SIZING - INVESTIGATION OF THE MECHANISM OF PAPER SIZING THROUGH A DESIZING APPROACH

A series of chemicals were employed to investigate the chemical proper ties of size-fiber bonds in different sizing systems. The bonding stre ngth has been proved to be dependent upon the type of bonding. In rosi n-alum size the size bond is indirect (through an aluminum coordinate complex), which is vulnerable to attack by acid, alkali and, especiall y, aluminum-complexing ligands, in which ligand substitutions take pla ce and determine the rate of ink penetration in the Hercules size test (HST). Alkyl ketene dimer (AKD) can react with cellulose to form dire ct beta-keto ester bonds. This covalent bond is strong enough to resis t the attack of acids or bases, and it is almost inert to these chemic als. However if a small amount of alum is used in AKD sizing under aci dic conditions, two types of size bonds are formed. Therefore, differe nt HST values will be observed depending on what ink is used. A hypoth esized mechanism regarding ligand substitution has been proposed and v erified indirectly. We suggest a surfactant, such as Tween(R) be used to accelerate testing of calcium carbonate filled sheets in place of f ormic acid which is clearly inappropriate with this use of the HST tes t. This simple desizing approach provides important information on siz ing mechanisms and will benefit new sizing agent research as well as r outine process control.