Introduction

The current electronics industry poses significant direct and indirect environmental impacts, such as the formation of electric and electronic waste (e-waste), great demand for critical raw materials (CRMs), and high energy consumption during manufacturing. Global and European sustainability actions, such as EU’s Green Deal [1] and Circular Economy Action Plan [2], and United Nation’s Sustainable Development Goals (SDGs) [3], push the electronics industry towards a circular economy and to decrease environmental impact of their products. Global e-waste is the fastest-growing domestic waste stream, projected to double between 2014 and 2030 [4, 5], with only 20% of this recycled properly in global scale and 40% in the EU [6]. At the same time, the global consumption of materials is expected to more than double during the next decades [7], concerning also rare and valuable materials used for electronics. This might result in running out of some primary raw material sources. Furthermore, new types of electronic solutions are emerging that at some point of their lifecycle might end up in a biological environment, such as environmental sensors for, e.g. agriculture, or are attached to non-traditional product platforms, such as packages or textiles.

Product design is a critical stage in the lifecycle of a product. We know that typically 80% of the environmental impacts are determined at the design board [8]. Further, the current proposal of the ecodesign directive sets targets for safe and sustainable designs, with a particular emphasis on electronics. This forces the electronics industry to rethink how the products are designed so that their environmental footprint during their lifecycle can be minimized. This becomes ultimately an optimization task between cost, performance, and sustainability attributes. However, tools for such elaborate considerations are at the moment missing.

The electronics industry can decrease its environmental burden by (i) shifting from fossil-based materials to bio-based materials, (ii) decreasing the use of critical, rare, harmful, and valuable metals, (iii) utilizing material- and energy-efficient additive manufacturing processes, and (iv) developing miniaturized and integrated components [9]. There are also several opportunities in (v) utilizing efficient circular economy business models that enable recovery, reuse, recycle, and repair of critical materials and components [10]. Also, (vi) extending the use life of an electronic product can decrease the environmental burden of a product significantly. Ecodesign is a concept that considers environmental aspects at all stages of the product development process, striving for products which make the lowest possible environmental impact throughout the product lifecycle, including considerations for the use of materials and resources, generation of pollution, and waste, benefits for user, durability, and end-of-life management [11, 12]. Ecodesign can offer great benefits also to the electronics industry, especially if we apply sustainability thinking already in the early design phase.

Life cycle assessment (LCA), social LCA (s-LCA), and life cycle costing (LCC) are widely used for analysing sustainability from environmental, social, and economic perspectives, respectively [13]. However, for developmental products that possess yet no industrial scale and use phase data, these methods might be too time-consuming and inaccurate due to the lack of Life Cycle Inventory (LCI) data. Therefore, a holistic and streamlined assessment tool specifically targeted at the electronics sector would be beneficial for product design and development phases. To meet this need, the knowledge of how different factors affect sustainability and the environmental footprint of electronic products is used in this paper for the development of a sustainability benchmarking tool—named as GreenTool—that provides an overall estimate of how product design, material, and manufacturing choices affect the overall electronic product sustainability, in particular of printed, electronic devices. The GreenTool considers raw materials, manufacturing processes, use phase, end-of-life management, and maturity of sustainability aspects, such as the use of sustainable approaches, to provide a simple comparison between the different alternatives on a qualitative scale for helping the implementation of sustainable materials and processes, especially in printed, electronic applications. The GreenTool criteria are based on, e.g. EU’s Ecodesign directive [14], UN’s SDGs, and EU’s regulatory framework for batteries, circular economy, and CRMs. The purpose of the GreenTool is to benchmark flexible and printed electronics solutions under development against state-of-the-art solutions and to compare different approaches taken towards sustainable electronics. Smart labels for monitoring packed product conditions are used as a test case here.

This paper first describes the theoretical background for sustainable electronics (Theoretical Background) that forms the basis for successful comparison of technologies with the GreenTool. The background review starts with an analysis of existing sustainability assessment methodologies and their development needs (‘Sustainability Assessment Methodologies’), followed by more technical details on the sustainability of electronics (‘Sustainable Manufacturing’ to ‘End-of-Life Management’) to enable a successful comparison of electronic technologies. Next, the methodologies used for the tool development and carrying out the comparison of the smart label technologies are described (‘Methodology’), followed by the results (‘Results’) to be discussed (‘Discussion’). Finally, conclusions are made (‘Conclusions’).

