Catalysing Change: Green Chemistry Solutions for Sustainable Plastics
Friday, 12 April 2024
In a world where sustainability goals are not only a priority but a must, the term ‘green chemistry’ is often used. But what does it actually mean, and how can innovations in the polymer industry be greener? The BPF’s Mary Aiken-Wood has collaborated with the University of York, leaders of Green Chemistry, to summarise how research in this field is increasingly influencing the chemical industry.
Green Chemistry: The History
The term ‘green chemistry’ was first used in the mid-1990s. Considering the chemical revolution took place at the end of the 18th century, with Lavoisier’s oxygen theory of combustion and his discovery that mass can neither be created nor destroyed, this makes green chemistry a relatively young branch of science.
Green chemistry and engineering principles go beyond concerns over hazards from chemical toxicity and include energy conservation, waste reduction and life cycle considerations. Examples include the use of more sustainable or renewable feedstocks and designing for end of life or the final disposition of the product.
Despite its infancy, there have already been five Nobel prizes in chemistry awarded for green chemistry research or for research that will enable greener synthesis (for example Chauvin, Grubbs and Schrock won the 2005 prize “for the development of the metathesis method in organic synthesis”, which can be used to make complex plastics whilst minimising byproducts.1 There are now numerous scientific journals dedicated to the subject.
But where did it all begin?
Recognised as one of the most influential books of the 20th century, Rachel Carson’s Silent Spring, published in 1962, documented the potential environmental and human harm that chemicals, particularly pesticides, can cause and raised public awareness about how certain chemicals can impact the living environment. Since then, the principles of green chemistry were already starting to be applied. In the 1980s, the Organisation for Economic Cooperation and Development (OECD) started to look at pollution prevention, rather than how to clean up pollution, reflecting the change in mindset of scientists and government. The US EPA Pollution Prevention Act was passed in 1990.2
In 1998, the twelve principles of green chemistry were published by Paul Anastas and John Warner - green chemistry was born.2,3
Inspired by the green chemistry movement, the EU Green Deal was published in 2019, which sets out how a zero-pollution chemical industry can be achieved. It is rapidly becoming a term used frequently in marketing and legislation.
A Philosophy
Green chemistry can be defined as “the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances”.4
It is an approach or philosophy that can be applied to all areas of chemistry. It is about reducing pollution at its source by minimizing or eliminating the hazards (human and environmental) of chemicals used and produced in a reaction.
The twelve principles serve as a framework that should be taken into account throughout all stages of chemical syntheses. They encourage scientists to prioritise the consideration of hazards alongside physical properties, such as density and solubility.
The Twelve Principles of Green Chemistry
The twelve principles and a corresponding explanation are given below:
Table 1. A Summary of the Twelve Principles of Green Chemistry.2
| Principle | Definition |
| Prevent waste | It is better to prevent waste than to clean it up afterwards |
| Atom Economy | A measure of conversion efficiency – the ratio of atoms from reactants that end up as atoms of product |
| Less Hazardous Synthesis | Chemical reactions should be designed to avoid generation of substances that are toxic to human health or the environment |
| Safer Chemicals | ‘Nasty’ chemicals should be substituted for ones with better safety profiles |
| Safer Solvents and Auxiliaries |
Solvents are often the most significant input into a chemical reaction and the most significant contribution to waste. Therefore, it is better to avoid where possible, and choose ‘greener’ chemicals that are safe for humans and the environment when necessary. Auxiliaries may be drying agents, separation agents, additives and so on. |
| Design for Energy Efficiency |
Factors such as temperature and pressure (influenced by factors such as drying time and method, heating and cooling) should be considered when designing a synthesis. Often removing a solvent is the most energy intensive step of a reaction, so choosing an appropriate solvent plays a role here. |
| Use of Renewable Feedstocks | Raw materials from renewable sources should be selected over materials that cannot be replenished in our lifetime. |
| Reduce Derivatives | Using derivatives in chemical reactions means additional steps are required (more steps mean greater reagent use and more waste). An example derivatisation step is using protecting and deprotecting groups to control which part of the molecule reacts. |
| Catalysis | Catalytic reagents (ones that are not used up in an overall reaction) should be chosen over stoichiometric reagents (ones that are consumed in a reaction and often lead to unwanted byproducts). Catalysts make a reaction more efficient. The ‘greenness’ of a catalyst should be considered e.g. some catalysts are toxic. |
| Design for Degradation | Chemical products should be designed so that they break down into products that are safe for humans and the environment. Degradation products should not be persistent in the environment. |
| Real-time Analysis (Process Analytical Chemistry) | Reactions should be monitored in real-time so changes in factors such as reaction temperature or pH can be detected before a reaction goes out of control or a major incident occurs. |
| Inherently Safer Chemistry for Accident Prevention | Substances and the form of substance used in a chemical reaction should be chosen to minimize the potential for chemical accidents, including releases, explosions or fires. |
Green Chemistry and the Chemical Industry
The pharmaceutical industry has been integrating green chemistry into research and development for years, with companies such as Pfizer and Astra Zeneca using green chemistry to create a culture of sustainable drug discovery.5,6
An example of green chemistry in industry is the Innovative Medicines Initiative (IMI)-CHEM21 project (which received €26M funding). The project was launched to address the negative effects that drug manufacture can have on the environment, human and animal health and it linked universities working on green chemistry research, including the University of York, with six pharmaceutical companies and three SMEs.7,8 The University of York’s Green Chemistry Centre of Excellence (GCCE) developed a metrics toolkit as part of this project. The toolkit can be used to assess and benchmark reactions whilst encouraging continuous improvement.9 The educational and training materials, which are freely available, aim to encourage sustainable methodologies in pharmaceutical synthesis.
