Films formation from latexes

There are limitations to the appHcabiHty of exterior latex house paints providing a small continuing market for oil or alkyd exterior house paints. Because film formation from latex paints occurs by coalescence, there is a temperature limit, below which the paint should not be appHed. This temperature can be varied by choice of the T of the latex polymer and the amount of coalesciag agent ia the formula. Ia the United States, most latex paints are formulated for appHcation at temperatures above 5—7°C. If painting must be done when the temperature is below 5—7°C, oil or alkyd paint is preferable. 

Even though the process of film formation from latexes has been thoroughly researched for conventional polymer latexes,there is still much work to be done on the dynamics of the process and the effects of the many chemical and physical factors that influence film formation and film properties for commercial latexes. Additionally, research into the factors affecting film formation and coating properties for the newer polymer colloids are required if they are to be fully developed. In hybrid systems, the effects of phase separation processes will be particularly important and are yet to be seriously studied. 

Fig. 26 Differences observed in the mechanism of film formation from latex and pseudolatex dispersions and from micronized coating materials.

Water is non-flammable and non-toxic. This is advantageous not only in the polymerization process, but particularly in applications. By film formation from latexes, several million tons of water are evaporated into the atmosphere annually. 

Latex Drying. Film formation from latexes poses a special problem in that one is not dealing with a continuum until a stage is reached at which most of the water has evaporated, the solid particles have undergone considerable distortion, and polymer begins to displace water at the interface. The residual stresses in this case are directed outward from the center of each particle in tiny domains. In the past, pigmentation and other means of achieving opacity exacerbated the problem (78). 

Dispersions of insoluble polymer particles form films by coalescence of the particles. The largest volume of such coatings use latexes as a binder. The lowest temperature at which coalescence occurs to form a continuous film is called its minimum film-formation temperature (MFFT). A major factor controlling MFFT is the Tg of the polymer particles. The MFFT of latex particles can be affected by water, which can act as a plasticizer (5). Most latex paints contain volatile plasticizers, coalescing solvents, to reduce MFFT. The mechanism of film formation from latexes has been extensively studied the papers in References 6-9 review various theories associated with it. Film formation occurs by three overlapping steps evaporation of water and water-soluble solvents that leads to a close packed... 

Equation (10.48) is particularly useful for studies of crack healing, welding time in molding operations, and film formation from latexes (21). Alternately, equations (10.47) and (10.48) can be cast in the form. 

In general, the two surfaces being healed are from different sources. Examples of this include molding operations, film formation from latexes, and adhesion. This section examines the micromechanisms involved in fracture and healing in polymeric materials. The effect of chemical bonding and adhesion between a polymer and a substrate surface is considered in Section 11.6. 

In the specific case of film formation from latexes the terminal stage is characterized by the removal of interstitial solvent and the deformation of the dispersed spheres into polyhedra (1). The continuum can be represented by a closed array of hexagons each of which has been deformed radially (2). In practice one formulates an emulsion so as to minimize the stresses accompanying this type of deformation otherwise film integrity would be lost. 

Figure 1. Film Formation From Latex Paint...

The technique of film formation from aqueous polymer dispersions is widely used in the field of paints ( dispersion paints , latex-paints ), coatings, and adhesives. The equipment is simple brush, scraper, rake, or roller. 

Film formation from a polymer latex upon evaporation of the dispersing medium. 

It is obvious, that correlation of anisotropy of structure and physicomechanical parameters of properties is most pronouced in the presence of anisodiametric morphological formations. Comparison of physicomechanical properties of films obtained from latex treated by vibrowave action and in solid-phase mixturing of the same polymers, where defining criteria are stress and deformations of a shift, allows to prove the efficiency of vibrowave influence. 

Surface tension forces are important in the process of film formation from latices. Brown (37) has developed equations that include surface tension as the prime force in the coalescence process. Use of solvent in the latex can change the modulus of the polymer, which is also a critical factor in regulation of coalescence temperature. 

The efect of crosslinking on the dynamic mechanical properties of polymers has been studied for many years. But one should note a clear distinction in the case of film formation from disposions of crosslinked latex particles. Each particle is a microgel. The crosslinks are confined to the particle itself without any additional ctosslinking across the particle boundaries [68]. Of course in some systems, like those formed from butadiene-containing latexes or from other latexes containing reactive functional groups, cross-boundary crosslinking can occur subsequent to film formation. 

Film formation from poljmer latexes is a complicated, multi-stage phenomenon and has been the subject of much theoretical and experimental attention. Many studies of the individual stages, utilising a variety of different techniques, have been published. The use of latex films to investigate... 

Eckersley S, Rudin A. Mechanism of film formation from polymer latexes. J Coat Technol 1990 62(780) 89. 

MOLECULAR WEIGHT EFFECT ON VOID CLOSURE AND PACKING AT DIFFERENT ANNEALING TEMPERATURES DURING FILM FORMATION FROM HARD LATEX PARTICLES... 

