Minimum Film Formation Temperature Research Articles

Starve fed emulsion copolymerization of vinyl acetate and 1‐hexene at ambient pressure

A novel emulsion copolymer of vinyl acetate (VAc) and 1‐hexene was synthesized at ambient pressure. The feeding technique, initiation system and reaction time of the copolymerization were optimized based on molecular characteristics such as the weight contribution of 1‐hexene in the copolymer chains and glass transition temperature (Tg) as well as on bulk properties like minimum film‐formation temperature (MFFT) and solid content. According to nuclear magnetic resonance spectroscopy and differential scanning calorimetry results, the combination of starve feeding and redox initiation, within a reaction time of 4 h, effectively led to the copolymerization at ambient pressure between highly reactive polar VAc monomers and non‐polar 1‐hexene monomers of low reactivity. The copolymer showed a lower Tg and MFFT, and a reasonable solid content compared to the poly(vinyl acetate) (PVAc) homopolymer. The consumption rate, hydrolysis of acetate groups and chain transfer reactions during the polymerization were followed using infrared spectroscopy. Based on the results, the undesirable reactions between the VAc blocks were hindered by the neighbouring 1‐hexene molecules. Tensile testing revealed an improvement in the toughness and elongation at break of VAc–1‐hexene films compared to PVAc films. © 2014 Society of Chemical Industry

Semi-continuous emulsion copolymerization of vinyl acetate and butyl acrylate in presence of AMPS

The emulsifier-free emulsion polymerization of vinyl acetate (VAc) and butyl acrylate (BA) in the presence of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) was carried out by a semi-continuous process. AMPS was a reactive surfactant in the aqueous emulsion, due to its amphiphilic structure and the unsaturated double bonds. Potassium persulfate (KPS) was used as initiator. The following factors were mainly examined: quantity of AMPS, BA and KPS concentrations, which could significantly affect the particle size and its distribution, conversion, gel content, minimum film-forming temperature, etc. The particle size and its distribution were characterized by dynamic laser particle size analyzer, and morphology of the latex particles was characterized by transmission electron microscopy (TEM). Fourier transform infrared spectroscopy was used to characterize chemical structure of copolymers. The results indicated that AMPS was successfully reacted onto the resulted copolymer of vinyl acetate and butyl acrylate. A hydrophilic sulfonic acid group in the molecular structure of AMPS tended to be distributed in particles surface after polymerization. As a result, an electrostatic repulsion between the particles was produced in order to maintain stability of the system. Thermogravimetric analysis curves suggested that as BA content increased, thermal stability of the polymer increased accordingly. The conversion-time plots with varying AMPS and initiator contents were obtained, which illustrated that the initiator concentration could greatly influence the polymerization rate and the final conversion. The TEM micrographs of the final emulsifier-free latex particles for P(VAc/BA/AMPS) system revealed small particle size in monodisperse polymer latex. The particles of the latex were measured as about 150 nm.

Polyvinyl acetate-based film coatings

Polyvinyl acetate-based colloidal aqueous polymer dispersion Kollicoat(®) SR 30 D results in coatings characterized by moderate swelling behaviour, lipophilicity, pH-independent permeability for actives and high flexibility to withstand mechanical stress and is therefore used for controlled release coating. The colloidal aqueous polymer dispersion of Kollicoat(®) SR 30 D can be easily processed due to an optimal low minimum film forming temperature (MFT) of 18 °C without plasticizer addition and a thermal after-treatment (curing) of coated pellets. The drug release from Kollicoat(®) SR 30 D coated pellets was almost pH independent. Drug release could be easily adjusted by coating level or addition of soluble pore forming polymers. Physically stable Kollicoat(®) SR 30 D dispersions were obtained with the water-soluble polymers Kollidon(®) 30 and Kollicoat(®) IR up to 50% w/w. The addition of only 10% w/w triethyl citrate as plasticizer improved the flexibility of the films significantly and allowed compaction of the pellets. The drug release was almost independent of the compression force and the pellet content of the tablets. The inclusion of various tableting excipients slightly affected the drug release, primarily because of a different disintegration rate of the tablets. A combination of Kollicoat(®) SR 30 D and Kollicoat(®) IR with higher coating levels>10 mg/cm(2) is a relatively new alternative to OROS system which does not require drilling.

