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Author:Hii, Collin Ching Tyn
Title:Hygroexpansivity of paper
Publication type:Master's thesis
Publication year:2008
Pages:ix + 119 s. + liitt. 28      Language:   eng
Department/School:Puunjalostustekniikan laitos
Main subject:Paperi- ja painatustekniikka   (Puu-21)
Supervisor:Paulapuro, Hannu
Instructor:Lipponen, Pasi
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark TKK  996   | Archive
Keywords:anisotropy
hygroexpansion
hygroexpansivity
image analysis
shrinkage potential
Abstract (eng): This thesis work attempts to study the effects of paper's MD and CD anisotropy on their respective shrinkage potentials and hygroepansivities.
Three types of papermaking fibre raw materials supplied by UPM-Kymmene are used for this study: TMP, bleached pine kraft pulp (SW) and mixture of 71%TMP and 29%SW.
The scope of work includes the laboratory study on oriented sheets made using KCL Dynamic Sheet Former, Mixture Design of Experiment to study effects of fines, filler clay and long and medium fraction and finally mill verification studies involving three UPM-Kymmene paper mills.

A pre-study enables familiarization with the sheet forming method and implementation of the measurement system analysis; as a result, significant improvement in the repeatability and reproducibility of the measurement system reduces the errors in final experimental results.

The laboratory experimental study compares actual fibre orientation anisotropy from image analysis using the sheet splitting method with the anisotropy from tensile stiffness ratio and tensile stiffness index orientation (max/min), measured using ultrasonic method.
The correlations between fibre orientation anisotropy and hygroexpansivity can be useful for modelling paper structural deformation using finite element method; the paper local structural deformation can be simulated with local hygroexpansivity caused by the local fibre orientation anisotropy.

Freely dried SW has the highest degree of shrinkage potential and hygroexpansivity with increasing anisotropy degree while TMP has the lowest.
Oriented sheets made using TMP furnish shows the least influence of drying restraint on hygroexpansivity.
All three pulps show linear correlation between increasing CD hygroexpansivity and increasing CD shrinkage potential as CD anisotropy increases; the increasing MD hygroexpansivity correlates linearly with increasing MD shrinkage potential as MD anisotropy decreases.
TMP pulp also shows lowest effects of drying restraint on hygroexpansivity as shrinkage potential increases probably due to the lignin content in the pulp.

The Mixture Design of Experiment uses fines generated from MATSUKO ultra fine grinder, filler clay and medium and long fraction bleached pine kraft pulp; the sheet forming uses membrane cell with vacuum assisted dewatering.
The result shows increases filler clay in proportion increases hygroexpansivity.
However, more studies are required to ascertain the effects from the layered structure and to decouple the non-linearity effects from the ash-fines and ash-fibre interactions.

The mill verification trials confirm that the MD of machine made paper at centers and edges are highly restrained during drying; However, the CD components at the centers are restraint dried while the edges show some degree of restraining during the drying process.
ED:2008-11-25
INSSI record number: 36542
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