Analysis of factors influencing Circular-Lean-Six Sigma 4.0 implementation considering sustainability implications: an exploratory study

ABSTRACT In this study, we develop a new paradigm, Circular Lean Six Sigma 4.0 (CLSS4.0) to promote manufacturing sustainability. This paper aims to provide a practical and holistic view of the drivers and barriers that can help companies design an integrated CLSS4.0 model. The paper is based on a qualitative exploratory study using multiple case studies within 12 Moroccan manufacturing firms conducted through semi-structured interviews with top executive managers. The results show that the drivers are related to expected operational and environmental performance, increasing customer requirements, gaining competitive advantage and market growth while barriers are related to insufficient tangible (finance, human and equipment) and intangible (skills and techniques) resources, data privacy, technical issues and management support. The proposed framework identifies the assessment of drivers and barriers and their attributes as a starting point for managers to lead the CLSS4.0 transformation, thereby contributing to its successful implementation. To the best of our knowledge, this study is among the very first studies to discuss the CLSS4.0 drivers and barriers. It could be useful to managers as a diagnostic tool to assess their ability to implement CLSS4.0 before investing in the initiative.


Introduction
Sustainability is defined generally as the capacity to endure and maintain a balanced and healthy ecosystem, economy, and society that can meet the needs of the present without compromising the ability of future generations to meet their own needs (Kiel et al. 2017).It involves balancing economic growth and development with social progress and environmental protection.The concept can be applied to many different areas, including environmental sustainability, economic sustainability, social sustainability, and cultural sustainability.Indeed, the subject is increasingly relevant in the changing world, where issues such as climate change, resource depletion and social inequality are becoming ever more pressing (Cherrafi et al. 2016).
In the industrial landscape, sustainability is commonly used as a guiding principle for achieving long-term success and reducing environmental impact (Seuring and Müller 2008).By considering the environmental and social impacts of their operations, industrial organisations can identify ways to reduce waste, conserve resources, and minimise their carbon footprint.This not equilibrium among all three to sustain organisations.Specifically, our research focuses on the economic facet of sustainability, exploring how economic factors contribute to sustainable practices and outcomes.By examining the economic dimension of sustainability, our study aims to offer insights and recommendations for promoting sustainable economic practices while considering the broader context of the environmental and social aspects.
Given the above arguments and the challenge of climate change, pollution and resource scarcity induced by their activities (Edwin Cheng et al. 2022), manufacturing companies are looking for innovative and competitive paradigms to streamline their operational processes, gain productivity, reduce the damage to the environment and become sustainable.Industrial activities are considered a major source of global environmental pollution and resource waste, which should actively and significantly contribute to promoting sustainability (Sharma et al. 2023).To this end, manufacturers are required to integrate environmental practices as part of their business strategies in order to mitigate resource depletion and environmental damage (Cherrafi et al. 2021) and gain a competitive advantage simultaneously (Trevisan et al. 2023).Yet manufacturing companies remain faced with the cost of doing business sustainably.While adopting sustainable practices may entail short-term costs, the long-term benefits can offset these costs in terms of savings, reputation and market competitiveness.
To address the aforementioned challenges and achieve sustainable manufacturing, various approaches have been extensively studied and empirically tested, demonstrating their effectiveness in integrating sustainability into manufacturing processes such as lean management, six sigma (SS), green approach, zero defects manufacturing (ZDM), Eco-design and eco-innovation.Six Sigma is a data-driven methodology that reduces defects and improves quality, whereas ZDM focuses on preventing defects during the manufacturing process.Green practices refer to environmentally friendly initiatives and actions while eco-design integrates environmental considerations throughout the entire product design and development process (Giuffrida and Mangiaracina 2020).
Previous studies have explored the intersections between LSS and sustainability in the context of green practices.As a result, the concept of Green Lean Six Sigma has gained significant notoriety and firmly established its contribution to achieving long-term sustainability goals.Green LSS emphasises process optimisation and waste reduction while considering sustainability aspects (Garza-Reyes 2015).Six Sigma and Zero Defects are quality management (QM) methodologies primarily focused on quality improvement (QI).They offer organisations structured frameworks and techniques to drive continuous improvement and attain higher levels of quality and customer satisfaction.However, QM and QI are distinct concepts, as highlighted by Juran and Gryna in their book on Quality Planning and Analysis published in 1993.While QM encompasses a broader range of strategies and methodologies, QI specifically targets improving quality over time.Six Sigma emphasises process efficiency and defect reduction through statistical analysis while ZDM aims for zero defects by integrating quality management principles with digital tools for real-time monitoring and optimisation.ZDM aims to achieve defect-free production, indirectly promoting sustainability through waste reduction while, on the other hand, Eco-design/Eco-innovation focuses on environmentally conscious product and process design to minimise environmental impact (Psarommatis et al. 2019;Dahmani et al. 2021;Fragapane et al. 2023).Each approach addresses sustainability in manufacturing from a different perspective but ultimately aims to drive positive economic prosperity for manufacturing firms.It results in increased revenue through customer satisfaction, cost savings through defect reduction, and improved efficiency and productivity.
However, given the evolving nature of manufacturing systems and the continuous pressure to integrate sustainable practices into manufacturing operations, new perspectives can be explored by combining innovative approaches such as circular economy (CE) principles and industry 4.0 (I4.0) technologies with LSS to promote sustainable performance (Ghaithan et al. 2023).Various researchers have proposed various integrated approaches to address the challenges of transforming the industrial sector into a more sustainable industry (Bucea-Maneaţoniş et al. 2021;Kaswan et al. 2023;Cherrafi et al. 2022).This article presents an integrated framework that combines CE, LSS and I4.0 to meet the requirements of sustainable manufacturing.
We build on the CE, LSS, and I4.0 concepts to introduce a new perspective in sustainability called Circular Lean Six Sigma 4.0 (CLSS4.0),defined in this paper as the embodiment of I4.0 technologies and CE practices with the LSS continuous improvement strategy.This combination will lead to more sustainable results.CLSS4.0 can therefore be promoted as a new perspective to accelerate sustainability.In our perspective, sustainability is considered an intrinsic value covering three concepts, namely LSS, CE and I4.0.The circular economy is conceived as a sustainable and innovative solution to the pressing environmental challenges we face today.By adopting a circular economy approach, companies can minimise waste and maximise resource efficiency, resulting in reduced carbon emissions, better resource management and a healthier environment.It focuses on the reuse of materials and resources rather than the traditional linear economy of buy, use and waste.It aims to reduce the production and consumption of new materials and energy while maximising the use of resources by reusing and recycling them.This reduces waste and keeps resources in use for longer, creating more efficient and sustainable systems.The CE is receiving increasing attention both academically and in practice and is being positioned as a sustainable model offering solutions to resource depletion and waste management problems (Cherrafi et al. 2022;Edwin Cheng et al. 2022).The benefits of circular economy can be seen from an economic, social and environmental perspective.Economically, a circular economy can help to create more efficient and sustainable economic systems that create less waste, while increasing employment and productivity.It can also help reduce material and energy costs, making companies more competitive, and can increase consumer spending power.Socially, circular economy can help reduce inequalities by creating jobs in the recycling industry, increasing access to resources for low-income communities, and helping to alleviate poverty.it can also reduce the global burden of pollution through reduced resource and energy consumption.Environmentally, circular economy can help reduce the use of resources and energy, reduce pollution, and mitigate climate change by reducing waste and emissions.It also helps preserve valuable resources by encouraging reuse and recycling.By reducing waste and developing efficient energy usage, it can also reduce environmental damage and promote sustainable development.In literature, many researchers have demonstrated that CE has a positive impact on the cost-effectiveness and longterm viability of manufacturing businesses (Hina 2022), where the recycling of materials and assets creates both additional wealth and new revenues (Bag et al. 2022;Edwin Cheng et al. 2022).
