A Materials Chemistry Student’s Take on Fast Fashion

By Hana El-Haddad, Secretary for the GCI

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!

Figure 1. A non-comprehensive list of fast fashion retailers2.

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

Figure 2. Environmental impacts of different textiles7.

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:

  1. 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!
  2. 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.
  3. 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!).
  4. 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.
  5. 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.
  6. 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.

References

  1. Claudio, L. Waste Couture: Environmental Impact of the Clothing Industry. Environmental Health Perspectives 2007115(9). 
  2. Segura, A. Mass-market fashion retailers. https://fashionretail.blog/2019/04/22/mass-market-fashion-retailers/.
  3. Stanton, A. What Is Fast Fashion, Anyway? https://www.thegoodtrade.com/features/what-is-fast-fashion.
  4. KEMI Swedish Chemicals Agency. Chemicals in textiles – Risks to human health and the environment. Report from a government assignment. Report 6/14. kemi.se https://www.kemi.se/global/rapporter/2014/rapport- 6-14-chemicals-in-textiles.pdf
  5. GreenChemUofT. Textiles True Colours: How Sustainable are they? https://greenchemuoft.wordpress.com/2020/03/24/textiles-true-colours-how-sustainable-are-they/.
  6. 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 International 201360, 242–248. 
  7. Niinimäki, K.; Peters, G.; Dahlbo, H.; Perry, P.; Rissanen, T.; Gwilt, A. The Environmental Price of Fast Fashion. Nature Reviews Earth & Environment 20201 (4), 189–200. 
  8. Ducasse, P.; Finet, L.; Gardet, C.; Gasc, M.; Salaire, S. Why Luxury Brands Should Celebrate the Preowned Boom. https://www.bcg.com/publications/2019/luxury-brands-should-celebrate-preowned-boom.aspx.

Upgrading Health: Using Supercritical CO2 to Increase Drug Efficacy

By Shreya Kanade, GCI member-at-large

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.

Figure 1. The different phases of carbon dioxide with varying temperature and pressure (2).

              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.

Works Cited

Monomer Spotlight: Multifunctional and Renewable Itaconic Acid

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.  

Figure 1. Chemical structure of itaconic acid (1) and its ester derivatives (2, 3) along with acrylic (4) and methacrylic acid (5).

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

Figure 2. Select polymerization pathways for itaconate.

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).

Figure 31. (a) Bio-sourced monomers from IA. (b) Bio-sourced thermoplastics and thermosets derived from IA.

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.

2. Step-Growth Polycondensation Polymerizations – Synthesis & Characterization

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.

Figure 4.1 Synthesis of (a) fully unsaturated poly(MB-alt-CS) (PMBCS), (b) fully saturated poly(MB-alt-MS) (PMBMS), and (c) statistical ternary PMBCSx-stat­-PMBMS1-x.

3. IA-Derived Thermosets

By controlling the feed ratio of the CS monomer, the authors produced ternary 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, PMBCSxstat­-PMBMS1-x (Figure 5c).

Figure 5. (a) A model reaction for thiol-ene “click” chemistry on PMBCS. (b) A potentially renewable retro-synthetic route to the tetrathiol cross-linker. (c) Cross-linking reaction of crude PMBCSx-stat­-PMBMS1-x with the tetrathiol cross-linker and DMPA initiator to give IA-derived thermosets.

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.

Figure 6.1 Chain extension of HO-PMBMS-OH to give PMBL-PMBMS-PMBL.

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.

Table 1. Green metric evaluations of various reactions presented by Trotta et al. aDefined as the percent of the molecular weight of the desired product compared to the molecular weight of all starting reactants. bDefined as the ratio of the mass (in kg) of all the raw material used in the synthesis of the desired product (including all reagents, mass of solvent(s) and other materials such as silica used in purification) to the mass (in kg) of the isolated product.

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).

6. Summary  

            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.

REFERENCES

(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.

(6)      Transparency Market Research, Market Report Itaconic Acid, 2015; 2015.

