polymers
Review Alkenyl Succinic Anhydride: The Question of Covalent Bonding and Chemistry Considerations for Better Sizing—Review Yao Ntifafa 1, * ,† , LeboXu 1,† , Sara Bollinger 1,† , Yun Ji 2,† and Peter W. Hart 1,†
1 WestRock, 2742 Charles City Road, Richmond, VA 23231, USA; peter.hart@westrock.com (P.W.H.) 2 Department of Chemical Engineering, University of North Dakota, Grand Forks, ND 58202, USA * Correspondence: yao.ntifafa@westrock.com † These authors contributed equally to this work. Abstract: Alkenyl Succinic Anhydride (ASA) is a sizing agent used in papermaking to increase the water repellency of paper. Almost 60 years after the introduction of the chemical in papermaking, scientists still have differing views on how ASA interacts with cellulose. Several experiments were conducted to bring more clarity to the ASA sizing mechanism, especially on the contentious question of ASA-cellulose covalent bonding or the esterification reaction between ASA and cellulose during papermaking. Herein, research papers and patents, including experiments and results, from the 1960s to 2020 were reviewed. Our investigation revealed that the ester bond formation between ASA and cellulose is insignificant and is not a prerequisite for sizing effectiveness; the main ASA-related material found in sized paper is hydrolyzed ASA or both hydrolyzed ASA and ASA salt. In addition, ASA emulsion stability and ASA emulsion retention are important for sizing efficiency improvement.
Keywords: Alkenyl Succinic Anhydride (ASA); cellulose; paper sizing; covalent bonding; sizing agent stability; sizing agent retention
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Citation: Ntifafa, Y.; Xu, L.; Bollinger, S.; Ji, Y.; Hart, P.W. Alkenyl Succinic Anhydride: The Question of Covalent Bonding and Chemistry Considerations for Better Sizing—Review. Polymers 2023 , 15 , 2876. https://doi.org/10.3390/ polym15132876
1. Introduction The objective of paper sizing is to delay wetting by reducing the fiber absorbency. Alkenyl Succinic Anhydride (ASA) was introduced as a sizing agent in papermaking in 1963 by Wurzburg and Mazzarella [1]. ASA is an organic compound with cyclic dicarboxylic anhydride and a tetrafurandione (Figure 1). The chemical is light yellow color, oil-like, non-soluble in water, and liquid at room temperature [2,3]. emulsion particles are retained in the forming paper sheet at the wet end and forming section. Sizing development mostly happens in the dryer section, where the particles break down to release ASA in contact with the fi bers [9,10].
Academic Editor: Lili Wang
Received: 13 June 2023 Revised: 23 June 2023 Accepted: 25 June 2023 Published: 29 June 2023
Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
Figure 1. Scheme of ester bond formation between ASA and cellulose. Figure1. Scheme of ester bond formation between ASA and cellulose.
The proposed and widely cited ASA sizing mechanism is the formation of an ester or covalent bond between ASA molecules and fi bers. Figure 1 illustrates the ester bond for- mation between ASA and fi ber (cellulose). However, during the last 60 years of papermak- ing research, this popular mechanism has been questioned. Several scientists are still un- certain about the binding mechanism between ASA and cellulose. In addition, most sci- entists agree that ASA hydrolyzes in water during the papermaking process (Figure 2) [7,11–13]. Today, common internal sizing chemicals (e.g., alum/rosin, AKD [Alkyl ketene dimer] and ASA) are introduced into a pulp slurry at the wet end during the papermaking process. https://www.mdpi.com/journal/polymers
Polymers 2023 , 15 , 2876. https://doi.org/10.3390/polym15132876
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