Minimum film-formation temperature

Minimum film formation temperature (MFFT) is the minimum temperature needed for a binder to form a coherent film. This measurement is based on, although not identical to, the glass transition temperature (Tg) of the polymer. 

If a coating is applied below the MFFT, the water evaporates as described for Stage 1 (see Section 3.3). However, because the ambient temperature is below the MFFT, the particles are too hard to deform. Particles do not coalesce as the interstitial water evaporates in stage 2. A honeycomb structure, with Van der Waals bonding between Ae particles and polymer molecules diffused across particle boundaries, does not occur. 

The MFFT can be measured in the laboratory as the minimum temperature at which a cast latex film becomes clear. This is simply because if the coating has not formed a coherent film, it will contain many voids between polymer particles. These voids create internal surfaces within the film, which cause the opacity. 

Latexes must always be applied at a temperature above the MFFT. This is more difficult than it sounds, because the MFFT is a dynamic value, changing over time. In a two-component system, the MFFT begins increasing as soon as the components are mixed. Two-component waterborne paints must be applied and dried before the MFFT has increased enough to reach room temperature. When 

If a latex paint is dried below the MFFT, no particle deformation occurs. However, if the temperature of the dried (but not coalesced) latex is then raised to slightly above the MFFT, no coalescence as described in Section 3.3 should occur no receding air-water interface exists to generate capillary forces, and thus no particle deformation occurs. If the temperature is further raised, however, particle deformation eventually occurs. This is because some residual water is always left between the particles due to capillary condensation. At the higher temperature, these liquid bridges between the particles can exert enough force to deform the particles. 

---

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. 

Minimum Film Formation Temperature (MFT). Equipment described by Protzman and Brown (24) was built, calibrated, and used for all measurements. A series of 25% emulsions, adjusted to pH 9.5 with NH3, was used throughout unless otherwise indicated. 

Minimum Film Formation Temperature C >90 Ionic Charge Anionic pH as packed 9.8 Density Ibs/US gal 8.7 Brookfield Viscosity, cP 100 Performance Properties ... 

Film formation requires deformation of polymer particles and reptation of polymer chains, and is strongly temperature dependent. The temperature at which a film will form is commonly measured on a minimum film formation temperature (MFFT) bar. Latex is applied to a metal bar with a pre-assigned temperature gradient. The coating is allowed to dry and a number of transitions are noted. Below a certain temperature the film displays cracks. This is called the crack point MFFT. At a lower temperature there is a transition from cloudy to clear, as the pores between particles become much smaller than the wavelength of light. This is called the cloudy-clear MFFT. A further transition is the temperature at which the film is able... 

A series of latex copolymers were prepared using a typical emulsion polymerization recipe and procedure only the monomer composition was varied. The control composition (80/20 vinyl acetate/butyl acrylate) is similar to that used for interior latex paint. Table V lists the compositions and properties of the latexes. Percent solids, pH, and particle size are similar for all the latexes. Viscosity varies somewhat, but is within limits for this type of latex. The only unreacted monomer detected was the vinyl acetate. Thus, the incorporation of VEC into the emulsion polymerization via the monomer mixture did not affect the latex synthesis. The Tg and minimum film formation temperature (MFFT) of the latexes increase with increasing VEC content, which is expected based on the previous results. 

The addition of comonomers during polymerization enables a higher flexibility to be obtained compared to PVAc homopolymers. This causes also a lower glass transition temperature and a lower minimum film formation temperature. Possible comonomers are acrylic acid esters (butylacrylate, 2-ethylhexylacrylate), dialkylfumarates, ethylene, and others. 

Mechanical stability of dispersions was determined using a laboratory centrifuge with rotational speed of 3700 rpm. Particle size, particle size distribution and zeta potential of the dispersions was determined using Malvern Zeta Sizer 4 equipment. Minimum film formation temperature (MFFT) was measured using a Coesfeld apparatus. 

As a first step in the study of the molar mass dependence of film formation, the rate of deformation and the spreading of individually adsorbed latex particles is measured under dry conditions using atomic force microscopy. These data recorded at different temperatures and particles with different molecular weights are compared with glass transition temperatures and minimum film formation temperatures. The preliminary results indicate that the speed of the deformation process depends on both molar mass and temperature, while the... 

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... 

Temperature is important in achieving ideal latex film formation. Each latex resin has a specific minimum film-formation temperature (MEET) the proper coalescent solvent will provide a lower MEET (at least 40 T) for ideal film formation. The amount of coalescent solvent necessary will vary and depend on resin type and the solvent s coalescent efficiency. 

Actually, the threshold point for film formation is called the minimum film formation temperature, which is slightly lower than Tg. 

FIGURE 2.16 The effect of minimum film-formation temperature (MFFT) of a dispersion on its drying behaviour. Primal (Rohm Haas) dispersions were allowed to dry at room temperature, =21 °C, in a silicone rubber mould. An MFFT above room temperature results in incomplete coalescence of particles and poor film formation. The cracks and distortion that occur in the films result from the movement of water and shrinkage during drying, (a) AC-34 MFFT, 12 °C. (b) AC-73 MFFT, 37 °C. (c) B-85 MFFT, 90 °C. 

Balance of monomer VAC. Co-monomers BA, butyl acrylate 2-EHA, 2-etbyl hexyl acrylate Vcaprate, vinyl caprate. PlastJcizers DBF, dihutyl pbtbalate dibutyl maleate. Minimum film-formation temperature. 

---