Supply Chain Sustainability: A Model to Assess the Maturity Level

Abstract

Today, frameworks and models are critical for enabling organizations to identify their current sustainability integration into business and to follow up on these initiatives over time. In this context, the maturity models offer a structured way of analyzing how a supply chain meets specific sustainability requirements and which areas demand attention to reach maturity levels. This study proposes a five-level maturity model to help supply chains managers identify their level of engagement with sustainability practices combining three perspectives: the intra- and inter-organizational sustainability practices, the triple-bottom-line approach and the critical areas for sustainability. All the steps followed in constructing the maturity model were based on a literature review, and case studies supported its improvement, application, and testing. The proposed model presents many advantages, such as being used as a self-assessment tool, a roadmap for sustainability behaviors improvement, and a benchmarking tool to evaluate and compare standards and best practices among organizations and supply chains.

1. Introduction

Companies are rethinking their supply chain (SC) operations, considering their environmental and social impacts [1,2]. This has given rise to the concept of sustainable supply chain management (SSCM), which refers to the management of material, information, and capital flow as well as cooperation among companies throughout the SC, considering the triple bottom line (TBL) based on customers’ and other stakeholders’ requirements [3]. Hynds et al. [4] (p. 50) argue that “achieving true sustainability means integrating TBL concerns into all aspects of a business”, and Müller and Pfleger ( [5] (p. 313) contend that “single actions do not achieve sustainability, but rather [it] is an on-going process”. Hepper et al. [6] highlight the importance of frameworks and models to enable organizations to identify their current level of sustainability integration into their business, establish more advanced integration levels, and follow up on these initiatives over time. However, it seems that most of the existing frameworks do not account for environmental and social issues [7], cultural change, or the involvement of internal and external stakeholders [8,9]. Moreover, few tools and frameworks within the company or SC consider the TBL [10].

A maturity model (MM) allows for describing a current state and “offers a structured way of analyzing how an organization meets certain requirements and which areas demand attention to reach mature levels” [11] (p. 3). Because a MM is a conceptual framework made up of parts that describe the development of a particular area of interest over time [12] or state [13], a framework that describes a specific system over time, it is a valuable tool for analysis and evaluation when applied to SC sustainability [14]. To Müller and Pfleger [5], sustainability maturity models (MMs) are prominent examples of sustainability measurement systems. According to these authors, “the basic idea of [sustainability] maturity models [...] can be used to evaluate a company’s state with regards to sustainability objectively, and thus provides organizations with a sensible tool to manage their sustainability capability” [5]. Thus, the development of MMs in the scope of SC sustainability is relevant because: it is a descriptive tool for evaluating strengths and weaknesses; it is an instrument to help develop a roadmap for performance improvement, and it is a comparative tool for assessing processes/organizations that compares them with the standards and best practices of other organizations, allowing them to implement external benchmarking [12,15,16].

The need for more procedures for evaluating and operating MMs may be a barrier that prevents their use as a management and diagnostic tool [17]. In addition, there is a need to develop more empirical work to confirm the validity and usefulness of sustainability MMs [14]. Considering these research gaps, the objective of this paper is to propose a MM with an integrated approach to sustainability to assess the level of sustainability at individual company and SC levels by considering three integrative perspectives: (1) intra- and inter-organizational sustainability practices involving various SC partners, (2) TBL perspective, (i.e., economic, social, and environmental sustainability dimensions), (3) critical areas for sustainability considering the sustainability governance, product and process level, customer and supplier management, and stakeholder focus.

This paper is organized as follows: first, we report the findings of a literature review on sustainability MMs; then, the research methodology followed in this study is described; after that, the different phases followed for the development of the sustainability MM are described, including its proposal and test; and finally, some conclusions are drawn.

2. Background

With the growing interest in sustainability issues [18], several instruments have emerged, and others have been adapted to assist their integration into companies and supply chains (SCs). The institutionalization of sustainability issues has led to the emergence of standardized management systems (e.g., ISO 14000, SA 8000), guidelines and official recommendations for environmental and social reporting (e.g., GRI guidelines), and tools for measuring corporate sustainability (life cycle assessment, sustainability balanced scorecard) [5,19,20]. While some of these instruments are more focused on issues related to one of the dimensions of sustainability, there are internationally recognized frameworks that take a holistic approach by considering the social, environmental, and economic aspects of sustainability (e.g., GRI guidelines) [20,21]. We should point out that many sustainability assessment frameworks need to be more consistent regarding their purpose (reporting, monitoring, rating, management, or performance assessment), are indicator-based, and, for the most part, their focus is not on the entire organization.

From the analysis of the previous instruments (e.g., standards, tools to assess sustainability in individual companies and SCs), there seems to be no instrument that simultaneously does the following: (i) presents a comprehensive approach to sustainability that considers the three dimensions of sustainability; (ii) contemplates the different management-oriented functional/acting areas and concrete actions (structuring the field of action) to be carried out to improve sustainability; (iii) considers not only the practices to be developed internally but also those involving its SCs and other stakeholders.

Despite the popularity of the MM concept, as pointed out by Wendler [22], there is no clear definition of the term “maturity model” [14]. A MM can be understood as “a conceptual framework made up of parts that describe the development of a particular area of interest over time” [23]. We have adopted this definition, as it assumes a comprehensive viewpoint of MMs and does not limit it to a specific area (e.g., project management or processes). The literature shows that MMs can be oriented toward the integration of sustainability in specific areas such as design [23], the company [24], or the SC [25]. Since sustainability incorporates a temporal dimension as it implies a dynamic process of change over time [9,26], the company will benefit from using tools to track its progress toward sustainability efforts. MMs assume an evolutionary perspective considered by Liebetruth [27] as a potent and flexible tool not only for SC performance measurement and management but also for integrating all aspects of sustainability. Although several authors highlight the increasing interest in MMs [17], the literature on sustainability MMs considering the individual company or the SC is scarce [14,25,28]. Correia et al. [14] provide a systematic literature review (SLR) on MMs and their application in the SC sustainability context for the period between 2000 and 2015 and found 11 studies that seek to develop a new MM. More recently, Pavan et al. [28] analyzed the current knowledge regarding the use of MMS in the SC context resulting in the identification of 19 studies published from 2013 onwards. They conclude that 50% of these works focused on proposing new MMsRegarding the sectors where the studies were carried out, some studies on MMs for SC sustainability either do not fit into any specific sector or may be related to several sectors (e.g., [23,29,30,31]). Other MMs are carried out in a specific sector. For example, in information technologies [32] and remanufacturing [33]. Research on MMs for SC sustainability in the area of manufacturing is predominant compared to MMs in the area of services [28]. Pavan et al. [28] also point out that studies on MMs for SC sustainability are poorly grounded in theory, following what is seen in other domains of application of MMs, such as information systems [34], project management, SC, education, etc. [22]. In an SLR where 237 studies were analyzed, Wendler [22] concluded that only 5% of these studies paid attention to theoretical issues.

