circular economy is to minimize the need for virgin raw material, especially when it originates from non-renewable resources. This effort is being spearheaded by the Ellen MacArthur Foundation with major industry partners like Google, Unilever, Solvay, and Philips, among others . A critical component to the function of the circular economy is developing the capability to turn waste into a desirable product.
There are several methods of recycling all the different types of materials we use in every day life. This blog will discuss a niche in the ‘plastic to monomer’ field. Evidently, in April of 2019, IUPAC named ‘plastic to monomer’ as part of the 10 chemical innovations that could have high impact in society . Before discussing ‘plastic to monomer’, I must clarify the term ‘plastic’. Generally, plastic is made up of many polymer chains that are physically entangled with one another. A macroscopic analogy is when many electrical wires (think of Christmas tree lights) become entangled: the wires are stuck to each other and the rigidity of the ball of wire is greater than the rigidity of a single wire.
Much like the type of wire influences the tangled ball it forms, the chemical structure of the polymer influences the material properties of the plastic. Examples of properties of plastics include rigidity, elasticity, malleability, gas permeability, friction to skin, transparency, and many others. The polymers that are used for commercial plastic products have been studied and developed for decades to be able perform a specific function. For example, polyvinyl chloride and polystyrene were initially discovered in the 1800s [2,8]. Thus, it would be ideal if the currently used polymers can be de-polymerized back into monomers for recycling purposes. This would be a major move by the plastics industry to become environmentally friendly.
The conventional method to turn polymers into monomer is thermal decomposition. Samples of polymer can be heated to high temperature (typically 220-500 °C) to break some of the bonds that hold the monomers together . When this occurs, radicals can form at the site of the broken bond, which can lead to de-polymerization . The required temperature and how much monomer is formed is dependent on the chemical structure of the monomers that are formed. Thermal decomposition to recover monomer is suitable only for a few types of polymers, such as poly(α-methylstyrene), which has ceiling temperature of 66 °C to propagate depolymerization; the monomer recovery after thermal decomposition of poly(α-methylstyrene) is excellent at 95% . However, for polymers like polyethylene (PE, the most produced polymer) and polypropylene (PP, 2nd most produced polymer), the monomer recovery yield is poor (0.025-2%) . In some cases such as polyvinylchloride (PVC, 3rd most produced polymer), thermal decomposition is even more problematic because PVC will release harmful hydrochloric acid and vinylenes upon heating . Thus, the monomer recovery is poor (1 %) and the process is highly corrosive.
Therefore, one of the key challenges to address for ‘polymer to monomer’ is to perform de-polymerization at a low temperature. There are 4 recent publications that explore this challenge [5,7,9,12]. In general, the authors synthesized polymers using reversible-deactivation radical polymerization (RDRP) techniques and explored the de-polymerization reactions they encountered. Below is a brief highlight from the publications from the Haddleton group  and the Gramlich group .
Scheme 1: De-polymerization of RAFT polymers with trithioester end-group . Reproduced from ref.  with permission from The Royal Society of Chemistry.
Flanders et al. polymerized methacrylate monomers, including methylmethacrylate (MMA), using reversible addition-fragmentation chain-transfer (RAFT) polymerization with a trithioester chain-transfer agent (CTA) . This type of polymerization places trithioester end-group at end of the polymer chain (Scheme 1). Typically, this end-group is used to re-start the polymerization at the trithioester end of the polymer. However, as we will see, it may have another function. The authors isolated the polymer, then re-dissolved the polymer in 1,4-dioxane at 70 °C (Scheme 1). This caused monomers to be released from the polymer chains at a temperature much less than the ceiling temperature of MMA, which is 227 °C . Analysis of the polymer after partial de-polymerization demonstrated that the trithioester end-group was still attached to the polymer and the size dispersity (range of polymer ‘molecular weight’) was low, which suggested that the de-polymerization was moderated by the trithioester end-group. The authors observed 10-35% de-polymerization after heating at 70 °C for 12-60 hrs.
