Chemoenzymatic modifications of charge in chemithermomechanical wood pulp

Chemithermomechanical pulp (CTMP) of Norway spruce has been treated by alkali, pectinesterase and pectinase, in order to modify the content of methyl esters of pectin and the total pectin content in the pulp, and to study the effect of pectin on the CTMP fiber charge. De-esterification of unbleached CTMP, by sodium hydroxide and pectinesterase, resulted in an increase in both surface and total negative fiber charge as shown by conductometric and polyelectrolyte titrations. The total fiber charge increased more by alkali treatments (+26%). The pectinesterase activity was restricted to the pulp-fiber surfaces, thereby inducing a surface specific negative charge modification (+ 19%). The effect of the treatments on the degree of methyl-esterification of galacturonic carboxyl groups in surface localized pectin was corroborated by a colorimetric bioassay specific for acidic galacturonan. Pectinase treatments reduced surface charge (- 14%) and total charge (-9%) of unbleached pectinesterase pre-treated CTMP, and the surface charge (-29%) of alkali pre-treated unbleached CTMP. The effects of chemoenzymatic modifications of pectin on CTMP regarding strength properties of paper sheets were also discussed