Date of Award
Bachelor of Science
Paper Science and Engineering
Poor size response and size reversion have been major concerns with the use of an alkyl ketene dimer (AKD) sizing system. Poor retention of calcium carbonate fillers and fiber fines are believed to be the cause of poor size response. A number of materials, including carbonate fillers, promoters and retention aids are believed to contribute to size reversion.
The focus of this study was to determine the effectiveness of retention aids in obtaining good size response. Size permanence was also studied The performance of the retention aides were studied by preparing handsheets at five different zeta potentials.
It was determined that when no retention aid was added to the system, size response was not dependent on zeta potential. It was dependent on the amount of polyethyleneimine (PEI) present in the system. Low sizing levels in the absence of PEI indicate poor retention of the size molecules.
When cationic polymers were added to the stock, sizing levels showed a dramatic increase. This increase was do to superior retention of the fiber fines. As zeta potential was increased to highly cationic, size levels dropped due to poor retention of the sizing chemical. Cationic polymer was not observed to contribute to size reversion.
Size response with the addition of an anionic polymer was highly dependent on the presence of a cationic fixative. When no PEI was present in the stock, the anionic polymer was ineffective. Small amounts of PEI provided cationic sites for the anionic polymer to bridge the fibers. Contrary to previous literature studies, the anionic polymer did not contribute to size reversion.
When PEI was added to the system, large increases in sizing levels were observed PEI promotes excellent retention of the fiber fines. Good fines retention will increase sizing levels. Not only did PEI promote the reaction between AKD and cellulose, no size reversion was observed when it was used.
Matthews, Jeremy, "Effect of Retention Aids on AKD Size Response and Permanence" (1995). Paper Engineering Senior Theses. 306.