The effects of peroxide bleaching on thermo-mechanical pulp self-sizing

Newsprint sizing is becoming more critical to the papermaker because of inc reased water application to the sheet during printing operations. This stud y used a fiber balance technique and Electron Spectroscopy for Chemical Ana lysis (ESCA) to examine the effects of peroxide bleaching on the self-sizin gs ability of TMP from two wood species commonly used in mechanical pulp ma nufacture, Western hemlock and Lodgepole pine. Under the conditions of this study, Western hemlock TMP did not self-size t o any significant effect. Lodgepole pine did size significantly when expose d to elevated temperatures, and in addition was more hydrophobic in its unb leached state than hemlock. When bleached with alkaline peroxide, neither s pecies was able to self-size to a large extent. Differences in inherent ext ractives content of these two species, along with the solubilizing effect o f alkaline conditions on extractives are speculated to be the cause of the observed behavior. A significant finding was that the presence of alkali al one, without peroxide, caused a loss of sizing. The significance of these f indings is to point out the water sensitivity of newsprint bleached under a lkaline peroxide conditions, and the inability of Western hemlock pulp to s elf-size, whether subjected to peroxide bleaching or not.