The evolution of industrial manufacturing systems has revealed real advances and innovation resulting from the era of digitisation called I4.0 referring to the fourth industrial revolution, making smarter, more connected production systems possible (Cherrafi et al. 2022).I4.0 advancements have allowed manufacturers to reduce costs, increase scalability, improve efficiency, increase compliance with regulations, and the accuracy of their products.Additionally, these technologies have enabled factories to be monitored in real-time and provide insights into the production process (Lasi et al. 2014).Furthermore, I4.0 T involves support for operational and environmental excellence.Industry 4.0 has far-reaching implications on the social sustainability side.It has the potential to greatly increase efficiency and productivity, reduce the cost of production, improve safety, decrease energy consumption, reduce the cost of services, create new market opportunities and increase the competitiveness of enterprises in their respective markets.Lean Six Sigma (LSS) methodology is well established to help manufacturers meet the challenges of sustainability (Cherrafi et al. 2017).LSS involves a set of methods and tools for process improvement (Skalli, Charkaoui, and Anass 2022a).It combines lean, which focuses on eliminating waste in a process to become more efficient and Sigma, which looks at improving the quality of a process to reduce defects and increase customer satisfaction (Alexander, Antony, and Cudney 2021).The goal of LSS is to identify and eliminate any errors or inefficiencies in a process to save time and money while providing the highest possible customer satisfaction.LSS is based on the principle of continuous improvement and focuses on eliminating process defects (Antony et al. 2022).The use of LSS encourages and supports the development of sustainable processes and products, helping organisations to become more sustainable over time.It provides a framework for organisations to effectively measure and track their environmental impact, allowing to continuously improve the sustainability performance.The interaction between LSS and sustainability performance has been widely debated over the last few years, and evidence from previous studies has revealed a strong synergistic effect (Belhadi et al. 2020a).The literature has highlighted a great synergy between I4.0 and CE practices and their valuable impact on sustainability (Ghaithan et al. 2023).I4.0 technologies and LSS are presented in the literature as powerful tools for improving sustainability performance in manufacturing firms (Dounia Skalli et al. 2023).The integration of LSS and I4.0 known as LSS4.0 has the potential to be an important part of the answers to sustainability.Furthermore, LSS and CE practices can leverage various I4.0 technologies to provide economic, operational and environmental benefits to companies.The adoption of the triple approach of I4.0, CE and LSS would have a tremendously positive effect on the three sustainability dimensions.However, it is not yet clear which driving factors and barriers are most critical to the success of CLSS4.0 adoption, and how knowledge of these factors can influence the decision-making process concerning CLSS4.0 deployment.
Despite the recent growing interest and various studies exploring the drivers and barriers of the tree concepts (LSS, CE and I4.0) alone or in dual combination, as well as the different research streams proposed, existing research to support their combination remains very limited while knowledge on drivers and barriers is missed (Belhadi et al. 2020a;Kurdve and Bellgran 2021).Most prior studies have relied on theoretical research and statistical methods in their research design.Previous literature has studied the implementation of I4.0, LSS and CE in a fragmented way, without proposing a comprehensive integrated framework to address how they interact and influence sustainability.
To our knowledge, there is no research in the literature investigating the drivers and barriers of CLSS4.0 implementation towards the sustainability performance of manufacturing companies.This study, therefore, aims to fill these gaps in the literature by exploring the drivers and barriers in the Moroccan manufacturing companies' context.Despite their critical importance, the drivers and barriers factors to CLSS4.0 adoption have not received significant scholarly attention and thus no empirical evidence has been reported in the academic literature.
Based on the above argument and the very limited body of knowledge in this area, an extensive comprehension of these elements is needed.The driving and hindering factors have a major influential role in the decision-making process for adopting CLSS4.0.Accordingly, we argue for the need to explore these elements, as a better understanding of these elements will boost a company's commitment to this initiative.Hence, empirical research is required to advance knowledge in this field.In this line, an exploratory study is necessary to mitigate this gap in the literature and develop insights.Compared to earlier studies, this paper examines both drivers and barriers to develop a comprehensive interpretation of the CLSS4.0scale based on in-depth case studies and interviews within Moroccan multinational manufacturing companies.The contribution of our study stems from the conceptualisation of a new decision tool for sustainability.
The adoption of CLSS4.0 will help processes, resources and energy optimisation while reducing cost and quality defects, thereby generating added value, profitability and competitive advantage.
Given the purpose of the study to explore the drivers, barriers and best practices for the successful adoption of CLSS4.0 initiatives, three research questions arise: RQ1.What are the main drivers and barriers of CLSS4.0?RQ2.What are the best practices and actions to be taken to overcome the various barriers and challenges?
RQ3.In what ways can manufacturing companies implement the integrated CLSS4.0 approach?
Accordingly, this research aims to achieve the following objectives: (1) identify the drivers and barriers to CLSS4.0 adoption as well as the best practices for mitigating barriers and challenges (2) propose a comprehensive structured CLSS4.0 framework to promote sustainability.
To achieve the objectives of the study, multiple case studies based on semi-structured interviews were employed as a solution methodology.By applying this approach, we can grain a comprehensive understanding of the drivers and barriers factors affecting CLSS4.0 adoption and sustainability.Additionally, the semistructured interviews can provide rich qualitative data on the experiences and perspectives of industry experts, which can be used to identify best practices and develop a comprehensive CLSS4.0 framework.
Overall, this research makes several contributions.Firstly, we are responding to the growing interest among scientists in further exploring the new facets of sustainability enabled by I4.0 technologies and CE practices.There is a great need for studies aimed at improving our knowledge of how to combine the three approaches of LSS, CE and I4.0 to promote sustainability.Our study is an important initial effort towards enhancing our understanding of the factors affecting CLSS4.0 adoption sustainability in manufacturing, particularly in emerging economies.The fact that authors take an example from an emerging economy, such as Morocco, is a unique contribution to the literature.This is because research on sustainability in emerging economies is scarce, and our study has the potential to provide valuable insights into how these approaches can be implemented in such contexts to promote sustainability.Second, the CLSS4.0integrated paradigm is complex.Therefore, clarifying the drivers and barriers with existing adopters can help improve the adoption success rate for future initiatives.
This paper is organised into five sections.The literature background is presented in Section 2. The research methods are discussed in Section 3. Section 4 examines the semi-structured interviews' insights and presents a holistic framework for promoting digitalisation and circularity as organisational capabilities.In section 5 we discuss the findings and highlight the theoretical and practical implications derived from our study.Finally, Section 6 presents the conclusion as well as limitations and directions for future research.

