major research project was undertaken to address the problem of significant losses to drain of process materials in a lightweight paper mill. Current thinking among papermakers is that minimisation oflosses is best achieved by focussing on internal mill efficiencies rather than post-process technologies. Additionally a technologically effective solution to the problem of raw materials losses must also be a cost effective solution. The approach adopted therefore was to apply known principles of paper science to focus on the needs of a specific mill, as identified by comprehensive survey of the mills' operations. Two key areas of mill operations were identified by preliminary investigations as having significant impacts on drain losses at the mill: the control of and influence on product quality of entrained gases and the role of wet end chemistry in determining fibre and filler retention and product quality. Levels of entrained air in the papermaking stock were found to be in the range 0.2 to over 1.0% by volume. These levels were controlled by large volumes of fresh water addition and by chemical defoamers. Entrained air levels in excess of O.2% were found to have a deleterious effect on paper formation and caused unacceptable cross machine variations in air permeability, a key parameter for this grade of paper. An optimum level of chemical defoamer addition was found which controlled the levels of entrained gases and brought about significant improvements in formation, tensile strength and CD air permeability variation. Air permeability variation was reduced by 21% and bonding strength increased by 5%. This optimum level also removed the necessity for the addition of large volumes of fresh water to control stock temperatures.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:616999 |
| Date | January 2001 |
| Creators | Curley, J. E. |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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