Asymmetric Polymer Bridging Between Starch‐Coated Colloidal Particles and Pulp Fibres by Cationic Polyacrylamide

Abstract

charged and deposit readily on negatively charged pulp fibres, the calcium carbonate fillers require a retention aid, such as cPAM, which will affect the deposition of AKD on fibres as well. The deposition of AKD particles on fibres has been studied before. It is concluded in the literature that the improvement of AKD retention is not caused by direct adsorption of retention aids Internal sizing agents are commonly used as additives in papermaking to impart hydrophobicity to paper. They are commonly added in the form of colloidal particles, stabilized by cationic starch. As an example we studied the deposition of micron-sized Alkyl Ketene Dimer (AKD) particles on pulp fibres by cationic polyacrylamide (cPAM), a common flocculent. It was found that cPAM did not adsorb on AKD particles stabilized by cationic starch. Despite this inability to adsorb, cPAM was found to drastically improve the deposition of AKD particles on pulp fibres. This deposition was ascribed to asymmetric polymer bridging, a phenomenon observed by us before, while studying clay deposition on fibres by polyethylene oxide. In asymmetric polymer bridging between two types of particles, the bridging polymer first adsorbs on one type of particle, since it is unable to adsorb on the second type. Asymmetric polymer bridging occurs when the enthalpy gain on both surfaces exceeds the entropy loss. The kinetics of AKD deposition on fibres was found to agree with the predictions of the asymmetric bridging theory. In addition, an increase in bond strength with time was found, due to starch and cPAM reconfiguration. The increase in AKD retention by cPAM is also observed in experiments on a laboratory twin-wire sheet former. Asymmetric polymer bridging by cPAM between starch-coated AKD particles and fibres is compared with classical polymer bridging by cPAM between fibres and AKD particles coated by carboxymethylcellulose.Des agents d'encollage internes sont communément utilisés comme additifs dans la fabrication du papier pour transmettre l'hydrophobicité au papier. Ils sont communément ajoutés sous la forme de particules colloïdales, stabilisées par l'amidon cationique. À titre d'exemple, on a étudié la déposition de particules microniques de dimère de cétène d'alkyle (AKD) sur des fibres de pâte par le polyacrylamide cationique (cPAM), un floculant commun. On a trouvé que le cPAM ne s'adsorbait pas sur les particules d'AKD stabilisées par l'amidon cationique. Malgré cette incapacité à s'adsorber, on a trouvé que le cPAM améliorait considérablement la déposition des particules d'AKD sur les fibres de pâte. Cette déposition est imputée au pontage de polymères asymétriques, un phénomène que nous avons observé précédemment, lors de l'étude de la déposition d'argile sur les fibres par l'oxyde de polyéthylène. Dans le pontage de polymères asymétriques entre deux types de particules, le polymère de pontage s'adsorbe d'abord sur un type de particules, vu qu'il est incapable de s'adsorber sur le second type de particules. Le pontage de polymères asymétriques survi...

Cationic polyacrylamides increase the rate of liquefaction and hydrolysis of cornstarch

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Preparation of Water-Based Alkyl Ketene Dimer (AKD) Nanoparticles and Their Use in Superhydrophobic Treatments of Value-Added Teakwood Products

“…Alkyl ketene dimer (AKD) is a water-insoluble solid with a melting temperature ranging between 40 and 60 °C. It is a widely used neutral sizing chemical in the papermaking industry, as the compound decreases the rate of aqueous liquid penetration into papers. − The compound possesses one unsaturated β-lactone ring and 16–18 carbons of the alkyl groups. Its β-lactone ring can readily react with hydroxyl groups of cellulose to form a β-ketoester bond, enabling its hydrophobic tails to arrange into hydrophobic domains.…”