High Solid Content Acrylic Copolymer Emulsion Rheological Behavior And Its Influencing Factors

An improved synthetic method for preparing high solid content polymer emulsions is studied in this paper, which is based on semi-continuous seeding emulsion polymerization. Using this method, a series of acrylate copolymer emulsions with 68%-72% (weight) solid content were prepared, where butyl acrylate (BA) and methyl methacrylate (MMA) were used as the main monomers, methyl acrylic acid (MAA) as functional monomer, ammonium persulfate (APS) as initiator, sodium dodecyl sulfate (SDS) and OP-10 as combined emulsifiers. The products have wide particle size distribution (PSD) and changeable viscosity between 100-2000 mPa·s.The rheological property and storage stability of the emulsion products were measured by rotary viscometer, while the emulsion particle morphology and PSD were examined using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and laser particle size analyzer (LPSA). The relationship between monomer ratio and polymer property was also investigated. The results show that the emulsion PSD may be the predominant fact for the rheological behavior when BA/MMA is less than 60/40 but other conditions remain unchanged. The wider the PSD and the worse the PSD symmetry, the lower the viscosity. The agglomeration of emulsion can be observed when BA/MMA is equal to 60/40, with increasing viscosity. The rheoligical behavior is beyond the PSD control. The degree of emulsion agglomeration may control the rheological behavior when BA/MMA is more than 60/40, heavier agglomerating can cause higher viscosity.The effects of synthetic parameters on emulsion properties are also concerned in detail in this paper, including the amount and ratio of combined emulsifiers and monomers, the amount of initiator, functional monomer, buffer, and reaction conditions such as temperature, stirring rate, monomer dropping rate, etc. The optimal synthetic technique is concluded as follows: The total amount of emulsifiers should be within 2．60%～3．90% of the total amount of monomers, the content of initiator within 0．18%～0．27%, the content of buffer (NH₄HCO₃) within 0．18%～0．27%,the dropping rate of monomers should be within 1．2～1．7g per minute, the reaction temperature is at 83±1℃.This study can be a guide to the production and application of high solids acrylate copolymer emulsions with wide PSD.