AN EXPERIMENTAL STUDY OF THE UNRESTRAINED SHRINKAGE OF ISOTROPICPAPER SHEETS

Abstract

The influence of several hardwoods and softwoods pulp fibre on the free shrinkage ofisotropic paper sheets was investigated. The Effect of properties such as density,grammage, Fractional Contact Area (FCA), Water Retention Value (WRV), fines contentand fibre morphology were also investigated on the free shrinkage of isotropic papersheets. Further, the influence of Lyocell fibre and glycerol on the free shrinkage ofisotropic paper sheets is reported. Experimental results showed that in general the freeshrinkage of hardwood pulps is a few percent higher than that of softwood pulps at thesame density. It was found that although free shrinkage increases with fines content, ahigh fines content does not imply high shrinkage, and some pulp samples with higheramount of fines, exhibited lower free shrinkage. For all pulps at low densities there is littleinfluence of grammage on free shrinkage, though as density increases a significantdependence is observed. The results showed that the free shrinkage of isotropic papersheets formed from hardwood pulps is more sensitive to grammage compared to that ofsoftwood pulps. Interestingly, it was shown that some pulp samples with the same intrinsicdensity, 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 exhibitedhigher free shrinkage. Experimental results showed that longitudinal shrinkage of a fibre isan important parameter and pulp samples with higher microfibril angle (MFA) exhibitedhigher longitudinal shrinkage. Finally, the free shrinkage of isotropic paper sheets wasreduced by applying Lyocell fibre and glycerol. Interestingly, by adding a small amount ofLyocell fibre, 2%, an increase in tensile index, tensile energy absorption (TEA) andmodulus is observed, while the free shrinkage reduced up to 2%. In addition, addingglycerol to the pulp samples not only reduced the free shrinkage of isotropic paper sheetsup to 1.5%, but also mechanical properties, such as tensile index and stretch slightlyimproved.

Date of Award	1 Aug 2016
Original language	English
Awarding Institution	The University of Manchester
Supervisor	William Sampson (Supervisor) & Arthur Wilkinson (Supervisor)