FORMATION OF PITCH-RELATED DEPOSIT IN A TMP-BASED SPECIALITY PAPER MILL

摘要

The formation of pitch-related deposit on process equipment, such as supercalender rolls can have a negative impact on both product quality and paper machine operation. In this paper, deposit samples on a supercalender stack were collected and analyzed for their chemical compositions, metal ion contents and thermal properties. The results showed that acetone soluble substances, which were considered as pitch or wood extractives, account for the majority of these deposit samples. The thermogravimetric analyzer (TGA) gave the results that, the mass losses due to heating in the temperature range of 50-200°C were less than 5%. The gas chromatography (GC) results showed similar chemistry for the samples before and after the TGA analysis, indicating that fatty and resin acids, rather than the volatile components, were the main components in the deposit samples and the migration of the softened acids may be responsible for the formation of the deposit. The extractive contents of various pulp and water samples were determined. The results showed that a large portion of wood extractives passed through the TMP mill and entered the paper mill with the pulp streams. Two control programs, dispersant/detackification versus fixation by PAC, were tested to decrease the extractives-related deposit formation on the supercalendering stack.