Executive Summary: Polymers from bread waste

Summary of Project and Key Findings:
This project aims to address two sustainability challenges facing the NZ bakery sector, the return of unsold near expiry bread from retailers, and single-use plastic bags. The Baking Industry Research Trust (BIRT) has identified these challenges as priorities against internal sustainability KPIs, and to anticipate potential regulatory mandates against single use plastics. The clients long-term goal of replacing low density polypropylene (LDPE) would typically involve a cost premium because the current best practice sustainability replacement plastic is a costly commercial thermoplastic starch (TPS) based polymer formulation. The recovery of starch from returned bread and its utilisation to replace single use plastic bags is therefore a potential solution and the subject of this work.

In this collaborative project between Plant & Food Research, Scion and BIRT , a bread starch extraction protocol was scaled and the extracted starches extruded into TPS. Further work was then carried out where the bread TPS was blended with a co-polymer to produce a biodegradable polymer with mechanical properties in line with a commercial equivalent polymer product and the performance tested. It was found that the bread TPS was able not only able to match the technical performance in line with a preblended commercial product or if a virgin TPS ingredients were to be used but also delivers a positive net return, without a cost premium.