Addressing the Sustainability Conundrums and Challenges within the Polymer Value Chain

Abstract

Sustainability is a buzzword across numerous industries, and the polymer value chain is no exception. Due to the ubiquitous nature of polymer products, the conundrums and misconceptions revolving around them are universal too. In this review, we attempt to meticulously undertake some of the polymer-based sustainability conundrums and challenges, driven by technical knowledge and supported by facts. Four major topics of relevance are selected and reviewed without any bias. A basic understanding of all sustainability-related jargon is examined at the beginning to provide the necessary fundamental awareness. Thereafter, the emergence of biobased polymer products is critically analyzed against its distinct biodegradability conundrums. This is followed by an outlook and comparison of plastic products versus their alternatives. Greenwashing in the fashion industry is also reviewed in depth. Among the challenges, issues related to microplastics are assessed owing to their importance currently. It is critical that readers can understand the actual scenario and call out product propaganda with superficial claims. A meticulous overview of the existing literature and information is conducted to summarize all the conundrums, challenges, and future aspects. This examination of pertinent topics is carried out in the hope of spreading knowledge, enabling a higher critique within the polymer research community and a sustainable environment.

1. Introduction

In the current era, sustainability is the most discussed topic in almost every industry possible. Polymer products, being very common in everyday life, are the most critically examined value chain [1]. A polymer product can be as simple as the toothbrush we use every day to complex medical implants and automotive substrates [2,3,4]. Composites, coatings, textiles, and tires are a few polymer product classes that have witnessed the most impactful sustainability approaches to date, with evolving focus areas [5,6,7]. Although, technically, polymer constitutes plastics, elastomers, fibers, films, thermosets, etc., these distinctive polymer products are just referred to as ”plastics” in everyday discussion [8]. The ubiquitous nature of the plastics we ”notice’” in everyday-use products may offer a simplistic reason for such a lack of distinction. Regardless, conundrums and misconceptions revolving around the polymer value chain are innumerous. It is evident that the approaches usually involve using a more sustainable polymer as an alternative or a completely new material [9]. In this short review, we attempt to address some of the most common polymer-based sustainability conundrums and challenges within the polymer value chain.

To give clarity of the terms used in sustainability forums, an introductory structure is adopted initially. The jargon around polymer sustainability or just sustainability in general is abundant. Without a standardized and established guideline for each, these terms remain words with very little value [10]. A good understanding of these terms is important for distinguishing what each term encompasses in terms of sustainability. Further, people need to be aware of the global forums, certification authorities, and eco-label systems in place for polymers. Herein, we demonstrate the relation of these terms to current important topics like greenwashing in the textile industry, biobased and biodegradable conundrums, plastic alternatives, and microplastic challenges. Therefore, an effort is made in this review to contextualize the challenges by representing the best scientific knowledge available. In each section, a holistic system-level approach is adopted to review the topic and simultaneously advocate steps to minimize the environmental impact of the polymer value chain.

2. Decoding the Jargon Regarding Sustainability

Before we dive into polymer sustainability, it is necessary to understand the jargon revolving around sustainability in general. Terms such as circular economy, sustainability, carbon sequestration, low greenhouse gas (GHG) emissions, biobased materials, recycling, and upcycling are some common terms. However, it is unfortunate that no clear standardized definition or established methods are currently available for all of them. Regardless, guidelines in terms of certification standards are mounting up and are being acknowledged by various industries, in an attempt to set a common customary product specification. Let us first look into some of these terms in detail, in an attempt to seek clarification and general understanding. The United Nations (UN) sustainable development goals (SDGs) can be considered one of the main global forums for establishing a standard for sustainability. The SDGs take up a holistic approach on sustainability through 17 goals as directed in its 2023 SDG summit report [11]. These 17 guidelines span across healthcare, human rights, economic development, clean energy, manufacturing responsibility, climate action, peace, and partnership among many others. Similarly, the US Environmental protection agency (EPA) correlates sustainability to the principle of natural environmentally derived products, maintaining productive harmony between humans and nature, to support present and future generations. These guidelines fundamentally adhere to the National environmental policy act of 1969 (NEPA) [12]. The EPA (via NEPA) has also set sustainability factors and indicators (DOSII) involving resource flow, adverse outcomes, system conditions, and value-creating indicators [13]. NEPA is also regarded as a foundational guideline for various other national agencies in the United States (e.g., Department of Defense) [14]. To that extent, the need for education systems to incorporate factors and definitions of sustainability into curricula to better equip future generations is also in motion [15].

