Sample Overview
This section presents the first part of the systematic literature review’s obtained results and aims to give a brief overview of the article sample. As explained in detail in “Methodology”, the final sample consists of 127 research articles. Figures 2 and 3 display these 127 articles and their distribution per publication year (time span from 2010 to 2022) and per publication source.
With the exception of the two publications in 2010 — which are extended conference papers — all other reviewed articles were published from 2016 onward. From 2016/2017 to 2018/2019/2020, a noticeable steady increase in publications was recognized. To date, the peak in publications was reached in 2021, with 47 articles addressing the CSC framework overall. As of March 1, 2022, 12 articles have already been published, indicating that the peak from 2021 may be exceeded this year. This development reflects the growing interest in this research field and stresses the need for a systematization and identification of key articles within the field.
Figure 3 presents the distribution of the final sample across the journals in which they were published. Overall, 51 different journals published contributions to the research field. It was found that 35 journals published only one article on this topic. The Journal of Cleaner Production, an international and transdisciplinary journal focusing on sustainability research, tops the list with a 20% share of publications (26). The journals Production Planning & Control (11) and Sustainability (10) rank second and third, respectively. This distribution indicates that the research field itself is represented from a variety of perspectives and angles and thus has a strong interdisciplinarity.
Bibliometric Results
To address RQ1 — concerning the research streams and core topics within the research field — bibliometric analysis was carried out using VOSviewer. The software allows for the identification of the leading publications and connections not only in terms of citations and co-authorship but also in terms of the co-occurrence of (author-provided) keywords. The central feature of the applied software is the creation of network maps based on bibliometric data obtained from search databases [56].
To identify current topics and thematic developments within the CSC research field, the co-occurrences of author keywords were mapped. In addition, a temporal overlay function provided by the software was used to connect the keywords with the dates of their source documents. Both the search results from WOS and Scopus were used as a data basis with the aim of obtaining a comprehensive picture of the CSC research field.
The VOSviewer settings were set to at least 15 co-occurrences per keyword, resulting in 36 mapped keywords overall. To avoid duplications in the visualization, synonymous terms or different variants of keywords were merged using a thesaurus file. The temporal co-occurrence map is depicted in Fig. 4. The most used keywords appear in the largest circles, and the strength of the co-occurrence between two keywords is indicated by the strength of the combining link. Table 4 presents the list of the top 20 keywords, their absolute occurrence, and their link strength.
Table 4 Data on author keywords (top 20) The most common keywords retrieved were — unsurprisingly, as the map was created based on these search terms — CE, sustainability (and sustainable development), and supply chain (management). Setting aside these keywords, the next most frequently studied topics were industry 4.0; literature review; sustainable development and three different supply chain management frameworks, namely, closed-loop, circular, and sustainable. The only methodological keyword within the top 20 was “literature review” (R5). This underscores the early research stage of the CSC framework and its theoretical and conceptual nature.
As the colors in the map do not represent thematic similarity but, rather, how recently the keywords appeared in the body of literature [58], topics of current interest or so-called hot topics within the field can be identified (Fig. 5). Three main temporal clusters can be identified: starting with an emphasis on environmental issues, the research concentration shifted toward an early circular and more holistic sustainability focus before the CSCM research field emerged as a separate one. While the earliest cluster still features concepts such as green supply chain management — which shows an average publication year of 2016.35 — the second cluster focuses more on R-imperatives such as recycling (R10) or reuse (R18) and sustainability-related concepts. Most recently, new approaches concerning the Fourth Industrial Revolution (I4.0) and other digitally enabled developments, such as the Internet of Things, big data, and blockchain, have arisen in the body of literature. A current application of the circular supply chain research field is the food supply chain (R20; average publication year 2020.76). Publications focus on issues such as waste flows [59], food redistribution [60] and knowledge sharing and the impact of technology [61]. The most recent development within the research field is — also unsurprisingly — the COVID-19 pandemic. With an average publication year of 2021.06 and 19 overall occurrences, the influence of the global pandemic can be recognized within the CSCM research field (see, e.g., [62]).
Qualitative Results
This section explains the results of the second part of the systematic literature review and presents the qualitative results obtained from the content analysis. These thematic results are divided into two parts. The first part reviews the final sample of research articles for explicit definitions on the terms CSC and/or CSCM and gives an answer to RQ2: What are the definitions, conceptualizations, and understandings within the research field? Based on an analysis of those findings, six CSC archetypal elements are proposed that synthesize the framework’s current understanding in the scientific literature. The second part includes a detailed discussion on the CSC framework’s relationships to other, traditional, and sustainability-related, supply chain frameworks and thus answers RQ3: What makes the CSC concept unique, and thus, what differentiates it from other concepts? Four propositions on the CSC are formulated to position this framework in the sustainability management research.