Theoretical Background

For developing a tool for the sustainability assessment of electronic products, a solid understanding is required of how different aspects of a product’s lifecycle and value chain affect its sustainability (Fig. 1). The following literature review presented in ‘Sustainability assessment methodologies’ to ‘End-of-life management’ forms a basis for the GreenTool development and technology comparison with the factors shown in Fig. 1 in mind.

Fig. 1
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Factors affecting sustainability of electronic products

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Sustainability Assessment Methodologies

Sustainability is becoming increasingly important in product development due to different political initiatives as pointed out in ‘Introduction’. Paying attention to sustainability is often also a competitive advantage to a company and its products. As a result, there has been growing interest in tools measuring sustainability. Various tools have been developed to analyse sustainability either on a product, company, or system level, e.g. [15, 16]. However, many of the developed tools are complicated, requiring knowledge and competence in sustainability assessment, and are time-consuming to conduct.

Perhaps the most well-known methodologies for evaluating sustainability include the Global Reporting Initiative’s sustainability reporting standards and the different ISO standards (e.g. ISO 14040 for LCA), including those for environmental management systems and for life cycle assessment [17, 18]. Tools and indicators for measuring sustainability have also been considered important for the purpose of simplifying information, making it visual to able comparisons between, e.g. different companies or products [19]. Singh et al. [16] provide a wide analysis of the different types of sustainability assessment methodologies. The first tools usually covered only one side of the three aspects of sustainability, or even only one indicator like material flow analysis, or product energy analysis [15], while later, more tools were produced that covered all three sides of sustainability [19]. Some of these are based on life cycle data, such as the life cycle sustainability analysis [20], while some focus only on the product, process, or company level and not the whole life cycle, e.g. [16]. In their extensive review. Cagno et al. [21] identified over 30 contributions that included all three dimensions of sustainability, i.e. environmental, economic, and social. However, when the focus of the tools becomes wider, the analysis becomes more complicated.

Overarching, extensive sustainability assessments, like LCA, are often quite time-consuming to conduct and require high expertise. In some cases, it may be useful to get an overview of the different aspects related to product sustainability and of the issues that would require deeper attention. In the literature, some sustainability assessment tools for holistic and streamlined analysis have been proposed [21]. Moldavska and Welo [22] have proposed a value chain approach for sustainability assessment that takes into account the customer’s perspective by addressing value chain activities, linkages, material flow, information flow, and customer relationships to provide a holistic view of sustainability. In a recent review by Kaur and Garg [23], the urban sustainability assessment tools have been analysed and are found to lack a holistic vision, aspects of social and economic sustainability, and an integrated approach. To overcome these challenges, specifically for a circular economy, Rossi et al. [24] have developed a set of indicators that link circular economy principles, circular business models, and the complex dimensions of sustainability (social, economic, environmental) to help companies to identify areas with high importance and potential for improvement.

According to our knowledge, none of the sustainability assessment methodologies developed so far specifically address the electronics sector, which is one of the most challenging ones for sustainability assessments [13], even though some tools cover the manufacturing sector, e.g. [25]. Further, the current sustainability assessment tools typically require accurate data from the supply chain and manufacturing, but such data is often unavailable at the design phase of a product. The GreenTool presented in this paper aims to provide a streamlined and holistic tool for the sustainability assessment of the different printed electronics products, specifically to support their design and development phase. In the tool, different aspects related to sustainability are listed to provide a product designer with an understanding of what are the aspects that should be considered and where the product under development would have limits. The example case presented here is based on developmental smart label concepts compared to an existing state-of-the-art solution.

