The influence of several hardwoods and softwoods pulp fibre on the free shrinkage of isotropic paper sheets was investigated. The effect of properties such as density, grammage, Fractional Contact Area (FCA), Water Retention Value (WRV), fines content and fibre morphology were also investigated on the free shrinkage of isotropic paper sheets. Further, the influence of Lyocell fibre and glycerol on the free shrinkage of isotropic paper sheets is reported. Experimental results showed that in general the free shrinkage of hardwood pulps is a few percent higher than that of softwood pulps at the same density. It was found that although free shrinkage increases with fines content, a high fines content does not imply high shrinkage, and some pulp samples with higher amount of fines, exhibited lower free shrinkage. For all pulps at low densities there is little influence of grammage on free shrinkage, though as density increases a significant dependence is observed. The results showed that the free shrinkage of isotropic paper sheets formed from hardwood pulps is more sensitive to grammage compared to that of softwood pulps. Interestingly, it was shown that some pulp samples with the same intrinsic density, WRV and FCA exhibited different free shrinkage over the range of grammages. In addition, some pulp samples with stiffer fibres but higher amount of fines exhibited higher free shrinkage. Experimental results showed that longitudinal shrinkage of a fibre is an important parameter and pulp samples with higher microfibril angle (MFA) exhibited higher longitudinal shrinkage. Finally, the free shrinkage of isotropic paper sheets was reduced by applying Lyocell fibre and glycerol. Interestingly, by adding a small amount of Lyocell fibre, 2%, an increase in tensile index, tensile energy absorption (TEA) and modulus is observed, while the free shrinkage reduced up to 2%. In addition, adding glycerol to the pulp samples not only reduced the free shrinkage of isotropic paper sheets up to 1.5%, but also mechanical properties, such as tensile index and stretch slightly improved.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:734224 |
| Date | January 2016 |
| Creators | Mayeli, Nader |
| Contributors | Sampson, William |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/an-experimental-study-of-the-unrestrained-shrinkage-of-isotropicpaper-sheets(6f0e3356-2e17-4433-8303-723a863c11f0).html |
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