Summary of Mass Balance Model and Its Challenges in Application to Industrial Materials

Abstract

Chain of custody （CoC） models certify traceability of the claim made on materials or products with a set of specified characteristics. Initially, a CoC model was applied to certify the sustainability of agricultural products. Recently, mass balance （MB） model, one of the CoC models, has been applied to the environmental claims of engineering materials. However, there are many challenges when implementing MB model in engineering materials. MB model allows flexibility in determining the ratio of specific feedstocks within materials, raising concerns about deceptive environmental claims. Credible claims with MB model need to establish requirements for applying the model. Defining system boundaries and identifying inputs and outputs are essential for CoC models. However, current MB model lacks consistency in determining system and allocation method of the specific characteristics. In addition, for most engineering materials other than chemicals, claiming methods depend on individual entities. Establishing a uniform evaluation method and certification scheme is desirable. Moreover, under conventional definitions, distinction between MB and book and claim models is vague in terms of relationship between input and output. Differentiation of these models requires further discussions. Establishing requirements and eligibility for MB model applied to engineering materials is necessary, which leads to a unified methodology.