Abstract:
The aim of this research is to study the effects of using cationic polyacrylamide (CPAM) as a retention aid and sodium polyacrylate (NaPA) as a dispersant (exhibiting dispersing ability) in order to enhance retention of 2 fillers, i.e. precipitated calcium carbonate (PCC) and nano calcium carbonate (NCC), in paper. The pulp was mixed commercial bleached kraft pulp, with a hardwood/softwood ratio of 70:30 by weight which was then beaten to 325 ± 25 mL CSF. The amount of CPAM and NaPA additions was individually optimized in order to get the total filler retention of 30%. The experimental results showed the addition of CPAM significantly offered filler retention, especially when using at 1.1 wt.% of dry pulp weight. Meanwhile, NaPA decreased filler retention particularly in NCC-containing suspension due to excessive deagglomeration. However, the dispersed NCC particles were generally too small to be entrapped in the sheet structure. It could be easily lost as white water during handsheet forming process. When the optimum amount of additives was determined, the effects of mixed PCC and NCC addition at five different ratios between 100:0 75:25 50:50 25:75 and 0:100 on paper properties compared with the controlled condition were observed. It was shown that PCC and NCC provided similar printability and optical properties. However, when the proportion of NCC was increased, the apparent density and smoothness of paper handsheets were decreased. During tensile and tear testing, it was found that there was some misting of filler particles in the handsheets with large amount of NCC.