Sustainable Manufacturing

Sustainable production can be achieved by efficient energy and material use, as well as by replacing fossil-based feedstock with, e.g. bio-based feedstock [26]. Printing-based additive and high-throughput methods allow the electronics industry to reach these goals. Flexible printed circuits have several advantages compared to rigid circuits, including reduced dimensions and weight, and optimization of component real estate [27]. In addition, less material is used both during manufacturing and in products. Circular design concepts can be used to enable component disintegration, material recovery, repairability, and durability. With additive methods, energy consumption during manufacturing can be even five times less than with conventional methods [9]. Furthermore, the use of environmentally hazardous etching chemicals can be avoided. Benefits from printing-based additive manufacturing are thus in line with the circular economy goals, specifically with the use of renewable materials without generating extensive manufacturing waste [28].

Renewable, Bio-based, and Abundant Raw Materials

Conventional electronic devices are primarily fabricated with fossil-based polymeric and composite substrates, such as polyimide and FR4 (Flame Retardant 4, glass epoxy laminate with flame-retardant properties), respectively, and different metals. With printed electronics, the substrate materials are also mostly polymeric, such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN). Therefore, in printed electronics, the main sources of environmental impacts are the fossil-based substrate materials and metals used [29, 30].

Bio-based flexible substrates from renewable resources are a new opportunity, specifically for printed electronics. The introduction of bio-based substrates to etching-based processes is more challenging, since the existing processes, such as copper plating or bonding, are not compatible with porous or temperature-sensitive materials. The main bio-based materials towards flexible electronics are currently different biopolymer-based bioplastics, such as polylactic acid (PLA), and cellulose-based materials, such as paper-based products [31, 32]. Bioplastics might present some limitations in thermal or moisture resistance [33, 34] as well as in price, but the price is expected to decrease when markets evolve. PLA has already been shown to be a feasible substrate for printed electronics, although processing conditions need to be carefully controlled [35]. Using paper and other cellulose-based materials as a substrate for printed electronics has obvious advantages such as low cost, flexibility, biodegradability, compostability, and ease of disposal through fibre recycling or incineration, but its high roughness and absorbency, poor barrier and optical properties, and sensitivity to elevated moisture levels can create challenges [36, 37]. So far, the paper has been evaluated as a substrate for thermochromic and electrochromic displays, resistive memory devices, transistors, disposable radio frequency identification (RFID) tags, smart labels, batteries, photovoltaic cells, and sensors and actuators [38,39,40,41,42]. It is calculated that in different life cycle impact categories, such as global warming potential, water use or eutrophication, stratospheric ozone depletion, or ecotoxicity, the use of a paper substrate would cause only 10–20% of the environmental impact of PET [43].

The electronics sector depends on a variety of CRMs including antimony, beryllium, cobalt, germanium, indium, platinum group metals, natural graphite, rare earth elements, silicon metal, and tungsten [44]. Critical metals are increasingly used in various components but always in small quantities per application, making their recycling challenging. Thereby, efforts to substitute CRMs to reduce reliance on these materials should be taken. Substitution is a feasible route for improving material supply security, if suitable candidates, e.g. renewable, organic, bio-based, and abundant alternatives providing similar performance as CRMs, can be identified and developed. Printed electronics are not heavily reliant on CRMs, so opportunities for substitution can be found there.

Many of the printed devices utilize silver-based inks as the conductive material; however, virgin silver has a relatively high environmental impact due to its mining process as a side-product from other mines, among other reasons, and its high cost is also an economic issue [43, 45]. Another sustainability issue for metal inks is sintering at high temperature, since many bio-based substrates are heat-sensitive materials [35]. Replacement of silver with other metals, such as copper or aluminium, can lower the environmental impact, and a further reduction can be achieved when replacing at least part of the metals with carbon-based materials, such as carbon paste, carbon nanotubes, or graphene [46, 47]. Formulation of ink vehicles from renewable materials and the use of low or no volatile organic compounds offer a further reduction in environmental footprint.

Many printed electronic devices also need the assembly of SMD (surface-mounted device) or IC (integrated circuit) components to be fully functional. With hybrid assembly, the environmental issues can be managed by selecting integrated and bare die components that consume less materials and by using assembly materials with lower environmental impact. High curing temperatures can cause dimensional changes and yellowing of bio-based substrates. Reducing the curing time and temperature with material selection will make the assembly process more environmentally friendly with reduced energy consumption and, at the same time, improve compatibility with bio-based substrates.

