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UBC Theses and Dissertations

Interaction of fibres and additives in mechanical pulp suspensions Modgi, Shivamurthy


Precipitated calcium carbonate (PCC) is used in the production of high value communication papers from thermo-mechanical pulp (TMP) suspensions to improve optical properties like opacity and brightness. Addition of PCC also reduces the cost of papermaking. However, the increasing use of PCC in producing high value communication papers from bleached TMP has resulted in the requirement for using cationic starch as a strength enhancing agent. Starch addition compensates for the strength loss due to addition of PCC. This thesis examines the interactions of TMP fibres, PCC, starch and other additives used in mechanical grade papermaking. The thesis also illustrates the use of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDX) as a non-destructive technique to obtain the z-direction PCC filler distribution in paper. In TMP suspension loaded with PCC high degree of substitution (DS) tapioca starch was found to be better strength developing agent and retention aid compared to high DS potato starch. It was also found that Polyaluminum chloride (PAC) should be used as a coagulant when using potato starch and poly diallyldimethyl aluminum chloride (DADMAC) when using tapioca starch to get maximum benefits in terms of facilitating starch adsorption to the fibres. The effect of poly DADMAC and cationic polyacrylamide (CPAM) on total and fines/filler retention in the presence of starch was studied separately. It was found that the interaction of poly DADMAC and CPAM in the presence of starch does not help in total retention but the interaction is positive for fines/filler retention. Finally, drainage experiments showed that poly DADMAC and CPAM in the presence of tapioca starch increase drainage of TMP suspensions loaded with PCC. The z-direction filler distribution is important as it affects a number of paper properties. A total of seven industrial paper samples manufactured on the same paper machine (Horizontal Bel Baie-III) were used to illustrate the SEM/EDX technique to obtain the z-direction distribution of calcium. The calcium content was related to the filler content in the sheet. The technique for z-direction mineral distribution was further established by analyzing hand sheets prepared with a known amount of calcium carbonate. The method is expected to aid the efforts of papermakers to produce a sheet structure for various end uses if one establishes a relationship between z-direction filler distribution with paper machine operating parameters and additives used.

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