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H. Praast and L. Göttsching. Local orientation of flocs in paper. In The Fundamentals of Papermaking Materials, Trans. of the XIth Fund. Res. Symp. Cambridge, 1997, (C.F. Baker, ed.), pp 1293–1324, FRC, Manchester, 2018.


So far little attention has been paid to the orientation of flocs in paper sheets . It can be measured by means of an image analyser and the two-dimensional Fourier transform. The principal direction in the power spectrum of a paper in transmitted light is a measure of the floc orientation.

It can be shown that the coefficient of correlation between fibre orientation (Lippke – Tester) and floc orientation amounts on average to 0.7, when profiles across the web are taken into account. Papers, particularly those which are made on hybrid formers, show a two-sidedness concerning floc orientation and anisotropy . The orientation has no significant effect on the uniformity of formation but determines the orientation of cockles. The power spectrum of the local orientation of a paper seems to be very useful in the detection of deterministic variations in orientation, which are invisible in light transmission images.

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