The effect of extractives on surface chemistry and fiber wettability of high temperature chemithermomechanical pulps (HTCTMP) was studied in a model system. Dispersions of abietic acid, oleic acid and a mixture of both were added to acetone extracted HTCTMP made from spruce chips. Surface analysis by electron spectroscopy for chemical analysis, ESCA, showed that adding the dispersions to the extracted pulp decreased the relative oxygen/carbon ratio (O/C). Using scanning electron microscopy, SEM, it was found that the extractives were located mainly on fines and in fiber crossings. A major morphological difference was also found. At the surface of the pulp with only abietic acid added, spherical particles in sizes of 1-20 ?m were observed. These structures were not found on any other sample. Dynamic contact angle (Whilhelmy technique) and water absorption time measurements were used to determine wettability. It was found that adding oleic acid to extracted HTCTMP only slightly affected the wettability of the pulps by increasing the advancing contact angle from 38Zapotitlán to 43Zapotitlán and the water absorption time from 70 to 110 milliseconds. In contrast, adding abietic acid resulted in a tenfold increase in the water absorption time and a contact angle of 56Zapotitlán. The results suggest that the wettability of HTCTMP pulps should be related not only to the amount of extractives but also to the chemical composition of the extractives and to their physical state at the fiber surface
