Retention - Papermaking System First pass retention True...

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Papermaking System
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First –pass retention
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True retention (Over-all retention
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Typical Paper Furnish Components Size Relations
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Electric Double Layer Model
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Acryl amide
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Anchoring of AKD
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Anchoring of ASA
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Britt Jar
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Anionic Fiber AND Cationic GCC Natural Attraction (Model)
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Charge Neutralization
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Polymer Bridging
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Polymer inversion
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Colloidal Silica
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Silica Bridging
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Good retention is important to the efficiency of the papermaking operation Low retention can lead to many problems, including: Poor runnability Increased deposits Sheet defects Higher additive costs More downtime for wash-ups • Higher sewer losses Retention aids can improve the overall runnability of the machine, allow increases in speed through better drainage, reduce deposits and sheet breaks caused by high levels of fillers and fines circulating at the wet end, and reduce furnish costs through better use of fillers or other additives. A good retention program can help the papermaker achieve desired sheet qualities by optimizing the retention of expensive additives such as titanium dioxide, wet and dry strength additives, and alkaline size. This paper reviews the mechanisms of retention, describes the types of chemicals that are effective retention aids and shows how these products can be applied to achieve optimum results. Introduction
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Retention on the Paper Machine Retention of chemicals – essentially a physical and colloidal chemistry problem At normal pH’s , and in the absence of chemical additives – particles exhibit a negative (anionic) charge For a higher affinity – many chemical additives manufactured with positive charges (cationic) % Single-Pass Retention Major factors that affect the retention – Table 15-2 Retention of non-fibrous additives occurs through the mechanisms of: filtration, chemical bonding, colloidal phenomena, and adsorption.
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Filtration is important for retaining large particles Retention aids often act through flocculation and entanglement - primarily the dispersive action of the headbox system must be adequate to avoid overfloculated stock that would be detrimental to sheet formation Retention on the Paper Machine cont.
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Wet End Chemistry Deals with: all interactions between furnish materials and the chemical/physical processes occurring at the wet end of the PM Major interactions (molecular and colloidal level) : surface charge, flocculation, coagulation, hydrolysis, time-dependent chemical reactions and microbiological activity To achieve effective retention, drainage, sheet formation, and sheet properties – necessary that the filler particles, fiber fines, size and starch be flocculated and/or adsorbed onto the large fibers with minimal flocculation between the large fibers themselves Three major groups are involved in wet-end chemistry: solids, colloids and solubles Most attention is focused on the solids and their retention
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Electrokinetics Zeta potential – a measurement used to characterize the
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Retention - Papermaking System First pass retention True...

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