(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. Molecules 2015, 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.

The Looming Problem of Lithium-Ion Battery Waste

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.

Figure 1. Breakdown of LIB constituents. From Ref [3].

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 [1].

References

  1. 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.
  2. Gardiner, J. J. T. G., The rise of electric cars could leave us with a big battery waste problem. 2017, 10.
  3. It’s time to recycle lithium-ion batteries. C&EN Global Enterprise 2019, 97 (28), 29-32.
  4. Gaines, L. J. S. M.; Technologies, The future of automotive lithium-ion battery recycling: Charting a sustainable course. 2014, 1, 2-7.
  5. 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.
  6. Larcher, D.; Tarascon, J.-M. J. N. c., Towards greener and more sustainable batteries for electrical energy storage. 2015, 7 (1), 19-29.
  7. https://li-cycle.com/about-us/.
Just Keep Flowing

Just Keep Flowing

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.

Figure 1. on the left: 18th century laboratory used by Antoine Lavoisier (credits Sandstein / CC BY (https://creativecommons.org/licenses/by/3.0)); on the right: Modern synthetic chemistry laboratory ( credits Elrond / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

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.

Picture3

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

Picture4

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.

Picture5

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.

 

References:

  1. Malet-Sanz, L.; Susanne, F., Continuous flow synthesis. A pharma perspective. J. Med. Chem. 2012, 55, 4062-4098.
  2. http://www.csb.gov/UserFiles/file/T2%20Final%20Report.pdf
  3. Gomollón-Bel, F., Ten Chemical Innovations That Will Change Our World. Chemistry International 2019.
  4. Jensen, K. F.; Rogers, L., Continuous manufacturing – the Green Chemistry promise? Green Chemistry 2019, 21, 3481-3498.

Electrosynthesis: A Green Methodology for Organic Chemistry

By Dr. Matthew Leech, post-doctoral fellow, University of Greenwich

According to the International Energy Agency (IEA), global energy-related carbon dioxide emissions were estimated to be approximately 33 gigatonnes (Gt).1 It is perhaps unsurprising that the two largest sources of carbon dioxide emissions arise from transportation and the generation of electricity (Figure 1).  However, what is surprising is that the aggregate global emissions of the pharmaceutical sector far outweigh those of the automotive industry – 52 million tonnes vs 46.4 million tonnes in the year 2018.1

Figure 1

Figure 1: World carbon dioxide emissions by sector between 1990 and 2010. Source – https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions

 

This is because a large proportion of chemical syntheses in an industrial setting are conducted under thermochemical conditions, meaning that they must be heated to high temperatures for prolonged periods of time.  These conditions are very energy intensive, and the reagents used are often hazardous and difficult to remove from the final product.  The latter is particularly problematic for redox reactions (reactions involving the addition or removal of electrons), where toxic metal complexes are often used.

In contrast, the electrochemical synthesis of organic molecules, also known as Organic Electrosynthesis, uses the cheapest and most versatile redox agent available on the market, electricity, to perform chemical transformations at room temperature.  Organic electrosynthesis has experienced a resurgence in interest in recent years, owing to the increasing availability of affordable and standardised equipment,2 which has improved experiment reproducibility, and the growing desire by the chemistry community to find milder and greener reaction conditions. A typical modern academic electrosynthesis setup can be seen in Figure 2.

 

Figure 2

Figure 2: Modern organic electrosynthesis equipment, comprising of a combined stirrer/potentiostat, cell lid, 10 mL glass cell, and two carbon graphite electrodes.