Regarding the existent sustainability MM, they present significant differences in their various components, such as the number and characterization of maturity levels, their descriptors, and the elements used to analyze/measure maturity [14,28]. Following the methodology proposed by Correia et al. [14], a new literature review about sustainability MM focusing on the unit of analysis, sustainability focus, and maturity levels was carried out for 2015–2021. The review is reported in

Table 1. Main research on Maturity Models.

Authors	Unit of Analysis	Scope—Sustainability Focus		Maturity Levels (Number/Descriptors)
		Scope	Elements/Characteristics Considered
Robinson et al. [35]	Process—knowledge management	Scope—TBL approach	Not Applicable	5/Start-up, Take-off, Expansion, Progressive, Sustainability
Standing and Jackson [36]	Process—information system management	Scope—TBL approach	Not Applicable	6/Non-existent, Initial/ad hoc, Repeatable but intuitive, Defined process, Managed and measurable, Optimised
Babin and Nicholson [32]	Company—IT outsourcing providers	Scope—Environmental sustainability	Three capabilities (Understand and adopt global sustainability standards. Anticipate and respond to stakeholder sustainability requests. Embed and develop sustainability capabilities within the organization)	3/Mature leaders, Aspirant, Early stage
Pigosso et al. [23]	Process Eco-design	Scope—Environmental sustainability	8 elements resulting from 5 capabilities (Deployment of eco-design practices: incomplete, ad hoc, formalized, controlled, improved) and 3 dimensions for eco-design implementation (Implementation paths, Company widening for implementation, Knowledge level on eco-design)	5/Level 1, Level 2, Level 3, Level 4, Level 5
Okongwu et al. [29]	Network	Scope—TBL approach	8 areas (Use of standards, Performance management; Pollution management; Relationship management of suppliers, customers and society, Employee management; Profitability management; Economic value distribution management	4/Primeval, Initial, Intermediate, Advanced, Word Class
Srai et al. [30]	Network	Scope—TBL approach	5 clusters of capabilities (Sustainable Supply Network strategic design, Network connectivity, Network efficiency, Network process development and reporting, Network product and service enhancement)	5/Not applicable
Edgeman and Eskildsen [37]	Company	Scope—TBL approach	6 areas (Strategy and governance, Process implementation and execution, Financial results and refinement, Sustainability results and improvement, Innovation results, Human capital results and refinement)	5/Very low maturity, Low maturity, Moderate maturity, High maturity, Very high maturity
Golinska and Kuebler [33]	Company—remanufacturing companies	Scope—TBL approach	3 dimensions (Economic, Ecological and Social performance) subdivided into 15 key areas	5/Level 0, Level 1, Level 2, Level 3, Level 4
Hynds et al. [4]	Process—new product development (NPD)	Scope—Environmental sustainability	2 dimensions (Strategy and Design Tools)	4/Beginning, Improving, Succeeding, Leading
Kurnia et al. [38]	Network	Scope—TBL approach	6 capabilities (Sustainable data collection, Sustainability reporting, Sustainability benchmarking, Sustainability training, Sustainability risk analysis, Sustainability governance)	4/Unaware, Unprepared, Committed, Advanced
Reefke et al. [39]	Network	Scope—TBL approach	Not Applicable	6/Un-aware and Non-compliant, Ad-hoc and Compliance Basic, Defined and Compliance, Linked and Exceeds Compliance, Integrated and Proactive, Extended and Sustainability Leadership
Gouvinhas et al. [40]	Company—companies from various sectors	Scope—TBL approach	12 different categories of indicators (company’s strategic vision, company’s values, company’s general policy, top management commitment, company relationship with stakeholders, company’s purchasing policy, company’s economic indicator performance, company’s environmental indicator performance, company’s social indicator performance, environmental communication, legislation, standards and company’s “green” marketing procedures)	6/Complete immature companies, Immature companies, Initial mature companies, Mature companies, Maturated and teaching companies, Integrated companies
Rudnicka [31]	Network	Scope—TBL approach	6 drivers (knowledge, impact, social risk, environmental risk, cooperation, communication)	5/Starting, Aware, Aspiring, Sustainable business leaders, Masters of sustainability
Verrier et al. [41]	Process – production	Scope—Environmental sustainability	Not Applicable	5/Initial, Managed, Defined, Quantitatively managed, Optimizing
Machado et al. [42]	Process –operations management	Scope—TBL approach	17 capabilities (Occupational Health and Safety Management, Social Accountability, Sustainability Business Case, LCA, D4S, Reverse Logistics, Closed Loop Supply Chain, Lean and green process, Eco-efficiency strategies, Cleaner Production, Quality and Environmental Management System, Sustainable Purchasing, Suppliers Development Program, Stakeholder engagement, Information System, Sustainable Marketing)	5/Compliance and conformity, Operations’ eco-efficiency, sustainability management system, network and stakeholder’s integration, sustainable operations’ integration
Subramanian et al. [43]	Network	Scope—TBL approach	6 groups of capabilities (Supplier– Buyer Relationship, Governance, Production, Distribution, Waste, Customer Relationship)	4/Stage 0, Stage 1, Stage 2, Stage 3
Xavier et al. [44]	Process – Eco-innovation	Scope—Environmental sustainability	4 dimensions (Resources, Culture, Structure, Strategy)	5/Level 1, Level 2, Level 3, Level 4, Level 5
Santos et al. [25]	Network	Scope—TBL approach	4 dimensions subdivided in 14 subdimensions: Environment dimension; Social dimension; Economic dimension; Cross dimension.	5/Nonexistent; Aware; Intermediate; Advanced; Sustainable
Sari et al. [45]	Company	Scope—TBL approach	65 domains (SC driver (external); SC driver (internal); SC strategy; SC action; SC performance) subdivided in 29 subdomains/indicators	3/Level 1—Initial; Level 2- Managed; Level 3—Optimised

Source: Adapted from [14].

, where the differences between the various MMs can be seen.

3. Research Methodology

There are different approaches to developing a MM (e.g., [46,47,48]). De Bruin et al. [46] propose one of the most recognized methodologies for developing MMs as described in Figure 1. It consists of six iterative phases whereby the results of a given phase may require that a previous phase be revisited for improvement. This study follows the methodology suggested by De Bruin et al. [46].

The objective of this study is to propose a MM comprising the following phases: scope definition, design, populate and test. The “deploy” phase was excluded from this study because the deployment should be extended to other companies besides those used in the model’s development. The “maintain” phase is related to the need to ensure its update and to provide the necessary conditions (e.g., resources, software) so that the use of the MM lasts. This phase is outside this research scope as it deals with the future use of the model. Figure 2 shows the research design followed herein.

