The flocculation of a dilute titanium dioxide (TiO2) suspension using homop
olymers and graft copolymers of acrylamide (AM) and diallyldimethylammonium
chloride (DADMAC) was investigated. The graft copolymers produced by gamma
-irradiating the mixtures of polyacrylamide (PAM) and polyDADMAC gave bette
r flocculating performance than homopolymers, reflecting the higher fractio
ns of large particles and bigger floc size. A kinetic delay in the onset of
flocculation was observed after adding the copolymers in the dose range 5-
30 [mg polymer]/[g TiO2]. Increasing dosage resulted in a longer delay peri
od. No significant flocculation was observed when the dose was above 50 [mg
polymer]/[g TiO2]. This delay was interpreted in terms of the re-conformat
ion of polymer chains driven by charge neutralization, between the positive
ly charged polymer branches and the negative particle surface. Depending on
the dosage used, the flocculation behavior of the graft copolymer has been
suggested to be equilibrium and non-equilibrium flocculation. It was also
observed that re-conformation is not affected by the ion strength of the me
dia, but a strong shear force significantly reduces the chain reconformatio
n time.