Mechanism of paper sizing with ASA .2. Roles of reactive alkenyl succinic anhydride (ASA) in paper sizing

Alkenyl succinic anhydride (ASA) gives sizing features efficiently to papersheet by being added to pulp suspensions as cationic ASA emulsions. Although the reactive structure of ASA is necessary for paper sizing, the previous paper revealed that alkenyl succinic acid (ASAcid), the hydrolyzed form of ASA, is the predominant component present in ASA-sized papersheet [1]. Then, the roles of reactive ASA in paper sizing were studied in terms of hydrophobicity and coalescent and crystallizing behavior of ASA and ASAcid. The results obtained by sizing features of handsheets prepared with ASA-ASAcid-mixed emulsions, microscopic observations of the ASA ASAcid-mixed emulsions, X-ray diffraction patterns of cellulase-treated residue of handsheets and apparent contact angles of water drops on ASA and ASAcid showed that ASAcid is hydrophobic and has coalescent, coagulating and crystallizing behavior in aqueous media, compared with ASA. These differences in properties between ASA and ASAcid may lead to the following hypothesis of mechanisms of efficient paper sizing with reactive ASA emulsions; (a) the reactive structure of ASA is necessary for achieving sufficiently distributed slates of size components with smaller coagulating structures on hydrophilic pulp fibers in the papermaking process, (b) then more hydrophobic ASAcid molecules are formed without forming large coagulating structures probably during drying process of papermaking, maintaining the sufficiently distributed states, and (c) thus sizing features appear efficiently on ASA-sized papersheet by sufficiently distributed ASAcid molecules on pulp fibers.