New techniques for measuring fiber properties have been developed to improve communications between pulp and paper manufacturers and paper users.
Quality fluctuations in the raw material can be strongly correlated to the quality of the end product - the paper. This means that both the process and product can be optimized.
Automatic pulp measurement makes it possible to ascertain quality more frequently and at a lower cost, reducing dependency on manual methods. Traditional techniques did not provide a sufficient measurement frequency to ensure pulp quality. ABB’s L&W Freeness and Fiber Online, a specially developed automated sampling system, means that multiple measuring points can be monitored repeatedly by the same system. This makes it possible to detect quality deviations on a completely different scale than available previously.
Important measurable fiber properties include length, width, shape factor, fines, vessel cells, shives and coarseness.
Length – Fiber length influences sheet strength but can also have a negative effect on sheet formation. ABB’s L&W fiber analyzers have been designed to measure fiber length regardless of the degree of deformation, this information is important as fiber deformations weaken the sheet.
Width – Thinner fibers provide a better and more even sheet formation. Chemical fibers are thinner than mechanical fibers since the width of the fibers decreases when lignin is removed and the fibers partly collapse.
Based on information on fiber surface area and circumference, the length and width for an equivalent rectangular object is calculated. Data from all pixels in the fiber image are used for the calculation. This explains why the resolution in measurement of width is much higher than the size of the pixel size in the image. Length and width describe a model of the actual fiber, which in itself has a less defined form.
Shape factor – A seemingly small variation in shape factor between 81 and 85 percent can make a difference of 30% of tensile index. This difference remains subsequent to refining with constant energy even if tensile index has increased due to fibrillation of the fiber surface.
Coarseness – Coarseness is used to express fiber wall thickness and is defined as weight per fiber length unit. Specifically available in ABB’s L&W Fiber Tester Plus, the lab instrument calculates coarseness and reports coarseness on the standard laboratory report. As the analyzers also measures fiber width means that weight per fiber surface area also can be calculated.
Vessels – In hardwood pulp, vessels may cause problems due to the fact that they may limit the viability of the pulp in certain applications. A typical vessel, for example a eucalyptus wood cell,is typically around 200×200×20 µm. A typical eucalyptus fiber is 800×20×20 µm. The ratio of number of vessel cells to the number of fibers and the length/width distribution of the vessel cells are measured. Number of vessels per gram etc. can also be measured.
Minishives – The software for analysis of vessel cells includes general blob analysis tools, which makes it possible to be used for measuring other objects by using other settings. This means small shives that are not normally measured by traditional equipment like PQM or PEX can be measured.
Kink – Local deformations may cause local weakening of the fiber. The raw data can be saved to permit subsequent study of individual fibers and the calculated kink angles. Segment lengths are calculated in accordance with the figure. Information about kinks may be more important than fiber length.
Shives – Shives are often regarded as fibers that have not separated and that are wider than 75 µm and longer than 0.3 mm. Shives may give rise to surface imperfections of the paper and thereby weaken the paper. In addition, this may cause stoppages in the paper machine and during post production, for example, in a printing press. Shives are formed when unbleached chemical pulp and mechanical pulp are manufactured.
Freeness – Uneven drainage properties may give rise to operating problems in the paper machine. Freeness is a measurement of the speed with which water drains from a pulp sample. The standard test for freeness is based on gravity driven drainage through a strainer plate. L&W Freeness Online has modules for automatic standard freeness test according to both Canadian Standard Freeness (CSF) and Schopper-Riegler (SR). True consistency and temperature compensation is included.
Blend – two dimensional fiber distributions. The blend software calculates the fiber components present in the pulp sample. The ratio of short fibers to long fibers in the mix or the ratio of chemically produces long fibers in a mix with thermo-mechanical pulp (TMP) can be calculated and used online to control the process. For example a short fiber mix in a reinforcement pulp lowers the value of the pulp, while chemical fibers in the recycled pulp makes stronger paper.