Latex stability during

Typical enulsifiers used in emulsion polymerization of VC are anirmic emulsifiers like sodium alkyl sulfonates, sodium diaUcyl sulfosucdnates, fatty acid soaps and sodium ethoxy sulfates. Neutral emulsifiers like alltyl phenol ethoxylates and fatty acid ethoxylates are often added during after polymerization in Oder b> increase latex stability. The emulsifiers are not only chosen for control of the particle formation and latex stability during polymerization, but for a number of other reasons like mechanical stability, reactor wall build-up, plastisol formation, heat and colour stability and water resistance of the final product [1]. 

Paine et al. [99] tried different stabilizers [i.e., hydroxy propylcellulose, poly(N-vinylpyrollidone), and poly(acrylic acid)] in the dispersion polymerization of styrene initiated with AIBN in the ethanol medium. The direct observation of the stained thin sections of the particles by transmission electron microscopy showed the existence of stabilizer layer in 10-20 nm thickness on the surface of the polystyrene particles. When the polystyrene latexes were dissolved in dioxane and precipitated with methanol, new latex particles with a similar surface stabilizer morphology were obtained. These results supported the grafting mechanism of stabilization during dispersion polymerization of styrene in polar solvents. 

Grafting and Stabilizers. The degree of grafting of poly(vinyl acetate) (PVAc.) on poly(vinyl alcohol) (PVA) and other stabilizers during emulsion polymerization strongly affects latex properties such as viscosity, rheology, and polymer solubility. 

The failure of latex stability,and the resultant flocculation of the latex par tides, may cause the formation of coagulum that is recovered from the latex after polymerization as well as a buildup on the reactor surfaces. Moreover, the inherent instability of the latex may also cause flocculation during storage or transportation. 

One important requirement in replacing a conventional, nonreactive surfactant with a reactive one is that neither the molecular weight nor the particle size distribution of the latex may significantly change. Also, the Surfmer reactivity is important if the Surfmer is too reactive compared to the other monomers in the recipe, it will become partially buried inside the growing polymer particles. This will cause poor stability during polymerization and broadening of the particle size distribution. 

A prolific variety of composite latex particles appears in both the open and patent literatures. The subject has been reviewed (1,2) by several authors. Composite implies the presence of at least two dissimilar components either of which could, in principle, constitute the major component by volume. Some features of composite particles, which retain colloidal stability during preparation and subsequent storage, that is where the product is a dispersion in which flocculation, aggregative, and coalescence processes are largely absent so long as the continuous phase remains, will be described here. There are alternative and important processes for preparing composite particles which give flocculated particles readily separated from the liquid diluent phase and dried for use as powder. 

Similar results to those obtained here by the stability measurements have been reported by Roe and Brass (7.8) They studied polystyrene latex stabilized by potassium palmitate. The analysis supplied by these authors shows that the order of magnitude of the slope of the stability curves can be accounted for as an entropic effect of crowding of adsorbed molecules during an encounter between two particles. They pointed this out as a possible explanation as the amount of emulsifier adsorbed strongly affects the stability without altering the electrophoreti-cally derived double-layer potential. 

Latex stability. Effect of temperature. Usually no temperature control was imposed. The rise in temperature during the test was 1-2 °C. For purposes of temperature control the bottle containing the sample was provided with a water jacket through which water at specified temperature was circulated. The effect of temperature on the stability is described in Figure 9 To avoid confusion the experimental points are not indicated on the figure, except those obtained at room temperature. The temperature dependence was found to obey the Arrhenius equation. At any given emulsifier level a linear plot of the logarithm of the stability versus 1/T could be obtained. 

In addition, the polymeric surfactant, necessary as a stabilizer during the emulsion polymerization, becomes, after drying of the latex, a constituent of the final paint film. This opens therefore the possibility for controlling the mechanical and surface properties of the film. The main advantage of polymeric surfactants is their double role, as stabilizer of the latex and modifier, i.e. as a plasticizer of the final polymer product. 

UF has also been used to clean up polymerization kettle wash waters before disposal. The dilute latex can be concentrated from 0.5 to 25%, thus reducing the volume to be hauled away to /so of the original volume. In some cases, the waste latex is recycled for reformulation. Where there is a significant sewer tax, UF is an economical alternative even without recovery of the latex. The dilution of latex during polymerization kettle rinse-down may deplete the surfactant on the polymer particles or introduce multivalent ions, resulting in decreased latex stability. Adjustment of pH or addition of surfactant can prevent coagulation of the latex on the membrane. 

Ionic and nonionic surfactants to stabilized the latex dispersions during storage... 

A number of patents have emphasized acrylic elastomers as a method of rubber-toughening plastics.The latexes are crosslinked, in part, to impart mechanical stability during processing. Acrylic latexes have improved stability to light and heat over SBR or NBR, and thus offer an improvement to ABS materials. In general, saturated elastomers have proved superior to the diene types for outdoor use because of their superior weather resistance. 

It is recognized that commercial HA latex increases the mechanical stability during storage, but it is always accompanied by an increase in the gel content by as much as 60% after storage for a long period. NR contains both soft gel... 

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