Preparation, Polymerization Kinetics And Properties Of Acrylic Thickeners

Acrylic thickening agents were synthesized by emulsion polymerization, precipitation polymerization, inverse emulsion and inverse micro-suspension polymerization (ISP) processes respectively. Some outstanding issues that affect the stability, mechanism, kinetics of polymerization and properties of the synthesized products were studied systematically.It was found that the product of ISP process has very high thickening ability, more than 105mPa.s for 0.5% polymer solution in water.For (NH4)2S2O8 initiated ISP system consisted of AA (S), SPAN emulsifier and kerosine, it was found Rp [M]1.1[I]0.8[E], Eap=78.8kJ/mol for acrylic acid system and Rp [M]1.5[I]0.6[E], Eap=57.8-83.7kJ/mol for ammonium acrylate system The value of was negative when [E], the emulsifier concentration ,was low and became positive when [E] was high for both systems.The redox initiation system that formed from the trace reductive substances in the monomer and emulsifier with (NH4)2S2O8 is the major factor that caused much different results of Eap and relationship of Rp vs. [M], [7] and [E] in the experiments. The stability of the ISP process increased with the amount of water in the ISP system and the dissolving ability of monomer in the water.The thickening mechanism and factors that affect the anti-flushing ability (ATF) and anti-electrolytes ability (ATE) of thethickening agents were discussed based on the experimental results. It was found that for the giving constituent of polymer, the lower cross-linking degree the polymer possess, the better ATF, ATE and thickening ability (at low viscosity range) it has, but the lower the rheological index I0 it possess. In other hands, for the printing thickening agents, the larger Qm (max. water absorbing ability) and G (modulus at the same water absorbency of polymer) polymer possess, the higher ATF and ATE it has. The ATF and ATE of the acrylic acid polymers are therefore better than those of the acrylamide polymers and its copolymers.According to the gel modulus measurements, we found that the system at conventional viscosity range thickened with thickening agent is constituted of closely packed multi-face micro-particles of gel or concentrated suspension of spherical micro-particles of the gel. The viscosity of the system was mainly controlled by the Qm, the G and the adhesive force between the particle surfaces. The bigger the above three factors, the higher the viscosity of the system. The influence of G to 70 is due to the difference of the small deformation of the closely packed multi-face micro-particles when bearing shear force.