Literature review
To identify relevant insights into potential drivers and barriers as well as research gaps concerning an integrated CLSS4.0 approach from past studies, a systematic literature review (SLR) was performed following the  well-established PRISMA protocol (Xiao and Watson 2019;Ghobakhloo et al. 2022) as presented in (Figure 1).PRISMA is recognised as a rigorous and widely accepted methodology for conducting SLR.It is widely considered to be a valuable method for defining a specific concept and fostering theory development (Seuring and Müller 2008).The use of SLR guarantees rigour, precision and reproducibility of results.It involves a four-step process that includes identifying relevant studies, screening and selecting studies based on inclusion and exclusion criteria, extracting data from the selected studies, and finally synthesising and reporting on the results.By following this methodology, the review is likely to be more thorough and transparent, reducing potential biases and increasing the reliability of the findings.After defining the research objectives and main research questions, we identified relevant studies in several high-quality search engines and databases, mainly Elsevier, Scopus, Emerald, Springer, Taylor and Francis, Wiley Online Library, and Google Scholar for the period between 2011 and June 2023.The initial search period 2011 was chosen by the authors because it is the year of the advent of I4.0.The search strings included the selected keywords listed in Table 1, using Boolean operators (AND and OR).The keywords selection was based on previous studies (Skalli, Charkaoui, and Cherrafi 2022b) As a result, a total of 76 articles was initially identified, which was then reduced to 58 studies after removing duplicates.The list of articles was then examined and filtered using the following inclusion and exclusion criteria, presented in Table 1.We considered only (1) peer-reviewed journal papers including both empirical and conceptual studies (2) written in English, (3) available in full-text reading and (4) consistent with the study purpose.Only articles addressing the drivers and barriers to LSS, CE, and I4.0 paradigms within the manufacturing industry landscape were considered, whereas conferences, books and book chapters, and white papers were considered as exclusion criteria.Performing the four screening rounds in line with the inclusion and exclusion criteria presented in Table 1 led to the exclusion of 20 articles as demonstrated in Appendix 2. Finally, in the last stage of analysing and reporting, a total of 38 articles were considered relevant and valuable to the analysis, and then a full-text content analysis was conducted for each of these articles during the report development phase to find the multiple factors that support the CLSS4.0integrated approach, as well as the barriers that hinder it.Details of the relevant papers assessed in this study, including, authors, journal, and methodologies used are presented in Appendix 1. (Further completed details of articles assessed in this study can be provided by the authors on request).Considering the aforementioned inclusion and exclusion criteria, we were faced with some challenges in conducting the SLR, including insufficient literature available about CE and I4.0 in the manufacturing sector of emerging economies.However, we tried to overcome this challenge through careful keyword selection, accurate screening and cross-checking among the team.

Drivers of CLSS4.0
For successful CLSS4.0 implementation, it is critical to know what motivates companies to adopt CLSS4.0.The main competitive advantage of a company resides now in its power to meet the requirements of customers and stakeholders and to generate value as well as to acquire new capabilities related to sustainable organisational performance (Chaouni Benabdellah, Zekhnini, and Cherrafi 2021).Thus, high competitiveness level has pushed companies to seek innovative and cost-effective strategies (Lasi et al. 2014;Bauer et al. 2018).By adopting CE practices and new digital technologies of Industry 4.0, companies can increase their productivity and profitability and promote sustainability.Empirical evidence has demonstrated the strong effect of LSS, CE and I4.0 concepts, alone or in combination, on improving business performance (Belhadi et al. 2020;Buer, Strandhagen, and Chan 2018;Edwin Cheng et al. 2022;Kamble, Gunasekaran, and Dhone 2020).In today's challenging and dynamic market environment, gaining a competitive advantage and improving performance is the main priority and strategic focus of manufacturing companies (Ivanov et al. 2021).LSS has shown for decades its potential to eliminate waste and reduce process variability leading companies to operational excellence.However, with the advent of Industry 4.0 technologies such as sensors, Cyber-physical systems (CPS), Internet of Things (IoT), Big Data Analytics (BDA) and simulation among others, there is a major expectation of customised products and increased manufacturing capabilities (e.g.resiliency, agility, sustainability, flexibility) (Ivanov et al. 2021).I4.0 refers to a new way of managing the organisation based on emerging technologies with the ability to collect and analyse big data in real-time throughout the value chain to monitor and control product quality, detect deviations and failures, and adjust production systems leading to operational efficiency (Kristoffersen et al. 2020).Similar goals are shared by circular economy, which has emerged as an alternative strategy to address resource efficiency and saving costs.Among the most revealing results of the literature review analysis is the profound compatibility in drivers between the three concepts.Theoretical and practical evidence suggests that the three concepts are complementary, and thus share common driving factors, namely customer satisfaction, increased revenues, and reduced losses, defects, and waste (Gandhi, Thanki, and Thakkar 2018).(Y.Ali et al. 2021;Cherrafi et al. 2016;Nascimento et al. 2019).The combination of LSS and I4.0 called LSS4.0 is classified as a strategy for making organisations competitive through improvements in defects, quality, productivity and waste (Buer, Strandhagen, and Chan 2018).CE shares the same objectives as LSS4.0 and is progressing rapidly as a promising manufacturing strategy to generate value, and improve productivity and competitiveness by optimising the use of energy, natural resources and waste (Rosa et al. 2020).CE replaces the concept of 'end-of-life' with a circulatory logic using various strategies such as remanufacturing, reuse, recycling, reduction, return, and restoration, among others (Edwin Cheng et al. 2022;Hina 2022;Leipold et al. 2021;Geissdoerfer et al. 2017).The integration of the proposed CE 9Rs framework throughout all stages of the value and supply chain is a practically complicated process, hence there is a need to find a trade-off between the business plan, operational performance and environmental concerns (Acerbi and Taisch 2020).Accordingly, implementing advanced digital technologies of I4.0 can mitigate the complexity by automating tasks, providing real-time monitoring, allowing predictive maintenance, and improving data collection and analysis capabilities for good decision-making, thereby improving environmental and operational performance (Zekhnini et al. 2021).

