Feasibility of Superabsorbent Polymer Recycling in Disposable Absorbent Hygiene Products

Abstract

The objective of this work is to evaluate the life cycle impacts of recovering superabsorbent polymers from absorbent hygiene products (AHPs). AHPs, which include baby diapers, feminine hygiene products, and adult incontinence pads, have a considerable environmental impact. While convenient, these single-use products, which typically contain combinations of polypropylene, polyethylene, elastics, cellulose, and superabsorbent polymers (SAPs), are disposed by the billions worldwide. Current practice of AHP disposal results in the loss of valuable materials like SAPs, generation of large volumes of municipal solid waste, and increased manufacturing burdens. Though manufacturers have taken significant strides to reduce the environmental impact of AHPs through product design, developing a potential circular economy of AHPs will be crucial to reducing total life cycle impacts. This is more important than ever, since the disposable diaper industry is reporting exponential growth and its global production is expected to exceed US $71 billion/year by 2022. While recognition of AHP impacts is increasing, it is important to consider that the most significant life cycle impacts of AHPs stem from resource extraction, production, and manufacturing, not disposal itself. The SAPs in these products are a particular focus as they contribute substantially to these upstream life cycle impacts. SAPs can make up as much as one third of the total mass of AHPs and are responsible for the highest proportion of greenhouse gas emissions of AHP materials. We aim to shed light on how we might lessen upstream impacts by focusing on the potential for SAP recovery and re-use. We evaluate three end-of-life options for baby diapers in Europe using a life cycle approach in order to explore alternative options to conventional disposal of AHPs. This research analyzes the environmental trade-offs associated with AHP waste under the following three scenarios: 1) baby diaper disposal via landfill or incineration in a standardized European context; 2) diaper recycling without SAP recovery; and 3) diaper recycling with SAP recovery. Environmental impacts of these scenarios were modeled in the LCA software SimaPro using the ReCipe 2016 impact assessment framework. Results show that SAP recovery has potential to decrease life cycle emissions by 54% compared to standard landfilling and incineration and by 35% when compared to the recycling technologies assessed in the study. SAP recovery and reuse also results in large potential offsets of energy and water burdens involved in SAP manufacturing. By assessing these environmental impacts, we aim to clarify the point at which SAP recovery demonstrates potential for circular economy.