A Compact, High Speed Lignin Sensor for the Automated Sorting of Newsprint from Mixed Waste, 2004 Paper Summit, Spring Technical & International Environmental Conference, (including Papermakers; Process Control, Electrical & Information; Product & Product

A non-contact optic sensor for real time measurement of lignin content of paper has been designed to automate the sorting of lignin-rich papers, such as the newsprint from other grades of paper, based on lignin content. The fluorescence of lignin molecules when excited by a green laser at 532 nm on the surface of the paper is measured at 650 nm. The fluorescence intensity is measured in real time and converted to actuation signal for sorting mixed waste. The measurement correlates well with actual lignin content. The effect of printed text, color of print, and basis weight, and distance from the sensor tip are reported. Finally, the sensor electronics has been packaged into a standalone enclosure with only a fiberoptic cable leading to the sample test site, the conveyor, making it simple for implementation. However, as a binary sensor to identify high and low lignin content, the sensor works extremely well. A commercial trial on a moving conveyor was carried out to assess the usefulness of the sensing concept for lignin identification in sorting of mixed waste and results were satisfactory.