PERFORMANCE OF WET-END CATIONIC STARCHES IN MAINTAINING GOOD SIZING AT HIGH-CONDUCTIVITY LEVELS IN ALKALINE FINE PAPER

Cationic wet-end starches from different sources (including potato, waxy corn, dent corn, and wheat) and with various cationic charge levels (degree of substitution) were evaluated in the laboratory for pigment retention (CaCO3) and internal sizing efficiency (using AKD) as a function of the conductivity of the papermaking stock. In all cases, high stock conductivities had a detrimental effect on sizing and on pigment retention. In one case, a starch with a very high degree of cationicity could maintain high levels of sizing at conductivities as high as 5000 mu S/cm. The amphoteric waxy maize starch retained apr acceptable degree of sizing at intermediate conductivities. Dent corn and wheat starches, containing a larger amount of amylose, showed very poor pigment retention. Some of these findings led to actual mill applications.