TO STUDY THE EFFECTS OF SURFACTANTS ON THE PROPERTIES OF POLY (METHYL METHACRYLATE CO-ACRYLIC ACID) PREPARED BY BATCH EMULSION POLYMERIZATION

Abstract

The growing demand for environmentally friendly and high-performance waterborne coatings has significantly increased the importance of emulsion polymerization in the coatings industry. Acrylic emulsions prepared through emulsion polymerization are extensively used due to their excellent film forming ability, durability, chemical resistance, and low volatile organic compound (VOC) emission. Among the various factors influencing the properties of acrylic emulsions, surfactants play a crucial role in determining particle formation, colloidal stability, rheological behavior, and final coating performance. In the present study, the effects of different surfactant systems on the properties of poly (methyl methacrylate-co-acrylic acid) [PMMA-co-PAA] prepared by batch emulsion polymerization were investigated. The emulsion polymerization was carried out using methyl methacrylate (MMA) and acrylic acid (AA) as monomers in an aqueous medium through free radical batch emulsion polymerization. Sodium dodecyl sulfate (SDS), cocamidopropyl betaine (CAPB), and amphoteric fluorosurfactant (AMF-1) were employed as surfactants to study their influence on emulsion characteristics and coating properties. APS was used as an initiator for the polymerization process. Several formulations of latex were prepared with different concentrations of surfactants while keeping the other variables constant. The latexes obtained through this process were characterized on the basis of monomer conversion, solid content, particle size, zeta potential, rheological behavior, and wettability properties. From the gravimetric determination, it was found that the prepared emulsions had high conversion rate of the monomers along with good solid content values. This suggested the efficient polymerization of the monomers in addition to adequate stabilization of the latex particles. The use of various types of surfactants played a significant role in the efficiency of the polymerization process as well as stability of emulsions. DLS studies indicated that surfactant type plays a very important role in determining particle size and colloidal stability of the prepared emulsions. It was found that the fluorsurfactant systems gave rise to relatively smaller particles size with narrower distribution than others. Rheology studies conducted such as viscosity testing, amplitude sweep, and frequency sweep tests have provided useful information regarding the viscoelastic nature of the emulsions. All tested latex systems showed a non-Newtonian shear-thinning behavior, which is favorable when it comes to use in coating applications. It was found that rheological properties of emulsions depended strongly on the type of surfactants used and the interactions between the particles within the emulsion system. Amplitude sweep testing showed the presence of the linear viscoelastic region in all samples studied and differences in structural stability of tested latex samples. Differences in elastic and viscous VI

behavior of the emulsions depending on the used surfactants could be observed from frequency sweeps data. Wettability behavior of coating films obtained from various surfactant systems was determined by measuring the water contact angles. Latex systems with fluorosurfactants were found to show much higher water contact angles than traditional surfactant systems, demonstrating the increased hydrophobicity and reduced surface energy of such emulsion systems. Increased water repellent property of fluorosurfactants can be explained by the presence of fluorinated portions in the molecular structure of fluorosurfactants, reducing the surface tension and making coating films more hydrophobic. In summary, the current study revealed that surfactant choice is an essential factor for influencing the physicochemical, rheological, and surface characteristics of PMMA-co-PAA emulsions using batch emulsion polymerization techniques. Of all the tested surfactants, amphoteric fluorosurfactants have exhibited excellent performance in respect to particle size, emulsion stabilization, rheology, and enhanced hydrophobicity. The results from this study will offer useful information in formulating advanced acrylic emulsions for eco-friendly coating purposes.