UBC Theses and Dissertations
Experimental characterization of tissue structure and the impact of forming fabric on tissue properties Srivastava, Prabhat
Low basis weight tissue papers (≤ 25 gsm) are extensively used in our day-to-day life. They are softer, stretchy and have high water absorbency compared to writing or printing paper. During tissue paper manufacturing, a slurry of pulp and water is carried on a forming fabric which is pressed onto a chemically coated “Yankee” dryer which rotates at high speed (1200-2200 m/min) and is maintained at ≈ 100◦C. After drying on Yankee, the sheet is scraped off Yankee with the help of a stationary creping blade. The process of removing the sheet from the Yankee is called “creping”. Creping imparts a folded structure to the sheet that is responsible for the desired properties of tissue paper like high bulk, high failure strain, high work to rupture, and increased softness and absorbency. A scientific understanding of the process and its influence on the properties can be useful for enhancing the quality and efficiency of the manufacturing process. The current research studies the influence of creping by performing measurements through experiments on tissue paper samples. An experimental technique based on focus stacking is used to image the edge of a tissue paper. Measurements made using this new technique are quantitatively compared to measurements from scanning electron microscope images. The edge images captured are used to calculate a parameter that quantifies the creped structure and correlates well with the stretch. It provides a measure of foreshortening of the sheet that occurs during creping. The forming fabric imparts an embedded structure on the sheet before pressing on the Yankee. These patterns affect the creping process and thus the tissue quality. Surface images of the forming fabric and the tissue paper formed on it in conjunction with measurements from uni-axial tensile tests are used to study the influence of the forming fabric on tissue paper. A method is proposed through which a surface image of the tissue can be used to estimate stretch. Tissue samples over the life of forming fabric are studied to understand the impact of forming fabric wear on tensile properties.
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