 

Aside from saving energy by switching from thermochemical to electrochemical synthesis, electrosynthesis is often safer than traditional methods, as it reduces or eliminates the need for toxic solvents and catalysts.  In 2019 it was reported that substituted lactones, which are known for their fungicidal, antibiotic, and anticancer properties, can be synthesised using photochemistry (Scheme 1).3 However, the reported procedure necessitates the use of a potentially toxic nickel catalyst, in addition to a solvent mixture comprising of benzene and 1,4-dioxane, both of which are suspected carcinogens.  Fortunately, a complimentary electrochemical method was reported in the same year which not only removed the need for the nickel catalyst, but also uses methanol as a solvent, which is less toxic and is considered to be greener by comparison (Scheme 1).4

Scheme 1

Scheme 1: Synthesis of substituted γ-butyrolactones via photochemical (top) and electrochemical (bottom) methods.

 

Photochemistry also necessitates the use of a photocatalyst, a compound which can convert absorbed light into useable electrons.  These are normally based upon third-row transition metals such as iridium, which makes them very expensive (a typical photocatalyst costs between £40 – 60 for 0.1 g), which usually limits the uptake of photochemical methods within industry.  In contrast, electricity is cheap, with 1 mole of electrons (6.02×1023 electrons) costing around £0.83.4

 

Furthermore, through electrosynthesis, it is possible to avoid the use of reactive and often highly toxic reagents by generating them in-situ.  For example, methoxymethyl (MOM) ethers, which are used as protecting groups in organic chemistry, are normally synthesised using chloromethyl methyl ether (CMME) which, aside from being flammable and toxic, is known to cause cancer.  However, it is now possible to synthesise these ethers using electrosynthesis at room temperature, using a very low current, inexpensive graphite electrodes,  and greener solvents (Scheme 2).5,6

Scheme 2

Scheme 2: Electrochemical synthesis of methoxymethyl ethers from carboxylic acid derivatives in methanol at room temperature using graphite electrodes.

 

But organic electrosynthesis is not limited to university laboratories, as electrosynthetic methodologies can often be scaled-up to be used in industrial laboratories with relative ease.  Perhaps the most well-known example of industrial scale electrosynthesis is the electrohydrodimerisation of acrylonitrile into adiponitrile by Monsanto, which is a key intermediate in the manufacturing of nylon (Scheme 3).7–9  Under aqueous conditions, it has been possible to synthesise approximately 300 000 tons of adiponitrile worldwide, with the sole by-product being oxygen, arising from the oxidation of water.

Scheme 3

Scheme 3: Industrial electrochemical synthesis of adiponitrile from two acrylonitrile molecules using cadmium and stainless-steel electrodes under aqueous conditions.

 

In summary, organic electrosynthesis represents a modern, greener, more economical, and safer alternative to traditional chemical syntheses.  With the advent of new and more user-friendly equipment, the field has experienced a resurgence in interest, with many new methodologies being developed in recent years.  Through the use of electrosynthesis, the challenge of making the pharmaceutical sector greener is starting to look much more achievable.

References

 

1            L. Belkhir and A. Elmeligi, Carbon footprint of the global pharmaceutical industry and relative impact of its major players, J. Clean. Prod., 2019, 214, 185–194.

2            M. Yan, Y. Kawamata and P. S. Baran, Synthetic Organic Electrochemistry: Calling All Engineers, Angew. Chem. Int. Ed., 2018, 57, 4149–4155.

3            L. E. Overman, N. A. Weires and Y. Slutskyy, Facile Preparation of Spirolactones by an Alkoxycarbonyl Radical Cyclization Cross-Coupling Cascade, Angew. Chem. Int. Ed., 2019, 58, 8561–8565.

4            A. Petti, M. C. Leech, A. D. Garcia, I. C. A. Goodall, A. P. Dobbs and K. Lam, Economical, Green and Safe Route Towards Substituted Lactones via the Anodic Generation of Oxycarbonyl Radicals, Angew. Chem. Int. Ed., 2019, 58, 16115–16118.

5            X. Luo, X. Ma, F. Lebreux, I. E. Markó and K. Lam, Electrochemical methoxymethylation of alcohols – A new, green and safe approach for the preparation of MOM ethers and other acetals, Chem. Commun., 2018, 54, 9969–9972.