One of the decisions to be made in the development of MMs is the choice of the research methods to be used, which influences the scientific and practical quality of the resulting MM [47]. In this study, a combination of theory-driven and practitioner-based approaches was used.

A literature review of existing sustainability MMs and their characteristics provided the background knowledge to develop the first three phases of MM t (i.e., scope, design, and populate). These phases are described further. Literature on the development of MMs recommends exploratory research methods such as the Delphi technique, nominal group technique, focus groups, and case studies [34,46]. De Bruin et al. [46] highlight the importance of these methods, especially for the populate phase, as the literature review needs to provide more information for MM development at this stage. These qualitative methods are more frequent in constructing MMs than quantitative ones [34]. Despite criticisms of the case study method [49,50], it provides valuable insights into the complex behaviours of the subjects of interest, allowing the researcher to obtain a holistic view of the phenomenon to be studied [50]. The case study method has been considered in constructing and validating the MMs in several areas, such as information systems [22]. Various studies certify the proposed or analysed MM in SSCM through a case study or multiple case studies [28]. For example, Srai et al. [30] developed and validated an MM using a case study analysis of 12 companies. According to the authors, this method produces a first-hand understanding of complex phenomena. Marco-Ferreira and Jabbour [51] used a case study of five companies. The importance of the case study in sustainability MMs had already been verified in the SLR carried out by Correia et al. [14]: 50% of the empirical studies analysed in this work used this method to construct MMs and their validation. In the SLR on MMs in SSCM performed by Pavan et al. [28], the case study method is the most used, accounting for 68% of the methods used in empirical studies to validate the analysed MMs (i.e., excluding literature reviews and conceptual frameworks/models). The case study method was also used to improve and validate the proposed MM.

One of the main criticisms of MMs is the need for more validation in selecting the MM dimensions or variables [34]. De Bruin et al. [46] suggest that MMs should be validated considering the model’s constructs and the model instruments’ performance (i.e., scale and assessment procedure). Pöppelbuß and Röglinger [52] also suggest analyzing the MM usability. In this study, the improvement and validation process took place in two stages: 1) first stage of the validation process—the objective is to obtain contributions for the improvement and clarity of several aspects of the design and populate phases, namely: (i) in the validation of the areas, practices, and sub-practices; (ii) in the allocation of sub-practices to the evolution levels and maturity levels defined based on the literature review, and (iii) in the assessment process for determining the maturity level of the areas and the company; 2) second stage of the validation process—the objective is to test the MM resulting from the previous phases (final MM) and validate it based not only on its content (i.e., areas, practices, and respective sub-practices) but the maturity levels. Additionally, the MM usability (i.e., understandability, ease of use, and practicality) is analyzed, as suggested by Salah et al. [53] and Pöppelbuß and Röglinger [52].

Case Study

The case study methodology can be used to study under-researched phenomena, which require an in-depth study of a few cases [49], as is our case. The use of multiple case studies seemed appropriate for developing our MM. The cases are used to improve and validate the MM in the populate phase and test the model’s final version. Furthermore, the case study allows the target audience of the MM (organizations) to be involved in its development process. Compared to the single case study, this research strategy is more robust and reliable [54]. In addition, it allows an exhaustive and in-depth analysis of different situations [49], providing richer information for the development of the MM. For the case selection, the Portuguese mould industry was focused on because Portugal is one of the world’s leading manufacturers in this industry, supplying large multinationals from different sectors [55]. Sustainability is considered one of this industry’s main challenges [56], which makes developing a MM for SC sustainability a relevant issue.

To find companies interested in participating in the study, the research team contacted the TOP 100 Portuguese companies in the mouldmaking industry [57]. Five companies confirmed their interest. These companies are characterized by: (i) being small and medium-sized enterprises (SMEs) (number of employees <250; turnover <EUR 50 million); (ii) using a make-to-order production strategy exporting more than 90% of their production; (iii) supplying various industries (their main customers are from the automotive industry).

Table 2. General characterization of the case-study companies.

Companies	General Characterization
Company 1	It manufactures compression and plastic injection moulds, with a capacity of up to 120 tons, for the automotive industry. Nevertheless, it tries to preserve the markets of other sectors, namely electronics/telecommunications and housewares. It employs 248 workers and has a turnover of EUR 29.8 million.
Company 2	It makes plastic injection moulds for the automotive sectors, appliances, and housewares, exporting almost all its production. Its focus is moulds of medium and large dimensions (up to 60 tons). It employs 126 workers and has a turnover of EUR 8.5 million.
Company 3	It makes moulds with a capacity of up to 20 tons, producing die-casting moulds for the automotive, appliances and packaging sectors. This company employs 69 workers and has a turnover of EUR 7.7 million.
Company 4	It makes high-precision moulds for parts of various industries such as automotive, aeronautics, medical/pharmaceutical, electrical and electronics. The company produces moulds of multiple types: thermoplastic injection, die casting, rotary injection, two-component injection, compression, and transfer sandwich. The company additionally injects plastic parts. It employs 73 workers and has a turnover of EUR 4.3 million.
Company 5	It manufactures compression and plastic injection moulds for the automotive, appliance, and packaging industries. It employs 68 workers and has a turnover of EUR 5.6 million.

presents a brief characterization of the companies participating in this study.

The five companies were informed of the study’s objectives, procedures to be followed, and the type of information sought. The companies indicated the experts to be engaged in the study attending to their skills and functions: managing partner (Company 2 and Company 4); quality and environmental manager (Company 1); director of quality and maintenance (Company 3); and quality manager (Company 5). These experts were the contact point between the company and the researcher. If necessary, they could discuss with colleagues from other functional areas to obtain an appropriate answer.

Multiple data collection instruments were used that are considered valid for case studies [49], such as interviews, document collection and analysis, and questionnaires, which also allow for a greater understanding of the phenomenon to be studied [58]. The interviews were conducted after sending a protocol indicating the aspects to be covered in them, as Voss et al. [59] suggested.

The interview aimed for the researchers to become familiar with the company’s approach to sustainability, present the MM in development and its main elements, and obtain contributions that would improve the MM. In addition to the interviews, three questionnaires were administered with the following intentions: (i) the first questionnaire sought to obtain information on areas, practices, and sub-practices to be considered in the MM and the allocation of sub-practices by evolution level; adequacy of the MM as to maturity levels; and adequacy as to discrimination criteria to be considered in the MM; (ii) the second questionnaire intended to discover the level of application of sub-practices in the company; (iii) the third questionnaire was to understand how the company evaluated the MM in managerial terms.

This process was accompanied by secondary data collection, which allowed for a deeper and better understanding of the aspects under analysis and clarified some doubts.