Barriers to CLSS4.0
Along with a comprehensive overview of the driving forces of CLSS4.0, it is therefore essential to consider the barriers and factors that can impede companies from adopting this approach.Being aware of the barriers to CLSS4.0 is crucial for organisations before implementation.Although LSS has been widely applied over the past decades, there remain several challenges impeding its successful adoption.Digital technologies offered by I4.0 can help overcome traditional barriers in operations management.The main barriers to I4.0 adoption as reported by scholars are a high-cost investment, complexity, lack of workforce skills and expertise and resistance to change (Ghobakhloo et al. 2022;Raj et al. 2020;Tura et al. 2019).All studies suggested that the lack of competencies, high-cost investment and technological issues are the main challenges that can mitigate the successful implementation of CLSS4.0.The introduction of new I4.0 digital technologies and CE practices adoption will change processes, generate increased complexity and employee resistance and will require new skills and competencies (Trevisan et al. 2023).Also, the lack of knowledge about the integration roadmap can prevent organisations from embarking on this project.The lack of a well-defined, tested and validated CLSS4.0 implementation model can be a serious barrier.In addition, the lack of estimated financial benefits and the short history of the initiative may limit implementation.Several authors (Kiel et al. 2017;Raj et al. 2020;Ghobakhloo et al. 2022) have identified the lack of financial resources as a major and significant barrier to implementation.Several barriers were specific to Industry 4.0.For example, one of the major barriers associated with Industry 4.0 and supported by several authors are cyber security concerns, data security and privacy risks, infrastructure concerns and standardisation (Cimini et al. 2017;Trevisan et al. 2023).Despite these efforts, academics and practitioners still lack empirical knowledge of the common barriers to the implementation of a CLSS4.0 initiative.
The key drivers and barriers of CLSS4.0 implementation are reported in Table 2. Figure 2 depicts the theoretical outline of the CLSS4.0drivers and barriers.

Research methods
This study uses a two-pronged approach to minimise the biases likely to be present with a one-pronged approach.It relies, therefore, on both a systematic literature review and semi-structured interview-based case studies, to make the study more exhaustive, structured, robust and significant.Figure 3 shows the research design.We first carried out a systematic literature review, the results of which are presented in the preceding sections, s.An exploratory qualitative method was perfectly suited to our research topic, as it allows new learning, and rich and in-depth analysis of an under-studied issue (Yin 2009) without the need for numerical data (Rowley 2002).Interviews are a very effective way to collect extensive empirical data (Kurpjuweit et al. 2019).Indeed, to collect data and build theory, the semi-structured interview was preferred as it allows for practical insights from multiple sources (Eisenhardt 1989), hence participants can respond to questions freely and openly, allowing for a better understanding of the topic and better results (Eisenhardt 1989;Voss, Tsikriktsis, and Frohlich 2002).Figure 3 illustrates the research design phases of this study.

Case selection
We targeted large and medium-sized multinational manufacturing companies located in Morocco that have experience with the LSS improvement process and have adopted digital and circular transformation within the framework of CE practices and I4.0 technologies.We followed the company size classifications defined by the European Union, considering companies with 50 to 249 employees as medium-sized companies, and those with more than 250 employees as large companies (Belhadi et al. 2020).In approaching the prospective manufacturing companies, we provided them with a brief overview of CE, LSS, and I4.0 and the study aims and ensured that the companies had implemented all three paradigms at least 18 months ago.Table 3 illustrates the characteristics of the case studies.Prospective interviewees were selected based on three criteria as cited by (Gibbert, Ruigrok, and Wicki 2008): (1) Position and role, (2) Year of Experience and (3) Expertise and knowledge.All participants had a high managerial position, more than 10 years of experience and were experienced with LSS and involved in I4.0 and CE deployment projects.They were approached using several ways: through the authors' professional network, by using the snowball technique and by contacting the companies' experts via LinkedIn.The company represents the unit of analysis.Following the purposive sampling (Glaser and Strauss 2017), we targeted 18 manufacturing companies from various sectors to allow for theoretical representativeness (Miles and Huberman 1994).

Data collection
One senior manager involved in CLSS4.0 implementation projects was the representative for each case study in the semi-structured interview.The twelve semi-structured interviews were performed digitally via Microsoft Teams and lasted between 68 and 90 min.Two researchers were involved in conducting the interviews using an interview guide and a defined protocol (see Appendix 3).The use of a case study protocol positively contributes towards reliability (Yin 2009).The interview guide was elaborated based on previous literature and tested with six senior academics and four practitioners (2 operations managers, 1 Information Technology director, and 1 quality, security and environment manager).Their feedback was used to refine the questionnaire.A study briefing protocol including the background and purpose of the study, estimated duration of the interview, confidentiality conditions, the consensus form, and contact information for the principal interviewer and associated research team was emailed to all   respondents to get well-informed and prepared for the interview.To address ethical issues, there was no reference to any participant's details and a consent form was provided to be signed by the interviewees.All interviews were recorded and transcribed for further analysis.After completing 12 interviews, we realised that the information collected from the last 2 interviews was similar to the previous ones and that no new insights emerged from the 10th interview.Therefore, according to (Glaser and Strauss 2017), we assumed that data saturation was reached, for which the data collection was then followed (Bakhtawar 2020).We extended our data collection with information from additional available internal documentation (policies and procedures) and public sources (website and annual reports) (website, flyers, and documentation).In total, we examined twelve firms, exceeding (Eisenhardt 1989) the suggestion of four to ten cases.

Data analysis
All semi-structured interviews were recorded and then data were transcribed and analysed by two researchers using inductive thematic analysis based on Nvivo software (Braun and Clarke 2006).We used both within and cross-case analysis based on the grounded theory approach (Eisenhardt 1989;Miles and Huberman 1994).We conducted a thematic analysis of transcripts and documented data for each interview (within-case approach) to identify key findings (Eisenhardt 1989) and then a cross-case analysis by grouping and categorising the data into common patterns and clusters and subsequently matching them to the literature to increase external validity (Yin 2009).Interviewees were made anonymous to avoid bias and to increase the reliability of the results.For construct validity, we adopted a triangulation approach (Yin 1994).The present research used interview insights as a primary source of data, additional data were extracted from internal documents (policies and procedures) and public documentation (website and annual reports) to help build theory.For better data reliability and results accuracy (Ardichvili, Page, and Wentling 2003), the data summary was returned to the participants for validation.Thus, minor comments were received and included in our analysis.We closed the coding and discussion process once all authors agreed.

Results
Through an inductive data analysis, codes were generated and grouped into main factors, and main themes, and then reported to dimensions.Accordingly, twenty-nine drivers' factors and thirty-one barriers factors were identified and categorised into six dimensions namely operational, organisational, technological, economic, financial and regulatory.Figure 4 summarises the detailed thematic analysis.This section presents answers to the research questions outlined in the introduction in four subsections: Section 4.1 presents the main driving factors, Section 4.2 the main barriers, and Section 4.3 the actions taken or proposed by manufacturers to mitigate the different challenges and Section 4.4 presents a proposal CLSS4.0 framework.

