Study On The Synthesis And Application Of Acrylic Hyper-dispersants

In recent years, with the development of coating technology, the demand for ultrafine ground calcium carbonate has been increased dramatically, and the volume fraction of GCC with sizes smaller than w (≤2 μm) was required to 98%, or even 99%, while it was 90%10 years ago. Therefore, the quality of grinding aids should be high. In the wet grinding process, two kinds of grinding aids are used at two different grinding stages, they are the front dispersant and the rear dispersant. Because of the more stringent requirements of the rear dispersant, further research is necessary to improve its performance.Two series of rear dispersants were developed in this paper to meet the requirement for ground calcium carbonate in an ultrafine wet grinding process. The two series were as follows. Solvent acrylic acid/2-acrylamido-2-methyl propane sulfonic acid copolymer hyper-dispersant [SV-P(AA/AMPS)] and solution acrylic acid/2-acrylamido-2-methyl propane sulfonic acid copolymer hyper-dispersant [SL-P(AA/AMPS)]. Then the products were characterized by FT-IR, NMR, GPC and TGA, and the most important factor, the grinding effects of the dispersants were also studied.The main discrimination between SV-P(AA/AMPS) and SL-P(AA/AMPS) was chemical reaction environment. The reaction environment of SV-P(AA/AMPS) was made up of isopropyl and water. According to the technology of free radical polymerization, acrylic acid and 2-acrylamido-2-methyl propane sulfonic acid as monomer, ammonium persulfate as initiator, the following optimal synthetic conditions were determined by single factor experiments:weight ratio of monomers 2-acrylamido-2-methyl propane sulphonic acid(AMPS)/acrylic acid(AA) 3:7, weight ratio of isopropanol/water 1.25, reaction temperature 80 ℃, reaction time 5.5 h, initiator dosage 4%(based on total monomers). The influence of SV-P(A A/AMPS) on the grinding of GCC was investigated by SEM and ATR-FTIR, and the adsorption of the polymer chain on the particle surface was found to prevent aggregation through an electrostatic effect, thus reducing the viscosity of the GCC slurry.The reaction environment of SL-P(AA/AMPS) was made up of water and sodium hydroxide. According to the technology of free radical polymerization, acrylic acid and 2-acrylamido-2-methyl propane sulfonic acid as monomer, ammonium persulfate as initiator, hypophosphite as chain transfer agent and reducing agent, the following optimal synthetic conditions were determined by single factor experiments:weight ratio of monomers acrylic acid(AA)/2-acrylamido-2-methyl propane sulphonic acid(AMPS) 4:1, hypophosphite dosage 9%(based on total monomers), reaction temperature 75℃, reaction time 5.5 h, initiator dosage 3% (based on total monomers).The molecular structure, molecular weight distribution and thermal stability of the two series of rear dispersants were characterized by FT-IR, NMR, GPC and TGA, respectively. The results indicated that the two series of rear dispersants included AA and AMPS organic functional groups and had a narrow molecular weight distribution, what’s more, the thermal stability of the two series of products was good enough for the grinding process.Compared with two kinds of commercial rear dispersants (MN-9 made in China, LX-7 made in Japan), the results showed the grinding effect of SV-P(AA/AMPS) was slightly better than that of LX-7, and much better than MN-9. The grinding effect of SL-P(AA/AMPS) was much better than MN-9, but slightly worse than LX-7. Although the synthesis process of SV-P(AA/AMPS) was relatively complex, the grinding effect was better; Although the grinding effect of SL-P(AA/AMPS) was not so good, the synthesis process was relatively simple. Therefore, the industrialization could be achieved step by step in the future based on the practical situation.