Investigating the mechanism of paper sizing through a desizing approach and a new approach to rosin sizing without mordants

A series of chemical penetrants are employed to investigate the chemical characteristics of size bonds in different sizing systems. The bonding strength has been proved to be determined by the type of bonding. In rosin-alum size the size bond is an indirect coordinate bond, which is vulnerable to the attack by acid, alkaline and especially by aluminum-affinited ligands, in which ligand substitutions take place and determine the rate of ink penetration in the Hercules Size Test (HST) test. Alkyl Ketene Dimer (AKD) can react with cellulose to form a direct {dollar}beta{dollar}-keto ester bond. This covalent bond is strong enough to resist the attack of acid or alkaline and is almost inert to these chemicals. However, if a small amount of alum is used in AKD sizing, there will be two types of size bond existed in the acid condition. Therefore, different HST values will be observed depending on what ink is used. A hypothesized mechanism about ligand substitution has been proposed and verified indirectly. This simple desizing approach provides important information on sizing mechanisms and will benefit new sizing agent research.; As a new approach to rosin soap sizing, it was found that dipping handsheets in the rosin soap solution and drying the sheets at elevated temperatures could induce effective sizing on different pulps. No mordant (alum) is needed in this process. The pH of the dipping solution seems to have little effect on the sizing result. Some desizing inks with strong effects on conventional rosin soap sized paper were found to have little desizing effect on these type of handsheets. These facts strongly indicate that covalent ester linkages could be the bonds that form between rosin molecules and fibers in this process. The dry schedule, heat temperature, and the concentration of dipping solution have shown various effects on the sizing results depending on the types of pulp used. Completely understanding the sizing mechanism and making this process commercial is well worth additional research work. This method, however, suffers from its speed of fugitiveness.