In sustainability circles, ”biobased” is considered as the most significant term. A separate section is devoted to it this review owing to its resurgence in commercial polymer products. If we look closely at the SDGs, only seven of them actually concern the polymer value chain directly or indirectly to an extent [16]. All seven of the SDGs (Figure 1) draw their essence from three foundational guidelines: prevent or reduce plastics in the environment, avoid plastic-related health risks, and shift to more environmentally friendly processes and products. Likewise, the EPA also focuses on reduction of toxic products and the 3Rs (reduce, reuse, and recycle) [17]. Carbon is a primary factor that relates to global warming [18]. Moreover, understanding the carbon cycle has become a vital part of critical knowledge needed to make sense of all other related sustainability jargon. Examples include carbon footprint, carbon sequestration, circular economy, etc. (Figure 1). Being the sixth most common element on Earth, the occurrence of carbon spans from the calcium carbonate in shells to the carbon dioxide in the atmosphere. The carbon regulatory process, commonly called the “carbon cycle”, constitutes a carbon storage system involving respiration, decomposition, and photosynthesis processes. Within living organisms and the atmosphere, carbon is stored for a relatively short period of time compared to the storage of carbon within oceans or fossils; the latter’s timeframe can reach millions of years. This is where human activities come into picture. The use of fossil fuel resources releases CO₂ into the atmosphere (at a greater rate than it is removed by atmosphere exchanges, photosynthesis, and other processes) and disturbs the carbon cycle, thereby resulting in “global warming” [19]. Global warming also paves the way for adverse climate change, which is currently stirring the environmental policies of nations on a global scale. In this regard, carbon sequestration is a positive part of the carbon cycle wherein plants absorb CO₂ via photosynthesis processes and break it down into growth components [20]. Some biomass fillers like sorghum, grown on several acres of land, were reported to be very beneficial in carbon sequestration [5]. A number of research articles and manufacturers even report that it facilitates “carbon negative” benefits [21]. Biomass or plant-made polymer products help reduce the carbon in the atmosphere and, thus, reduce one’s carbon footprint, especially considering that greenhouse emissions (carbon dioxide, methane, nitrous oxide, fluorinated gases) constitute a major part of the carbon footprint calculation [22]. In 2021, CO₂ was reported to contribute to 79% of all US GHG emissions by the US EPA [23]. Reduction of carbon emissions by virtue of the Scope 3 methodology has become common in manufacturing industries, with companies evaluating their total carbon footprint based on it [24]. It was created by Greenhouse Gas Protocol in a global framework applicable to all classes of organizations and industries for GHG emissions evaluation [25]. Scope 1 mainly involves direct GHG emissions (fuel combustion, vehicles, furnaces). Alternatively, Scope 2 (electricity, heat, steam) and Scope 3 (upstream and downstream activities) link indirect GHG emissions [26]. Tools or methodologies that can monitor or trace environmental impact indicators throughout the polymer value chain are undoubtedly needed. Some examples of platforms/tools that help manufacturing companies measure their carbon emissions data include Sphera, watch wire, systems applications and products (SAP), and M2030 (Figure 1). Further, two major forerunners in regard to manufacturing companies with globally recognized sustainability assessment partners are Eco Vadis and Science Based Targets (SBTi) [27,28].

Another term discussed alongside sustainability is “circular economy”. Earlier, manufacturing processes implemented an economic model with a straight-line process from the start point to the waste disposal stage. However, there was a complementary shift to the circular economy that is prevalent now, as opposed to the linear economy [29]. This circular/recirculation economic model utilizes wastes from one process as nutrients/building blocks for another [30]. In simple terms, “circular economy” refers to an economic system proposed with the intention that resources are used at their maximum efficiency but with minimal waste generation. This concept is in accordance with both European Union and US EPA policies [31,32]. It resembles a cradle-to-cradle concept established by McDonough and Braungart wherein the reshaping of resources is facilitated by decoupling growth from material extraction [33]. Recycling and upcycling are another two closely knit terms discussed as part of sustainability. The recycling of polymers, though not necessarily implemented enough, is not a new concept. Mechanical and chemical methods of recycling are very common among polymers with specialized catalysts and specific temperature, time, and reaction parameters [34]. However, most of the recycled products are of inferior quality and are not always cost-effective or even implemented. In this regard, upcycling represents a new approach wherein polymers are selectively deconstructed into molecular intermediates and reconstructed into high-value products under specified mild reaction conditions [35]. Vitrimerization (recyclable thermosets), additive manufacturing, catalytic transformation (specific and selective), and industrial biotechnology (using enzymes) are some of the most recent advancements in plastic waste recycling as reported in detail in many recent works in the literature [36]. From a sustainability point of view, improved recycling processes and new upcycling methods are critical as they facilitate efficient product development, envisioning a circular economy via effective waste management [9]. Figure 1 serves as a summary of the jargon related to sustainability with a simplistic illustration of its relevance to the polymer value chain.