4. Results

This section describes the phases (scope, design, populate, and test) associated with the proposed maturity model’s construction.

4.1. Scope

The scope will determine the degree of the model application within its domain [14]. De Bruin et al. [46] suggested an extensive literature review to understand domain issues deeply. To define the scope of the MM, we ground our search in [14] and [25]. Following Correia et al. [14], two characteristics were defined to analyze the MM scope: (i) unit of analysis, which is the SC hierarchic level and can range from the process and company to the network level; (ii) sustainability focus, which is the sustainability dimensions targeted by the MM. These characteristics are highlighted in

Table 3. Unit of Analysis and Focus of Sustainability Maturity Models.

Authors	Unit of Analysis			Sustainability Focus
	Process	Company	Network	TBL Approach	Env. Sustain.
Robinson et al. [35]; Standing and Jackson [36]; Machado et al. [42]; Subramanian et al. [43]	✓			✓
Babin and Nicholson [32]		✓			✓
Pigosso et al. [23]; Hynds et al. [4]; Verrier et al. [41]; Xavier et al. [44]	✓				✓
Okongwu et al. [29]; Srai et al. [30]; Kurnia et al. [38]; Rudnicka [31]; Reefke et al. [39]; Santos et al. [25]			✓	✓
Edgeman and Eskildsen [37]; Golinska and Kuebler [33]; Gouvinhas et al. [40]; Sari et al. [45]		✓		✓

.

Table 3’s analysis suggests the following: (i) the MMs’ scope ranges from the process, company, and network level; (ii) some MMs address the maturity considering only the environmental dimension, which, according to Correia et al. [14], makes it difficult “to identify critical elements that contribute to higher levels of sustainability”; (iii) many MMs present a TBL approach (but a more detailed analysis of the MMs identified in Table 3 shows that sustainability is mainly treated as a stand-alone element of the TBL); (iv) all the MMs with a network scope follow a TBL approach. However, these MMs have some shortcomings. For example, although several sustainability initiatives that address the TBL call for interactions and collaboration between organizations, these elements do not receive sufficient attention in MMs; (v) most of the MMs present several limitations, such as a lack of details on distinct sustainability aspects to measure (e.g., [35,36,39,41]), poor definition of each stage and a lack of explanation in depth of how a company can reach and surpass the maturity levels (e.g., [4,25,31,33,38,40,41,42]).

According to Seuring and Müller [3], integrating sustainable operations requires companies to engage in supply chain management (SCM) practices. Thus, a MM should consider integrating intra- and inter-organizational sustainability practices (across different areas and organizational levels). Measuring a company’s capacity to apply certain practices fulfils an essential purpose of MMs: diagnosing the company’s current situation.

4.2. Design

In the design stage, it is necessary to respond to why the model needs to be developed, how it will be applied, who needs to be involved, and what can be achieved [46].

• Why the model needs to be developed

A MM can be used for three purposes [46]: (i) descriptive tool—assessment of strengths and weaknesses (“as-is” assessments); (ii) prescriptive tool—development of a roadmap for improvement (“to-be” maturity); (iii) comparative tool—evaluation of the company, compared to standards and best practices.

• How will it be applied

Most of the sustainability MMs proposed in the literature need to address the implementation of the MM or describe in detail the application considering the resources involved. For example, Paz et al. [60] and Xavier [61] argue for using a computer software program to facilitate the application of their model, but they need to provide details about it. Pigosso et al. [23] state that their MM is applied with documents, interviews, questionnaires, and computer resources to collect information about companies’ processes, to understand how they are organized, structured and documented, and to evaluate which eco-design management practices companies apply. According to Xavier [61] and Xavier et al. [44], interviews are the preferred method. Based on the literature review, in this study, we apply and test the MM using interviews, document collection and analysis, and questionnaires as data collection instruments. We suggest the application of structured questionnaires in the future using a computer software program and cloud computing to collect data from respondents regarding intra- and inter-organization sustainability practices.

• Who needs to be involved

A MM could be deployed by self-assessment or an external auditor [46]. Fraser et al. [62] emphasize that self-assessments are more beneficial if approached as a team exercise because the team’s involvement contributes to eliminating single-respondent bias and providing an opportunity for consensus and team-building. In this work, a self-assessment option of Pigosso et al. [15] and Xavier [61] is followed since the suggested MM intends to describe different sustainability dimensions and involves intra- and inter-organization processes to gather different perspectives.

• What can be achieved

At this stage, it is essential to specify the number of maturity levels of the model and their definitions. To this end, it is first necessary to clarify what maturity represents. The concept of maturity is usually associated with terms such as competency, capability, or even levels of sophistication [46]. Correia et al. [14] argue that there needs to be a more common understanding of the maturity concept and a guideline for gaining maturity within the SC sustainability domain.

Yimam [63] argues that two alternatives can contribute to achieving the development of a company’s maturity: (i) developing the capacity to employ more advanced and effective practices, techniques, methods and tools; and (ii) systematizing and refining the processes/practices that are explicitly defining and documenting, managing, standardizing, measuring, controlling, and continuously improving the organization’s processes/practices. Thus, maturity can be understood as an organization’s ability to use more advanced and effective practices, tools, methods, techniques, and procedures, thereby improving the possibility of achieving process or knowledge goals.

Maturity is a concept that indicates evolution and development. Moving from an initial to a more mature state means that the organization has greater sophistication, capability, or availability of certain specific characteristics [47]. In terms of sustainability, Göcer et al. [64] (p. 8) consider that maturity “refers to the level [at which] an organization can scan, seize, comprehend, disseminate, and control sustainability-related issues within itself, across the supply chain and even in the broad organizational environment”. Rudnicka [31] (p. 205) states that “the maturity can be defended as a level of engagement of the whole network and quality of management of the sustainable development in SC”. In this study, maturity can be understood as the level of the organization’s ability to plan, implement and control different types of sustainability issues/practices in its internal operations and in its SC to improve its sustainability performance. The maturity levels highlight predictable patterns about the present and future changes of the object under study (i.e., organization, individual, SC).

In this study, to construct the MM, the maturity levels are considered as a combination of the evolution levels of sustainability practices and their implementation level (IL). We cross some criteria (i.e., complexity, TBL approach, involvement, proactivity) to differentiate the levels of evolution.

Defining the number of maturity levels is another fundamental element of a MM. There needs to be a consensus or rule of thumb in the literature about the optimal number of maturity levels. The number ranges from three to six, with five being the number of maturity levels most common (e.g., [23,33,42]). We also propose a model with five levels. According to Srai et al. [30] (p.17), this number allows “a sufficient level of granularity to permit differentiation between hierarchies of network maturity whilst still being accessible to the practitioner in terms of making informed choices during applied assessment phases of the work”.