Sustainable Use of Products

Sustainable designs offer sustainability benefits also in the product’s use phase, e.g. by lengthening the product lifetime, improving energy efficiency, and offering better performance. These benefits may manifest themselves in, for example, reduction of waste, lower use-related carbon emissions, or increased productivity per product unit, especially in the packaging, diagnostics, and manufacturing sectors. The efficiency benefits can be achieved by applying new manufacturing technologies, such as additive manufacturing and roll-to-roll printing, to produce affordable and intelligent devices. In one example, the weight of a car was reduced when using flat printed cables, thus contributing to reduced emissions during the car’s lifetime [48]. In another case, printed RFID tags were used for tracking shipments. Here the results showed that the environmental impact of tags production could be compensated by the avoided impacts during its use from misplaced shipments. As a third scenario, the global amount of food wastage is estimated at 1.6 billion tonnes per year, of which the editable parts amount to 1.3 billion tonnes [49]. RFID or other intelligent tags could potentially be used to monitor and prevent this loss and the environmental footprint associated with that.

Yet another important sustainability aspect of the use phase is the energy efficiency of electronic devices. This can be achieved by using operating systems that consume less energy and increase operational use time. Embedded and green software, artificial intelligence, deep learning methods, and low-power computing are some of the key technologies.

End-of-Life Management

In the EU, e-waste continues to be one of the fastest-growing waste streams [2]. End-of-life management for electronics still holds challenges in separating electronic material fractions, such as metals, for recycling and reuse without losing material value in landfilling and incineration [50]. To overcome this challenge, end-of-life management based on efficient circular economy models is required, including ecodesign/circular design concepts and methods for material and component disintegration, also tailored for printed electronics. Circular product design can enable the recycling of product components, including easy removability of electronic components before waste management processes. Identification of reusable and recyclable electronic components and materials coming from multiple waste streams is also needed. This could be achieved by using machine-readable digital product passports (DPPs) that carry information on used materials and processes, even lifecycle use information, and guidelines for sorting and separation [51, 52].

Since new types of electronic products can end up in different types of waste streams, material and component recycling must be designed case by case. In mixed waste, the substrates would oxidize, generating energy, and metals could be potentially recovered from the ashes or as melt. From a separately collected plastics waste stream, electronics could be separated during the washing process before extrusion, and the metals could be potentially recovered from the rejects [37, 48]. However, in both cases, suitable methodologies for efficient electronics separation and recovery do not yet exist commercially. Electronic components, when attached to packages, can influence the composition of solid and liquid residues in the paper recycling process and thereby affect disposal costs of paper recycling [53, 54]. Another recycling challenge is fossil-based ICs and SMD components in connected devices [55]. These have been shown not to increase the fibre rejects significantly during paper recycling, nor the properties of the recycled paper, since they will be collected in the sieving systems to be disposed of by burning or in the landfill [56]. However, in the future, it is likely that the number of electronic components attached to recyclable products will increase, in particular to packages or textiles, and a more efficient collection and recycling of these components will be required. Almost 21 billion packages sold in 2030 are expected to contain an electronic feature to provide smart and intelligent functionalities [57]. Here, circular design-based concepts enabling electronics disintegration before, e.g. repulping processes, will be important. Otherwise, the electronic materials will need to be recoverable from the recycling process.

Besides recycling, biodegradable electronics are seen as one opportunity for the management of a growing number of electronic devices [58, 59]. However, biodegradability and compostability (industrial or home) in electronics are challenging topics, and merely biodegradable substrates are not enough for biodegradable electronics. There are still printed and assembled components and circuitry required for achieving sufficient electrical performance, and these components lack in biodegradability. It should also be noted that in biodegradation, materials are lost from secondary use. Therefore, the applicability and benefits should be verified case by case. Transient electronics concepts are also worth considering in environmental monitoring applications.

Methodology

The methods section is divided into the specification and development of the sustainability tool and carrying out a comparison for a selected use case of smart labels.

Tool Development

The goal of the GreenTool development phase was to create and implement a qualitative assessment and benchmarking tool for the sustainability of printed electronics. The purpose of the GreenTool was to benchmark flexible and printed electronics solutions under development against state-of-the-art solutions and to compare different approaches taken towards sustainable electronics.