Scheme 2: ATRP of NIPAM in carbonated water, followed by de-polymerization . Reproduced from ref.  with permission from The Royal Society of Chemistry.
Lloyd et al. used an alkylbromide initiator, Cu-based catalyst system to polymerize N-isopropylacrylamide (NIPAM) in Highland Spring carbonated water at 0 °C (Scheme 2) . This type of polymerization places a halide at the end of the polymer chain. The authors monitored the monomer conversion into polymer using 1H-NMR spectroscopy. They measured that ca. 99% of the monomer was converted into polymer chains within 10 min. Unexpectedly, in the next 50 min. the authors observed 50% de-polymerization. The authors attempted to optimize de-polymerization conditions by changing the pH, using dry ice in HPLC grade water instead of Highland Spring carbonated water, etc. which led to 34-71% de-polymerization after 0.5-24 hrs. Years later, the same group used a very similar polymerization condition to polymerize NIPAM . This time, non-carbonated water was used as the solvent and they did not report any de-polymerization.
The reports on RDRP followed by de-polymerization highlighted here are not yet ready to make an impact to ‘plastic to monomer’. The authors admit that the mechanism of de-polymerization is unknown. However, these seem to be the first set of reports on de-polymerization occurring at low temperatures. Perhaps these publications could be the birth of the reversible-deactivation radical de-polymerization (RDRDe-P) field. This is especially intriguing because RDRP have already been studied for decades in academia and are being adopted by the polymer industry . Companies like BASF, Solvay, DuPont, L’Oréal, Unilever, 3 M, Arkema, PPG Industries, etc. already claimed patents for technology and products based on RDRP . Somewhat ironically, RDRP was also part of the IUPAC’s 10 chemical innovations for impact on society but not for its potential to recycle polymer .
The polymers of the future may not be made from monomers abundantly used today, but the polymers of the future may be degradable through a low energy process.
Alsubaie, F.; Liarou, E.; Nikolaou, V.; Wilson, P.; Haddleton, D. M. Thermoresponsive Viscosity of Polyacrylamide Block Copolymers Synthesised via Aqueous Cu-RDRP. European Polymer Journal2019, 114, 326–331.
Baumann, E. Ueber Einige Vinylverbindungen. Justus Liebigs Annalen der Chemie1872, 163 (3), 308–322.
Destarac, M. Industrial Development of Reversible-Deactivation Radical Polymerization: Is the Induction Period Over? Chem.2018, 9 (40), 4947–4967.
Flanders, M. J.; Gramlich, W. M. Reversible-Addition Fragmentation Chain Transfer (RAFT) Mediated Depolymerization of Brush Polymers. Chem.2018, 9 (17), 2328–2335.
Gomollón-Bel, F. Ten Chemical Innovations That Will Change Our World: IUPAC Identifies Emerging Technologies in Chemistry with Potential to Make Our Planet More Sustainable. Chemistry International2019, 41 (2), 12–17.
Li, L.; Shu, X.; Zhu, J. Low Temperature Depolymerization from a Copper-Based Aqueous Vinyl Polymerization System. Polymer2012, 53 (22), 5010–5015.
Liebig, J. Justus Liebig’s Annalen Der Chemie. Annalen der Chemie1832, 1874-1978.
Lloyd, D. J.; Nikolaou, V.; Collins, J.; Waldron, C.; Anastasaki, A.; Bassett, S. P.; Howdle, S. M.; Blanazs, A.; Wilson, P.; Kempe, K.; et al. Controlled Aqueous Polymerization of Acrylamides and Acrylates and “in Situ” Depolymerization in the Presence of Dissolved CO2. Commun.2016, 52 (39), 6533–6536.
Moldoveanu, Șerban. Analytical Pyrolysis of Synthetic Organic Polymers; Techniques and instrumentation in analytical chemistry; Elsevier: Amsterdam ; Oxford, 2005.
Sano, Y.; Konishi, T.; Sawamoto, M.; Ouchi, M. Controlled Radical Depolymerization of Chlorine-Capped PMMA via Reversible Activation of the Terminal Group by Ruthenium Catalyst. European Polymer Journal2019, 120, 109181.