Perceived drivers for CLSS4.0
Based on a Pareto analysis, 10 driving factors were considered to be the most critical driver factors (see Figure 4).The majority of respondents were confident that the CLSS4.0approach has great potential to increase their operational and economic performance and improve their environmental and social impacts, as it could reduce energy, water and raw material consumption and boost competitiveness and profitability.Hence, Strategies for cost saving, resource optimisation, waste reduction and productivity increase are highly appreciated by manufacturers and represent the common driver for all cases.The findings show that achieving operational excellence, sustainable manufacturing performance, developing manufacturing capabilities such as flexibility, agility, resilience, and promoting brand image and labels were the relevant motivations for the adoption of the CLSS 4.0 approach.
The potential benefits and capabilities afforded by the integrated CLSS4.0 approach motivated us to take the plunge.C1 We launched the digitalization of our operations to boost customer satisfaction and process efficiency.C3 We look forward to expected benefits such as quality defects and cost reduction, energy and waste reduction, traceability and flexibility.C10 We have a long-term experience with LSS, so adopting advanced technologies with quality improvement tools such as lean and six sigma have helped us eliminate non-value added activities and generate better results and superior operational excellence in a short time.In addition, by applying sensors, data analytics and machine learning algorithms, we are now able to detect errors, and deviations in real-time and react rapidly to quality issues by 40% lower cost.C4 The connection between LSS and I4.0 has allowed us to accelerate our operational excellence and reduce energy consumption.In our case, we have implemented sensors connected to the plant manager's smartphone, which allows him to monitor critical process parameters in realtime and react immediately, avoiding process variability that causes quality problems while saving time, cost and resources.C8 As LSS, CE and Industry 4.0 coexist, they can support each other to create better products and processes with greater efficiency, accuracy, and sustainability.C11 All cases emphasised the need for adopting digital innovative technologies of I4.0 to achieve efficient process monitoring and enhance decision-making.Digital capabilities primarily connectivity, transparency and communication are vital capabilities highly appreciated by manufacturers.
Digital transformation in Industry 4.0 has become an irresistible force as it makes our business more competitive and responsive to market demand and turns our operations and supply chain more agile and resilient than before.C2 the new channels of communication offered by the advanced technologies have been of great support in covid-19 as it has allowed us to maintain our activities and to exchange with the world in a very fluid and easy way and has thus created an approach of proximity innovative.C6 All respondents agree on the potential I4.0 technologies benefits in terms of high connectivity and communication between man and machine, task automation and more efficient and safer work.
Acquisition of digital innovative technologies of indus-try4.0 remain not nice to have but a must have to sustain in the disruptive and networked market.C4 Most respondents mentioned at least one driver factor under the regulatory dimension, making it the third most cited driver after operational excellence.
the driving force behind the development of renewable feedstock products is the joint interest in reducing CO2 emissions resulting from the global and European legislation on CO2 emission reduction that we adhere to.C1 Our products are regulated by law, so compliance with national and international laws and standards related to the production, transportation of petroleum products and its derivatives and the control of their impact on the environment is an imperative and part of our performance.C10 In contrast, C6 has declared that internal corporate policies are driving forces to adopt CE practices: We have a global plan called Cap50, whose objective is to reduce CO2 emissions by 45% in 2030, and achieve neutrality in 2050.This plan is broken down into several actions carried out internally and also with suppliers and service providers.Industry technologies have been of great help to us in deploying it, so the commitment and dedication of all staff and general management have been the key to our success in this 5-year-old strategy.
C10 and C12 share the same thoughts: Global banks, funding institutions and insurance companies are embracing new ways of financing based on circular business achievements.
The high competitiveness, disruptive marketplace and fast-growing global market is most frequently identified as determinant driving manufacturers towards CLSS4.0transformation.
In adopting this integrated approach, we were motivated by the need to anticipate and respond to technological advances and environmental protection concerns, which is necessary to remain competitive in today's market.
The respondent from company 10, an aerospace company, claimed that digitisation helps to respond to increased demand and attract new customers with higher profits.In addition, the respondent added that digitised processes and adherence to environmental protection strategies represent an important business opportunity to improve the company's image and compete in overseas markets with rigorous requirements.
Under market disruptions, C7 stated: COVID-19 resulted in the suspension of our daily debriefing meeting, training, and travel to the subsidiaries."Similarly, C9 noted," CE and I4.0 are driven by our perspective and awareness of the need to sustain our business after the pandemic.
C3 reported 'the COVID-19 pandemic and its global impact have resulted in unprecedented disruption to our global operational systems and supply chains, particularly in response to customer demands, generating big losses', and explains that 'given these constraints and in response to future disruptive market happenings, we have embraced digital technologies to increase our resilience and agility.' C4 noted that The advent of the pandemic, disrupted supply chains, political instabilities and a growing shortage of raw materials, all of these factors among others, have prompted us to rethink our business strategy as a post-Covid action plan to account for digital technologies and circular practices for cost reduction, market increase and customer satisfaction while improving agility and resilience process capabilities.Some firms have mentioned that customers have high expectations for custom products and a growing demand for sustainable products.Looking at sustainable environmental performance, the perceived benefits are waste reduction, energy saving, optimisation of resources consumption, monitoring all negative emissions and environmental impacts, and improved lifestyle for future generations which are supported by the literature.Overall, all interviewees reported that Sustainability has become a core value to maintain the manufacturing systems.The company's strong position in the market can influence the willingness for LSS, I4.0 and CE adoption benefits.
Respondents also noted the ability of CLSS4.0 adoption to advance their brand image.In light of our analysis, three novel drivers have emerged that were not reported in the literature, namely: bank and financial institutions' requirements, insurance pressure, and subsidiaries' policies and instructions.Figure 4 illustrates the driver factors identified by the interview respondents.