In order to get a broad view, the assessment was carried out for several criteria based on the ecodesign directive being currently revised to extend the scope to a wider range of products, strengthen sustainability and circularity criteria, and introduce new information requirements for products. Seven main criteria were defined for the GreenTool. The first six criteria are adapted from the ecodesign directive, and the last criterion is included to highlight the maturity of the technologies used:

  1. 1.

    Raw materials refer to the use of materials in the product.

  2. 2.

    Manufacturing refers to manufacturing processes and workflows used for the product.

  3. 3.

    Logistics refers to the packaging, transport, and distribution of the product.

  4. 4.

    Installation and maintenance refers to the performance and circularity of the product.

  5. 5.

    Use refers to the use phase of the product.

  6. 6.

    End-of-life refers to the management of the product after its active use phase.

  7. 7.

    Sustainability maturity refers to the ability of the product to match circular economy requirements both from environmental, economic, and social aspects.

The scoring used in the GreenTool is presented as a comparison to a baseline (Table 1), a reference product typically representing a state-of-the-art mainstream product option already available in the market. The products under assessment are compared to this baseline per each sub-criterion, either as exceeding or falling under the reference product in the sustainability performance.

Table 1 Scoring used for the GreenTool
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Each criterion is divided into sub-criteria that are the actual data points used for the comparison (Fig. 2). If one or some of the sub-criteria are irrelevant for the product comparison, they can be left out. The different sub-criteria are explained in Table 2.

Fig. 2
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Taxonomy of the GreenTool

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Table 2 Sub-criteria used in the GreenTool
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The scoring for each sub-criterion per criterion is summarized and presented in a spider web graph that shows a clear comparison of the product performance under the different criteria. A normalized range is also created for each criterion and scaled for values from 0 to 100, where 0 corresponds to low sustainability and 100 to high sustainability, and visualized in a spider web graph. The normalization makes the differences between the different technologies more visible and uses the same scale for each criterion.

In addition, different criterion total scores are calculated together and normalized in a similar manner to specify a ‘GreenTool sustainability index’ that is representative of the specific comparison and gives a quick and simple overview of the sustainability of the technologies compared. The GreenTool sustainability index can be calculated as weighted, if certain criteria are considered more important for the comparison, e.g. due to significant differences between the technologies compared in a certain criterion. For this, the criteria summaries are weighted in a scale of 1–3, where the most important criteria (or with high differences) receive 3, and the least important (or with less differences) receive 1.

Smart Label Comparison

Four smart label technologies designed for monitoring the temperature of packed products and for wireless reading were compared with each other (Fig. 3, Table 3) to demonstrate the use and performance of the GreenTool.

Fig. 3
figure 3

Layout of Smart label 2 with batteries and Smart label 3 with organix photovoltaics and supercapacitors for reading logging data with mobile phone

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Table 3 Summary of smart label concepts used in the comparison
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Smart label 1 (SL1) is a state-of-the-art electric temperature logger that is used today for monitoring package conditions during logistics at TRL 9. It is the baseline of the comparison. Such loggers typically consist of small Li-Ion coin cell batteries, circuit boards on FR4, NFC (Near Field Communication)/RFID/Bluetooth connection, and a plastic casing.

Smart label 2 (SL2) is a thin and flexible smart label manufactured by printing and hybrid integration on the paper substrate (Stora Enso Lumisilk, thickness 125 µm) [60] at TRL 5. This smart label consists of two thin Zinc Manganese Dioxide batteries (BlueSpark 103-UT1, 1.5 V, 10mAh, h = 500 μm each), printed circuitry and NFC antenna, and a bare die IC chip containing the temperature logger (NXP NHS3100, h = 40 µm). The circuitry and antenna are screen printed (sheet-fed EKRA) with silver ink (Asahi LS-411AW) and dielectric ink (Acheson Electrodag PF-455B), and the chip and batteries are assembled afterwards. The electronics are protected by laminating on top another paper sheet with graphics.