SFPE Handbook of Fire Protection Engineering, 5th ed.; Hurley, M. J., Gottuk, D. T., Jr, J. R. H., Harada, K., Kuligowski, E. D., Puchovsky, M., Torero, J. L., Jr, J. M. W., Wieczorek, C. J., Eds.; Springer-Verlag: New York, 2016.
By Nina-Francesca Farac, Member-at-Large for the GCI
The impact of human activity on climate and the environment has moved beyond a mainstream headline. It has come to the point where we are considered the dominant influence on our ecosystems and geology, so much so that there is a buzzword for it: ‘Anthropocene’. Within the Anthropocene, our greatest challenge is lessening the effects of our immense footprint on Earth, mainly caused by consumption of fossil fuels and our obsession with plastics. Consequently, there has been a considerable spike in eco-friendly or ‘green’ marketing of numerous products labeled as ‘organic’, ‘biodegradable’, or ‘sustainable’ ranging from fuels, cars, skincare, all the way to clothing1. One common advertising theme for several everyday products is post-consumer recycled materials and their incorporation into the design and production of such commodities. But to what extent are the advertised claims legitimate and whether they allow for a circular economy (e.g. make, use, recover)? Here, we will cover the chemistry of popular sustainable alternatives to plastics and compare them to their non-sustainable counterparts to assess whether the ‘green’ hype is valid.
Recycling Plastics:Single-Use vs. Biodegradable vs. Compostable
Let’s start with why commonly used plastics, including single-use plastics, pose such an environmental liability. The reality of plastic recycling is that it is far less efficient in practice than one would hope. The types of plastics that can be recycled, the number of times they can be recycled and reused starts with the ubiquitous recycling symbols found on the bottom of plastic products2. A common misconception is to equate the presence of this symbol to the ability of recycling a given type of plastic; however, this is not the case. The truth is just because there is a recycling sign doesn’t necessarily mean it gets recycled3. According to Resin Identification Codes (RICs), plastics are organized into 7 categories according to the temperature at which the material has been heated, and this numerical categorization is only indicative of the kind of plastic it is, and not necessarily its recyclability (Fig. 1).
Figure 1. Resin Identification Codes (RICs) designating the seven categories of plastics, the corresponding chemical structure of each polymer, and graphical illustrations of common plastic products of each type.
In other words, just because we place it in a blue bin doesn’t mean it gets recycled. In fact, an astonishing 91% of plastics are not recycled2. You may be wondering, “how are recycling rates that low?” As with any commodity, recycling is ultimately determined by the market. If there is a demand, recyclers and companies will pay for post-consumer recyclables; but, without market demand, recycling bares no profit and placing them in a blue bin doesn’t make a difference3. For example, out of the seven categories of plastics depicted in Figure 1, only PET has a high recycling value (i.e. the price of PET scrap is high) while other plastics are projected to see a drop in recycling rates (at least in North America)4–6. In addition, certain types of everyday plastics are simply not recyclable, such as plastic bags, straws, and coffee cups (the latter is not possible unless the paper exterior is separated from the plastic interior)3; in effect, these items are tossed together in the “everything else” category #7 (Other) as non-recyclables and mainly contribute to plastic waste generation. Other limiting factors include the inability to recycle dirty plastic and how the quality of plastic is downgraded each time plastic is recycled7.
Since many everyday items are plastic-based and plastics are a staple of modern life, the most common sustainable alternative to single-use plastics are bioplastics, a.ka biodegradable plastics (Figure 2).
Figure 2. Types of biodegradable plastics in use today, their chemical structures, and their applications.
