Determination of suitable level of calcium carbonate to the kraft pulp treated by nanosilica

The main goal of this study was to explore the level of adding precipitated calcium carbonate (PCC) filler to the kraft fibers which treated by Layer-by-Layer (LbL) method. The kraft fibers treated by three layers of cationic starch-nanosilica-cationic. Then, the standard handsheets (60±3 g/m²) were made from untreated and treated fibers. The results showed that by using 3-layers treating of kraft fibers, tensile index was improved from 23.96 N.m/g to 38.50 N.m/g. In addition, the burst and tear index was increased from 1.46 kPa.m²/g to 3.58 kPa.m²/g and 9.14 mN.m²/g to 15.99 mN.m²/g respectively. Also, the SEM images illustrated the fibers surface gelation due to the cationic starch absorption and an improvement of bonded area in fibers network. Furthermore, the three levels of PCC filler (5, 10, and 15%) were added to the 3-layer treated kraft pulp and strengths loss was evaluated and compared to the untreated pulp. Tensile, burst, and tear index were measured and they were 24.01 N.m/g, 1.20 kPa.m²/g and 9.49 mN.m²/g respectively by adding 10% of filler. According to the ANOVA test, the results revealed that it is possible to add 10% of PCC filler to the kraft pulp which treated with LbL method. Furthermore, SEM images indicated the retention as well as relatively uniform distribution of the PCC filler in the fibers network particularly in the area which impregnated with cationic starch.