Smart label 3 (SL3) is similar to SL2, but the batteries are replaced with an energy module that consists of energy harvesting (organic photovoltaics, OPV) and energy storage (supercapacitor, SC) components [48] at TRL 4. For power management, additional SMD components are required. The substrate is PLA film (Luminy). The OPV module consists of eight serially connected OPV cells, and each cell contains the following layers: hole contact and hole transport layer (PEDOT:PSS), active material layer (NF3000), and electrode layer (lithium fluoride and aluminium). The first two layers are gravure printed, and the last one evaporated. Three printed supercapacitor cells are used, and each consists of current collectors (Electrodag PF-407C graphite ink), electrodes (activated carbon ink), separator (Dreamweaver Titanium cellulose paper), and electrolyte (NaCl and water). The energy module provides ca. 3 V operation similar to the batteries of SL2, but is rechargeable. The power management circuit consists of 23 components: 15 resistors, 6 capacitors, and 2 diodes. The graphics sheet is laminated to protect the circuitry. Optimization of printing materials and minimization of SMD components are opportunities for further reduction of environmental footprint in design and manufacturing.

Smart label 4 (SL4) is similar to SL3, but the printed silver is replaced with printed copper and SMD components for power management with printed diodes [61] and thin film transistors (TFTs) [62]. There is also a possibility to combine some of the process steps to further streamline the manufacturing phase. One example is printing of conductive parts of circuitry and the energy module in the same run. This next-generation vision at TRL 2 has not yet been integrated into practice but is a feasible opportunity due to on-going developments for printable copper inks and electronic components.

Results

GreenTool sustainability assessment was carried out by the authors assisted by expert discussions, as listed in the ‘Acknowledgements’ section. Table 4 lists the sub-criteria used for smart label comparison and the scoring as well as justification for the scores. The table includes the total per criterion, also normalized, that are calculated together at the end of the table to have the GreenTool sustainability index. Not all sub-criteria were used here due to lack of supporting data, or a particular sub-criterion was considered irrelevant for the comparison. Smart label 1 is the baseline product, so all its scores are 3, and the other products are benchmarked with it.

Table 4 Summary of GreenTool comparison for the different smart label products
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Figure 4 shows the spider web graph for the smart label comparison. It shows the biggest difference between the baseline product (SL1) and the other products in ‘Raw materials’ and ‘Manufacturing’ criteria. Since the SLs2-4 are based on sustainable materials and additive manufacturing workflows, it was expected that the differences would be found mostly here. In ‘Logistics’ criterion there are also significant differences, since the weights of the SLs2-4 are smaller than those of the baseline, and the manufacturing workflow is less distributed. The other criteria have smaller differences between the baseline and the other products. Notably, in the ‘Installation and maintenance’ criterion, SL2 is even worse than the baseline due to the use of a battery with poorer technical performance. SLs3-4 have the benefit of having an energy-harvesting power source. SL2 and SL3 are almost identical in comparison. The biggest difference can be found in ‘Logistics’ criterion, where the weight of SL3 is higher due to the use of more SMD components. SL4 is the best in all criteria, but there are uncertainties about how feasible this concept is due to being at a very early development stage at TRL 2.

Fig. 4
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GreenTool summary of the different smart label products

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Figure 5 shows the spider web graph for the smart label comparison, when the criteria values are normalized. This graph supports the conclusions from Fig. 4 but more clearly highlights SL4 being the most sustainable product with all normalized values at 100. At the same time, SL1 has the lowest sustainability, with almost all normalized values at 0. The normalized graph also makes the differences between SLs2-4 more visible.

Fig. 5
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GreenTool summary of the different smart label products when the values are normalized

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Figure 6 summarizes the GreenTool sustainability indexes for the comparison calculated normally and as weighted. In the weighted index the criterion with the largest differences between the technologies, i.e. 'Raw materials’ and ‘Manufacturing’, have been weighted with 3, ‘Logistics’ criterion with 2, and the rest with 1. In this case, the weighted index makes SL3 possess somewhat less sustainability. The maturity of the technologies has a significant impact here, since renewable materials and printing-based high-throughput manufacturing technologies for electronics are still in the development phase, with up-scaling just occurring.

