Carboxymethyl cellulose/alum modified precipitated calcium carbonate fillers: Preparation and their use in papermaking

Carboxymethyl cellulose and alum were used in the modification of precipitated calcium carbonate filler, and the use of modified fillers in papermaking was investigated. The alum dosage was found to be much critical to the effective precipitation and encapsulation of carboxymethyl cellulose on filler surfaces. When the dosages of carboxymethyl cellulose and alum were 4% and 12% (based on the dry weight of precipitated calcium carbonate), respectively, filler modification significantly improved filler retention by as much as 71.5%, and the brightness and opacity of the filled paper were strikingly enhanced; however, paper strength was practically unchanged, indicating improved affinity of filler particles to fibers in the aqueous papermaking wet end system. XPS analysis and SEM observations of the fillers confirmed the surface encapsulating effect of the modifiers on the filler. SEM images of the paper-sheets indicated that modified filler particles were more effectively adhered and bonded to the pulp fibers, in comparison to unmodified filler particles.