Consumer confusion often arises when the terms “biodegradable” and “compostable” are used interchangeably, although they do not convey the same concept. Biodegradable plastics are a class of polymers that can break down by the action of living organisms into natural byproducts such as water, biomass, gases (e.g. N2, CO2, H2, CH4), and inorganic salts within a reasonable amount of time8. The issue with this definition is that many plastic products eventually degrade; for instance, low density polyethylene (LDPE, category #4 – Fig. 1) has been shown to biodegrade slowly to carbon dioxide (0.35% in 2.5 years) and thus can be considered a biodegradable polymer according to the above description9. Because certain definitions of biodegradability do not state a time limit or timeframe within which degradation should occur, consumers can be easily misled, and companies can hide behind this ambiguity. It is assumed, however, that a biodegradable product has a degradation rate that is comparable to that of its application rate, i.e. the break down process is fast such that product accumulation in the environment does not occur.
To understand why certain polymers biodegrade and others do not, one has to consider the chemical structure of biodegradable polymers along with the mechanisms through which polymeric material are biodegraded. Structurally, many biodegradable polymers, both natural and synthetic, often contain amide, ester, or ether bonds10. Those deriving from biomass (i.e. agro-polymers) include polysaccharides (glycosidic bonds via condensation of a saccharide hemiacetal bond and an alcohol) and proteins (chains of amino acids linked via amide groups). The other major category is biopolyesters, which are typically derived from microorganisms or are synthetically made (Figure 3).
Figure 3. Categories of biodegradable polymers.
Mechanistically, biodegradation is defined as a process caused by biological activity, especially driven by enzymes, but it can occur simultaneously with – and sometimes even initiated by – abiotic process such as photodegradation and hydrolysis9. From the chemical perspective, biodegradation can occur in the presence of oxygen (aerobic, Equation 1.1) or in the absence of oxygen (anaeriobic, Equation 1.2), where Cpolymer represents either a polymer or a fragment from an earlier degradation process9.
Complete biodegradation is said to occur when no Cresidue remains, and no oligomers or polymers are left to be further broken down9. As polymers represent major constituents in living cells that have a high turnover rate, i.e. they are constantly degraded in response to environmental changes and metabolic requirements, numerous microorganisms are capable of breaking down naturally occurring polymers as a result of millions of years of adaption. However, for many new synthetic polymers invented in the last 100 years (categories 1-6, Fig. 1) which find their way into the environment, such biodegradation mechanisms have yet to be developed. Other key factors affecting polymer biodegradation include copolymer composition and environmental factors such as pH, temperature, and water content9. This suggests that even if a product is made from bioplastics, it doesn’t necessarily mean it will fully decompose. If such products end up in landfills, for instance, the low oxygen content of such an environment impedes complete degradation. Furthermore, although bioplastics fall within category 7 (Fig.1), these plastics aren’t suitable for recycling and can even degrade the quality of plastic if added to a recycled mixture.
In contrast, compostable materials can break down into water, carbon dioxide, inorganic salts and biomass at the same rate as cellulose, or roughly 90 days11,12. In addition, compostable plastics must disintegrate fully and be indistinguishable in the compost while leaving no toxic material behind. Although compostable plastics appear to have more environmental benefits, this material is equally limited by an inability to biodegrade in a landfill and being incompatible with mixed recycled plastics11. When it comes to biodegradable and compostable plastics, these products make for sustainable alternatives only if they are destined for the appropriate composting facilities whereby the specific conditions for their complete biodegradation are met.
In short, today’s environmental pressures have urged the mainstream production of sustainable alternatives to an ever-growing plastic problem. Although socially responsible plastic products exist with the intention of lessening their environmental footprints, their legitimacy as sustainable alternatives lies in their proper disposal and complete integration into a given environment without any adverse or toxic effects. For a more concrete circular economy, products made of glass and metal can be recycled infinitely without losing product quality, have no need for additional virgin material in the recycling process, and do not generate waste during the process3. Ultimately, a future with a reduced plastic impact depends not only on closed-loop recycling habits, but also on consumer education and awareness about how these products are made and disposed of.
(1) Schmuck, D.; Matthes, J.; Naderer, B. Misleading Consumers with Green Advertising? An Affect–Reason–Involvement Account of Greenwashing Effects in Environmental Advertising. J. Advert.2018, 47 (2), 127–145.
