The sorting of waste bottles into pure polymers fractions of PE, PP, PET and PVC with laser-induced breakdown spectroscopy has been investigated. Element and molecule structures were detected in spectra of laser-induced plasmas. Classification algorithms based on multivariate statistical analysis and neural networks were tested.
The achievable identification accuracy depends on the kinds of polymers and their additives. Typical results on recycled and virgin polymer samples achieved under laboratory conditions are 90-95% for PE and PP and > 99% for PET and PVC, where 20% of all measured samples could not be identified and have been sorted out. For bottle pieces, about 95% have been classified correctly. The measuring times are < 100 us, the evaluation times in the order of milliseconds, enabling sorting rates of 10 per second and more.
Autofocussing to the varying geometry of the bottles is a challenging problem. An autofocus system based on triangulation operates reliably with coloured samples, but not with transparent ones. Future work should aim to avoid the necessity of an autofocus system by proper handling of the bottles and usage of a focussing lens with a long focal length.
A modular handling and sorting equipment for singularization, pressing to +/- 10 mm surface position range and sorting 3 bottles per second was constructed and put into operation. The handling and sorting equipment is successfully combined with a PC for laser triggering and generation of sorting signals. Singularization and transport of about 10 bottles/s is assessed as feasible. Nevertheless, in order to avoid two bottles arriving at the identification point at the same time, the handling device has to be carefully adjusted,
In summary, after completion of the fundamental research project, the possibility of laser-based identification of plastics is realistic. Further work has to concentrate on technical oriented development.
For material recycling of plastics and polymers from domestic waste it is necessary to identify and sort the different parts to obtain pure material fractions.
A rapid piece-by-piece method is possible by identification of the composition of each waste particle with laser using laser-induced breakdown spectroscopy. It is the aim of this project to investigate the technical feasibility of this technique for the recycling of plastics and polymers from domestic waste. The project activities comprise the beam guiding of the laser to the plastic and polymer parts, the detection of spectra, determination of spectral features for the identification of different materials and handling, sorting and further processing of the different fractions.
Funding SchemeCSC - Cost-sharing contracts
71110 Heraklion Crete