l>Chalk

Mini-Encyclopedia the Papermaking Wet-End Chemistry Additives and also Ingredients, their Composition, Functions, techniques for Use

CHALK

Composition: Chalk is a type of calcium carbonate, having the very same chemical composition together ground calcium carbonate, limestone, marble, and precipitated calcium carbonate (PCC). In fact, all of the calcium carbonates noted in the vault sentence have actually the same crystal form, calcite. What renders chalk different is its origin as the shells of little "coccolith" organisms. Generations of coccoliths gradually built up deposits. Due to the fact that most the us have experience v chalk-board chalk it need to come together no surprise that the deposited mineral is quite easy come grind. The particles released by grind the chalk have a highly desirable property; almost every one of them are in an excellent particle size range for usage at fairly high levels together a filler. The moderately large size and also low surface area (about 4 m2/g) relative to other usual fillers way that chalk has actually less adverse impact on strength than most kinds of filler at any type of given filler contents in paper. Specifically abundant and high-quality chalk deposits are discovered in England and also Denmark - but not in north America. This truth is probably part of the reason that the European document industry was earlier in the widespread adoption of alkaline papermaking technology. The modest brightness the chalk (typically 80 come 86%) can be an issue, specifically when it is compared against ground limestone and precipitated calcium carbonate assets (both around 95 come 99% brightness). Also, chalk can not be expected to accomplish a high opacity. Opacity can be improved much more by making use of something v a high surface ar area, bulking ability, and open structure, e.g. Scalenohedral PCC. Chalk generally is distributed with anionic materials such together phosphates or polyacrylates.

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Function: document filler for price reduction, pH buffering (alkaline), and superior ability to keep acceptable document strength as a function of raising filler content.

Strategies because that Use: Chalk filler is a reasonably forgiving additive, as long as one stays clear of direct call with specific other additives that have the right to be adversely affected by it. These incorporate acidic products such as alum and sulfuric acid. Sizing agents commonly should be well separated from calcium carbonate filler in the plan of addition; typically the filler need to be included early, and the size must be included late in the process. However, chalk is most likely the most sizing-tolerant of all of the calcium carbonate filler varieties. Either a cationic or anionic retention help can job-related well with chalk due to the existence of Ca2+ web page on that is surface, and also due to the visibility of anionic materials (including filler dispersants) in the white water system. The lot of filler in the paper (if every one of it have the right to assumed to be chalk) can be identified by ashing the record at 900 oC in a tared crucible, then splitting the "percent ash" through 0.56. This coefficient comes from the reaction of CaCO3 come CaO + CO2. In the visibility of various other minerals one needs to execute a second ashing analysis for a standardized size of time at 500 oC or some other an ideal temperature. Under such problems almost every one of the calcium carbonate stays as CaCO3.

Cautions: because chalk is often ceded as dry powder, the is essential to take it precautions against breathing the the dust in the filler ready area.

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Illustration the the typical size, shape, and also partially fused nature that chalk as used for paper.

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PLEASE NOTE: users of the information had on these pages assume complete responsibility come make sure that their methods are safe and also do not infringe ~ above an currently 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 correction if you discover errors or points that need much better clarification.


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This page is preserved by young name Hubbe, combine Professor of wood and record Science, NC State University, m_hubbe