3. Greenwashing in the Fashion Industry

As discussed in the earlier section, the exacerbation of environmental problems has led manufacturing companies to develop and commercialize ”green” products. In this context, another conundrum that is discussed very often, mainly in the clothing industry, is ”green washing”. It involves companies making false or misleading statements in regard to the environmental benefits of a product [37]. Though many polymer product industries are accused of greenwashing (Volkswagen, Coca-Cola, IKEA, Walmart), most attention is directed at the fashion industry, simply because of the innumerous advertisements and product campaigns, the general propensity, and the pushback these companies receive from customers who have filed multiple petitions [38]. To cite pertinent examples to understand the nature of customer petitions, (1) Coca-Cola, while advertising 25% marine plastic waste-made PET bottles, failed to state that it is the world’s biggest plastic polluter; (2) Skims advertised a “not a plastic” label despite it being made of low-density polyethylene; (3) irregularities in carbon emissions measurements and data were provided by Volkswagen; and (4) Walmart erroneously labeled rayon products as bamboo products wherein the utilization of toxic chemical process was involved [39,40,41,42]. Further, the fashion industry also contributes enormous amounts of textile wastes, wherein only 20% are recycled and 80% end up in landfills or are burnt [43], resulting in 2–8% of total GHG emissions. Examples of clothing companies that have come under the radar of greenwashing include some top players like H&M, Zara, Shein, ASOS, Lululemon’s, Adidas, etc.

The core problem arises when companies try to cover unsustainable practices or high-polluting practices by pouring in millions of dollars into green companies and labels without any form of established standards or certifications [44]. Often, it is just a clever way of exploiting the public perception of brands. Some of the factors of greenwashing are hidden trade-offs, vagueness, irrelevance, false claims, misleading eco-labels, no proof, and the lesser-of-two-evils model [45]. For example, there are many nature-based images (animals, leaves, trees) incorporated into labels to imply sustainability even if the product might actually be harming the environment. To cite a few examples, Walmart claimed an inclination towards a low-carbon strategy, but the Federal trade commission (FTC) filed a suit alleging it to have falsely marketed textile items as made from bamboo and ecofriendly processes. It was found that a process involving rayon was used wherein toxic chemicals were reacted and harmful pollutants were produced in the bamboo–-rayon conversion process [46]. Analogous claims from Kohl’s were also scrutinized by the FTC. Walmart was asked to pay USD 3 million and Kohl’s USD 2.5 million for misleading consumers regarding their use of bamboo and rayon [47]. Next, H&M’s claims of using recycled polyester and organic cotton in its “conscious collection” were strongly criticized by the Norwegian customer authority [48]. Zara’s “sustainable clothing” line made from polyester via captured carbon emissions received backlash, as it promoted overbuying and overproduction concepts as a brand, which essentially nullified former efforts [49,50,51]. Amidst this pushback, Zara is still under fire for not disclosing an exhaustive list of its manufactures or its audit results. In the context of countermeasures, however, Walmart announced its project Gigaton in 2017, aiming to reduce a gigaton of GHG emissions from its global value chain by 2030. Likewise, Zara has claimed to be aiming for a circular economy model, using only reusable polyester and sustainable cotton by 2040 [52,53,54]. Greenwashing still thrives but might be curbed to an extent with new laws, regulations, and guidelines introduced by organizations like the United Nations (UN), the Committee of advertising practices (British), the Federal trade commission (USA), etc. The European Union stated that it is finalizing a draft banning misleading advertisement so as to contain greenwashing by 2026 [55]. The rule will impose stricter guidelines on environmental and climate-neutral claims, mandating verifiable proof [55].

4. Bioplastics Conundrum: Biobased vs. Biodegradable

Before we delve into the next topic, it is worth noting that biopolymer is a generic term that comprises several components like plastics, thermosets, elastomers, fibers, etc., whereas bioplastics is more specific and strictly refers to plastics that are biobased. One of the most common myths when it comes to sustainable products is based on the umbrella term “bioplastics”. It has become almost commonplace to use biobased and biodegradable interchangeably [56]. However, this is far from true. Biobased refers to a use of renewable resources in a product whereas a biodegradable product is degradable by biological methods (Figure 2). Whereas the former refers to a renewable or green-product characteristic in the formulation stage, the latter refers to the end of life or environmental impact of a product. The lucrative attention and interest that biodegradability characteristics bring to a product may encourage companies to make such superficial advertisements. This driving force for such misleading labels is similar to that of the greenwashing practices we discussed earlier. Recent reports show that big companies like Amazon, Costco, JNB, etc., paying large amounts of money to the state of California, incorrectly claim ”biodegradability” in some of the products they sell [57]. When we look at some of the methods to evaluate the percentage of biobased content, it is a common practice to correlate the amount of biobased raw materials in a product [58,59]. However, this approach gives a high biobased content which might not always be true. Instead, industries must resort to one of the established standardization methods wherein there is high reliability in the comparison of “biobased” products. Companies producing coatings, tires, bottles, and composites and all types of polymer product manufacturers are actively investigating biobased alternatives to petroleum-based raw materials in products [6,60]. Initially, in coatings manufacturing, high-solids, solvent-free, waterborne, and powder coatings were used but now a strong shift is being seen toward biobased raw materials [61]. Examples include petroleum-based adipic acid being replaced with bio-based succinic or sebacic acid in polyesters, biobased polyols like 1,3-propanediol and seed oil-based polyols in two-component polyurethane-coating formulations, etc. [62,63,64]. Similarly, partially bioderived PE are used in plastics whereas seed oil-based polymer precursors and natural fibers are used in composites [2].