In cosmetics, The Estée Lauder Companies have been adopting green chemistry for over 15 years, recently creating a ‘Green Score’ methodology so that formulation chemists can evaluate their ingredient and formulation choices using the twelve principles. They decided not to patent the work and published the method hoping to encourage sustainable innovation across the consumer products industry.10 Green chemistry is also incorporated into the company goals of fragrance houses, including Givaudan and Symrise.11,12
The chemical industry is now adopting the principles of green chemistry, is there opportunity for the plastics industry?
Antoine Buchard, from the GCCE at the University of York, explains:
Plastics are used because they can do things no other materials can do. Many of the future technologies that will be central to reducing our dependence on fossil fuels and to achieving Net Zero will depend on plastics. However, the plastics industry must re-think plastics feedstocks, design, manufacture and end of life, to make them fully sustainable.
Nonisocyanate Polyurethane (NIPU) Foam
In 2021, U.S. Environmental Protection Agency (EPA) awarded the Green Chemistry Challenge Award to Clemson University for their work developing the first lignin-based NIPU foam.13 The award recognizes ‘chemical technologies that incorporate the principles of green chemistry into chemical design, manufacture, and use.’ Since the first award in 1996, EPA has received over 1800 nominations and in 2022 the winning technologies to date saved 7.8 billion pounds of carbon dioxide equivalents (CO2e) being released into the atmosphere each year – equivalent to taking 770,000 vehicles off the road.14
Traditional polyurethane foams are manufactured from diisocyanates, a known carcinogen, however these lignin-based NIPU foams can be made from non-toxic organic carbonates (derived from vegetable oils) and are specifically designed for chemical recycling at end of life. The potassium carbonate catalyst used in synthesis can also be recycled.13
Producing Chemicals for Making Plastics from Biomass
In 2022, research relevant to the plastics industry was also awarded one of the Green Chemistry Challenge Awards, for the ‘development and implementation of a novel technology for the production of chemicals from biomass (such as forestry, agricultural and municipal wastes) that can replace products that are commonly made from petroleum’.15
The chemicals produced have been used to make PET plastic, but their synthetic variability opens opportunity to make other materials which are net zero-carbon and recyclable.15
Materials such as bio-HDPE, PLA and PHA have been in use for some time.
Summary
To conclude, green chemistry has been used to drive sustainable innovation by sectors of the chemical industry for many years. It allows companies to evaluate the ‘greenness’ of their own products, highlighting areas where improvement is needed.
As consumers demand more sustainable products, green chemistry can play a key role in guiding scientists to design better and safer materials, whilst providing an alternative to life cycle assessments (LCAs) in evaluating product impact.
If you are interested in learning more about this topic, please contact Mary Aiken-Wood from the BPF ([email protected]) or visit the GCCE website to learn more about York’s ongoing projects.
References
1. Mehrkhodavandi, P. (2022). ‘Robert Grubbs (1942-2021)'. Nature. 602, p. 573.
2. American Chemical Society. [no date]. Green Chemistry History. [Online]. [Accessed 4 February 2024]. Available from: https://www.acs.org/greenchemistry/what-is-green-chemistry/history-of-green-chemistry.html
11. Givaudan. 2020. Our Sustainability Approach. [Company Brochure]. [no place]. [no publisher].