Some MMs (e.g., [30]) present no descriptors for the maturity levels. Others do, but the descriptors are different for each MM. Regarding this issue, the proposal of Edgeman and Eskildsen [37] was followed. Thus, the following more generic descriptors are used: very low maturity, low maturity, moderate maturity, high maturity, and very high maturity. The definition of each maturity level and individual descriptor results from the comparative analysis of the existing MM and is presented in more straightforward and specific Appendix A and Appendix B. These levels represent the evolution of the sustainability MM for SCs. The low maturity levels represent less complex sustainability practices’ non-application or incomplete application. The higher levels of maturity represent the application of more complex practices and imply a more substantial involvement of the SC partners and other stakeholders, addressing the three TBL dimensions.

4.3. Populate

In this phase, it is necessary to identify what needs to be measured in the maturity assessment and how it can be measured [46].

• What needs to be measured

De Bruin et al. [46] suggest that an extensive literature review can be used to identify domain components and subcomponents (what needs to be measured). The MMs are available in the literature addressing sustainability in a vast number and diversity of elements [14]. To identify areas that are mutually exclusive and collectively exhaustive [46], the three levels of analysis proposed by [65] were considered: (i) the firm’s operations; (ii) the inter-organizational level where strong economic ties are found involving suppliers, customers, and consumers; (iii) the external level, which involves other external stakeholders such as the community, NGOs, and regulators.

Sustainability practices can be grouped into critical areas considering similarities in features/characteristics. Correia et al. [10] consider these essential components to assess the evolution of sustainability, addressing an intra-company perspective and the SC perspective. Our study considers four main areas that coincide with several critical success factors for implementing a sustainable SC identified in MMs with sustainability concerns [14] (Figure 3). Each area is broken down into a set of sub-areas (i.e., practices), which in turn are broken down into sub-practices that enable their operationalization. Each area of the proposed MM is briefly described as follows: (i) Sustainability governance: focuses on the institutions, structures, and mechanisms that guide, regulate, and control the activities of stakeholders in the SC [66]; (ii) Product and process level: Organizations can adopt various practices related to products and processes to improve sustainability. Baumgartner [67] highlights that implementing corporate sustainability in a balanced fashion requires its introduction at all business levels and in all business processes. Karaosman et al. [68] point out that a company’s commitment and engagement with sustainability implies integrating social aspects at the product and process level; (iii) Customer and supplier management: Supplier management comprises efforts with suppliers in planning and executing joint environmental and social solutions; or supporting suppliers to improve their sustainability performance [69]. Customer management reflects a company’s focus on working with customers to understand sustainability-related problems and monitoring activities better to ensure that products are safe for the customer and to identify emerging issues that need to be addressed [70]; (iv) Stakeholder focus (not considering customers and suppliers), which includes business initiatives that are not directly related to the company’s SC operations and that may involve regulatory stakeholders and community stakeholders [29].

• How can it be measured

The next step in MM development is to clarify how each area can be measured. The strategies followed by companies to integrate sustainability into their intra- and inter-organizational process should be carefully and reasonably broken down into several practices to aid its comprehension [71]. Identifying and systematizing the practices for each area is essential to constructing a MM [44,61]. To describe the practices’ evolution process, either in the company or in its SC, sub-practices need to be identified by levels of evolution [23,61].

Based on the literature review on sustainability MMs (e.g., [4,30,31,38,39,41,42,43,60]), it was first suggested to distribute the sub-practices and their allocation by evolution levels.

Table 4. Example of Areas and Sub-areas of the proposed Maturity Model by Evolution Level.

AREAS AND SUB-AREAS	Evol. Level
AREA: SUSTAINABILITY GOVERNANCE
Practice: Corporate environmental governance
Sub-practices:
Consideration of environmental issues in some functional areas	1
Data collection on environmental aspects	2
Environmental compliance and auditing programs in all departments	3
Commitment to GSCM from senior and middle-level managers	3
Obtaining ISO 14001 certification	4
(…)
AREA: PRODUCT AND PROCESS LEVEL
Practice: Green purchasing
Sub-practices:
Materials that should not be used in products and should not be used in purchases are identified	1
Compliance with environmental legislation, such as external purchasing directives	1
Suppliers are selected using environmental criteria	2
Providing design specifications to suppliers that include environmental requirements for purchased items	3
Purchase of efficient materials/products in terms of energy/water consumption and non-polluting, toxic, or dangerous	3
(…)
AREA: CUSTOMER AND SUPPLIER MANAGEMENT
Practice: Social supplier management practices
Sub-practices:
Ensuring that suppliers obtain OHSAS 18,001 certification or other health and safety management system certifications such as SA 8000	3
Perform audit procedures for suppliers’ internal management system related to social issues (e.g., related to health and safety, appropriate labor working conditions)	3
Guidance and support to suppliers helping them to improve their social performance	4
Develop new product/process with suppliers that reduce health risks for consumers	5
(…)
AREA: STAKEHOLDER FOCUS (NOT CONSIDERING CUSTOMERS AND SUPPLIERS)
Practice: Stakeholder focus (environmental issues)
Sub-practices:
(…)
Development of its initiative of programs for society related to environmental protection	3
Collaboration with universities and research institutions in the development of new environmental technologies or more environmentally friendly products	4
Innovative partnerships (e.g., NGOs and community groups) related to projects focused on environmental protection)	5

presents examples of sub-practices for each area and their allocation to evolution levels after validation.

It is also necessary to develop evaluation scales that allow for assessing maturity. Various types of scales may be used: (1) binary nominal scales—for ”yes or no” decisions and responses and to facilitate the quantitative evaluation process (grades 0 or 1) (e.g., [4]); (2) continuous scales, quantitative (e.g., increasing range 0–5) or qualitative, (e.g., low, medium, high) [72]. Similar to other authors (e.g., [23,44]), in this study, it is suggested to measure each sub-practice implementation level using a scale from 1 to 5, where 1 means “Not implemented or not fully implemented” and 5 means “The sub-practice is fully implemented and embedded in the company processes and continuously improved”. Figure 4 presents the evaluation scale used in this study.

The discrimination criterion establishes the minimum number of practices for each maturity level and how to move from one maturity level to another. The literature presents different suggestions regarding this criterion (e.g., [4,23,44]). For example, [23] considers that 100% of practices at an evolution level must have an implementation level greater than or equal to 3 to move from one maturity level to another. An MM with a vast scope and presenting several areas of analysis and with a high number of practices may have a more flexible criterion [61]. For our MM, which fits this type, we adapted the proposal of [44], which suggests a percentage of 90%. Figure 5 presents the matrix with the discrimination criteria for each maturity level. An area (e.g., Sustainability Governance) has maturity level 1 if fewer than 90% of its sub-practices associated with evolution level 1 present an implementation level below 3. For an area to have a maturity level of 5, at least 90% of the sub-practices at evolution levels from 1 to 5 must have an implementation level greater than or equal to 3.