One critical aspect often lost in conundrums and doubts are the types of bioplastics and the certifications that are available and recognized across the globe (Figure 2). Certifications provide authenticity and general characteristics of any biobased product. Among the most common biobased certifications utilized by different industries is the ASTM D6866. It measures the biobased organic carbon content of a product by an isotope quantification method [58,74,75]. It is a highly advanced analytical technique with a high level of reliability and reproducibility in replicating data. However, there are two possible reasons why some companies still elect to use simplistic raw material composition-based biocontent measurements: (1) ASTM D6866 generally requires sending samples to an outside testing facility and can be an expensive process; (2) there is a vested interest to align with the simpler biocontent method as it gives higher biobased content value than ASTM-based methods [76]. After all, it is obvious that the number speaks volumes and might influence a customer’s perspectives and decisions in a substantial way. Several polymer industries seemingly follow different criteria for their biobased products but ASTM D6866 continues to receive a great deal of mutual agreement. In terms of official certifications, the United States Department of Agriculture (USDA) has established a bio-preferred program or biobased label that follows the ASTM 6866 testing guidelines. In Europe, the ¹⁴C carbon-dating method follows standards like EN 16640 and EN 16137 and certification bodies like TUV Austria and DIN CERTCO award eco-labels if biobased carbon content is equal to or more than 20% [59]. Another method of biobased content evaluation is the mass balance method wherein a material’s footprint is traced across the value chain. Certification bodies that support the mass balance approach of biobased products include the International Sustainability and Carbon Certification (ISCC) PLUS, REDcert, and the Roundtable on Sustainable Biomaterials (RSB). The ISCC and REDcert focus on reduction of GHGs throughout value chains via the protection of nature, sustainable land use, and social sustainability for commodities manufacturing [77]. RSB drives development of the bioeconomy through certification, innovative advocacy, sustainability solutions, and collaborative partnerships, keeping UN SDGs as the foundation [78]. Within REDcert, certification schemes slightly differ: (1) REDcert-EU for sustainable biomass, bioliquids, and biofuels; and (2) REDcert² for sustainable agricultural raw materials for use in the food industry alongside biomass-derived materials for the chemical industry [79]. The ISCC and RSB are global standards while REDcert can only be obtained within EU borders.

Biodegradable, however, has a more stringent regulatory framework. While a biobased product can be any product that contains a biobased content from 1% to 100%, the biodegradability of a product is evaluated by a different criterion entirely. A biodegradable product can be either be biobased or even petroleum-based but must be capable of degradation when exposed to naturally occurring microbes [74]. Figure 2 showcases the different classifications within bioplastics, sources, and degradation ability. ASTM D6691, D6400, and D5511 are existing ASTM methods defining plastic degradation and the requirements for biodegradable labels for different products, though more established methods need to be published. In accordance with the aforementioned ASTM standards, the Biodegradable Products Institute (BPI) provides certificate labels for commercially compostable products in the United States [80]. Likewise, in accordance with analogous European standards, TUV Austria and DIN provide certification in Europe. Ideally, products that claim biodegradable and compostable labels should also state relevant conditions, environments (specific or natural), and time periods and effect of different parameters on degradation [75,81,82]. If biobased addresses a product’s origins, ”biodegradable” addresses end-of-life issues. Example of real-life products include expensive polylactic acid straws that need temperatures above 58 °C for composting and bags that are compostable only under specific industrial conditions [56,74,75,83]. It is important that the customers are equipped with knowledge to distinguish between actual green and compostable products and advertisements propagandizing false claims.

