Stability of latex products

In this case, it is the steric stabilization mechanism that protects the interactive particles from coagulation. In addition, the use of non-ionic t)rpes improves the stability of latex product against electrolytes, freeze-thaw cycles, water and high shear rates. As a result of them, in many emulsion pol3merization recipes (particularly in industry), mixtures of anionic and non-ionic emulsifiers have been widely used together in a s)mergistic manner to control the particle size and to impart enhanced colloidal stability [33-35]. The cationic and zwitterionic emulsifiers are used infrequently in emulsion pol3metizafion applications. 

The colloidal properties of latex products are of great importance from both academic and industrial points of view. Some representative charaeteristics include the particle size and particle size distribution, the particle surface charge density (or zeta potential), the particle surface area covered by one stabilizer molecule, the conformation of the hydrophilic polymer physically adsorbed or chemically couplet onto the particle surface, the type and concentration of functional groups on the particle surface, the particle morphology, the optical and rheological properties and the colloidal stability. 

It should be noted that the probability for the continuous particle nucleation throughout the emulsion polymerization increases with increasing surfactant concentration. For constant monomer weight, the higher the surfactant concentration, the smaller the latex particles produced in the emulsion polymerization system. In addition, the longer the particle nucleation period, the broader the residence time distribution of particle nuclei within the reactor (i.e., the broader the resultant particle size distribution). These rules of thumb, based on a large number of fundamental studies on nucleation and growth of particle nuclei, have been widely used in industry to effectively use surfactant to stabilize various latex products with balanced performance properties. 

Soap. A critical ingredient for emulsion polymerization is the soap (qv), which performs a number of key roles, including production of oil (monomer) in water emulsion, provision of the loci for polymerization (micelle), stabilization of the latex particle, and impartation of characteristics to the finished polymer. 

In suspension processes the fate of the continuous liquid phase and the associated control of the stabilisation and destabilisation of the system are the most important considerations. Many polymers occur in latex form, i.e. as polymer particles of diameter of the order of 1 p.m suspended in a liquid, usually aqueous, medium. Such latices are widely used to produce latex foams, elastic thread, dipped latex rubber goods, emulsion paints and paper additives. In the manufacture and use of such products it is important that premature destabilisation of the latex does not occur but that such destabilisation occurs in a controlled and appropriate manner at the relevant stage in processing. Such control of stability is based on the general precepts of colloid science. As with products from solvent processes diffusion distances for the liquid phase must be kept short furthermore, care has to be taken that the drying rates are not such that a skin of very low permeability is formed whilst there remains undesirable liquid in the mass of the polymer. For most applications it is desirable that destabilisation leads to a coherent film (or spongy mass in the case of foams) of polymers. To achieve this the of the latex compound should not be above ambient temperature so that at such temperatures intermolecular diffusion of the polymer molecules can occur. 

Salts of a-sulfo fatty acid esters can work as emulsifying agents for the preparation of asphalt emulsions and asphalt-latex emulsions. The ester sulfonates improve the storage stability of the emulsions [101,102]. In the manufacture of lightweight gypsum products air bubbles have to be mixed into the slurries. The use of salts of sulfonated C10 l8 fatty acid alkyl esters as foaming agents produces uniformly distributed fine bubbles [103]. Salts of C10 16 fatty acid alkyl ester sulfonates can also be added to cement mixtures to prevent slump loss of the mixtures [104]. 

Acrylic resins are generally well characterized by Py-GC/MS without the need for any derivatization reaction. However, in waterborne polymer dispersions it is common to have minor amounts of acrylic and/or methacrylic acid monomers added in the copolymerization to help the stability of the final latex. These monomers can also appear in the pyrolysis products, and it has been shown that with on-line derivatization they can be more efficiently revealed [85]. 

Polychloroprene latex adhesives, 1 533-534 Polychloroprene latexes, 19 854-861 applications for, 19 857, 859-861 compounding, 19 857-859 global product line of, 19 855 stabilization of, 19 855-857 Polychloroprene polymers branching parameters of, 19 839 commercial, 19 851-852 crystallization of, 19 843-844 cure site for, 19 837... 

For some applications, eg, foam rubber, high solids (>60%) latices are required. In the direct process, the polymerization conditions are adjusted to favor the production of relatively large average particle-size latices by lowering the initial emulsifier and electrolyte concentration and the water level in the recipe, and by controlling the initiation step to produce fewer particles. Emulsifier and electrolyte are added in increments as the polymerization progresses to control latex stability. A latex of - 35-40 wt% solids is obtained and concentrated by evaporation to 60—65 wt % solids. 

Typical emulsion polymerization recipes involve a large variety of ingredients. Therefore, the possibilities of variations are many. Among the variables to be considered are the nature of the monomer or monomers, the nature and concentration of surfactants, the nature of the initiating system, protective colloids and other stabilizing systems, cosolvents, chain-tranfer agents, buffer systems, short stops, and other additives for the modification of latex properties to achieve the desired end properties of the product. 

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