Fig. 6
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GreenTool sustainability indexes for the different smart label products

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Discussion

This paper has presented a new qualitative assessment tool for analysing the sustainability of electronics. The tool was tested by comparing a state-of-the-art electronic device for package condition monitoring with new printed alternatives featuring sustainable materials and manufacturing processes. The results show that these new technologies may provide sustainability benefits in comparison to the baseline product. However, care must be taken when interpreting some of the results. First of all, in this experiment, not all the tool categories have been used due to a lack of scientific or industrial data and other information to support a comparison between the different product concepts. Secondly, some of the categories are more future-oriented, such as the use of DPPs and circularity labels. However, the GreenTool is specifically tailored to the needs of the electronics industry, that is one of the most challenging sectors due to the complex process routes to make electronic products [13]. The electronics industry faces a change at the moment with the introduction of new designs, materials, and manufacturing processes, and thus, a sustainability assessment tool tailored for the development phase is needed. The GreenTool visualizes the different aspects of sustainability to a product developer. Even though the methodology does not give precise information on the sustainability indicators, it provides an overall view of the different aspects that need more attention.

As Nikolaou et al. [65] and Cagno et al. [21] pointed out, a considerable weakness in many sustainability frameworks published so far is the selection process of proper indicators for the different sides of sustainability. The GreenTool is built on requirements of the legislative framework of the EU to support future efforts, such as industrial uptake of the upcoming Ecodesign for Sustainable Products Regulation that establishes the framework for setting ecodesign requirements for specific product categories to significantly improve their circularity, energy performance, and other environmental sustainability aspects [66]. The GreenTool indicators are based on existing policy instruments and can therefore be considered fairly stable.

A further strength of the GreenTool is its wide focus and simplicity. There is increasing pressure on companies and product developers to improve their sustainability performance covering all three pillars of sustainability [21]. Yet, the analysis is often very time-consuming and requires thorough expertise. The GreenTool provides a simple qualitative framework for the analysis of the relevant sustainability indicators, thus enabling the user to identify those issues that seem the most important ones for the particular product and require further analysis.

Printed electronics are often said to enable ‘electronics everywhere [67] with smart labels on packages as one example’. The multiple use cases and applications pose a challenge: it is difficult to separate and collect these devices from the different waste streams, for example, from package, textile, and mixed waste. The different matrix materials further complicate the treatment. Schischke et al. (2020) have acknowledged this issue of mixing complex material compositions with recyclable waste and propose more emphasis on the design phase to make the electronic systems obsolete but suitable for disintegration [68]. On a system level, e-waste could either be collected in an e-waste facility or handled as part of existing waste management at different facilities. In the first scenario, the CO2 emissions from transportation must be balanced with the achieved environmental benefits, which may include a higher yield of recovered material via higher volumes and tailored processes. In the latter case, new investments and development work would be needed to integrate the printed electronics treatment into the existing waste management processes. A sufficient volume of waste material would need to be secured for each facility to justify the investment. The potential benefits would include carbon savings in logistics. On the whole, recycling new types of electronic products enabled by printed and flexible electronics is not a simple task and calls for a holistic understanding combining market, technology, and sustainability optimization. Therefore, for ‘End-of-life’ criterion the differences are small between the different products due to novel circularity concepts being still under development [10].

A challenge specifically for printed electronics products is how to separate electronic material fractions, such as metals, and disintegrate components for recycling and reuse from non-traditional substrates, such as bio-based materials, and among different types of waste streams, such as package or textile waste. However, such methods do not exist yet, and in this experiment, the end-of-life part is highly hypothetic assuming that such methods would come reality in the future. O’Connor et al. (2016) have discussed the different opportunities for electronic circularity and support the objective of developing new methodologies for material separation and recovery, since the existing technologies are solvent intensive, harmful to the environment via emissions to air and water, inhibit solid residue accumulation, and often yield oxides rather than pure metals [69]. Since the current electronic waste recycling mostly focuses on metals recycling, and, e.g. polymer recycling is done only for bulk plastics [68], many material fractions are left out of circularity. When the electronic systems are attached to package cardboard or similar materials, they will enter the recycling streams of those materials and contaminate the recycled materials. According to O'Mahony et al. (2016), the ideal material in terms of recycling is a monomaterial that ensures a material can be broken down at the same temperature and process [70]. Printed electronics typically uses less different materials than traditional electronics, thus making these products more suitable for recycling.

