Paper surface diffraction to characterize the fiber orientation distribution

Abstract

Many paper mills use ultrasonic techniques to measure the Tensile Stiffness Index, TSI, of the paper sheet. They then assume that the TSI value is the same as the fibre orientation anisotropy. This is true if the paper is allowed to dry without any internal tension or elongation, but does not apply to paper manufactured in a paper machine. The paper machine introduces tension and elongation as soon as the fibre is placed on the forming fabric. These factors increase through the press section and are accentuated in the drying section. In order to uniquely measure the fibre orientation anisotropy on the surfaces, the proposed method uses replicas of both paper surfaces to produce a laser diffraction pattern. The obtained pattern reveals an elliptical shape, which is related to the fibre orientation anisotropy of the paper surface. By measuring the ellipticity of the diffraction pattern and the deviation with respect to the machine direction, one can quantify the fibre orientation distribution. Different papers from the bench market have been successfully tested with the developed system. This article describes the new developed optical system and its innovative capabilities in the field to produce maps of the fibre orientation of a complete paper sheet surface. A selection of the obtained results to prove its feasibility is also presented.

Study of repeatability of an optical laser system for characterization of the paper fiber distribution and mass density

“…Due to the relevance of this thematic in the paper manufacture, many studies have been carried out by different researchers in this particular area 7-12 . Our team has also performed research work in this area and had implemented, in the past, several experimental methodologies for the paper characterization [13][14][15][16][17][18][19] . Our more recent system [17][18] , based on the original system designed for the same general purpose 15 , was implemented having in mind the characterization of the paper fiber distribution and mass density analyzing both surfaces and the bulk of paper samples, at the same time, using the retro-diffusion and transmission of the radiation derived from two lasers placed in the system in opposite sides relatively to the position of the paper samples.…”