By Alana Rangaswamy (Vice-President, Dalhousie University Green Chemistry Initiative)
The iconic Halifax Ferry is one of many boats to traverse the Harbour every day.
One great part of attending Dalhousie University is living steps away from the ocean. Much of Halifax’s history and development is due to its access to water, both as a naval base and port of call. With the massive amount of boat traffic seen daily by the harbour, marine industries strive to maximize the efficiency of travel. And one major way to do that is preventing small creatures from hitching a ride on your boat, causing drag and lowering the efficiency of your vessel. Enter antifoulants: coatings that kill organisms or otherwise block their ability to stick onto your ship. Antifouling is a necessary technology, but introducing biocidal agents into a marine environment, unsurprisingly, poses many environmental challenges. Let’s take a look at two commonly used antifoulants, their issues, and how scientists have tried to fix them:
You may have heard of tributyltin (TBT) as a biocidal agent. TBT is an excellent poison – effectively nonpolar due to its alkyl groups, it’s able to accumulate in organisms, rapidly killing them due to the high toxicity of SnIII. This property makes TBT an extremely effective antifouling agent, however, it easily leaches from boat hull paint into the ocean where it persists due to its high stability. Fortunately, the dangers TBT have been recognized worldwide and use as a biocidal agent has been banned as of 20081. Canada jumped on the bandwagon slightly earlier, with the last TBT-containing paint product registered in 1999.2 With this restriction, the industry is searching for alternatives that are as effective as TBT, without the environmental drawbacks.
Copper as a bulk metal is naturally antiseptic, promoting the formation of reactive hydroxyl radical species which lead to cell death in living systems.3 Copper has been used on boat hulls since the 1700s, and now usually shows up in paints as its metal oxide4 or as a suspension of copper powder.5 Although copper is less bioavailable than TBT, it persists and continually forms unstable radical species (and can, therefore. wreak ecological havoc) in a marine environment. Since copper is widely considered the new “gold” standard in antifouling, the sheer amount of it present on (and leaching off of) boat hulls today points to a long-term impact.
New Antifouling Tech
Green chemistry and engineering are all about designing cleaner systems that work as well as, or better than, the existing standard. TBT and copper are high bars to clear, but scientists are up to the challenge. As early as 1996, the environmentally benign Sea-Nine antifouling compound had received the Designing Greener Chemistry Award as part of the US EPA’s Presidential Green Chemistry Challenge.6 Sea-Nine is a derivative of isothiazolinone, a 5-membered heterocycle containing nitrogen and sulfur atoms. The compound is acutely toxic to marine organisms at the surface of boats, but biodegrades rapidly in marine environments through a ring-opening mechanism to form non-toxic by-products. Sea-Nine (and its derivatives) is currently present in commercial boat hull paints,7 however, degradation times may vary based on geographical location and local environment8 so our job isn’t done yet.
There are many newer studies in the works. For instance, investigation has been done into using natural products as antifouling agents. Natural products are secondary metabolites produced by microorganisms as a defence mechanism in response to stress. As such, they often have antimicrobial properties, while being naturally biodegradable. For example, 1-hydroxymyristic acid, a simple alpha-hydroxy fatty acid, was isolated from the marine bacterium Shwanella oneidensis. When panels were coated with paint containing the fatty acid, and subsequently immersed in a marine environment, no growth of foulants was observed even after 1.5 years.9 Other studies have added hydrophobic coatings which disrupt the binding interactions between the microorganism and the vessel’s hull, and promote detachment due to the natural flow of the water over the hull.10 Some research has diverted away from chemical modifiers altogether, using microtextures, which remove the flat surfaces required for spores to settle,10 to deter growth. UV-LEDs11 which are mutagenic and cytotoxic at a small scale, have also been used to reduce growth of foulants.
The long history and many methods developed to prevent boat hull fouling demonstrates that this is an important and challenging problem. But many results are promising, and green chemists and engineers are well on their way to solving it.