6            C. G. W. van Melis, M. R. Penny, A. D. Garcia, A. Petti, A. P. Dobbs, S. T. Hilton and K. Lam, Supporting-Electrolyte-Free Electrochemical Methoxymethylation of Alcohols Using a 3D-Printed Electrosynthesis Continuous Flow Cell System, ChemElectroChem, 2019, 6, 4144–4148.

7            D. E. Danly, Development and Commercialization of the Monsanto Electrochemical Adiponitrile Process, J. Electrochem. Soc., 1984, 131, 435C.

8            M. M. Baizer, Electrolytic Reductive Coupling, J. Electrochem. Soc., 1964, 111, 215.

9            M. C. Leech, A. D. Garcia, A. Petti, A. P. Dobbs and K. Lam, Organic electrosynthesis: from academia to industry, React. Chem. Eng., 2020, Advanced Article, DOI: 10.1039/D0RE00064G

 

 

A Quirky Chemistry Break: Solvent-less Polymerization with Ball Milling

By Hyungjun Cho, member-at-large for the GCI

In April of 2019, the International Union of Pure and Applied Chemistry (IUPAC) named reactive extrusion as part of the 10 chemical innovations that could have high impact in society [1]. One of the reactive extrusion technique that is of interest is the use of ball mills instead of solvents to mix reagents. An exciting example of such a reaction is solvent-less polymerization. This method of making polymers in a ball mill has been blossoming in recent years but has not attracted much mainstream attention in the chemical community. This article will present the pivotal publication that re-invigorated interest the field of solvent-less polymerization.

There is the typical list of ingredients required for making polymers: 1) monomer, 2) an initiator and/or catalyst, 3) a constant input of energy, and 4) a solvent. Like in organic chemistry, the solvent is almost always critical to the success of the process. Although some solvent-less polymerization techniques are have known for (such as bulk [2] and solid-state polymerization [3]), these methods are not widely applicable and often requires elevated temperatures, which needs a lot of energy. In contrast, ball milling polymerization is a solvent-free technique that is at its early stages of development, but may avoid these issues.

 

Figure 1

Figure 1. A cartoon diagram of the vibrational ball milling process.

 

Ball milling is a mechanochemical process, where solid chemical samples are added to a grinding jar with solid metal balls (Figure 1). The grinding jar is shaken or spun which results in collisions between the balls and the chemical material. This generates high instant pressure and heat through impact and friction [4].

Although ball mills are conventionally used to break down polymers [5], a handful of reports demonstrated the synthesis of polymers using ball mills [6-10]. In 2014, Ravnsbaek et al. synthesized the polymer poly(p-phenylene vinylene) using a ball mill [5]. This work seems to have reinvigorated the field of ball mill polymerization, and is briefly presented here.

Figure 2

Figure 2. Solvent-less synthesis of poly(2-methoxy- 5-2′-ethylhexyloxy phenylene vinylene) in a ball mill. ACS Macro Lett. 2014, 3 (4), 305–309 [5]. Copyright 2014 American Chemical Society.

Briefly, the solid chemicals bis(chloromethyl)-methoxy-ethylhexyloxy-benzene and potassium tert­-butoxide were added to a zirconium oxide grinding jar, along with a zirconium oxide ball (diameter = 10 mm) (Figure 2). The reaction mixture was shaken horizontally at a frequency of 30 Hz at room temperature to synthesize poly(2-methoxy- 5-2′-ethylhexyloxy phenylene vinylene) (MEH-PPV). The authors found that after ca. 10 minutes of shaking, the polymers grew to its maximum average molecular weight (Mn = 35 kDa) (Figure 3). The size dispersity of the polymer was broad (Đ ~ 4) which is typical of stepwise growth polymerizations. The yield was ca. 60% after 10 minutes of shaking and did not improve with longer shaking time. This was especially remarkable because similar polymerization in solution typically requires several hours and elevated temperature [11-13].

Figure 3

Figure 3. The synthesis and degradation of MEH-PPV with respect to ball milling time Reprinted with permission from Ravnsbæk J. B. and Swager, T. M. ACS Macro Lett. 2014, 3 (4), 305–309 [5]. Copyright 2014 American Chemical Society.