Correlation between water permeability of latex-modified concrete (LMC) and water diffusion coefficient of latex film

Cement-based materials are generally known as weak materials in flexure and tension in comparison with compression. Polymers are used in cement-based materials to improve their flexural and tensile behaviors. The composite is called as polymer-modified concrete/mortar. Furthermore, polymers decrease permeability of water into cementitious matrices. Polymers are usually used as admixtures in concretes in form of latexes. Latexes are water-based polymers, which are consistent with water-based concrete matrices. On this basis, these kinds of products are called latex-modified concretes (LMCs). However, it has been found that chemical composition, particle size distribution, molecular weight, physical/mechanical properties of latexes affect performance of modified concretes. In this investigation, six latexes in three categories (acrylic, SBR and polyvinyl acetate) were used as concrete admixtures. They were characterized for chemical composition (by FTIR analysis), minimum film formation temperature, pH, glass transition temperature (T g), particle size and particle size distribution to evaluate the effect of each property on LMC performance. Due to the formation of latex film in the microcracks and pores of concrete microstructure, it was suggested that diffusion of water into films controls permeability of whole concrete structures. On this basis, the diffusion coefficient of the latex films subjected to water was measured using a new method (continuous FTIR analysis). Capillary water absorption test was performed on concrete specimens to verify validity of the suggestion. It was found that there is a correlation between capillary water absorption of LMCs and water diffusion coefficient of latex films.

Improvement of film properties of vinyl acetate based emulsion polymers by using different types of maleic acid diesters

Two types of maleic acid diesters, dibutyl maleate (DBM) and dioctyl maleate (DOM) were used as comonomers in semicontinuous emulsion copolymerization of vinyl acetate (VAc) in order to improve the film properties of poly(vinyl acetate), PVAc emulsion polymer. The effects of the comonomer type and comonomer ratio on minimum film forming temperature (MFFT), glass transition temperature (Tg), polymer structure, molecular weights, water contact angle and water resistance of PVAc latex films were examined. It was found that MFFT and Tg of the PVAc emulsion polymer decreased by the presence of the maleic acid disters in copolymer composition. This decrease was more affected by the increasing content and alkyl chain length of the comonomers. The molecular weights of the emulsion polymers were also affected by the comonomers and their ratios. Moreover, hydrophobicity and water resistance of the PVAc latex films were increased by using DBM and DOM as comonomer.

Film Formation of a Non-Ionic Ethylene-Vinyl Acetate Latex Dispersion in Cement Pore Solution

Environmental scanning electron microscopy (ESEM) and complementary methods were employed to study the time dependent film formation of a non-ionic latex dispersion in water @ pH 12.8 and cement pore solution. A commercial liquid ethylene-vinyl acetate latex dispersion stabilized with PVOH possessing a minimum film forming temperature (MFFT) of 3 °C and a Tg of 19 °C was employed in the study. Prior to ESEM imaging the latex dispersion was stored at room temperature and then transferred into the ESEM instrument for imaging. Subsequently, micrographs monitoring its film forming behaviour are obtained. The analysis revealed that upon removal of water, film formation occurs as a result of particle packing, particle deformation and finally particle coalescence. In synthetic cement pore solution film formation occurs faster than in water and is complete within one day. This acceleration can be ascribed to the presence of PVOH on the surface of the latex particles. In water at neutral pH, PVOH forms a shell around the latex particle and hinders the interdiffusion of the macromolecules while in cement pore solution, PVOH precipitates due to high pH and high concentration of cations. This way the latex particles can coalesce faster into a polymer film.

