Efficacy of carbohydrate polymers in filler preflocculation for use in papermaking

Abstract

Preflocculation of inorganic fillers added to the paper could improve the inter-fiber bonding and enhance paper strength. Selection of a suitable flocculant and flocculating conditions for improved efficacy of the process is highly desired. The flocculating process conditions such as stirring speed, concentration of filler suspension and retention time were optimized through image analysis of the filler flocs when using cationic starch as flocculant. Two carbohydrate polymers, cationic and amphoteric starch, were used at 0.1%, 0.4% and 0.8% doses for the preflocculation of talc filler under optimized conditions. The colloidal charge and particle size distribution of the native and preflocculated fillers were analyzed. The native and preflocculated fillers were added to bleached mixed hardwood kraft pulp for preparing laboratory handsheets of 60g/m2 targeting varying ash levels of 15–24%. Various paper properties such as tensile, burst, tear indices, light scattering coefficient, Cobb60 and contact angle were analyzed for the native as well as preflocculated fillers. The median particle size of native filler was 6.0μm which on preflocculation using 0.8% dosage of cationic and amphoteric starch increased to 12.0μm and 14.8μm i.e. 100% and 146% increase in particle size, respectively. The preflocculated filler increased the physical and hydrophobic properties of the sheets as compared with the native filler. The increase in tensile index was about 20% when filler was preflocculated using 0.8% dose of amphoteric starch.