CSC Definitions and Archetypal Characteristics
To provide a valid view of the current understanding of CSCs in the scientific discourse, the final sample was reviewed for explicit definitions of the terms CSC and/or CSCM. Out of the 127 articles from the final sample, 17 mention (explicit) definitions and thus comprise the important partial sample for the thematic analysis. Table 5 depicts these 17 definitions along with details on the article types and their research focus.
Table 5 Research focus and definitions of CSCs (partial sample) Although the majority of the partial sample are systematic or structured literature reviews that analyze the CSC(M), no comprehensive compilation of definitions of the term circular supply chain (management) was found. Although the work of González-Sánchez et al. [7] is the exception as it includes a collection of definitions on the CSC, it also covers other, related supply chain concepts and focuses more on the configurations and enablers of the CSC rather than on the conceptualization behind each definition. Table 5 shows that the conceptualization is wide-ranging, varying in detail, scope, and focus. While some scholars merely describe what makes a supply chain a circular one and what its main characteristics are, others aim at holistically defining the CSC as a novel and, more importantly, distinct framework. Geissdoerfer et al. [18] and González-Sánchez et al. [7] each provide a definition of the term CSC as well as CSCM. Farooque et al. [3] and Vegter, van Hillegersberg, Olthaar [71] define only the term CSCM. However, the definition provided by Farooque et al. provides a comprehensive integrated view with the aim of distinguishing it from other sustainability research frameworks. The remaining definitions focus, with varying degrees of detail, exclusively on the term supply chain.
One of the most important conclusions that can be drawn from this analysis is that it appears that new definitions — and thus new, and possibly different, conceptualizations of the CSC framework — are no longer being introduced to the research field. In fact, out of the 17 definitions found through this systematic search, eleven are from 2017 and 2018. In the last year (2021), only one new definition was added — the one from Vegter et al. [72] that builds on their previous conceptualized definition formulated in a publication from 2020 and is only supplemented by a restorative and regenerative characteristic. The thesis that there is no longer a major accumulation of knowledge is also supported by the fact that the most recent articles from 2021 and 2022 almost all build on existing definitions, which is that presented in Table 5. For example, the definition provided by Batista et al. [2] is cited in recent works such as [73, 74], and [60]. However, the definition and conceptualization of Farooque et al. [3] is by far the most frequently cited and referenced (e.g., [75–79]); this suggests that the definition is the most comprehensive one as it captures the CSC as a differentiated concept.
A detailed analysis of the collected definitions, their further descriptions, and their detailed elaborations led to the extraction of key features. In this research paper, they are referred to as CSC archetypal characteristics. The identification of these characteristics followed the author-centric to concept-centric approach proposed by Webster, Watson [80]. This approach allows a synthetization of the literature by determining and discussing a framework’s key concepts or characteristics. It was further inspired by other sources, e.g., Stock, Boyer [81] and Ahi, Searcy [39]. Thus, it was possible to develop Table 6, which presents the six CSC archetypal characteristics resulting from the content-based literature review. These may be expressed as (1) R-imperatives, (2) restorative and regenerative cycles, (3) sustainability framework, (4) value focus, (5) holistic system-thinking, and (6) paradigm shift. These archetypal characteristics can be understood as distinct and unique features of the CSC concept that provide transparency for the CSC conceptualization. Too often, the term CSC means different things to different researchers and practitioners, and therefore, these characteristics aim to synthesize the various CSC properties. Table 6 presents them and their corresponding descriptions and contributing authors.
Table 6 CSC archetypal characteristics These characteristics were extracted to facilitate a clearer understanding of CSCs as a distinct concept within the sustainability management research field. In addition to the compilation of the definitions of the CSC, the identified archetypical characteristics provide a clearer profile of the CSC and thus help distinguish it more clearly from other frameworks such as SSCs and green supply chains. Only in this way will the newly emerging CSC concept have a chance of becoming permanently anchored in the sustainability management research field.
Table 7 shows the characteristics identified for each analyzed article in the partial sample. According to the analysis of these data, it is — again — evident that there is no total consensus between the 17 author groups and each of their CSC conceptualizations. The definition provided by Farooque et al. [3] (no. 12) is the most comprehensive one. While other definitions and research perspectives on CSCs lack some of the extracted archetypal elements, this definition comprehensively incorporates all of the identified main characteristics. Six definitions found within the literature review incorporate only three or less of the archetypal elements, which suggests that they do not provide as holistic or comprehensive an understanding as the others. There is some consensus among the authors regarding the archetypal characteristic restorative and regenerative cycles: 13 out of 17 articles (partially) consider this element, which demonstrates that it can be defined as a key characteristic for the CSC. The least-considered characteristic is paradigm shift: fewer than half of the analyzed contributions mention this element as an important feature of the CSC.
