Abstract
(A) The influence of wet pressing on the structure and properties of paper was studied for filler loaded papers. Handsheet prepared from hardwood kraft pulp and precipitated calcium carbonate as filler is subjected for the study. The results are as follows : (1) At the wet pressed sheets, the number of fibrous layers (Nf) at a given basis weight (excluding filler) increases with increasing filler content and approaches that of none pressed sheet.(2) In the wet pressed sheets, z-directional count and width, and area and area fraction of filler aggregates are smaller than those of none pressed sheets.(3) Although the area fraction of filler aggregates decreases with wet pressing, the result of pore size distribution from mercury intrusion technique show fine pore of filler aggregates remain constant.(4) The contribution due to fiber debonding (Sd) and the filler itself (Sp) to the total light scattering coefficient were caluculated, assuming that these contribution were independent and addible. The caluculation was bases on the light scattering coefficient measured before and after the removal of filler. It is apparent that Sd and Sp are larger for wet pressed sheets.(B) The influence of cellulosic fines on structure and properties of paper was studied for the sheets with varied filler loading level. Same pulp and filler as (A) were used. As cellulosic fines a micro-fibrillated cellulose (MFC) and a crystalline cellulose (Avicel) were used. The results are as follows : (1) In three sheets (sheets without cellulosic fines, with MFC, and with Avicel) Nf increase with increasing filler content. The incremental increase in Nf is largest for the sheets with MFC.(2) z-Directional count of filler aggregates is largest for sheets with MFC. However area fraction measured for three sheets is independent of z-directional count of filler aggregates.(3) Sheets with MFC show remarkably high Sd than others.(4) On the sheets with MFC, results indicate the contribution of the fibril detachment to the increase of optical efficiency of filler.
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