4.4. The Rationale for Improving the Maturity Model

In the first stage of the validation process, face-to-face interviews with the experts were conducted. After the presentation and explanation of an initial version of the MM under development, the experts were invited to answer a set of questions, give comments, and propose changes to improve the MM. The following aspects were discussed: (i) adequacy of the areas, practices and sub-practices of the MM; (ii) allocation of sub-practices by levels of evolution; (iii) several maturity levels and description of the levels; and iv) discrimination criteria to determine the maturity level.

Experts generally expressed a favourable position concerning the relevance of the areas and practices, the suggested discrimination criteria, and the number of maturity levels. There was no need to make changes to these MM elements.

However, concerning the sub-practices and based on the experts’ comments and suggestions, of the 218 initial sub-practices, 83 were excluded to minimize overlapping concepts and ambiguities. Some sub-practices (20) were modified by changing the sentences or including examples to make them more straightforward and avoid difficulties in their interpretation. This process resulted in a total of 135 sub-practices that comprise the final version of the MM distributed by the five levels of evolution. In the literature, other MMs present equally high numbers of practices (e.g., [61]). According to the experts’ suggestions, some practices were changed from one level of evolution to another. Of the 135 validated practices, the evolution levels of 14 were modified.

Regarding the maturity levels, the experts mentioned the need for greater clarity concerning some descriptions (change of expressions/words used) and the need to make the maturity levels more distinctive. Thus, some changes were introduced in the description of maturity levels to make them more straightforward and specific. Appendix A describes the maturity levels for each MM area following the improvements. Appendix B represents the maturity level of the whole organization and its SC (considering all areas) after implementing the interviewees’ suggestions.

4.5. Maturity Model Proposal

Using the literature review results and case studies contributions, the sustainability MM proposed is illustrated in Figure 6.

According to the proposed MM, a company with a very Low maturity level (level 1) is characterized by a focus mainly on internal and economic aspects of sustainability and a reactive attitude. The company is at this level when fewer than 90% of its sub-practices are associated with evolution level 1, and the different critical areas (sustainability governance, product and process level, customer and supplier management, and stakeholder focus) present an implementation level below 3. To reach higher levels of maturity, the company must implement more demanding and sophisticated practices that imply greater involvement with its SC partners (associated with higher levels of evolution). For example, when a company reaches level 3, it means that the company has a more proactive attitude towards sustainability, a broader implementation of internal sustainability practices and traditional SC partners and other stakeholders are engaged in a new collaboration on environmental and social issues. At this level, 90% or more practices associated with the level of evolution 3 and previous levels (Level 1 and Level 2) present an implementation level equal to or higher than 3. At maturity level 5, the company reaches a high level of maturity: sustainability is embedded in all processes at the corporate and SC levels. It presents high collaboration between SC partners in sustainability practices with an orientation towards value creation and innovation from a TBL perspective. Considering the sub-practices associated with the various critical areas and the level of evolution 5, 90% or more practices will have to present an implementation level equal to or higher than 3.

4.6. Test of the Proposed Maturity Model

The proposed MM was improved using the five case studies in the test phase. After the application of the MM, the companies were asked to evaluate the MM as a whole. The results of the application and evaluation of the MM are described next. To test the operationalization of the MM, a questionnaire was designed and used in each case company to indicate the level of implementation for each of the 135 sub-practices that comprise the MM. Based on this data set, each company’s maturity levels were calculated.

4.6.1. Application of the Maturity Model

None of the companies under study presents a maturity level of 5, either in any critical area or overall. Company 1 is the one that presents the highest maturity levels for each of the areas and overall. The overall maturity level is Moderate (Level 3), indicating that more than 90% of the sub-practices in evolution level 3 and above have an implementation level of 3 or more. The company also has already implemented (with IL≥3) other practices associated with the evolution levels 4 and 5 (66% and 72%, respectively), as can be seen in the last row of

Table 5. Maturity levels for each company by area.

Area Maturity Level *	Company 1	Company 2	Company 3	Company 4	Company 5
Stakeholder focus	Level 4	Level 1	Level 1	Level 1	Level 1
Customer and supplier management	Level 3	Level 1	Level 1	Level 2	Level 1
Product and process level	Level 3	Level 1	Level 1	Level 1	Level 1
Sustainability governance	Level 3	Level 1	Level 1	Level 1	Level 1
Company maturity level **	Level 3 Moderate	Level 1 Very low	Level 1 Very low	Level 1 Very low	Level 1 Very low
Implemented practices with IL≥3 (N./%) ***	L1: 22/100% L2: 26/96% L3: 30/94% L4: 19/66% L 5: 18/72%	L1: 21/95% L2: 11/41% L3: 12/38% L4: 7/22% L5: 15/47%	L1: 21/95% L2: 5/19% L3: 7/22% L4: 8/28% L5: 5/20%	L1: 20/91% L2: 16/59% L3: 18/56% L4: 14/48% L5: 6/24%)	L1: 22/100% L2: 13/48% L3: 15/47% L4: 12/41% L5: 4/16%

Notes: * The area maturity level ranges from level 1 to level 5, according to Appendix B.; ** The company maturity level ranges from level 1 to level 5, according to the descriptors in Appendix C.; *** Number of sub-practices in each level: Level 1 (L1)—22; Level 2 (L2)—27; Level 3 (L3)—32; Level 4 (L4)—29; Level 5 (L5)—25.

. The remaining companies present very low maturity (Level 1) overall and for almost all areas (except company 4 for the customer and supplier management area, which presents Level 2).

These outcomes result from the sustainability practices implemented by each company. Next, a brief overview of each company’s perspective is provided:

Company 1—Moderate maturity level. This company has formal structures with responsibilities in sustainability management and clear guidelines and principles established in both the environmental and social areas, not only internally but also directed towards managing its partners in the SC and other stakeholders. Implementing an environmental management system almost two decades ago made it possible to raise awareness, and it is an essential element in the company’s environmental management. Social data are collected to define objectives/indicators and evaluate performance, but these are mainly internal data. Most practices related to the product and process level are implemented. Above all, the company has focused on the integration and consolidation of green production and quality management, as well as the social practices related to its workers (such as employee development, training, education, employee health and safety, and labour practices). Because its production is primarily intended for the automotive industry, Company 1 has sought to respond to the demands of its customers. It has focused on implementing practices/sub-practices aimed at improving quality and other parameters associated with the economic dimension. It has also focused on environmental and social practices/sub-practices that involve communicating and regularly interacting with its customers. Environmental and social practices involving customers have started to be adopted by some customers but have progressively extended to others; this requires using more resources (time, skills, investments, structures). Those practices that require working with its suppliers are relatively recent but increasingly important. The company shows great concern and attention regarding sustainability with other stakeholders, such as its local community.