5. The Everyday Conundrum: Plastic Alternatives Assessment

Plastic alternatives have emerged in huge numbers by virtue of the widespread plastic pollution across the globe [84]. Among different polymer products, everyday plastics are the most scrutinized category [85]. Examples of everyday plastics include plastic bottles, shopping/grocery bags, food packaging, straws, etc. More than 430 million tons of plastics are produced annually, wherein single-use plastics become waste, culminating in wastes near oceans, and eventually work their way into the human chain [86]. Single-use plastic bags (SUPB) are the most common type and depicted as a real and current problem. Further, SUPB vs. paper bags is a subject of routine debate considering their ubiquitous nature. Single-use paper bags have emerged as prominent replacements for SUPB, considering the biodegradability of paper bags [87]. An example of such a shift is that towards paper bags in Aldi stores in the US among many others. However, several factors need to be evaluated before we deem paper bags as a better choice. In this context, Life cycle assessment (LCA) is one such tool used to study the environmental impact of a product. LCA is a systematic study used to understand the environmental impact of any product based on its life cycle, which includes raw material extraction, production, logistics, distribution, use, and end of life [88]. In addition to plastic pollution as landfill, solid waste generated by SUPB in the environment also affects wildlife. Hence, it is important to reduce, reuse, and recycle SUPB [89]. Earlier reports also demonstrated that paper bags have higher environmental impact compared to SUPB. Whereas paper bags end up in landfills and degrade, the type of fuel used for pulp and paper bag production imposes a higher impact on the climate as compared to SUPB [90]. One should also remember that trees are cut down to make paper. Amidst paper bags and singe-use plastic bags, reusable bags might be a better choice, depending on the number of times they are utilized. To provide a few examples on LCA as a foundational assessment technique for polymer products, cotton bags need to be reused 50–150 times, polypropylene bags 10–20 times, and polyethylene bags 5–10 times if a lower environmental impact than SUPB is to be expected [91]. Biodegradable bags are yet another alternative considered for SUPB. However, studies showing biodegradable bags as contributors to climate change [87] and toxic emissions [92] are concerning. In addition to the globally recognized ISO 14040 and 14044 [93,94], several reports in 2021 show an exemplary cumulation of factors or models specific to plastic products, encompassing feedstock, processing, product life endurance, and end of life [95,96]. Methodological aspects of the literature examine the LCA of biomass-derived polymers, polymers produced from waste CO₂, and polymers at their end of life. End-of-life evaluation in terms of recycling, reuse, degradability, and energy recovery is a key factor in properly considering the LCA and in being unbiased regarding a new product’s specifications [97].

Apart from plastic bags, plastic bottles and cutleries are the subject of analogous debate. In 2020, the UN published a report titled “single use plastic bottles and their alternatives”. The study was inconclusive and stated the highly variable environmental impact of bottles, depending on the number of variables considered. However, reusable alternatives were deemed to have particular benefits [98]. Hamade and coworkers published a study in 2020 comparing single-use, recyclable, and reusable PET bottles. They demonstrated that the reusable PET option saved 74% more energy and produced 182% less CO₂ with just one reuse compared to the recycling option [99]. Examples of reusable alternatives include specific reusable-grade plastic bottles, metal bottles, or glass bottles. However, 2016 reports showed that some alternatives can fall prey to higher GHGs, for example, glass production is a highly energy-intensive process, produces a heavier product, and has higher associated transportation emissions [100]. Cutleries are also another everyday plastic product. In 2022, Genovesi and coworkers reviewed disposable vs. reusable tableware, which included cutlery, crockery, etc. [101]. As stated in earlier cases, the reusable system was still found to be the best option, subject to the number of times it was used. Likewise, according to a UN report published in 2021, reusable tableware always outperforms single-use plastic in regard to life cycle analysis [102].

After a short review on everyday plastic alternatives, it becomes clear that reusable products are a better choice. If the usage of new ”recyclable” everyday plastics remains the same, there is not a lot that can be achieved. New plastic systems, if not completely biodegradable, also entail new sophisticated recycling processes [103]. Washing is the highest contributor to environmental impact when considering reusable products. However, a more meticulous review article states that reusable options are more favorable only if consumers use it multiple times [88]. Therefore, reduced consumption and multiple reuses constitute better choices.

6. Microplastics Challenge

It is well known that polymers are ubiquitous in everyday life and find their use in coatings, composites, tires, plastics, specialty applications, etc. [104,105]. In this context, microplastics are another term closely used in conjunction with sustainability and plastics. The term has been used since the inception of polymers but has also been studied extensively in recent years with advancements in technology and analytical capabilities. Microplastics are plastic fragments with sizes less than 5 mm (0.20 in) in length, according to the European Chemicals Agency and the U.S. National Oceanic and Atmospheric Administration [106]. Microplastics are considered a major pollutant as they enter natural ecosystems from a variety of sources, including cosmetics, clothing, food packaging, and industrial processes [86]. Plastic debris/microplastics occur as a result of land disposal of plastic wastes, coating/paint failure, wastewater treatment, tire wear, textile washing, etc. [107]. According to the International Union for Conservation of Nature (IUCN), over 14 million tons of microplastics have already been accumulated in the world’s oceans [108,109]. In terms of polymer industries, most microplastic pollution arises from tires, plastics, coatings, and textiles industries [110]. Figure 3 shows the major sources of microplastics in the environment.

