Synthesis of cationic polyacrylamide/silica nanocomposites from inverse emulsion polymerization and their flocculation property for papermaking

We describe the preparation and characteristics of cationic polyacrylamide/silica (CPAAm/ASNP) nanocomposites for papermaking. The nanocomposites were successfully prepared by in situ inverse emulsion copolymerizations of acrylamide and [2-(acryloyloxy)ethyl]-trimethylammonium chloride (AOTAC) in the presence of acryl-grafted silica nanoparticles (ASNPs). The ASNPs were synthesized through the reaction of fumed silica and (3-acryloxypropyl) trimethoxysilane (APTMS) in toluene, which yielded 30.7% grafting as measured by thermogravimetric analysis. They were then used in the copolymerization as a modifier with amounts of 1, 3, and 5 wt% of the total monomer. The chemical structure and properties were characterized by FT-IR, 1H NMR, capillary viscometry, and the charge demand. The flocculation and retention effects of the CPAAm/ASNP nanocomposites on the aqueous suspension models composed of filler and pulp were studied by flocculation tests and a dynamic drainage analyzer. The CPAAm/ASNP nanocomposites significantly improved the retention of the filler and pulp, which depended on the amount of ASNP particles. It was also found that ASNP particles bonded with the cationic copolymer play an important role in the retention system through a patching and bridging mechanism.