Company 2—Very low maturity level. The company focuses on economic issues, with its main concern regarding environmental and social aspects being to comply with legislation/compliance. This is reflected in the absence of dedicated sustainability structures. For example, when it is necessary to respond to a request/requirement from its stakeholders (e.g., customers, suppliers, official bodies) or solve a problem related to the environmental or social area, the management seeks to solve these issues without any structured approach. There are no defined policies regarding sustainability. The company ensures that environmental and social legislation is complied with in production, design, purchasing, distribution, and logistics, as well as in employee health and safety, employee development and training, and other working practices. It is worth noting that there is an effort to implement certain sub-practices, particularly in quality management, green production, employee health and safety, and labour practices, in a systematic and controlled way. The company values the relationship with its customers and has close contacts to maintain customer satisfaction with an essentially economic focus. The focus is on maintaining relationships that allow the company to achieve the best operational and economic performance. The company is very focused on its internal operations and makes little effort to make a beneficial contribution to society.

Company 3—Very low maturity level. The company has recently focused on increasing capacity and technological innovation. A single person is responsible for quality management, legal compliance with environmental issues, and workers’ health and safety. This is considered a barrier to implementing other practices, such as collecting and processing environmental and social data, which does not occur systematically in the company. It is a family-owned company, and the most recent and succeeding generations in management have shown greater interest in these issues, but this has not yet been reflected in a formal structure or control. The company has a reactive behaviour in almost all practices related to ecodesign, green production, distribution and logistics, green and social purchasing, employee health and safety, employee development and training, and labour practices. However, there is a more significant evolution in implementing quality and lean management practices. Concerning the environmental dimension, the company seeks to comply with legal obligations. The company pays attention to its stakeholders’ demands and expectations regarding sustainability. However, its involvement with other entities such as customers, suppliers, and the community in sustainability practices is practically non-existent; moreover, the resources allocated to their implementation are also insufficient.

Company 4—Very low maturity level. This company presents a very low maturity level (Level 1) for the MM areas: stakeholder focus, product and process level, and sustainability governance. The customer and supplier management area is more advanced in terms of maturity. There are no specific structures to deal with sustainability (from an integrated perspective). Environmental or social issues are the responsibility of several people in different areas (e.g., production, quality, and administration departments). These people are in charge of collecting environmental and social data, which is done for controlling the various measures implemented and reporting to official/governmental entities. The existing performance evaluation systems do not yet integrate these environmental or social aspects. However, the company recognizes that implementing this sub-practice is advantageous and necessary in the future. The company’s attention is turned towards its technological capacity and increased flexibility. However, the company is proactive regarding environmental production, distribution and logistics, employee health and safety, employee development and training, working practices, and quality management. For example, in green production, proactivity is explained because of the need to meet its customers’ demands. The focus on customers also stands out in the management of its SC. The company is attentive to the demands and expectations of its stakeholders and provides regular support to some stakeholders in various initiatives (e.g., offering sponsorships to sports clubs). However, these sub-practices do not require significant resources or joint working between them and the company.

Company 5—Very low maturity level. There is no holistic approach to sustainability, and the economic dimension takes precedence over the remaining dimensions. In this company, environmental issues are the responsibility of the quality manager, and the human resources department manages social issues. Environmental issues are already included in the company’s performance assessment tools and considered in the reporting to top management. It should also be noted that the company implemented some practices at the product and process level that are more demanding in terms of resources and more complex—for example, green production. The focus on supplier management is also fundamentally economic. In supplier management, the company implements some sub-practices from time to time in the environmental and social scope. However, it has already implemented some, which implies greater communication and involvement with its suppliers (associated with levels of evolution higher than level 1).

4.6.2. Presentation of the Results from the Validation of the Maturity Model

The assessment of the MM was performed by several criteria (i.e., the relevance of components, comprehensiveness of components, mutual exclusion of components, the sufficiency of maturity levels, the accuracy of maturity levels, ease of understanding, and level of usefulness and practicality). This assessment was based on a short questionnaire adapted from [73]. A five-point Likert scale using the levels (5) Strongly agree, (4) Agree, (3) Neither agree nor disagree, (2) Disagree, (1) Strongly disagree) (Appendix C).

All experts considered that the MM is comprehensive and suitable for assessing the maturity of SC. Regarding relevance and comprehensiveness, all the experts (three in level 5 and two in level 4 on the Likert scale) confirm that the areas, practices, and sub-practices are relevant and cover all aspects of the MM domain. The same results were obtained concerning the maturity levels. The experts agree with maturity levels’ “Sufficiency” and “Accuracy”. As for “Ease of understanding” and “Usefulness and practicality”, the results are also satisfactory (two experts in level 5, two in level 4, and one in level 3 of the Likert scale). Some concern was registered about the criterion “Ease of use”, with one expert disagreeing that this criterion is checked. The experts consider that the comprehensiveness of the model makes it more difficult to obtain information because it is dispersed over various areas of activity. The remaining experts agree with the “Ease of use” (1 expert in level 5 and the remaining three at level 4 on the Likert scale concerning this criterion).

5. Discussion

Sustainability has become a global concern; therefore, many forward-looking organizations are revisiting their internal and SC operations [25,74]. Several studies emphasize that integrating environmental, social, and economic concerns into corporate decisions is crucial for success. Formentini and Taticchi [75] consider that to have more significant impacts on sustainability, companies must involve more complex activities addressing various areas at the internal and SC level and the different dimensions of sustainability. However, this also means a more significant challenge for management. MMs can be a support tool on this path towards sustainability. The model proposed contemplates practices at the intra-organizational and inter-organizational levels, as highlighted by Formentini and Taticchi [75], and in different critical areas for sustainability identified in the literature on sustainability practices and emerging from sustainability MMs, such as [29] and [32]. In this way, the MM meets the approaches to SSCM that have become more integrated and include a broader range of issues [76].

According to Buckle et al. [77], MM, in this case for SC sustainability, should define constructs such as maturity and maturation and must identify observable indicators of maturity levels and the characteristics of paths between them. All these requirements are observed in the MM proposed in this paper since maturity is defined as “the level of organization’s ability to know how to plan, implement and control different types of sustainability issues/practices in its internal and SC operations to improve its sustainability performance”; the observable indicators of maturity levels are the number of sub-practices associated with each evolution level that should be equal or superior to 90% and with an implementation level greater than or equal to 3; the main characteristics of the 5 paths/levels were also defined in detail for each MM area (Appendix A) and the whole organization and the SC (considering all areas) (Appendix B).

