A comparison between laboratory-scale and large-scale high-intensity washing of flexible polyethylene packaging waste

Journal article, 2024

Sorted flexible polyethylene packaging waste was washed on a laboratory scale at both 25 and 40°C with water alone, with water and added NaOH, and with water and added detergent. The washed materials were then compounded using a twin-screw extruder and injection molded. The results were compared with those for an unwashed and a large-scale high-intensity sample washed with NaOH at 70–80°C. An intensive washing combined with high temperature gave a lower extensibility both in the molten and solid states presumably because of a greater degradation of the recycled material. Washing with NaOH resulted in the lowest strain-at-break in both the melt and solid states, whereas washing with water alone or with a detergent gave similar strain-at-break levels. The melt strength, the stiffness and tensile strengths at room temperature, and the thermal properties were less affected by the washing procedure. Although the final properties seem to be useful in general there were still some trade-offs between the washing condition and the degradation. While these results were expected, the influence of washing parameters on final product, for example, injection molded sample, has to our knowledge not been shown before especially regarding the mechanical properties. Highlights: Post-consumer flexible polyethylene packaging waste was studied with a focus on washing conditions. The influence of washing conditions on thermal, rheological, and mechanical properties of recycled samples was investigated. High-intensity washing at high temperature caused significant degradation of the material, this was to our understanding shown for the first time.