In another set of experiments, Ravnsbaek et al. obtained a pre-made sample of MEH-PPV with a larger Mn (Mn =150 kDa) and exposed it to the same grinding conditions used for their synthesis of MEH-PPV. The authors found that the Mn of the larger polymer sample decreased over time to 35 kDa (Figure 3), which suggested that there exists a maximum size of polymer that can be synthesized using a ball mill.

Since this report by Ravnsbaek et al., other research groups have been using ball mills for solvent-less polymerizations. The Borchardt group [14-16], the Kim group [17-18], and the Song group [19] published their findings within the last 4 years. These reports collectively demonstrate many novel ball mill polymerizations, including co-polymerization (more than one monomer) [15-16,19], metal catalyzed polymerization (palladium-catalyzed polymerization) [15-16], and the synthesis of non-conjugated polymers (i.e. poly(lactic acid) and polyurethanes) [17-19].

In 2019, Christensen et al. published an article in Nature Chemistry showing their work regarding a new type of polymer called the vitrimer [20], which was synthesized as the product of the reaction of ketones and amines in a ball mill. While the focus of this article was on the chemistry of the polymer, it is noteworthy that the ball mill polymerization has been highlighted in a high impact journal. This will likely encourage more polymer research groups to look into this unconventional technique as it has a lot of room for growth and improvement, and even more potential to reduce the use of solvent in polymer production.

