Superabsorbent polymer nanocomposites with surfactant- or acid-modified Ca-montmorillonite: synthesis and water absorbency

A series of clay polymer nanocomposites (CPN) were synthesized via the crosslinking polymerization of acrylamide and itaconic acid in the presence of calcium montmorillonite (Ca-Mt) clay mineral or modified Ca-Mt to form a superabsorbent polymer with improved swollen gel strength. Ca-Mt was modified by either organification with cetyltrimethylammonium bromide (CTAB) or hexadecanoic acid at surfactant levels of 0.25–4 times the cationic exchange capacity (CEC) of the Ca-Mt, or by acid-treatment with either hydrochloric acid or sulfuric acid at concentrations from 0.25 to 4 M. Fourier transform infrared spectroscopy and X-ray diffraction analyses revealed the successful modification of the Ca-Mt structure. The effects of Ca-Mt modification and its content on the equilibrium water absorbency and absorbency with or without an applied load, of the prepared CPN were characterized. The CPN with 1 % Ca-Mt modified with CTAB at 4 times the CEC (CPN/1%Ca-Mt-4CTAB) without load exhibited the highest water absorbency of 805 ± 6 g g^-1 in deionized water, 78 ± 3 g g^-1 in artificial reference urine (ARU) and 52 ± 2 g g^-1 in normal saline solution. Furthermore, it also exhibited the highest absorbency under load at 22.6 ± 0.4 and 19.7 ± 0.2 g g^-1 in ARU under a load of 1.93 and 4.83 kPa, respectively. The improved absorbency and absorbency under load could have resulted from the 1.52-fold increased basal layer spacing (d₀₀₁-value) of the CPN/1%Ca-Mt-4CTAB (2.41 nm) over that of CPN/1%Ca-Mt (1.59 nm), and the fine intercalated-dispersion of the Ca-Mt-CTAB within the CPN matrix, respectively.