Barriers to CLSS4.0 implementation
Similar to the drivers, we focused on understanding the factors that hinder the adoption of CLSS4.0.Based on PARETO, 10 barrier factors were considered to be the most critical factors to impede the successful implementation of CLSS4.0 as presented in Figure 6.Resistance to change, lack of knowledge, fear of failure, lack of roadmap, lack of standardisation and supportive policies were identified as the common factors among all firms.
All cases mentioned the critical role of workforce skills and competencies in the adoption of CLSS4.0.Technical skills are required to embrace this initiative.
Human resource profiles and skills, both operational and managerial, such as software engineers, automation, digital business market, artificial intelligence, big data analysts, with academic background and approved experience, are very limited, making us very dependent on external vendors and consultants.We need skilled talent with knowledge of I4.0 to collaborate with suppliers.It's not acceptable to rely only on vendors' recommendations to make our decisions.C5 The lack of skilled workforce, expertise and graduates people was addressed by all interviewees.
BDA requires specific skills and knowledge on the use of complex techniques, mainly machine learning and artificial intelligence.C1.
Insufficient number of digital graduates for recruitment.C2 C3 explained that 'the complexity and novelty of I4.0 have created new skilled jobs and functions'.Similarly, C9 added that 'it is time to redefine the university's curriculum to accommodate training in I4.0 technologies'.C10 stated that 'we faced the shortage of experienced consultants and digital project managers to lead our digital transformation because our managing directors lacked expertise'.The lack of knowledge of advanced technologies and CE practices is a huge impediment to such an approach.
C8 added 'the complexity of the operations involved in CE practices including re-engineering, remanufacturing, reusing, recycling and refurbishing models requires training in new operations and processes, as well as new skills and competencies.We had difficulty finding a highly qualified consultant and trainers'.C10 reported 'the lack of specialists is an obstacle to the accelerated development of digital technologies'.
Also, all firms confirmed that top management support and involvement, from multiple dimensions (organisational, financial, operational) is essential as this act as an enabler, barrier, and critical success factor.
Leadership is the best driver for all forms of changes in organizations.C5 The role of leaders is to provide leadership so that managers and employees follow it.A corporate culture and employee mindset must be developed to drive the transition to CLSS4.0.
'Going down to the site and following the production and teams closely is one of the ways our general manager has used to get people to more involved in the projects' C10 C1 added, 'as leaders and managers we are engaged in our firm's culture and that's pushed us move towards CE but believe it is important to bring coworkers on board with the corporate culture and keep it simple'.
Cyber security represents a big challenge for almost all firms' cases.The risk of over-reliance on systems and hacking risks associated with digitisation is the most discussed barriers related to cyber security.C4 said, 'most information is stored and shared on clouds and if systems fail, all the data will be lost'.
All respondents mentioned the lack of an integration roadmap as a barrier impeding the successful CLSS4.0 implementation.Manufacturing companies need welldefined, tested and validated guidelines to apply.Moreover, the absence of standards hinders many firms to commit in this initiative.High initial capital costs, lack of cost/gain estimates, training, expertise and consulting expenses, and maintenance/repair budgets as barrier factors under financial dimensions.CE practices and I4.0 technologies appear to be exceptionally expensive.C2 said, 'Cost is consistently a challenge for us'.Managers should find a trade-off between investments in CE and digital technologies and revenues.The key factor that can hinder the organisation in its journey towards digitisation and CE, especially SMEs, are the financial constraints related to technology and equipment acquisition, maintenance and repair costs, training costs, and consulting services.Interestingly, C3, C5, and C11, as SMEs, stated that they had engaged in CLSS4.0 through pilot projects and that there were plans to extend it to all business processes, but that they remained challenged by the high investment cost, In this way C10 said 'There is an expected high cost for hardware and software upgrading'.C5 suggested, 'Cost is often the first and biggest concern in the implementation of any project, change or implementation Figure 5.' 'Investments concerns not only technology infrastructure but moreover knowledge acquisition through the hiring of new skills and development of necessary knowledge through training' C5. 'We suffer from the availability of consultants and high cost of training providers' C6. 'we are currently facing difficulties to find maintenance service providers in our geographical proximity'.C11.
C10 and C12 both large companies shared the same thoughts: As far as we are concerned, we are using our funds to invest in this CLSS4.0project because the Moroccan government is not yet ready to invest in this field and government funding is a long-term process.Our customer market is based in developed economies so we need to align with their advanced and rigorous requirements.We believe that it is worth investing in this project because the return on investment is very high.
As for complexity, this factor was mentioned by seven interviewees who had experienced technical trouble in changing their plant to a smart plant.
Our experienced difficulty in changing toward smart operations management is the complexity of both technologies and process.C5 The use of new I4.0 technologies for the circular economy can make the implementation of the circular economy more complex.In addition, C3 commented, 'New technologies are complexes'.
Regarding support, the respondents mostly expressed the need for fiscal support, as well as assistance with technology, training, and consulting.
We were initially unprepared and unsuccessful in adopting I4.0 and CE because we had to recruit new staff, which was a big challenge given the scarcity of qualified and experienced people, and we needed government support and invoicing to make this project successful, and so staff were reluctant.C12 Unlike literature, we noted emerging barriers from participants: 'organizational changes management', 'designing digital management functions', 'deficit in the availability of job-ready university graduates', 'lack of information-sharing platforms', 'poor cooperation between academics and manufacturers', 'inadequate and inexperienced service and technology providers', 'lack of government support and tax incentives', 'evolution gap between university education against the economy and industry progress' and 'difficulty in recruiting new staff due to the scarcity of required skills'.Figure 6 summarises the major barrier factors revealed by interviewees.

Actions to mitigate barriers
In response to RQ2, we identified several ongoing or proposed actions by interviewees to mitigate the various barriers listed in the previous section.Based on the results of section 4.2, statistically 50% of the barriers were related to people (e.g.lack of skills, knowledge, awareness, management commitment, employees and stakeholders' commitment and resistance to change).To achieve the full potential of the CLSS4.0approach, it is recommended that businesses fully engage their workforce, establish an open communication channel, and prioritise sustainability.
All of the proposed actions addressed organisational barriers, as they were the most significant and common to all sectors Table 4.

Framework
In the present volatile, disruptive and complex world, there is tremendous pressure to address resource scarcity, energy consumption and waste generation through the use of environmentally friendly operational practices.Despite considerable progress in both the literature and practical applications regarding the drivers, barriers, and implementation framework for each approach, there appears to be a lack of a well-defined implementation model related to an integrated and holistic approach which could practically guide manufacturers to a successful CLSS4.0 implementation.We developed a framework for integrating CE practices and digital technologies into LSS projects to promote digital and circularity improvements in all dimensions of the DMAIC (Define, Measure, Analyze, Improve, and Control) project cycle.The proposed framework illustrated in Figure 7 highlighted the theoretical aspects of such integration mainly driving and impeding factors to help practitioners develop viability and sustainability.A clear assessment of these factors would contribute to management's increased knowledge of how to successfully implement CLSS4.0.We first consider the factors that drive firms to adopt the three manufacturing strategies, as well as the barriers that may impede this combination.Indeed, companies can consider this combination to improve their operational and financial performance, while strengthening their digital and sustainable business capabilities.Process efficiency and eco-friendly manufacturing were widely perceived by respondents as one of the most important driving factors in the success of CLSS4.0 implementation.However, a number of barriers such as a lack of knowledge and skills, an unfavourable organisational culture, along with specific technical issues, need to be addressed.The lack of expertise and skills is one of the most significant barriers to CLSS4.0.This factor appears to be more important to practitioners than it was in the literature.
To support the implementation of the CLSS4.0initiative, a specific skillset should be developed for employees working at the management and non-management levels.Industry 4.0 digital technologies enable real-time monitoring and better decision-making based on the analysis of machine-generated data.In other words, using the relevant technologies requires specific skills and competencies.In practice, possessing the right work skills and knowledge required within the workforce are important.On the other hand, a clear and comprehensive assessment of the complementarity between the three concepts of CLSS4.0 is a crucial step in our integration model.The model illustrates the relationship between the paradigms.LSS represented by DMAIC represents the core of our model with a close link to CE practices and I4.0 main technologies and a purpose of unlocking some of the trade-offs between the three.Given that Lean, CE, I4.0 and Six Sigma are complementary, accordingly, each method has the potential to minimise the drawbacks of the others.Building on the results of our study and considering the theoretical implications, the implementation of this integrated approach will lead to sustainable and viable achievements in a globally competitive environment.Companies can achieve better dynamic capabilities by applying LSS, CE and Industry 4.0.Finally, we find sustainability and viability at the bottom of the scale, which is the result of this combination, providing a good understanding of how to successfully implement the CLSS4.0method.The proposed model (Figure 7) serves as a framework where companies can assess the driving forces and barriers to implementing CLSS4.0 and appreciate the interplay between these concepts.It is a way to improve sustainability and gain a competitive advantage, which is the most common concern of a company.