References

  1. 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 International 2019, 41 (2), 12–17.
  2. Han, X.; Fan, J.; He, J.; Xu, J.; Fan, D.; Yang, Y. Direct Observation of the RAFT Polymerization Process by Chromatography. Macromolecules 2007, 40 (15), 5618–5624.
  3. Duh, B. Effects of Crystallinity on Solid-State Polymerization of Poly(Ethylene Terephthalate). Journal of Applied Polymer Science 2006, 102 (1), 623–632.
  4. Janot, R.; Guérard, D. Ball-Milling in Liquid Media: Applications to the Preparation of Anodic Materials for Lithium-Ion Batteries. Progress in Materials Science 2005, 50 (1), 1–92.
  5. Ravnsbæk, J. B.; Swager, T. M. Mechanochemical Synthesis of Poly(Phenylene Vinylenes). ACS Macro Lett. 2014, 3 (4), 305–309.
  6. Huang, J.; Moore, J. A.; Acquaye, J. H.; Kaner, R. B. Mechanochemical Route to the Conducting Polymer Polyaniline. Macromolecules 2005, 38 (2), 317–321.
  7. Murakami, S.; Tabata, M.; Sohma, J.; Hatano, M. Mechanochemical Polymerization of Acetylene. Journal of Applied Polymer Science 1984, 29 (11), 3445–3455.
  8. Posudievsky, O. Yu.; Goncharuk, O. A.; Barillé, R.; Pokhodenko, V. D. Structure–Property Relationship in Mechanochemically Prepared Polyaniline. Synthetic Metals 2010, 160 (5), 462–467.
  9. Posudievsky, O. Yu.; Goncharuk, O. A.; Pokhodenko, V. D. Mechanochemical Preparation of Conducting Polymers and Oligomers. Synthetic Metals 2010, 160 (1), 47–51.
  10. Thorwirth, R.; Stolle, A.; Ondruschka, B.; Wild, A.; Schubert, U. S. Fast, Ligand- and Solvent-Free Copper-Catalyzed Click Reactions in a Ball Mill. Commun. 2011, 47 (15), 4370–4372.
  11. Jin, S.-H.; Kang, S.-Y.; Yeom, I.-S.; Kim, J. Y.; Park, S. H.; Lee, K.; Gal, Y.-S.; Cho, H.-N. Color-Tunable Electroluminescent Polymers by Substitutents on the Poly(p-Phenylenevinylene) Derivatives for Light-Emitting Diodes. Mater. 2002, 14 (12), 5090–5097.
  12. Liu, B.; Lü, X.; Wang, C.; Tong, C.; He, Y.; Lü, C. White Light Emission Transparent Polymer Nanocomposites with Novel Poly(p-Phenylene Vinylene) Derivatives and Surface Functionalized CdSe/ZnS NCs. Dyes and Pigments 2013, 99 (1), 192–200.
  13. Schwalm, T.; Wiesecke, J.; Immel, S.; Rehahn, M. The Gilch Synthesis of Poly(p-Phenylene Vinylenes): Mechanistic Knowledge in the Service of Advanced Materials. Macromolecular Rapid Communications 2009, 30 (15), 1295–1322.
  14. Grätz, S.; Borchardt, L. Mechanochemical Polymerization – Controlling a Polycondensation Reaction between a Diamine and a Dialdehyde in a Ball Mill. RSC Adv. 2016, 6 (69), 64799–64802.
  15. Grätz, S.; Wolfrum, B.; Borchardt, L. Mechanochemical Suzuki Polycondensation – from Linear to Hyperbranched Polyphenylenes. Green Chem. 2017, 19 (13), 2973–2979.
  16. Vogt, C. G.; Grätz, S.; Lukin, S.; Halasz, I.; Etter, M.; Evans, J. D.; Borchardt, L. Direct Mechanocatalysis: Palladium as Milling Media and Catalyst in the Mechanochemical Suzuki Polymerization. Angewandte Chemie International Edition 2019, 58 (52), 18942–18947.
  17. Lee, G. S.; Moon, B. R.; Jeong, H.; Shin, J.; Kim, J. G. Mechanochemical Synthesis of Poly(Lactic Acid) Block Copolymers: Overcoming the Miscibility of the Macroinitiator, Monomer and Catalyst under Solvent-Free Conditions. Chem. 2019, 10 (4), 539–545.
  18. Ohn, N.; Shin, J.; Kim, S. S.; Kim, J. G. Mechanochemical Ring-Opening Polymerization of Lactide: Liquid-Assisted Grinding for the Green Synthesis of Poly(Lactic Acid) with High Molecular Weight. ChemSusChem 2017, 10 (18), 3529–3533.
  19. Oh, C.; Choi, E. H.; Choi, E. J.; Premkumar, T.; Song, C. Facile Solid-State Mechanochemical Synthesis of Eco-Friendly Thermoplastic Polyurethanes and Copolymers Using a Biomass-Derived Furan Diol. ACS Sustainable Chem. Eng. 2020, 8 (11), 4400–4406.
  20. Christensen, P. R.; Scheuermann, A. M.; Loeffler, K. E.; Helms, B. A. Closed-Loop Recycling of Plastics Enabled by Dynamic Covalent Diketoenamine Bonds. Chem. 2019, 11 (5), 442–448.

Textiles True Colours: How Sustainable are they?

By Brian Tsui, Website Coordinator for the GCI

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

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

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

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

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

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.

 

References

  1. Ellen MacArthur Foundation, A new textiles economy: Redesigning fashion’s future, (2017, http://www.ellenmacarthurfoundation.org/publications).
  2. Ikeuchi Organic – Our Philosophy. https://www.ikeuchi.org/about-us/en/concept/ (accessed Mar 15, 2020)
  3. STANDARD 100 by OEKO-TEX. https://www.oeko-tex.com/en/our-standards/standard-100-by-oeko-tex (accessed Mar 15, 2020)
  4. Yang, Q. M. Global Fibres Overview, Synthetic Fibres Raw Materials Committee Meeting at APIC, Pattaya, 16 May 2014.
  5. Shang, S. M. Process control in dyeing of textiles. Process Control in Textile Manufacturing, 300–338. (2013) doi:10.1533/9780857095633.3.300
  6. Kim, Y.; McCoy, L. T.; Lee, E.; Lee, H.; Saremi, R.; Feit, C.; Hardin, I. R.; Sharma, S.; Mani, S.; Minko, S. Green Chem. 2017, 19, 4031.
  7. Xia, L.; Wang, A.; Zhang, C.; Liu, Y.; Guo, H.; Ding, C.; Wang, Y.; Xu, W. Green Chem. 2018, 20, 4473.
  8. Ding, X.; Yu, M.; Wang, Z.; Zhang, B.; Li, L.; Li, J. Green Chem. 2019, 21, 6611