Effect of Ca<sup>2+</sup> Ions on the Film Formation of an Anionic Styrene/n-Butylacrylate Latexpolymer in Cement Pore Solution

Several methods were employed to study the time dependent film formation of a self synthesized anionic latex dispersion in water and cement pore solution. First, a model carboxylated styrene/n-butyl acrylate latex dispersion possessing a minimum film forming temperature (MFFT) of 18 °C and a glass transition temperature (Tg) of 30 °C was synthesized via emulsion polymerization. Next, its film forming behaviour was studied at 40 °C, using an ESEM instrument. The analysis revealed that upon removal of water, film formation occurs as a result of particle packing, particle deformation and finally particle coalescence. Film formation is significantly hindered in synthetic cement pore solution. This effect can be ascribed to adsorption of Ca2+ ions onto the surface of the anionic latex particles and to interfacial secondary phases. This layer of adsorbed Ca2+ ions hinders interdiffusion of the macromolecules and subsequent film formation of the latex polymer.

Emulsion Copolymerization of Vegetable Oil Macromonomers Possessing both Acrylic and Allylic Functionalities

AbstractSummary: A soybean oil‐based vegetable oil macromonomer (VOMM) was incorporated as a comonomer into an all‐acrylic copolymer via semi‐continuous emulsion polymerization. Structurally, VOMMs are comprised of long hydrocarbon fatty acid moieties with allylic double bonds which enable auto‐oxidative crosslinking at ambient temperature. VOMMs facilitate low temperature film formation and the fatty acid chains tethered to the polymer backbone auto‐oxidize upon film formation to yield crosslinked films. Latexes with varying VOMM levels were synthesized to elucidate the effect of VOMMs on the pre‐cure and post‐cure glass transition temperature (Tg) and minimum film formation temperature (MFT). Thermoplastic control latexes (without VOMM) were also synthesized via copolymerization of butyl acrylate and methyl methacrylate. This paper details the characterization performed to validate and quantify the VOMM allylic unsaturation retention before, during, and after polymerization, and to quantify and confirm the increase in Tg resulting from auto‐oxidative crosslinking via solid state 13C nuclear magnetic resonance spectroscopy and differential scanning calorimetry.

Physicochemical properties of dirt-resistant cool white coatings for building energy efficiency

The physicochemical properties of two newly developed dirt-resistant cool white coatings were systematically measured in light of the relevant standard testing methods, and the influences of dirt accumulation and washing on the long-term cooling performance of cool coatings were investigated and discussed. Both cool white coatings owe their outstanding physicochemical properties to the optimized formulations, high glass transition temperature and minimum film formation temperature of selected aqueous self-curing acrylic emulsions. The high solid content was also influential. Dirt accumulation leads to a decline in the cooling performance of coatings, which may be almost fully restored by simply washing the coatings with a mild soap solution.

Synthesis and Characterization of Allyl Fatty Acid Derivatives as Reactive Coalescing Agents for Latexes

AbstractThis work evaluated the use of allyl fatty acid esters derived from vegetable oil (palmitic acid, soybean and sunflower oils) as reactive coalescing agents in a waterborne latex system. Allyl fatty acid derivatives (AFAD) from vegetable oils were synthesized by two different processes. The synthesis was monitored by IR‐spectroscopy and the final product characterized by FT‐IR, GC–MS, 1H and 13C NMR. The presence of conjugated double bonds in the aliphatic chain was confirmed, which is a determinant for the proposed autoxidative latexes drying mechanism. Each of the AFAD were subsequently added to a standard acrylic emulsion, in order to study its potential as reactive coalescing agent. The minimum film‐forming temperature (MFT), glass transition temperature (Tg), drying time and rubbing resistance to solvents were evaluated. The results showed that, when added to water‐borne acrylic resins, an AFAD acts as a non‐volatile plasticizer capable of autoxidative crosslinking with itself.

