A quantitative model proposal for managing returnable transport items under horizontal logistics cooperation in closed-loop supply chains

Globalization and growing competition in the business world have caused business processes to become increasingly complex. As a result, companies began to collaborate and form business relationships, resulting in the formation of supply chains. Sustainability studies have become more important in supply chains as environmental awareness has grown, resulting in closed-loop supply chains. Returnable transport items (RTIs) management in closed-loop supply chains is a significant aspect of logistics operations today since they bring various environmental and economic benefits due to their ability to be reused several times. In this study, a mixed integer linear programming model is proposed for a multiple suppliers, multiple customers, closed-loop inventory routing problem where decisions about product distribution and collection of empty RTIs, vehicle routing, and the amount of inventory to be kept in warehouses are made. Within the scope of the study, the benefits of various types of horizontal logistics cooperation that can be established between supply chain elements are examined. In the study, the product demand structure is discussed both statically and dynamically. In addition, the effects of changes in the amount of demand within the planning horizon on the total cost in different horizontal logistics cooperation scenarios are also included in the study. As far as is known, there is no study in the literature that includes the factors mentioned together. The applicability of the proposed mathematical model is demonstrated in a base case scenario. Afterwards, numerical analyses were carried out to examine the above-mentioned effects. Following the analysis, it was discovered that, regardless of the demand structure, horizontal logistics cooperation between both customers and suppliers is the least expensive cooperation option in all cases examined. Furthermore, the analyses have revealed that the type of horizontal cooperation established has a different impact on different parts of the total cost throughout the supply chain.