Recycle vs. Virgin Fiber Characteristics: A Comparison, 1992 Papermakers Conference Proceedings

Although many articles appear in the literature which relate the strength of final paper products to the recycle fiber content of these products, there has been no effort to systematically analyze this data. The purpose of such an analysis would be to clearly identify the fiber properties which dominate the observed strength loss. Our approach is to utilize the network theory of paper as embodied in the work of Derek Page, et al. The Page equation for tensile strength has been successfully used by Institute of Paper Science and Technology personnel to predict the final properties of paper made from virgin pulp. This work is included with our Process Simulation Program MAPPS.

The approach used by Page stipulates that the tensile strength of paper can be expressed in terms of 1) tensile strength of the fiber, as measured by zero span tensile; 2) the perimeter, coarseness, and length distribution of the fiber, 3) the specific bond strength for fiber-fiber bonds; and 4) the relative bonded area. Several publications in the open literature provide sufficient data to analyze the strength properties of paper in terms of these fiber variables. We have found an ambiguity in the behavior of fiber tensile strength. Some authors report an increase in single fiber tensile strength over repeated drying cycles while others report a decrease. The impact of recycling on coarseness, perimeter, and length is small. We conclude that changes in these properties do not significantly impact on the strength development potential of recycle fibers. The literature teaches that the recycling of fibers impacts on the compliance of individual fibers to each other. This implies that the relative bonded area of paper made from recycled fibers is lower than from virgin fibers. Our analysis shows this effect. However, our analysis suggests that the contribution is small. We find that recycling lowers specific bond strength by as much as 55%.

Our current work focuses on a study of the principal fiber species found in the United States. We have undertaken a systematic laboratory study to identify the changes in fiber properties brought about by repeated recycling.