Mini-Encyclopedia of Papermaking Wet-End
Additives and Ingredients, their Composition, Functions, Strategies for Use
FINES (fiber fines)
Composition: When papermakers say the word "fines" they may be talking about just "fiber fines," or they may be referring to everything solid in the furnish that is small enough to pass through a screen. Though researchers tend to define "fines" in terms of a standard sieve size, papermakers usually will consider something to be a fine if it can pass through the forming fabric used on that machine. Sometimes the term "fine particles" is used to make it clear that one is including such items of clay or calcium carbonate filler within the description, in addition to the fiber fines. Fines from wood fall into a couple of different categories. So-called "primary fines" consist of such items as parenchyma cells that store food in a living tree or transport liquids and foods in a radial direction. These tend to contribute bulk and some opacity to a sheet of paper. So-called "secondary fines" are produced by refining. Because secondary fines mainly are produced by delaminating the outer layers of the fiber, they tend to be slender and flexible - ideal for bonding. Unfortunately, these same fines, if the paper is recycled and then made into a recycled sheet, loose much of their bonding ability. Various studies have shown that fiber fines tend to have 3 to 5 or more times as much surface area per unit mass, compared to the fibers.
Function: Fiber fines, in general terms, tend to contribute to the smoothness and resistance to air penetration through paper. A moderate content of fines, e.g. up to about 10 to 35%, often achieves maximum strength, depending on the type of furnish and the quality of the fines. Fiber fines tend to impede dewatering throughout the papermaking process.
Strategies for Use: When they get desperate, papermakers occasionally will sewer their fines. But, when they can, they would much rather add the weight of the fines to what they sell to their customers. It often comes down to a question of finding a way to retain the fines well, without hurting the uniformity of the sheet. And it comes down to a way of overcoming the drainage problems associated with high fines levels. Conventional drainage aid strategies, retention aid programs, and micro-particle programs can be very effective. The conventional drainage aid programs appear to work by neutralizing the colloid charges at surfaces. Such neutralization tends to reduce the level of swelling of materials at fiber surfaces, and it also tends to make fibers at the fiber surface lie down flat on the surface. Retention aid treatment can help by binding the fines to fibers. The bound fines are prevented from following flow channels through the wet sheet of paper and becoming stuck at points of flow restriction within the structure. Micro-particle programs (involving prior treatment with a very-high mass retention aid) tend to achieve a combination of retention and charge neutralization, and so they can be beneficial when running a system containing a lot of fines.
Cautions: Ordinary safe procedures should be followed.
PLEASE NOTE: Users of the information contained on these pages assume complete responsibility to make sure that their practices are safe and do not infringe upon an existing patent. There has been no attempt here to give full safety instructions or to make note of all relevant patents governing the use of additives. Please send corrections if you find errors or points that need better clarification.
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This page is maintained by Martin Hubbe, Associate Professor of Wood and Paper Science, NC State University, firstname.lastname@example.org .