Closed Loop Recycling of Bottle Crates Using the Restabilization Technique

A remelting-restabilization technique was applied for the recycling of post-used, yellow pigmented high density polyethylene (HDPE) bottle crates. In order to evaluate the potential of the recyclate to be used in the original apllication, the most important parameters were investigated: processing stability, long-term heat stability and light stability. A multiple extrusion cycles procedure at different reprocessing temperatures was performed for monitoring the processing stability of the restabilized and non-restabilized material. Oven aging was applied for about 8000 h (i.e., more than one year) to evaluate the long term thermal stability of the crate material, as manifested by melt flow rate, tensile impact strength, and time until embrittlement measurements. To evaluate the light stability of the recycled material artificial weathering was applied for about 8000 h, whereas the tensile impact strength was monitored. The latter data were enriched with microphotographs of the specimens surface. Finnaly, repigmentation was used to investigate the role of new pigments on the final performance of the recyled product. The results illustrate that restabilization is mandatory for the quality improvement of post-used crates ensuring its re-use in the original application and thus making closed loop recycling.