Estimating Wastepaper Pulp Content in Recycled Paper by Visual Observation using a Fluorescence Microscope

Abstract

The utilization of recovered paper for high-grade paper such as printing, communication, and tissue papers has been limited because using recovered paper tends to reduce the quality of these papers. Therefore, despite an increasing recovery rate, the wastepaper utilization rate in Japan was still only 61.8% in 2008. In Japan, the regulations of the Law Concerning the Promotion of Procurement of Eco-Friendly Goods and Services by the State and Other Entities were strengthened in 2009 to counteract the practice exposed in the so-called Wastepaper Camouflage Scandal. In order to assess the wastepaper pulp content in recycled paper, a new method using a fluorescence microscope is developed. As fluorescent whitening agents are commonly used to enhance the whiteness and brightness of paper, most recovered printing paper contains fluorescent whitening agents. Both visual observation and image analysis techniques were investigated to differentiate between virgin and wastepaper pulp fibers. Recycled handsheets were prepared to establish the fluorescence observation technique for evaluating the wastepaper content. More than 1,200 fibers should be counted to accurately determine the wastepaper content by this technique. The results obtained by the visual observation technique agree with image analysis of the recycled handsheets. The actual precision of the quantitative wastepaper pulp fiber analysis by the fluorescence observation technique depends on the wastepaper pulp content and the amount of fluorescent whitening agent in the recycled-content paper.