Mini-Encyclopedia of Papermaking Wet-End
Additives and Ingredients, their Composition, Functions, Strategies for Use
POLYETHYLENE IMINE (PEI)
Composition: The monomer is easy to describe. It consists of a three-membered ring. Two corners of the molecule consist of -CH2- linkages. The third corner is a secondary amine group, =NH. In the presence of a catalyst this monomer is converted into a highly branched polymer with about 25% primary amine groups, 50% secondary amine groups, and 25% tertiary amine groups. This product is sometimes called "pure polyethyleneimine" in order to differentiate it from certain copolymers of ethyleneimine and acrylamide. The latter mixture is copolymerized to produce so-called "modified PEI," that has a molecular mass up to about 2 million grams per mole. Each of these types of products is delivered to the mill in the form of viscous solutions. Solids contents are the range of about 10 to 50%, depending on molecular mass.
Function: Pure PEI is very effective for neutralization of excess anionic colloidal charge, especially under acidic and neutral pH conditions. Modified PEI copolymers having relatively high molecular mass can be effective for drainage and pitch control.
Strategies for Use: The branched nature and exceptionally high charge of pure PEI make it an excellent choice for treatment of highly anionic furnish, furnish that has a high electrical conductivity, or thick-stock furnish. The branched structure is believed to provide some resistance to penetration of the molecule into very small slit-like pores in the fiber cell wall. The colloidal charge, filtrate turbidity, and drainage characteristics of the furnish should be monitored when selecting or optimizing PEI dosage. The modified PEI copolymer is usually added relatively late in the thin-stock cycle in order to achieve a significant boost in first-pass retention and the rate of drainage. Neither additive is expected to be cost-effective in furnish having pH values in excess of about 8, since the amine groups rapidly lose their charged character above that point. Likewise, strongly varying pH values are expected to cause variations in the performance of PEI products.
Cautions: Read the MSDS and follow procedures recommended by the manufacturer.
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 .