The pore structure of thermomechanical pulp (TMP) handsheets and newsprints containing TMP was investigated by mercury porosimetry and IGT Penetration Volumeter which measures oil absorption rate into sheets. TMP handsheets are more porous than chemical pulp handsheets, because of rigidity of TMP fibers. The pores of TMP handsheets formed by the rigid fiber network are usually filled with fine fractions. Total pore volume, defined as mercury penetration volume from 0.15 to 1000kg /cm2 pressure,

more »

... decreses with increasing fine content of sheets. However decrease of pore volume levels off at about 50% fine content. The variation in pore structure of TMP handsheets due to fine content, does not always coincide with the changes in oil absorption rate. The two-sidedness of pore structure of newsprints was obtained from sheet splitting method, and confirmed by the difference in oil absorption rate. Therefore, it seems to be necessary for the evaluation of printability and coating aptitude of paper to develop a reasonable method of measuring the pore distribution along Z-direction of sheet.