Discussion
The study addresses the literature gaps on the lack of knowledge and a holistic assessment of CLSS4.0 drivers and barriers.The authors have mapped driving and impeding factors of CLSS4.0 adoption based on qualitative data.Discussing the results, we provided an overview of the key drivers and inhibitors of the CLSS4.0approach.
Our findings are consistent with the literature.Executives emphasised that they were seeking benefits such as improved operational and environmental performance, increased productivity and profitability, and high performance in a highly competitive and rapidly changing business environment.Findings highlight that increasing environmental concerns and continuous pressure from customers, stakeholders, government and institutional organisms (Cherrafi et al. 2022) related to resources depletion, energy consumption and climate change are the major's drivers of CLSS4.0 adoption.Corporate customers from the international side are encouraging manufacturers to implement the CLSS4.0(S. A. R. Khan et al. 2021).Also, promoting connectivity, transparency, process visualisation, human-machine communication and data exchange in real-time represents the driving forces pushing companies to embrace such an approach.Several novel driving factors such as corporate policies and guidelines, pressure from financial institutions, insurance, and non-governmental institutions, corporate image, and customer specifications, were cited as new factors that have not been sufficiently explored in the literature and not reported in previous studies (Govindan and Hasanagic 2018;Tura et al. 2019;Ghobakhloo et al. 2022;Hina 2022), which could be explained by the specific country study context.
As for the barriers that may hinder the successful implementation of CLSS4.0, the main factors highlighted by respondents are the lack and scarcity of both tangible (human resources, financial constraints, equipment) and intangible (standards, techniques, skills and methods) resources, which is consistent with the findings in the existing literature (Singh and Bhanot 2020;Stentoft et al. 2021;Govindan and Hasanagic 2018;S. M. Ali et al. 2020).Also, data privacy and cyber security issues represent the potential barriers impeding manufacturing companies.Different from the literature, participants noted the difficulty of changing the culture, attitude, and mindset of staff, hence the need for change management.Fear of change, lack of proximity ecosystems and knowledge-sharing platforms, and availability of consultants and providers with expertise are new barriers that were found but not reported in previous studies.These factors may be related to the specific context of a country studied.
In terms of best practices to mitigate barriers, collaboration with academic institutions, support from universities, creation of a local ecosystem and exchange platforms have emerged as interesting results.By collaborating with universities, companies can save the cost of recruitment by creating training courses tailored to their specific needs.
Universities should incorporate new courses designed for I4.0-CE skills and knowledge.Universities can go hand in hand with the industrial revolution and market progress to adapt their curricula to offer new graduates who can easily integrate into companies.No previous study has mentioned the role of collaboration between universities, government and industries in accelerating digital transformation and awareness of CE principles and potential benefits.Companies have great difficulty recruiting qualified graduates in new digital technologies.We, therefore, suggest that companies work with universities to define the skills required and adapt the educational programmes to future digital careers.Recruitment, training, technology acquisition, and maintenance require a high level of investment, so government funding and institutional support are needed.
Although most of the drivers and barriers identified in this study are consistent with the literature, the remaining new factors identified by respondents, which were absent in previous empirical studies in European countries, can be explained by the country-specific context.
In light of the gaps in the literature related to the lack of a holistic integrated model and based on the knowledge gathered, we developed a theoretical framework.The proposed model, illustrated in Figure 7, is based on a clear understanding of the drivers and barriers factors to initiate a CLSS4.0 approach in a company.
By following the model outlined in Figure 7, organisations can create a culture of continuous improvement and achieve long-term success while contributing to environmental sustainability efforts.The proposed model outlines key considerations for manufacturing companies seeking to adopt CLSS4.0.The model suggests that the identified drivers will motivate manufacturers to consider CE and I4.0 technologies in conjunction with LSS and may push them forward, while the identification of barriers is strongly recommended to assess the ability of companies to adopt CLSS4.0 and overcome them.
By integrating drivers and barriers, the proposed model offers an innovative approach for building the decision-making arena towards CLSS4.0adoption to promote sustainability.
One of the key factors that differentiates our study from previous works is the integration of CLSS4.0 with a sustainability perspective, specifically in the context of an emerging economy in North Africa.Unlike previous studies, which have explored the CLSS4.0integrated framework in developed economies, our research goes beyond by conducting a thorough analysis of the factors that impact its successful implementation.By examining the unique characteristics, challenges, and opportunities of the Moroccan context, this study offers comprehensive insights into the specific drivers and barriers of CLSS4.0 adoption in Morocco's industrial landscape, which may differ from other contexts.It identifies the key drivers that motivate organisations to adopt CLSS4.0,sheds light on the barriers they may encounter, and offers guidance for policymakers and industry leaders to formulate strategies and initiatives that support the implementation of CLSS4.0 practices.By addressing this research gap, our study offers a holistic understanding of sustainable manufacturing practices, incorporating a comprehensive and integrated approach that considers the entire system as a whole, rather than focusing on isolated aspects or individual components.Furthermore, our study employs an exploratory approach, uncovering new insights and identifying previously unexplored dimensions.The study's findings can inform policymakers, industry leaders, and decision-makers in Morocco about the potential of CLSS4.0 adoption.This can contribute to the overall sustainability and competitiveness of Morocco's industrial sector.Furthermore, the study enriches the global understanding of CLSS4.0 by incorporating a Moroccan perspective, stimulating further research and exploration of sustainable practices in developing regions and contributing to the advancement of theory.

Theoretical implications
Our study provides a strong contribution to different theories by bridging continuous improvement theory (underpinning LSS), technical-social system interface theory (underpinning I4.0) and sustainability theory (underpinning CE).This research contributes to the advancement of several theoretical implications.First, this study is one of the first empirical studies conducted in a developing economy to investigate the drivers and barriers to the successful adoption of CLSS4.0,thus adding new and significant insights into the academic CLSS4.0 research field.Second, we conducted an exploratory study of motivators and barriers to an integrated CLSS4.0 approach as they have not been identified in the prior literature.The research field did not receive enough scholarly attention.The authors proposed a CLSS4.0 model and a holistic view of the specific theoretical elements (drivers and barriers) making a significant theoretical contribution to the literature.To the best of the author's knowledge, this research is one of the first studies to discuss the drivers and barriers of LSS, CE, and I4.0 as an integrated approach, as well as define a holistic model for implementing CLSS4.0.Third, the strength of our study lies in the novel combination of these concepts that have not previously been linked in the literature.This work promotes a new vision of sustainability and viability.Finally, this study is conducted in a manufacturing context that is a major source of environmental problems (air emissions, energy consumption and waste production, resource depletion) providing novel insights and building academic research.

Practical implications
The proposed CLSS4.0 integrated approach will help organisations improve their organisational and environmental effectiveness.This study inspires practitioners to adopt the CLSS4.0integrated approach by drawing on theoretical evidence about the key drivers and barriers to CLSS4.0 and empirical evidence from case studies in emerging economies.We suggest that the proposed model will guide practitioners in their efforts to implement sustainable manufacturing.The proposed framework provides holistic guidelines for practitioners to execute this approach.This research will motivate manufacturers to rethink their operations and resources to move towards sustainability methods.The study provides guidance to practitioners on how to implement CLSS 4.0 more effectively.

Limitations and future research perspectives
Beyond research implications, this study entails some limitations that can serve as potential perspectives and directives for future research.First, since we used qualitative research, which is often vulnerable to subjective biases, including those of the researcher team's interpretations and the participants' opinions, it is important to consider the limitations of this approach.Future research could explore the perspectives of a more diverse range of participants, as well as the potential impact of contextual factors on the findings.By addressing these limitations, future research can build on the insights gained from this study and provide a more comprehensive understanding of the topic.Second, the small sample size of the study could limit the generalizability of the findings.While theoretical saturation was reached, it is possible that a larger sample size could have provided additional insights or revealed different perspectives.Therefore, it is important to consider the limitations of the sample size when interpreting the findings of the study.Further empirical research with larger sample sizes could help to validate the findings and provide a more comprehensive understanding of the topic.Additionally, it may be beneficial to explore the perspectives of participants from a wider range of backgrounds and industries to increase the generalizability of the findings.Finally, the results obtained are valid for Moroccan companies representing multinationals that adhere to international regulations and corporate policies.As such, the results of the study need to be supported by further studies in other emerging country contexts to confirm the outcomes of our research.
This study contributes to the theoretical understanding by providing scholars with directions for further research.Given the qualitative design of our study and the limited sample size, we propose that further quantitative studies should be conducted to complement and validate our results and improve the generalisation of the model proposed.The efforts initiated in this research can be further investigated to find how CLSS4.0 may support resilience in the post-COVID-19 era, and explore what technologies are useful and suitable for each DMAIC step and CE practice.Additionally, the main focus was on Moroccan manufacturing companies as a hence we invite scholars to conduct the same study scope in other developing economies' geographical contexts to validate our findings.The drivers and barriers are partly determined by the size of the company, the sector and the geographical region in which the companies operate.In this context, we highlight the need for conducting a similar study in the context of developed economies to obtain a cross-comparison of results and then provide a holistic understanding of the drivers and barriers of CLSS4.0.Scholars may extend our findings to the service sector.Also as our topic is a growing research field that is in an early stage, a well-defined framework and agreed stepwise roadmap for CLSS4.0 implementation are still missing.Scholars are invited to refine the proposed integration framework, develop a detailed model and present empirical evidence on its validation.Lastly, it is suggested to study the impact of the CLSS4.0integration on the improvement of staff development and environmental performance and to assess the role of the workforce in the success of CLSS4.0 implementation and estimate and explore trade-offs between deployed resources to implement CLSS4.0 and potential financial savings generated.

Conclusions
The article examines CLSS4.0 as an enabler of sustainability.Its main purpose is to identify potential drivers and barriers regarding the implementation of CLSS4.0 in manufacturing companies.The results will benefit production and transformation managers.Given that various internal and external motivations and challenges from cultural, organisational, financial and technical perspectives influence the deployment of CLSS4.0, its deployment in developing economies appears to be limited.Given these limitations, decision-makers should be well aware of these challenges, hence the value and contribution of our study, which aims to shed light on the various drivers and barriers to be considered for any CLSS4.0project.
Given the limited study exploring the drivers and barriers for a CLSS4.0 approach, we deployed a qualitative research design to generate in-depth knowledge in this field.We have explored the drivers and barriers for the transition towards a CLSS4.0 in manufacturing industries by studying twelve multinational companies based in Morocco.Our study provides a clear knowledge of the various drivers and barriers required to be undertaken for a successful CLSS4.0 implementation.Since the LSS approach is considered a well-known practice for manufacturers to eliminate waste and process variability while reducing costs and improving operational performance, the drivers are very familiar and the barriers are now impeded, hence the respondents have focused on CE and I4.0 concepts as they are still novel and not well known.
This paper highlights ten key drivers and ten barriers to the application of CLSS4.0 in the manufacturing industry.Our approach was to systematically review the literature, and then identify and analyse the drivers and barriers of CLSS4.0 from a practical perspective.We, therefore, used both quantitative and qualitative methods to better understand the drivers and barriers of the integrated CLSS4.0 approach.We found that the main driving forces behind implementing CLSS4.0 are increased operational excellence, sustainability, high market pressure, regulations and corporate strategies and policies.Management's expectation to improve the company's image and comply with regulations and label requirements can be a powerful driver for CLSS4.0 adoption.By implementing CLSS4.0, business leaders can simultaneously improve operational and environmental performance, ensure compliance with customer and stakeholder requirements, and develop digital capabilities and sustainable practices.The results of our research converge with the literature in that CLSS4.0 adoption presents several barriers factors.The most significant barriers factors include a lack of understanding of the technology, implementation difficulties due to resource constraints, and the cost and complexity associated with implementation.Among the rising obstacles, aspects relating to standardisation, management and leadership, as well as the lack of skills and competencies, are also important.Standardisation refers to the need for organisations to establish consistent practices and processes for implementing and managing change.Management and leadership involve the need to ensure that leaders have the skills and competencies to effectively guide their teams and organisations through change initiatives.Leadership skills such as communication, motivating others, setting expectations and making tough decisions, as well as knowledge of change management principles and practices, are essential to the success of change initiatives.The absence of these skills and competencies can lead to costly mistakes, poor communication and delays in the implementation process.In addition, a lack of sufficient resources to undertake change initiatives can also be a problem, as organisations may not have the budget or personnel to complete the process.
By understanding the benefits of the CLSS4.0,consulting with stakeholders, and providing education and training, a company can promote a smoother transition towards CLSS4.0 and contribute to superior sustainable performance.
The authors have identified several challenges that could be taken into account in future research.First, the range of organisations that were implementing CE was very limited, and given the focus of this study on Moroccan manufacturing companies, it was difficult to find the right candidate for the interview, with expertise in LSS and experience in both I4.0 and CE implementation.Second, while CE is an emerging concept, it is not yet well-known among manufacturers and practitioners, and its implementation is still limited.The effective move towards a circular business model and CE practices in manufacturing companies vary between cases.The discussion of common drivers and barriers to CLSS4.0 requires further research to provide additional clarification of the various internal and external facets of this new paradigm.

Table 1 .
Summary of the review protocol.

Table 2 .
CLSS4.0 drivers and barriers identified from the literature.

Table 3 .
Characteristics of companies involved in the study.