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"Niskanen, Kaarlo"
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Fragmentation of fibrous particles in LC refining
Low-consistency (LC) refining is used in mechanical pulping and in general to give a final touch to a papermaking pulp. The desired—and undesired—effects come from changes in the property and size distributions of the different kinds of fibrous particles. In our study, we focus on the changes in the size distributions of mechanical pulps, measured with an optical fibre analyser. Pulp samples were collected before and after industrial LC refiners of thermomechanical pulps with spruce as raw material. We demonstrate that changes in the observed size distributions of fibre length and diameter can be reproduced with a stochastic model with just two parameters for particles breaking uniformly at random locations. One probability controls the breaks per unit length that shorten fibres, and another the splits per unit diameter that generate more fines. Our findings support the hypothesis that these two processes are separate so that breaks in length do not govern the increase in fines. Both fibre shortening and fines generation increased with refining energy but, at a given energy, only fibre shortening showed clear differences between trials. In a two-stage refining trial, the probability that fibres shorten was equal to the product of the single-stage probabilities. In addition, the two-stage probability fell on the same straight line as the one-stage probabilities when both were plotted against the refining energy measured from the threshold energy at which breaks start.
Journal Article
Mechanics of Paper Products
This graduate level textbook focuses on the mechanical properties and performance of products made of fiber-based materials such as paper and board. The book aims to help students develop effective skills for solving problems of product performance and engineering challenges in new product development. Therefore the material is organized with a problem-based approach - a practical example of product performance is presented and then the relevant mechanics are analyzed to deduce which material properties control the performance.
eBook
Functional additives can improve newsprint pressroom runnability
Printing press operators expect newsprint to expand a certain amount during printing. To compensate, they adjust press-operating variables so that proper text and image alignment occurs. However, when changing from one source of newsprint to another, this expansion varies and can require press adjustments that may introduce difficulties in obtaining the desired print quality. Expansion of the paper often leads to printing problems such as misregistration, fan out, or even web breaks. This article describes results from a study conducted to evaluate the effect of different chemical additives on newsprint composed of different furnishes. The study showed that both size and wet strength resins can help control paper expansion and may be used to help solve pressroom runnability problems. Also, control of newsprint hydrophobicity is important for the sheet's dimensional stability during printing. The study demonstrated that controlling both hydrophobicity and wet strength are also important for improving pressroom runnability.
Magazine Article