A Greener Future for Chemicals

By Jose Jimenez Santiago, member-at-large for the GCI

Over the last four decades, the development of the chemical industry has transformed the global economy and provided a better quality of life for societies worldwide. However, the mass production and disposal of persistent chemicals has been a threat for the environment and the human health. Understanding the effect of chemicals in the environment is necessary in order to replace current harmful molecules with more benign ones1. Fortunately, chemist have learned from negative past experiences and the next generation of chemicals are expected to cause less toxicity and be less environmentally persistent.

Some chemicals have had a negative impact on wildlife populations, some of those effects appear after several years of exposure and bioaccumulation of the toxic molecules in the environment (Figure 1). The first step to prevent further tragedies in wildlife populations is to know the environmental impact of every chemical that is released into the market. However, in places where this data is available, like the United States and Europe, the percentage of chemicals with known environmental information is relatively small. There are around 75, 000 to140, 000 chemicals on the market, out of those, empirical data on persistence is available for only 0.2%, bioconcentration data for only 1% and aquatic toxicity for 11%2,3. Without this information, how can we make an accurate risk assessment of those chemicals? Moreover, molecules with high persistence in the environment may show a negative impact after many years of accumulation. It is important to keep in mind that that for most molecules on the market, we do not know the extent of their negative effects on the environment in the short term and long term2,4.

Jose blog picture

Figure 1. Examples of wildlife scenarios where chemicals have had or are having population effects 1,6,7,8.

 

 

It is hard to shift to a greener chemical industry that prioritizes the environment due to the cost involved in testing the toxicity of molecules. However, there have been advances from the government and chemistry community towards that goal:

  1. More regulation of chemicals in the environment.

Previously, chemical regulations were targeting the emission of a limited number of pollutants into the environment. New regulations, such as Registration, Evaluation, Authorization and Restriction of Chemicals (REACH2006) in the European Union, are looking to ensure that new chemicals entering the market will conform to minimum human safety and environmental standards5. Thus, manufacturers are responsible for evaluating the impact of new compounds being introduced into the market.

  1. Analytical development and computer models

Many analytical methods have achieved low limits of detection (LOD). It is now possible to identify all the molecules present in a sample. For example, these methods have been used to analyze urban runoff water and identify unusual pollutants4. With the help of these new, sensitive methods approach it is possible to investigate pollution incidents and identify the industrial location responsible for those incidents.

One major ethical concern when running toxicity tests is the large number of animals needed2. In addition, the many thousands of chemicals yet to be tested make this approach unreasonable. Recently, computer models were used to predict which chemicals will be of greatest concern; namely chemicals which are persistent, bioaccumulative and toxic (PBT). In this survey, out of 95,000 chemicals, only 3-5% were likely to be PBT4. These tolls can make feasible the lab test of the most hazardous chemicals and will reduce the ethical concerns.

  1. Better wastewater treatment

The incorporation of a secondary biological treatment into wastewater has considerable benefits for the water quality and chemicals reduction. The Activated Sludge Process is the most common method and has been applied in cities all around the world. For example, in China, 81% of the water distributed to the urban population undergoes the Activated Sludge Process9. This shows how we can find cost effective ways to remove chemicals that have accumulated in the environment for many years.

The amount of chemicals used worldwide, their production, diversity, and incorporation has never been greater1. As chemists, it is important to understand the environmental challenges that we face. In addition, chemists should be aware that chemical problems require chemical solutions. We can be pessimistic about the current status of pollutants, but there are tangible reasons to be optimistic about solutions and methods to reduce the negative impact of our current chemical production. Learning from the past is the starting point to ensure that the next generation of chemicals will have less negative impact on the environment.

