A model for green order quantity allocation in a collaborative supply chain

Several models have been proposed in the literature for allocating quantity orders, but few of them consider collaboration to enhance supply chain (SC) performance sustainably. Despite the increasing attention given to sustainability and the triple bottom line (TBL) criteria, the existing models for order allocation are limited to considering TBL scores only in the phase of selecting suppliers, thus evaluating mainly environmental attributes, without integrating economic and social ones. For these reasons, based on the main research gaps in the current literature, this paper aims to investigate the green order allocation problem in an SC with high operational variability, exploiting the advantages of a collaborative and sustainable SC. The model we propose considers the uncertainty of the demand, the limited capacity of the suppliers, the minimum levels of purchase and production, the environmental, economic, and social scores of suppliers, and the total emissions related to the production, ordering, maintenance, and transport of the allocated items. Our model is based on allocation curves that are continuously updated and shared between the customer and the supplier. On the customer side, it allows to dynamically optimise order allocation, and on the supplier side, it provides clear information on the possible future requests from the customer based on the overall and real economic, environmental, and social perfor-mance. To validate the model, the authors applied it to a numerical example, which resulted in minimising both costs and the TBL impacts. Moreover, considering the TBL scores only in the selection of suppliers led to non -optimal choices in the present case study; for example, assigning the largest share of the order to the supplier with the lowest TBL score did not result in the most sustainable allocation. The continuous exchange of infor-mation and the synchronism triggered by the buyer-supplier collaboration allows managers to know in advance of any critical issues that may arise in the future and intervene promptly to reorganise the allocation. Therefore, the proposed model can help both researchers and practitioners establish a systematic approach to green order allocation and might help firms increase their sustainability degrees throughout the supply chain.