This study represents a significant contribution not only to the sustainability area but also to systems theory. According to Bucke [78], businesses focus on what is known about success, what works, and what can be improved. Companies are not interested in awaiting fully developed theories and formalized knowledge before action can be taken. However, given the urgent nature of many of the problems to which systems thinking is being applied, undertheorized systems thinking could also be risky. In this context, researchers could help mitigate this risk by clarifying knowledge and other relevant constructs, such as sustainability, thus allowing the industry to have confidence in the validity of what gets measured and is believed to help to create success, such as the MMs. The same author argues that MMs can assist in developing a comprehensive theory about systems thinking, criticizing the value of some of those MMs regarding their construction methods.

The concept of maturity from the systems theory perspective is conceptually defined as an emergent property of the organization, which arises due to the degree of alignment and integration of their processes. This concept is operationalized through a systemic function that measures the maturity of organizations and its validation by measuring maturity in some organizations [15].

Another critical point in the proposed MM is that it targets the SC. This approach is aligned with what has been defended for a long time by several authors [79,80,81,82,83]: “the most significant changes in the paradigm of modern business management is that individual businesses no longer compete as solely autonomous entities, but rather as supply chains”. Business management has entered the era of inter-network competition, and the ultimate success of a single business will depend on management’s ability to integrate the company’s network of business relationships”. Moreover, from the perspective of Gripsrud et al. [84], the research would benefit from going “back to the future”. This means that one can learn from frameworks developed previously to understand better the supply system as a whole, the role of the individual participants in that system, and the underlying economics of such a system. We can say that the approach followed in this study was based on these perspectives because the SC was used as a research unit of analysis, and the proposed MM was constructed with a previous analysis of the models that already exist in many different areas but with a more complete and reliable methodology.

Reefke and Sundaram [85] argue that sustainability in the SC still needs to be improved to operationalize. According to the literature in SSCM research, there are still many fields to explore, a need for more knowledge about practices to support SSCM, and available frameworks and models geared for transforming existing SC processes towards a sustainable focus. The proposed MMs contribute to the research in this area. Moreover, about the MMs present in the literature, the MM proposed simultaneously presents a more comprehensive approach at the level of practices and contemplates the different dimensions of sustainability (economic, environmental and social), which is a central aspect of SSCM [3,86]. Furthermore, the areas and practices into which the MM can be broken down are validated by the companies involved in the model construction process. The validation of MMs is a limitation of MMs recognized in the literature being highlighted, for example, by Tarhan et al. [87].

It is also important to note that companies approach the integration of sustainability into their operations differently [75]. For example, they may integrate sustainability internally into specific functional areas or different processes (e.g., purchasing and production processes), focus only on the environmental or economic dimension, or take a TBL approach. Companies also may or may not have a SCM orientation integrating sustainability into their SCM practices.

The proposed MM supports the practical application of sustainability principles and provides a guide for practitioners who want to use MMs to assess the level of maturity of their company and SC regarding sustainability. The MM can work as a descriptive tool since the effective integration of sustainability in SCs requires the evaluation of their maturity and identifying their strengths and weaknesses; used to support the identification of improvement actions and changes that lead to higher sustainability levels; and works as a comparative tool for benchmarking analysis. Since the MM is structured into several levels (areas, practices and sub-practices associated with the different dimensions of sustainability), it was possible to verify through the MM test that companies have various options regarding the practices they implement, as highlighted by [75]. For example, Company 1 has a higher maturity level than the other companies but still has to make significant efforts in some critical areas. The MM thus allows companies to analyze where they should develop more extraordinary efforts and improve and compare their status with other companies on the path towards sustainability.

6. Conclusions

The interest in using MMs to help integrate sustainability in organizations and their SC has been growing. However, the literature on sustainability MMs still needs to be explored, with more empirically validated models for practice and considering a holistic approach in terms of sustainability (i.e., environmental, social, and economic dimensions). Moreover, the previous sustainability MMs considering the SC level present several limitations (e.g., the need for more information on how to reach and pass the maturity levels), making it difficult to understand how they work and their operationalization [14,25,88].

This study proposes a sustainability MM for SCs with the main objective of mitigating the limitations identified in sustainability MMs proposed in the literature. Thus, it contributes to going deeply into theory regarding the sustainability MM research area, an emerging area that needs to be developed [14].

The previous sustainability MMs were reviewed to identify research gaps and approaches used in developing the model and help define the scope of the MM to be proposed. An extensive literature review on corporate sustainability and SSCM was also performed to identify, among other aspects, the MM’s levels and define the components (areas) and subcomponents (practices) of the MM. The model was improved with the collaboration of five companies from the Portuguese mouldmaking industry and applied to them to test its validity and reliability and whether it is user-friendly.

The model suggested is based on the TBL approach, contributing to the sustainability MM literature with a more comprehensive method at the level of the elements (areas/practices) that comprise the model. This research systematizes intra- and inter-organizational sustainability practices through a MM to guide the integration and evolution of sustainability maturity in SCs. These sustainability practices are associated with various critical areas for sustainability and its different dimensions. Many of these practices considered in the proposed MM require the involvement and collaboration of the organization with its SC partners and other stakeholders. Despite being of great importance for the sustainability of SCs [3,69,69,89,90], this dimension needs to be explored in sustainability MMs considering the SC level proposed in the literature. In that sense, this model contributes to filling this gap by strengthening this aspect.

In addition, the proposed MM provides a guide for practitioners who want to use MMs to assess the level of maturity of their organization and corresponding SCs regarding sustainability. Since the maturity levels are associated with the implementation of sustainability practices, the self-evaluation through the model and identification of improvement actions is a task that may be performed with the collaboration of the managers and those responsible for the various performance/functional areas (e.g., purchasing, production, logistics, etc.). It may contribute to their greater involvement and motivation in the assessment and improvement actions.

Nevertheless, the model presents some limitations. The high number of practices to be evaluated is a positive aspect because it illustrates the comprehensiveness of the model and its detail. However, it may represent a difficulty in assessing the maturity levels’ implementation and determination. Future work could analyze the possibility of developing software systems that support the MM application method and facilitate its use, for example, a computer application for information-gathering and treatment or using the internet. Additionally, MMs were improved and applied in SMEs belonging to a sector very dependent on the automotive industry and with a specific production strategy (a make-to-order production strategy). As a result of applying MMs to the several companies studied, it was found that many of them presented a very similar profile in terms of maturity, either about the MM areas or in general terms. To increase the external validity of the model, multiple studies must be carried out in organizations with other characteristics (for example, size, position in the SC, etc.) and belonging to different activity sectors.

Analyzing the barriers and facilitators to implementing this model may be an interesting research topic for future work. Another is to focus on monitoring the implementation of this type of model and adopting a longitudinal analysis. Furthermore, based on the proposed model, it will be interesting to develop a user-friendly quantitative analysis method to enrich its information outputs and to perform a deep benchmarking analysis.