 

  • Johnson, A.C., Jin, X., Nakada, N., Sumpter, J. P. Science, 2020, 367, 384-387.
  • Egeghy, P.P., Judson, R., Ganwal, S., Mosher, S., Smith, D., Vail, J., Cohen Hubal, E. A. Total Environ. 2012, 414, 159-166.
  • Judson et al., Environ. Health Perspect. 2009, 117, 685–695.
  • Strempel, M. Scheringer, C. A. Ng, K. Hungerbühler, Environ.Sci. Technol. 2012, 46, 5680–5687.
  • European Commission, Introduction to REACH regulation, 2019; https://ec.europa.eu/environment/chemicals/reach/reach_en.htm
  • P. Desforges et al., Science, 2018, 361, 1373–1376.
  • L. Oaks et al., Nature, 2004, 427, 630–633.
  • D. Sayer et al., Environ. Sci. Technol. 2006, 40, 5269–5275.
  • H. Zhang et al., Environ. Int. 2016, 92–93, 11–22.

 

The Great Step Backwards: Polymer to Monomer

By Hyungjun Cho, member-at-large for the GCI

There is a movement to develop a new type of product life system called ‘the circular economy’ [3]. 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 [3]. 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 [6]. 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 [10]. When this occurs, radicals can form at the site of the broken bond, which can lead to de-polymerization [10]. 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% [11]. 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%) [11]. 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 [11]. 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 [9] and the Gramlich group [5].

Picture1

Scheme 1: De-polymerization of RAFT polymers with trithioester end-group [5]. Reproduced from ref. [5] 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) [5]. 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 [13]. 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.

Picture2

Scheme 2: ATRP of NIPAM in carbonated water, followed by de-polymerization [9]. Reproduced from ref. [9] 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) [9]. 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 [1]. 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 [4]. Companies like BASF, Solvay, DuPont, L’Oréal, Unilever, 3 M, Arkema, PPG Industries, etc. already claimed patents for technology and products based on RDRP [4]. 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 [6].

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.

References

  1.  Alsubaie, F.; Liarou, E.; Nikolaou, V.; Wilson, P.; Haddleton, D. M. Thermoresponsive Viscosity of Polyacrylamide Block Copolymers Synthesised via Aqueous Cu-RDRP. European Polymer Journal 2019, 114, 326–331.
  2. Baumann, E. Ueber Einige Vinylverbindungen. Justus Liebigs Annalen der Chemie 1872, 163 (3), 308–322.
  3. Circular Economy – UK, USA, Europe, Asia & South America – The Ellen MacArthur Foundation https://www.ellenmacarthurfoundation.org/ (accessed Jan 5, 2020).
  4. Destarac, M. Industrial Development of Reversible-Deactivation Radical Polymerization: Is the Induction Period Over? Chem. 2018, 9 (40), 4947–4967.
  5. Flanders, M. J.; Gramlich, W. M. Reversible-Addition Fragmentation Chain Transfer (RAFT) Mediated Depolymerization of Brush Polymers. Chem. 2018, 9 (17), 2328–2335.
  6. 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 International 2019, 41 (2), 12–17.
  7. Li, L.; Shu, X.; Zhu, J. Low Temperature Depolymerization from a Copper-Based Aqueous Vinyl Polymerization System. Polymer 2012, 53 (22), 5010–5015.
  8. Liebig, J. Justus Liebig’s Annalen Der Chemie. Annalen der Chemie 1832, 1874-1978.
  9. 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.
  10. Microwave-Assisted Polymer Synthesis. Springer eBooks 2016
  11. Moldoveanu, Șerban. Analytical Pyrolysis of Synthetic Organic Polymers; Techniques and instrumentation in analytical chemistry; Elsevier: Amsterdam ; Oxford, 2005.
  12. 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 Journal 2019, 120, 109181.
  13. 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.