Polymer emulsions, freeze/thaw stability

Acrylics. There are two principal classes of acrylic sealants latex acrylics and solvent-release actylics. High molecular weight latex acrylic polymers are prepared by emulsion polymerization of alkyl esters of acrylic acid, The emulsion polymers are compounded inlo sealants by adding fillers, plasticizers, freeze-thaw stabilizers, thickeners, and adhesion promoters. As is true of the silicone lalex sealants, die acrylic latex sealants are easy to apply and clean with water. 

Specifications and Standards. Borax stability is an important property in adhesives, paper, and textile applications. Ollier emulsion properties tabulated by manufacturers include tolerance to specific solvents, surface tension, minimum film-forming temperature, dilution stability, freeze-thaw stability, percent soluble polymer, and molecular weight. 

Many polymerizations are performed by the emulsion technique to prepare a polymeric substance. The latex obtained is then coagulated, and the polymer is isolated. A paint latex, however, is used as such in the paint formulation, which leads to some special requirements for its stability, such as storage, mechanical, electrolyte, and freeze/thaw stability. 

The essential ingredients in an emulsion polymerization are the water, monomer, surfactant, and free-radical source. Other ingredients are frequently added for a variety of reasons. Stabilizers, which are usually water-soluble high polymers or carbohydrate gums, are employed to control latex viscosity and freeze-thaw stability of products that are used in the latex form. 

A typical gun-grade acrylic emulsion sealant (Table 15) contains about 18% acrylic polymer solids and 9-10% of a polymeric plasticizer. Sodium polymetaphosphate is a primary pigment dispersant aided by a water-soluble polyacrylate. A nonionic surfactant acts as a wetting agent and emulsifier. Often small amounts (up to 2%) of glycols are included for additional freeze-thaw stability. Mineral spirits (about 2%) retards skin formation. Acrylic emulsion caulks are used indoors as bathtub caulks, baseboard and trim seams, and outdoors for glazing, masonry joints, and roof and siding joints. 

Uses Used in oil-sol. emulsifiers and detergents dispersant as chem. intermediate for mfg. of lubricants, antlstats, and other surfactants plasticizer and antlstat for PVAc freeze/thaw stabilizer for latex emulsions corrosion inhibitor for small motor engine oils food-pkg. adhesives, paper, polymers Features Alkali and acid stability... 

The freeze/thaw (F/T) stability of a polymer emulsion serves as a macroscopic probe for investigating the properties of the average particle in a polymer emulsion. A review of the factors which contribute to this stability is included. A study of styrene-ethyl acrylate-methacrylic acid polymers shows the existence of a minimum in the plot of minimum weight percent acid required for F/T stability vs. the minimum film formation temperature (MFT) of the polymer. This is considered to be a function of both the amount of associated surfactant and the minimum acid content. Thus, both the type of surfactant and the copolymer ratio—i.e., MFT—play major roles. Chain transfer between radicals and polyether surfactant resulting in covalently bonded surfactant-polymer combinations is important in interpreting the results. 

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