Microfibers are fiber-shaped microplastics originating from textiles. Even natural fibers release microfibers, just not of plastic origin [111]. Microfibers are stated as filaments of staple fibers with a linear density of 0.3 dtex to 1 dtex (one gram per 1000 m) [86]. Some of the factors influencing widespread microplastics pollution are rapid consumption, large-scale production, slow degradation, fast fashion culture, and insufficient recovery and management [112]. Several sampling techniques are being suggested, with hotspot collection of samples (air, water, soil) being the most common [113,114]. Separation techniques of microplastics are being complemental by several advanced analytical technical like Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), chromatography techniques like pyrolysis–gas chromatography–mass spectroscopy (Py–GC–MS), etc. [115,116]. Textile-based fibers and microplastics are estimated to comprise 6–30% of all microplastics across the globe [117]. Additionally, tire particles or tire road-wear particles (TRWPs) are also closely studied as part of microplastics by many research groups across the globe [118]. It should be noted that TRWPs do not (technically) fall into microplastics categorization as they are an elastomer/rubber product. Regardless, TRWPs are reported as microplastics by many research groups worldwide [115,119,120,121]. Further, TRWPs reportedly contribute the largest share (45%) of terrestrial microplastics [122,123]. With 60% of clothing materials being polymers (polyesters, nylon, and acrylic), microfibers are released due to abrasion when washed or worn. UNEP estimates that 9% of microplastics are sourced from textile and cloth fibers [124]. Cosmetics and personal care products including hand sanitizers and gels are also reported to contain significant amounts of microplastics. Another significant study by researchers from Europe investigated plastic particles in water samples [125]. They postulated a high presence of binders/resins and antifouling components used in marine coatings and previously estimated that these contribute to between 9 and 21% of all paint failure-based microplastics [107,125,126]. The percentage may vary depending on the location but this “skid mark” left by ships in water, comparative to analogous TRWP generation by vehicles, cannot be ignored. The same components used to protect ships’ hulls against subaquatic organisms like barnacles constantly rub off due to waves and wind, resulting in paint-related microplastics in the ocean.

It is critical that we look at the potential consequences and environmental impact of microplastics. Further, numerous toxicology reports, TRWP studies, life cycle analyses, and microplastics impact studies have surfaced in recent years [86,127]. These studies involve environmental impact assessments of microplastics in food, water resources, soil, etc. Immense attention and concerns were expressed by environmental conservationists when Tian et al. investigated TRWPs in water bodies and noted that N-phenyl-N’-(1,3-dimethylbutyl)-p-phenylenediamine(6-PPD) derivatives caused acute toxicity in Coho salmon species [128,129]. 6-PPD is a common antioxidant used in tire formulations [130]. As microplastics proliferate around the world, an essential question arises on the harm it causes to human health. The criticality of the matter is heightened by the fact that microplastics have been reported in a wide range of beverages and food, including drinking water, salt, sugar, beer, seafood, etc. [127,131]. Serious health impacts were attributed to the presence of microplastics by a recent report by UNEP [109] and included changes in human genetics, respiration rates, and brain development. Further, they are also believed to induce toxicity and inflammatory reactions and are even reported deep inside the lungs of surgical patients and in the blood of anonymous donors [127,132]. In laboratory tests, damage to human cells, including both cell death and allergic reactions, were evidenced as consequences of microplastics [133,134,135]. Since then, numerous studies on tire and road-wear particles in soil, water, and air and their harmful derivatives were conducted by several academia–industrial collaborations as part of the TIP (Tire industry project), CenTire (Centre for tire research), etc. [120,136]. Tire manufacturers are also making efforts regarding the microplastics issue and sustainable efforts like Goodyear’s introduction of 70% sustainable tire materials are in motion [137]. Similarly, Bridgestone and Michelin have also published reports of using plant oil-based feedstocks, pine tree resins, rice husk-derived silica, etc., in their tires [60,138]. It is, thus, critical that microplastics are researched on a global scale by concentrating on specific industries followed by compilations within the entire polymer product horizon.

7. Discussion and Future Directions

As discussed in earlier sections, the conundrums in the sustainability of polymer products are numerous. Some of the alternatives suggested are a good choice for environmental safety, while some are not. It is noteworthy to discuss some of the conundrums critically to understand what lies ahead for future generations in regard to polymer sustainability and how we can be a part of the change (Figure 4).