Table 7 Appearance of CSC archetypal characteristics (in partial sample) It is possible that the lack of consensus among the authors can be explained by the absence of a holistic view of the supply chain in the CE context. This highlights the research gap that this article attempts to fill and confirms the purpose of this paper to facilitate the understanding of the CSC framework, including the collection of definitions on the concept as well as the clarification and categorization of archetypal characteristics. The latter, in particular, serves as the basis for answering RQ3, specifically, the differentiation of the CSC framework from other research concepts in sustainability management. In the following section, four CSC propositions and their associated categorizations are presented in detail.
CSC Propositions
To answer RQ3 and the issue of what makes the CSC unique, specifically, what distinguishes the CSC concept from other sustainability concepts, this section presents four propositions to provide conceptual transparency for future CSC research. These four propositions are the result of the literature synthesis of the CSC framework and summarize the unique CSC characteristics, which clearly distinguish the CSC framework from related concepts.
Regeneration
As presented in “Conceptual Background” and “Qualitative Results”, the restorative and regenerative cycles constitute a distinctive attribute of the CE ideal. It was explained that there is a clear distinction between restoration and regeneration and their corresponding cycles. According to McDonough, Braungart [97], the planet on which we live has two different metabolisms: the biological (biosphere) and the technical (technosphere) cycle [97]. In the second cycle — the cycle of the industry — the technical nutrients (inorganic or synthesized materials such as metals or plastics) stay in a closed loop by applying restorative processes in such a way that they are returned to a previous, original or improved state [2, 85, 97]. Restoration can be achieved by repairing, refurbishing, remanufacturing, and recycling [83, 98].
While this restorative dimension is one that is commonly known from other sustainability-related concepts within the SCM field (e.g., in green or closed-loop supply chains [99]), it is the regenerative dimension that defines the CE and thus distinguishes the CSC from other frameworks [3, 100]. Although the term regeneration is not easily differentiated from the previous term of restoration [85], the two terms can and should be distinguished based on metabolism cycles: while recovery processes for technical nutrients take place within the technical cycle, regeneration for biological nutrients takes place within the biological cycle. A biological nutrient can be defined as “a material or product that is designed to return to the biological cycle — it is literally consumed by microorganisms in the soil and by other animals” [97]. Such materials are organic and therefore can decompose in the natural environment (e.g., water or soil) and provide food and balance for the ecosystem [97, 101]. Compared to technical materials and products, biological materials have the ability to become nutrients in the soil and other ecosystems in the biosphere, creating natural capital for reuse [102].
Figure 6 illustrates the dimensions of restoration and regeneration with a four-field matrix, with either a low or high expression of the property. Although this separation is quite rigid and simple, it allows for a clear classification that furthers the understanding of the CSC, facilitating its differentiation from other sustainability management frameworks. Traditional — and mostly linear — supply chains typically incorporate only some or no restorative and regenerative flows at all. SSCs and closed- and open-loop supply chains, on the other hand, include restorative flows at their core (e.g., repairing, recycling, remanufacturing). However, CSCs set themselves apart from these frameworks by adding a regenerative dimension to their supply chain activities. Hence, the following proposition is suggested:
Open Loops and Cascading Flows
Closely related to the previous dimension of regeneration is the open-loop and cascading dimension that represents a second important pillar, which is thus a distinguishing characteristic of the CSC. Within the well-established closed-loop supply chain, reverse directed recovery flows of material and products (such as reuse, refurbishing, remanufacturing, or recycling) are already a major supply chain activity [86, 103]. The direction of these flows is reversed and therefore in the opposite direction of the original, forwarded flow of materials and products. In addition, these reverse flows remain — as the name already suggests — within the supply chain. More explicitly, reverse flows are beneficial, for example, by returning recovered packaging material to the producer within the supply chain for further value recovery [40].
In a CSC — in addition to the closed-loop recovery flow — there is another type of material flow. This flow is an open-loop, forwarded cascading flow that brings secondary material (such as used goods, parts, components, byproducts, and useful waste) to other organizations outside of the supply chain [2, 3, 83, 86]. These open-loop flows are advantageous because recovered material that cannot be further used within the supply chain substitutes for virgin material in other supply chains, leading to an overall reduction in waste and virgin material use [3, 98]. Furthermore, these open-loops aim toward the zero-waste ideal and can be directed to other supply chains within either the same or other sectors [86].
It can therefore be concluded that the CSC extends the earlier sustainability management research frameworks via an open-loop and cascading flow dimension (see Fig. 7). Hence, the following proposition is suggested:
Proposition 2: In a CSC, closed- and open-loop flows are applied with the goal of reducing waste and virgin material use within as well as across supply chains.
