Mechanical separation models for material recycling applications

Mechanical recycling of common materials such as plastics requires appropriate material segregation, which is usually performed adopting processes similar to those developed for mineral engineering industry. Due to the need to increment amount and quality of selection products, such processes - still developed through trial-and-error approach - are also facing improvements in order to fit with the needs of different waste flows. The work here presented deals with methodologies for virtual and practical development of mechanical separation processes and, in particular, about the preliminary definition of densimetric tables devices; for this reason, a brief review on typical waste flow is provided. The case study considered is a mixed polymeric fragmented flow comprehending two main fraction (elastomer and rigid plastics), which have been subjected to a preliminary separation test. Due to the need to optimize the process, a model for material fluidization is proposed to investigate the relevance of process parameters (e.g. air speed value) depending on material bed characteristics. After this, an image processing tool for the rapid analysis of fragments has been prepared, its scope being to find out typical shape and size characteristics, needed as input to the model, and color identification and number, which can be used for output characterization and performance analysis. Model and image processing tool together constitute the basis for process redesign, optimization and verification.