Closing the Loop – Frugal Innovation in Plastic Sorting: Design, Implementation, and Testing of a Sink-Float Separator for Waste Recycling in Malawi

This thesis addresses the recycling of mixed post-consumer plastic flakes in Blantyre, Malawi, where property differences between plastic types had left large quantities unusable by two local NGOs after failed attempts to mold them into bricks. A literature review and small-scale proof-of-concept tests were used to compare plastic separation methods, identifying sink-float separation as most suitable for the local context due to its simplicity and robustness. A manually operated, two-stage sink-float separation prototype was then designed and manufactured from locally available materials and validated through field testing. The prototype achieved separation purities of 96.55% for PET and 99.77% for HDPE, sufficient for reuse in local recycling operations, while purity for PP remained insufficient at 69.76%, and contamination and quality-control needs were identified for future work.