Date of Award

8-2001

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Advisor

Adriaan R.P. van Heiningen

Second Committee Member

Douglas W. Bousfield

Third Committee Member

Yang Xiang

Abstract

The water uptake behavior of fibers, especially those at the surface of paper, influences printing and coating operations. The dynamic water uptake behavior of the surface fibers may determine the initial consolidation of the coating at the surface and the penetration of coating into the paper, but clear studies on this topic have not been reported in the literature. Four different fiber types and seven different paper sheets were investigated in the present study. The three different fiber types were prepared by carboxymethylation of softwood kraft pulp thereby producing pulps with different water uptake values. The fiber length and water retention value (WRV) were measured for the different fibers and sheets. The contact angle, liquid absorption time, porosity, sheet formation and roughness of all sheets were determined. Kaolin clay coatings with and without a soluble polymer carboxymethylcellulose (CMC) were applied by a lab draw down and high speed laboratory coater. The roughness of the paper side of the coating was measured after dissolution of paper fibers. Carboxymethylaltion increases the water retention value and swellings of the fibers. It was found that the effect of the carboxymethylation on the fiber length is small. Carboxymethylated fiber sheets have a higher initial contact angle and faster absorption times than the original softwood kraft for non-swelling fluids. However, the most swellable carboxymethylated fiber handsheet had a slower absorption rate than that of the original fiber. This indicates that swelling of the carboxymethylated surface fibers may lead to closure of the surface pores. The commercial sheets have higher initial contact angle than original softwood and three different carboxymethylated sheets. The carboxymethylated sheet give the better formation based on the original softwood sheet. Carboxymethylation also increases the pore diameter and the pore volume of the original sheets by the formation of pinholes. Although carboxymethylated sheets have a larger pore volume and roughnesses than the original sheets, the roughness of the backside of the coating layer was smaller. This result indicates less coating penetration with swellable fibers. This trend is seen with the commercial samples. The mercury porosimetry test results show more coating penetration in to the treated fibers than the original softwood sheets, but paper volume changes during coating may explain this result. Based on the roughness results, it can be concluded that fiber swelling decreases the coating penetration. It was also shown that blade pressure increases the coating dive-in, and that CMC addition reduces the coating penetration in to the sheets.

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