To build a society that achieves sustainable development with less environmental impact, the recovery rate of wastepaper has increased by reducing paper waste and protecting forest resources;the utilization rate of wastepaper as a raw material for papermaking has increased accordingly. As the recycled paper is widely used as an environmentally friendly product, estimating and evaluating the wastepaper pulp content in paper and paper products is necessary. However, discriminating between virgin pulp fibers and wastepaper pulp fibers in paper and paper products is challenging because there is a wide range of wastepaper types. Moreover, the pulp fibers are physically or chemically altered during the wastepaper process.
In this paper, we prepared recycled-paper model handsheets from softwood bleached kraft pulp (SBKP) with an internal additive of fluorescent whitening agent (FWA) and compared three test methods for estimating the blending rate of wastepaper pulp. In addition to estimating the blending rate of wastepaper pulp from the image analysis of paper samples using confocal laser scanning microscopy (CLSM), the blending rate of wastepaper pulp from pulp fiber was examined through fluorescence microscopy (FM);evaluation by the visual method and image analysis was also conducted.
The mean luminance (mean fluorescence intensity) of paper samples calculated from the images obtained by the CLSM method showed a high correlation with the wastepaper pulp content regardless of changes in the amount of FWA added or the type of bleached pulp. Another advantage of the CLSM method is that it enables the estimation and evaluation of wastepaper pulp content without the need to defibrate the recycled paper sample.
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