Effect of particle size and preflocculation of talc filler on sizing characteristics of paper

Five talc fillers of different particle size distribution (PSD) and platy shape were used in a laboratory papermaking study, along with two reference fillers viz., ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC). Sheets were prepared from all fillers using 0.5% (w/v) dosage of alkyl ketene dimer sizing chemical with the ash in paper ranging from 14 to 24%. The effect of PSD, shape and increasing filler content on sizing characteristics of paper measured by Cobb60 and contact angle was studied. The Cobb60 values increased and contact angles decreased on decreasing particle size of talc. The worst sizing performance was observed with calcium carbonate fillers; PCC was worse than GCC. Talc provided excellent hydrophobicity in paper due to its intrinsic hydrophobic nature. Contact angles of filled sheet with talc and calcium carbonate were in the range of 96 to 120o and 28 to 109o, respectively. Talc preflocculated with starch further improved the hydrophobicity of paper.