Beginning with greenwashing, the real issue is that consumers’ faith starts to erode, and they start to dismiss all environmental claims, even the legitimate ones. Therefore, it is critical that awareness is built among consumers and an action-oriented approach utilizing certification and corporate accountability is implemented [139]. Greenwashing plays a critical role in the sustainability horizon as GHG emissions are a direct consequence of human activities, and sustainable practices are mandatory [140]. Fashion industry charters for climate action backed by the UN can be regarded as a strong first step that aims to achieve net-zero GHG emissions in the fashion industry by 2050 [141]. Unless consumers understand what the differences are between biobased and biodegradable products from a scientific perspective, they will remain ambiguous. The bioplastics section of this review provides an exemplary explanation. It is expected that the growth of the biobased polymer sector will be impeded, with stringent regulatory conditions within polymer industries as part of carbon footprint reduction, coupled with an environmentally aware consumer base. It always seems to be a good idea to blend bioplastic components with commercial products at first, since fully fledged bioplastics are currently causing problems for recycling facilities. This challenge can be attributed to the fact that bioplastics actually contaminate the recycling stream, rendering it unusable and ruining batches of otherwise reusable plastic waste. In terms of recycling, a drop-in replacement might also suffer from product performance challenges. In this context, researchers from Aarhus University recently took a step forward regarding polyurethane foam recycling, utilizing a recycled polyol (64%) for reformulation without any compromise on performance properties [37]. Biobased plastics’ introduction to markets should be cognizant of the economic, environmental, legislative, and social conditions in order to achieve their true potential.

With the world producing 430 million tons of plastic per year, a great deal of single-use plastic finds its way to water bodies (11 million metric tons into oceans). This was mentioned in the SDGs as a major concern, with plastic remnants being found in marine species, thereby entering the food chain [84]. For tackling plastic pollution, a UN environment program proposed a systematic approach known as taping off the tap, introducing three major market shifts: reuse, recycle, and reorient/diversify [142]. It is vital that we discuss the scientific challenges and possible solutions to the microplastics problem rather than criticizing plastics altogether, due to their ubiquitous nature in everyday life. Challenges include understanding long-term behavior, ecosystem health risks, bioavailability, etc., which is only possible through advanced microplastics sampling and characterization methods. Moving ahead, it is critical that we understand the most hazardous types and forms of (micro)plastics regarding the damage to specific ecosystems and the mechanisms of the damage. It would be helpful to link the distribution and abundance of microplastics to human activities in order to mitigate the effects by reduction of use.

We acknowledge that contamination brings about significant ecological effects in low-population areas more so than the anthropogenic activities in more-populated areas. The perspective on polymer sustainability varies between developed and developing nations. An example would be the waste disposal of developed nations into other nations which has been reported to bring about extreme health effects to local communities [143,144]. The need to stop landfill as a waste management solution cannot be emphasized enough wherein the knowledge of how biodegradability actually works is critical. It would be counterproductive if companies were to greenwash a new polymer product as biodegradable and then dump it in landfill without providing specific degradation conditions. Rigorous toxicity and life cycle safety assessments need to be enforced to integrate environmental performance within polymer manufacturers with potential incentives. Moreover, regarding the manufacturing of new biobased products, regulatory frameworks need to be set for enforcing effective recycling routes, reutilization, and energy recovery. However, this would mean a higher initial investment and some companies would find this less lucrative. Several studies have tried to integrate the development of sustainable polymer products within a prospective international circular (bio) economy [145]. Critical press coverage and transparency of emissions data represent a challenge in some African and Asian countries. In Southeast Asia specifically, a very recent report in 2023 showed insights on plastic waste management systems [146]. Despite being a hotspot for receiving plastic waste from developed countries, there is a lack of any sophisticated waste management systems [147]. Bans are now being imposed by countries like Thailand, Vietnam, and Malaysia to restrict plastic waste from western countries [146]. Further, the amount of plastic waste generated by Asian countries was estimated to be about 121 Mt in 2021 whereas Asia’s share of the world’s imports of plastic waste was estimated to be 11 Mt in 2016 [148]. Along a similar line, in a study that presented the first historical continental analysis and inventory of the mass importation of polymers and its effects in Africa published in 2019, it was shown that more than 117.6 Mt of polymer waste entered Africa, primarily through Egypt (18.4%), Nigeria (16.9%), South Africa (11.6%), Algeria (11.2%), Morocco (9.6%), and Tunisia (6.9%) [149]. It is reasonable that plastic imports are taxed in consideration to the burden of plastic imports to finance plastic waste management [150] in addition to moving towards biobased feedstocks within Africa as reported in 2022. Furthermore, appropriate waste management policies should also be developed and enforced. Further, a collaborative pathway should exist between nations wherein technological advancements of one region could be leveraged in a coherent and focused way to improve the cumulative environmental profile of polymer products across the globe.

