Novel Analysis of Recycled Pulp-Containing Paper, Including Fluorescent Whitening Agent:

In recent years, the use of recycled pulp-containing paper has spread widely with the increase in the recovery rate of wastepaper. This increased use is sustained by the concern regarding environmental pollution and the concept of sustainable development. In Japan, the “Law Concerning the Promotion of Procurement of Eco-Friendly Goods and Services by the State and Other Entities” stipulated in 2009 that the percentage of wastepaper pulp should be at least 70% for recycled copy paper and 60% for recycled printing paper as the eco-friendly products. Recently, a precise method to assess the wastepaper pulp content in recycled paper products has been required with the increasing use of wastepaper pulp.A new method using a confocal laser scanning microscope （CLSM） to assess wastepaper pulp content in recycled pulp-containing paper was tested in this study. Most printing and writing papers contain fluorescent whitening agents that enhance the whiteness of paper and, partially remain after recycling treatment. This characteristic can be used to distinguish wastepaper pulp from virgin pulp.A wastepaper pulp sample was prepared using a typical deinking treatment of handsheets made from hardwood bleached kraft pulp and bleached chemi-thermomechnical pulp （BCTMP）. A controlled amount of fluorescent whitening agent was added to the pulps. Several recycled handsheets were prepared by changing the ratio of wastepaper pulp to virgin pulp. Images of pulp fibers with the adhered fluorescent whitening agent were observed without breaking the form of the sheet, and the difference between the wastepaper pulp content was confirmed by CLSM. Following image analysis, it was found that the mean intensity of the images of the handsheets correlated well with the actual wastepaper pulp contents.