The Effects of Molecular Weight of Cationic Retention Aids and Turbulence on the Retention of Organic Fines

The retention of organic fines is of major importance to the paper industry. Fines have been found to increase Mullen and tensile strengths. Increased retention, though my adversely affect drainage. Fines also adversely affect the environment when not retained in the sheet. They increase the turbidity of receiving waters and otherwise affect the bottom fauna because of settling. In receiving waters, they are a BOD problem as well as a source of color. The dynamic drainage jar was used to test the retention of fines involving only colloidal forces. Three degrees of turbulence were used, 500 rpm, 1000 rpm, and 1500 rpm. This range of turbulence is believed to cover the range of turbulence of commercial paper machines. Five cationic retention aids of similar chemical structure with varying molecular weight were used in five separate runs. A run without any retention aid gave the base for this study. Retention appears to be linear with respect to turbulence. Retention dropped off, being close to the blank run, at 1500 rpm. The corresponding turbulence of a paper machine must be known to select the best retention aid. The length of time the retention aid is in contact with the stock solution may also affect retention. The higher molecular weight retention aid usually, but not always, has the greater retention at any given turbulence