Reusable everyday plastic alternatives offer greater environmental benefits only after they have displaced a sufficient number of disposable alternatives. Everyone is aware of the current climate crisis. Everyone can contribute towards a sustainable future by making conscious choices, especially when it comes to day-to-day choices like selecting bags, tableware, and bottles. Therefore, as a scientific community, we need to help policy makers as well as consumers by increasing awareness of the available options. There is no straight-forward solution or right or wrong answer to this problem. However, reducing, reusing, and recycling should be among the first three choices. Reducing environmental impact does not necessarily mean banning, recommending, or choosing certain types of products but rather the adoption of the right mentality. In regard to everyday plastic alternatives, the following questions need to be asked before making any conscious decision:

1.

To reduce:

a. 

What are the alternatives available? (Paper, metal, glass, biodegradable etc.);

b. 

If degradable alternatives are available, compare degradable vs. biobased/polymer:

i. 

Which type of degradable material is the most suitable?

ii. 

How much energy is consumed during the product manufacture?

iii. 

Any special conditions requirement for degradation?

iv. 

Any environmental impact during degradation?

v. 

Does material need to be shipped somewhere to ensure degradation process?

2.

To reuse:

a. 

How many times do we need to reuse it before environmental impact is equivalent to single use plastic?

3.

To recycle:

a. 

feasibility to recycle?

b. 

Is infrastructure available for recycling?

It must be noted that plastic that cannot be recycled and will eventually end up as landfill. It will eventually turn into microplastics. Adverse effects of microplastics are already discussed in the paper. Increasing resource efficiency via biobased materials, decreasing hazardous chemical use, and increasing recycling rates constitute a good first step towards circularity. However, transforming the way that textiles, tires, plastics, and coatings are designed, produced, consumed, and disposed can be improved with a system-wide approach, as opposed to incremental improvements. Consequently, strong coordinated actions are required by all stakeholders and across the globe to achieve this. In summary, to genuinely tackle polymer pollution and its implications regarding public health, the climate, ecosystems, the polymer economy must be rethought from a circular, sustainable, and low-carbon-footprint perspective. In regard to the different terms related to sustainability mentioned earlier, different national agencies, manufacturers, and education institutions seem to work within the same overall guidelines of SDG fundamentally but often resort to individual standards of sustainability. However, in a generic simplistic approach taking sustainability guidelines and objectives into consideration, we propose that sustainable polymer products contain one of the following:

1. 

Use of biobased raw materials as opposed to petroleum-derived materials, lowering carbon footprint;

2. 

Value addition from recycled resources, recycling, or upcycling products;

3. 

Favorable life cycle analysis (LCA) in terms of carbon sequestration, minimal energy resources used, lowest GHG emissions, and degradability/reusability.

The main factors of profitability and performance are slowly paving the way towards negative environmental impacts of products and, thus, the need for innovative products is at its highest. To cite an example of a sustainability initiative, CARES is a consortium of different automotive manufacturing companies and suppliers formed to discuss and take considerable actions toward a sustainable future in automotive manufacturing [151]. Several automotive companies like Toyota, Honda, Nissan and Ford, and suppliers like PPG, Henkel, BASF, Arkema and Nippon paints engage in crucial circularity solutions. Such platforms need to be implemented in all polymer industries since it enables the participation of all relevant parties from the suppliers to the customers. It is vital that common measurement and assessment standards of sustainable products are established before tackling commercial competitiveness. We focus on tools to measure and reduce the negative impacts of plastics on the environment throughout their life cycle, the use of renewable sources for their synthesis, the design of biodegradable and/or recyclable materials, and the use of biotechnological strategies for enzymatic recycling of plastics that fits into a circular bioeconomy.

Economic growth and sustainability have always been regarded as contradictory since their inception, but things are looking optimistic. It is time that sustainability gradually be considered as an obligation to the industry and consumers, as opposed to a challenge. Overall solutions include improving globally based pollution prevention, developing degradable polymers and additives, and reducing consumption/expanding plastic reuse. Therefore, in short, it is important to instill a mindful consumption behavior in consumers, reducing supply chain impact and reducing energy and material intensiveness of products, ultimately promoting a holistic life cycle mindset in order to reduce overall waste and plastic pollution. This contribution attempts to highlight the several polymer-based sustainability conundrums and challenges. We would like to reinforce the call to action for a sustainable polymer economy and circularity among different polymer industries. We hope that this review stimulates further development in areas of polymer sustainability and proves to be useful tool for anyone wanting to understand the prospective sustainability of polymers.