Sustainability in Polymer Industry: Part 2
Polymers generally consist of two separate classes as thermoplastic and thermoset based on their nature. In a practical commercial application, polymer products do not consist of a polymer raw material alone; it is produced by adding many additives (pigments, flame retardants, etc.) to improve product properties. This complex material formed by one or more polymers with additives is defined as plastic [1-3]. Examples of widely used commercial plastics are polyethylene terephthalate (PET), polystyrene (PS), polyvinylchloride (PVC), high and low density polyethylene (HDPE, LDPE) [1, 2].
Being petroleum-based, containing different chemical types of polymers and additives for each application, and creating uncontrollable waste streams after end-of-uses are major obstacles to the sustainability of plastics [1-3]. While recycling and reuse are sustainable ways to overcome these obstacles, the complex nature of plastics makes these methods difficult to implement on an industrial scale. Instead, landfilling and incineration, which are widely preferred, do not contribute to polymer sustainability and are disposal methods that should be avoided because of their negative environmental effects [2, 3]. All these effects support sustainable polymer production based on renewable raw materials. [4-6].
There are intense studies on obtaining sustainable polymers from renewable sources by chemical modification of natural building blocks such as starch, cellulose, lignin or chitin [3, 5-7]. Sustainable bio-based polymers such as biopolyethylene (bio-PE), bio-poly(ethylene terephthalate) (bio-PET) and poly(lactic acid) (PLA) and poly(ethylene 2,5-furandicarboxylate) (PEF) can be synthesized using renewable monomers [4, 7]. Sustainable polymer materials produced from bio-based polymers can be used in packaging applications, disposable fast-moving consumer goods, automotive composite parts, bio-based adhesives and coatings, and medical and pharmaceutical applications [6, 7].
Obtaining polymer materials from renewable resources is not the only solution to design a sustainable polymer cycle. A holistic approach, where polymers can be recycled, is required for the material to be sustainable throughout its entire life cycle [1-4, 6]. The ability of a sustainable polymer to biodegrade into non-toxic small molecules (biodegradability) is important for its ability to reduce environmental problems from plastic waste management [3, 4]. In addition to biodegradation, mechanical or chemical recycling methods can contribute to the sustainability of plastic materials. By using mechanical methods, it is possible to obtain recycled plastic products without changing the chemical structure of end-of-life plastics. Plastic wastes can be recycled into building blocks that can be used in new productions by chemical processes (catalytic depolymerization, pyrolysis, solvolysis, etc.) [4, 6]. In recent years, an approach has emerged that extending the life cycle of materials by providing polymers with self-healing properties will contribute to polymer sustainability [3, 4].
It is not enough to apply the methods described above to create a sustainable polymer economy. Sustainable methods need to be designed to generate less waste and use less raw materials and energy, including all processes to be used in the production of sustainable polymers from renewable sources and all processes to reprocess and recycle these sustainable polymers [1, 4, 6]. The right thing to be done for effective polymer sustainability is the development of polymers with pre-designed life cycles and the industrial-scale applicability of these polymers. It is essential for a holistic circular polymer economy to determine the methods and principles in order to monitor the environmental effects of these sustainable polymers throughout their life cycle, and to create the awareness of responsibility in a way that will spread to all stakeholders of the society (states, industries, end users, etc.) [1-7].
References
[1] Zuin, V.G. Kümmerer, K. Chemistry and materials science for a sustainable circular polymeric economy. Nat Rev Mater 7, 76–78 (2022).
[2] Tarazona, N.A. Machatschek, R. Balcucho, J. et al. Opportunities and challenges for integrating the development of sustainable polymer materials within an international circular (bio)economy concept. MRS Energy & Sustainability 9, 28–34 (2022).
[3] Kam, C. Z. Kueh, A. B. H. Towards sustainable polymeric materials: zero waste, green and self-healing. Jurnal Teknologi vol. 74, no. 4, (2015).
[4] Fortman, D. J. Brutman, J. P. De Hoe, G. X. Snyder, R. L. Dichtel, W. R. Hillmyer M. A. Approaches to Sustainable and Continually Recyclable Cross-Linked Polymers. ACS Sustainable Chem. Eng. 6, 11145-11159 (2018).
[5] Scholten, P. B. V. Cai, J. Mathers, R. T. Polymers for a Sustainable Future, Macromol. Rapid Commun. 42, 2000745 (2021).
[6] Morneau, D. Sustainable polymers. Nat Rev Methods Primers 2, 45 (2022).
[7] Papageorgiou, G. Thinking Green: Sustainable Polymers from Renewable Resources. Polymers 10, 952 (2018).
Authors: Duygu Kahraman Date: October 2022