In addition, uncertainties for this experiment come from the assessment of novel materials, such as bio-based ones, and new sustainable manufacturing technologies, such as printing, that are not yet in large-scale use. The performance data is still missing or has been estimated with a potentially great variation marginal. Since such technologies are still scaling up, the future decrease in, e.g. energy consumption and environmental impact remains to be proven in practice. Sudheshwar et al. (2023) have reported that design aspects are important for the sustainability of printed electronics in addition to material substitution [71]. Sokka et al. [72] have analysed the LCA of a printed smart label product and have concluded that the biggest environmental impact for printed electronics comes from resource use, specifically the use of silver as the main conductive material. Energy consumption is also mentioned as one of the dominating factors. Therefore, is would be beneficial to weight ‘Raw materials’ and ‘Manufacturing’ criteria when comparing printed electronics products as done in the weighting example of this paper. The use of bio-based substrates is not a simple question, since their environmental impact might not be much smaller than that of plastic substrates, as reported by Nassajfar et al. [9]. This is specifically the case if the renewable substrate is not from the side stream and the fossil-based substrate is recycled [45]. However, with holistic sustainability assessment, more justification for the use of bio-based materials can be found, such as compatibility with end-of-life management or a shift away from non-renewable material sources to improve material sufficiency and autonomy.

From a life cycle perspective, according to Schischke et al., attention needs to be paid to the choice of raw materials, manufacturing technologies, use phases, and end-of-life scenarios to gain a thorough understanding of what happens to materials throughout product life cycles from material acquisition to upstream processes [68]. The importance of the holistic circular design of future solutions shows through the work in all of the categories. Sometimes, modifying the current product to match the future sustainability criteria will not be possible, and a new design and new manufacturing capabilities may be needed. For example, replacing traditional plastic structures with bio-based materials may not provide the same technical features in manufacturing, and the manufacturing line may have to be tailored for the new material, or a new manufacturing unit or technology and competences may be needed. As a second note, there may be trade-offs between recyclability and durability, and circular design needs to take a standing to these product strategies.

It has been largely recognized that lifetime extension is often the most powerful route to decrease the environmental footprint of a product [73]. We acknowledge that the product categories often set the frame—food packaging applications may be short-lived independent of technology selections, while some tracking devices may have a much longer use life and even second use cycles. Still, for many of the use cases, lifetime extension is the key. The reuse and update potential, which contributes to a longer lifetime, has been evaluated in the tool under ‘Installation and maintenance’ criterion. However, due to the importance of this category, some additional assessment parameters may be considered for relevant applications in the future.

The GreenTool could serve the purposes of internal product development and ecodesign and as an evaluation tool for a B2B customer looking for new sustainable product alternatives.

Conclusions

We have developed and evaluated a qualitative tool for comparing the sustainability aspects of different flexible and printed electronic product concepts. The principle of the tool is based on EU’s Ecodesign directive and other relevant European and global sustainability recommendations and guidelines. The intention of this GreenTool is to benchmark printed electronic solutions under development against state-of-art solutions, and to compare different approaches taken towards sustainable electronics. The tool was used in an experiment that compared four different smart label product concepts. One of the concepts was a state-of-art commercial product concept used as a baseline, and the others were developmental product concepts at TRL2-5 based on printing as a manufacturing technology and bio-based substrates.

Based on the sustainability comparison, the major differences among the product concepts were found in ‘Raw materials’ and ‘Manufacturing’ criteria. According to the literature, the use of bio-based materials and printing technologies lowers the environmental impact of electronic products, which is clearly visible in the results where the developmental concepts are better than the baseline concept. In ‘Logistics’ criterion also the developmental concepts are better than the baseline, because they have a lower weight, and their assembly potentially requires less components to be shipped worldwide. In the other criteria, the differences are smaller, but apart from ‘Installation and maintenance’, the developmental concepts are slightly better.

To conclude, the GreenTool worked well for the purposes of qualitative sustainability comparison, but sufficient scientific and industrial information is required to support the sustainability benchmarking process, as well as a proper technical understanding of the concepts in hand. However, more comparisons are required to support its adaptability also among other electronic concepts beyond the smart label study case presented here. The GreenTool could also be extended to other product categories with small modifications.