On the meaning of relative bonded area in mechanical pulps

摘要

Mechanical pulp R48 fibers and P200 fines were mixed and then wet pressed and press dried to various levels of bonding, in order to understand the effect of fines on the development of the specific bonded area, and relative bonded area. Using a linear relationship between scattering coefficient and tensile strength, the total unbonded specific area (S_o), specific bonded area (BA), and relative bonded area (RBA) were estimated, and the effect of fines content on these parameters was analyzed. TheS_o was a linear function of fines content (mass fraction) in the sheet. The specific bonded area (BA) was not a linear function of fines in the sheet. In heterogeneous mixed sheets, the bonded area was lower than would be expected from a linearly additive rule. This nonlinearity was more pronounced in heterogeneous sheets pressed at temperatures below the glass transition temperature of lignin (23℃), and approaches to a linearly additive relationship as pressure and temperature were increased. However, the specific bonded area is a linear function of fines content up to 80% fines. Relative bonded area (RBA) was also not linearly additive as a function of fines. However, RBA is a linear function of fines content when at least 27% fines are present in the sheet, above which most of the commercial mechanical pulps operate.