Journal of Applied Polymer Science 68, No.8, 23rd May 1998, p.1257-67 PHOTON TRANSMISSION TECHNIQUE FOR STUDYING FILM FORMATION FROM POLYSTYRENE LATEXES PREPARED BY DISPERSION POLYMERIZATION USING VARIOUS STERIC STABILIZERS Pekcan O Arda E Kesenci K Piskin E Istanbul,Technical University Trakya,University Hacettepe,University... 

Yoo et al. (77,78) confirmed this dependence using uniform polystyrene latex films. (See Section 5.4.4.) The process of film formation from a latex can be divided into three stages (a) evaporation of the water containing the latex, (b) coalescence and deformation of the latex particles, and (c) interdiffusion of the polymer chains into adjacent latex particles. The time for complete healing is given by the reptation time, T, = i l 37f D) where r is the end-to-end distance of the chain, D represents the diffusion coefficient, and Tif = 3.14. 

One feature which distinguishes latex film formation from other polymer sintering processes is that latex microspheres have polar groups at the particle surface. These groups are introduced during the emulsion polymerization process used to prepare the particles, and they serve to provide colloidal stability for the particle dispersion. When the dispersion... 

In the same year, Fulda and Tieke [75] reported on Langmuir films of monodisperse, 0.5-pm spherical polymer particles with hydrophobic polystyrene cores and hydrophilic shells containing polyacrylic acid or polyacrylamide. Measurement of ir-A curves and scanning electron microscopy (SEM) were used to determine the structure of the monolayers. In subsequent work, Fulda et al. [76] studied a variety of particles with different hydrophilic shells for their ability to form Langmuir films. Fulda and Tieke [77] investigated the influence of subphase conditions (pH, ionic strength) on monolayer formation of cationic and anionic particles as well as the structure of films made from bidisperse mixtures of anionic latex particles. 

Fig. 2.3.4 Film formation of a photoinitiated the lower surface (left) after a 90 min induction cross-linking latex coating as measured by period due to oxygen absorption. The profiles CARField. (a) The coating is exposed to air shown were recorded 10, 90, 100 and 110 min (evaporation) and light from above, (b) A sam- and 2, 3, 4, 5, 6 and 17 h after casting the layer, pie comprising a combination of only polymer (d)The full formulation film forms in the central and water dries from the upper surface (right) layers first. In this final time series, the profiles as shown by a time series of profiles, recorded shown were recorded after 10 min (dotted at 10, 20, 30, 40, 50, 60, 70, 100 and 120 min trace, T) attenuated) and then, from the top after casting the layer, (c) A combination of down, 30, 60 and 90 min and 2, 3, 6 and 17 h polymer and photoinitiator only cures from after casting the layer.

Acetic acid is an important industrial chemical. The reaction of acetic acid with hydroxyl-containing compounds, especially alcohols, results in the formation of acetate esters. The largest use of acetic acid is in the production ofvinyl acetate (Figure 1.1). Vinyl acetate can be produced through the reaction of acetylene and acetic acid. It is also produced from ethylene and acetic acid. Vinyl acetate is polymerized into polyvinyl acetate (PVA), which is used in the production of fibers, films, adhesives, and latex paints. 

The emulsifier provides sites for the particle nucleation and stabilizes growing or the final polymer particles. Even though conventional emulsifiers (anionic, cationic, and nonionic) are commonly used in emulsion polymerization, other non-conventional ones are also used they include reactive emulsifiers and amphiphilic macromonomers. Reactive emulsifiers and macromonomers, which are surface active emulsifiers with an unsaturated group, are chemically bound to the surface of polymer particles. This strongly reduces the critical amount of emulsifier needed for stabilization of polymer particles, desorption of emulsifier from particles, formation of distinct emulsifier domains during film formation, and water sensitivity of the latex film. 

The polarity and adsorption data discussed above reveal some interesting aspects of the surface chemistry of vinyl acrylic latex surfaces. It is quite likely that the polarity of the latex films, expecially of the two co-polymers, determined by contact angle measurements may not correspond exactly with their respective latex surfaces in the dispersed state due to reorientation of polymer chains during film formation. But the surfactant adsorption data shows clearly that the three latex surfaces in their dispersed state do exhibit varying polarity paralleling the trend found from contact angle measurements. The result also shows that the surface of the co-polymer latex surface is a mixture of vinyl acetate and acrylate units. This result is somewhat unexpected in a vinyl acrylic latex, prepared by a batch... 

To explain the fact that HSPAN swells in water to form gel sheets or macroparticles rather than disintegrating into a gel dispersion, we initially felt that chemical bonding must take place between individual particles of water-swollen gel as water evaporates. Although we cannot totally eliminate this possibility, the proposal of primary chemical bonding is not necessary to explain the behavior of these films and conglomerates. For example, Voyutskii (19) has reviewed the formation of films from vulcanized rubber latexes and concludes that film formation in these systems is observed because of interdiffusion of ends of individual macromolecules in adjacent latex particles. This diffusion can take place even though individual latex particles are crosslinked, 3-dimensional networks and the continuity of the resulting films, even when... 

---