Value Creation Focus
The integration of circular thinking into the production system changes the perspective on values and their potential for the supply chain [83]. The third fundamental proposition of the CSC is therefore one that was already mentioned within the archetypal characteristics of the CSC, specifically, the focus on values. By applying closed-loop as well as open-loop flows within and across the CSC, one major focus is on value creation. In particular, the supply chain is a key force for value creation because circular flows are the core of the CSC [18, 68].
The Ellen MacArthur Foundation developed four key principles of value creation that are fundamental to the CE ideal: the power of the inner circle, the power of circling longer, the power of cascaded use, and the power of pure inputs [8]. The inner circle refers to repairing or maintaining a product rather than remanufacturing or recycling it because more of the original value is preserved. The closer the circle in which a product flows, the more value is maintained [8]. Reike et al. conceptualized the closely connected R-imperatives and their preferred application within the supply chain. The lower the number associated with the imperative, the greater the focus on this imperative should be (e.g., R3 = repair preserves more value than R6 = repurpose where discarded goods or components are adapted for a different use). Longer circles aim at increasing the number of consecutive cycles and/or the time in each cycle. Through reuse or actions that extend product life, the timing of the resource loop is slowed [8, 104]. A cascaded use aims at substituting inflows of virgin materials, which results in a reduction of overall virgin material use [8]. Cascading refers to the above-described forward open-loop flows of secondary materials that connect producers, firms, and organizations across other supply chains [2]. One last key principle is the power of pure inputs. Value creation requires a certain level of purity of material and a certain level of quality of products and components. With nontoxic, easily separable inputs and designs, further potential for value creation is generated [83].
All four principles have one goal that they pursue: to create value whenever and wherever possible. This leads to a reduction or even complete elimination of waste. The conventional linear take-make-waste approach is neither designed nor targeted at value recovery or value creation. While, in SSCs, value creation takes place to some extent (e.g., R-activities such as recycling or reuse) and negative environmental and social impacts of the supply chain are reduced, the linear design is not fundamentally changed, so waste is still produced. A full CSC, on the other hand, focuses on value creation. By comprehensively redesigning the supply chain, the outputs of the production process become nutrients for further value creation rather than waste for disposal.
To distinguish the different supply chain concepts, Fig. 8 illustrates the intensity of value focus and waste elimination focus within different supply chain concepts. CSCs go beyond the boundary of related concepts and have a stronger focus on values and waste elimination [100]. The following proposition on the CSC is made:
Paradigm Shift
As described in the above sections, a transition toward a CE is associated with a major paradigm shift in production philosophy [2, 15, 52, 63]. Since supply chains are the key unit of action for the transition toward an ideal CE, the analysis of the adoption of CE principles into the supply chain is highly relevant.
Figure 9 links and synthesizes several findings and perspectives on the CSC framework, especially in research from Hussain, Malik [15], Geissdoerfer et al. [9], Reike, Vermeulen, Witjes [13], and Loiseau et al. [95]. Within this figure, different supply chain concepts are presented from a paradigm shift-sustainability-ambition perspective. Both perspectives can be synthesized from the previous three key propositions.
Since regeneration, open-loop, and cascading flows as well as a value creation focus are crucial principles of a supply chain in terms of a CE ideal, the supply chain’s organization and production in particular require major changes [7]. Angelis, Howard, Miemczyk [17] find that in the transition from linearity to circularity, major changes in terms of supply chain strategy, structure, flow, focus, scale, and scope are needed. While the authors draw on notions that have already been mentioned (e.g., closed and open material loops, technical and biological cycles), they reason that supply chain relationships and therefore organizations must change when moving toward a CSC (e.g., in terms of ownership or procurement). Hussain, Malik [15] and Geissdoerfer et al. [9] both argue that a radical change is needed, not only in how we produce goods and services but also in how we consume. In a CSC, consumers and especially their consumption behavior play a significant role in supply chain performance because consumers must be more actively integrated to successfully implement CE principles such as reuse and remanufacturing [6].
While in the sections above, linear, sustainable, and CSC were differentiated by various other dimensions, the distinction here is made directly with the sustainability ambition level incorporated in the different supply chain concepts. Although the relationship between CE and sustainability is still under discussion in the scientific community (see, e.g., Geissdoerfer et al. [9] and Korhonen et al. [52], the understanding in this paper follows the conceptualizations of Batista et al. [2], Farooque et al. [3], Hussain, Malik [15] and, most recently, Farooque et al. [100] that CSCs expand and enhance previous supply chain concepts (such as closed- and open-loop supply chains, green supply chains or SSC) in terms of sustainability orientation and sustainability ambition. However, CSCs distinguish themselves from other frameworks only if economic, environmental, and social goals are explicitly incorporated and aligned [18]. Only if the CSC concept strives to balance the sustainability dimensions will they have a transformative impact.
In summary, CSCs need major organizational, structural, and institutional change that is required to meet the challenges of sustainability in production and consumption [95]. Hence, the following and last proposition is suggested: