Design and optimisation of green closed-loop supply chain network considering additional selling agents and multilevel customers: a SME case study

Small- and medium-sized enterprises (SMEs) are crucial to economic development, yet they face challenges in enhancing supply chain (SC) performance while addressing environmental concerns. This study develops a green closed-loop supply chain (CLSC) model that integrates economic, environmental and operational objectives to support SME decision-making. The model introduces a reselling market to boost profitability by incorporating product reuse in reverse logistics for secondary customers. It also considers the strategic addition of selling agents and customer recategorisation. Three solution methods are proposed: elastic boundary objectives, modified weighted Chebyshev and a customised augmented e-constraint method (AUGMECON2). Among them, AUGMECON2 demonstrates superior performance through comparative analysis. Numerical examples validate the model, and a real-world SME case study reveals that integrating selling agents and multilevel customers leads to a 93% profit increase, a 33% reduction in environmental impact and a 36% improvement in delivery times. These results underscore the effectiveness of the proposed CLSC framework in optimising SME supply chains for both profitability and sustainability.