Free Swelling Indices, Permeabilities, and Microstructures of Polymerized Bentonites

The swelling properties and microstructures of three polymerized bentonites (PBs), namely, 0.1 PB, 0.1 PB-AA, and 0.1 PB-AM, were investigated experimentally. All PBs were produced by the free radical polymerization method and had a polymer content of 10%. 0.1 PB-AA was produced with acrylic acid (AA), 0.1 PB-AM with acrylamide (AM), and 0.1 PB with both AA and AM (AA/AM = 0.5) as monomers. The free swelling index (FSI) test results show that for the three liquids tested, i.e., deionized water (DI-W), 0.6 M NaCl, and 0.03 M CaCl₂ solutions, 0.1 PB had higher swelling capacities than the other PBs and natural bentonite (UB). For 0.1 PB, finer polyacrylic acid (PAA) and polyacrylamide (PAM) composite polymer nets were formed around bentonite particles, and it is interpreted that the nets increased the liquid holding capacity and therefore, the swelling capacity of 0.1 PB. The polymer nets also lowered the permeabilities of 0.1 PB by clogging the liquid flow channels. It is suggested that for producing PBs, using two monomers (AA and AM) is better than using only one monomer (AA or AM).