Drying and cracking of soft latex coatings

The minimum film formation temperature (MFFT) is the minimum drying temperature needed for a latex coating to coalesce into an optically clear, dense crack-free film. To better understand the interplay of forces near this critical temperature, cryogenic scanning electron microscopy (cryoSEM) was used to track the latex particle deformation and water migration in coatings dried at temperatures just above and below the MFFT. Although the latex particles completely coalesced at both temperatures by the end of the drying process, it was discovered that particle deformation during the early drying stages was drastically different. Below the MFFT, cracks initiated just as menisci began to recede into the packing of consolidated particles, whereas above the MFFT, partial particle deformation occurred before menisci entered the coating and cracks were not observed. The spacing between cracks measured in coatings dried at varying temperatures decreased with decreasing drying temperature near the MFFT, whereas it was independent of temperature below a critical temperature. Finally, the addition of small amounts of silica aggregates was found to lessen the cracking of latex coatings near the MFFT without adversely affecting their optical clarity.

Multiphase coatings from complex radiation curable polyurethane dispersions

The waterborne nature of radiation curable polyurethane dispersions largely respond to the current environmental concerns and do not require any additional coalescent since the film formation (drying) and hardening (photo-curing) take place in distinct steps. It is possible to design aqueous dispersions with distinct polymer particle populations resulting in micro-structured coatings with optimized properties over a wide range of curing conditions. Mixed dispersions based on hard and soft acrylated polyurethane particles were used as model systems for the present study. The minimum film formation temperature has been investigated as a function of the hard:soft polymer ratio. The elastic modulus of the dry coatings shows a reinforcing effect consistent with the inclusion of hard domains in a soft continuous matrix. However, the level of reinforcement is not properly predicted by the usual mechanical models and it is qualitatively accounted for by assuming a composition gradient (interphase) between the hard domains and the matrix. The multiple-phase structure was clearly established by Atomic Force Microscopy in agreement with thermal analysis data. Furthermore the local nanoscale mechanical properties were mapped using a new imaging mode based on real-time force–distance curve analysis. Finally, the coatings prepared using this multiple-phase pattern present a clear benefit over conventional homogeneous coatings by offering an improved balance of chemical and mechanical resistance in pigmented systems applied on melamine-coated MDF panels.

Preferred partitioning: the influence of coalescents on the build-up of mechanical properties in acrylic core–shell particles (I)

The partitioning of three coalescents of different polarity in different phases of multiphase acrylic particles was studied to provide a rationale for obtaining the desired performance of binders for wood coatings in terms of the ideal balance between hardness development, blocking resistance, and blushing resistance. Minimum film formation temperature- and aqueous differential scanning calorimetry-measurements on the hard phase polymer by itself showed the different extents to which both hydroplasticization and plasticization by the coalescent occur. Dynamic mechanical thermal analysis was subsequently used to visualize wet-T g effects of three different coalescents in the hard and soft polymer phase of these multiphase acrylic particles. The results have important consequences for the formulation of such binders in applications for exterior wood coatings and coatings in general.

Temperature and Relative Humidity Dependency of Film Formation of Polymeric Latex Dispersions

Thermogravimetric analysis and a synchrotron small-angle X-ray scattering technique were employed to characterize the structural evolution of a polymeric latex dispersion during the first three stages of film formation at different temperatures and relative humidities. Three intermediate stages were identified: (1) stage I*, (2) stage I**, and (3) stage II*. Stage I* is intermediate to the conventionally defined stages I and II, where latex particles began to crystallization. The change of drying temperature affects the location of the onset of ordering, whereas relative humidity does not. Stage I** is where the latex particles with their diffuse shell of counterions in the fcc structure are in contact with each other. The overlapping of these layers results in an acceleration of the lattice shrinkage due to a decrease of effective charges. Stage II* is where the latex particles, dried well above their T(g), are deformed and packed only partially during film formation due to incomplete evaporation of water in the latex film. This is because of a rapid deformation of the soft latex particles at the liquid/air interface so that a certain amount of water is unable to evaporate from the latex film effectively. For a latex dispersion dried at a temperature close to its minimum film formation temperature, the transition between stages II and III can be continuous because the latex particles deform at a much slower rate, providing sufficient surface area for water evaporation.

Attributes of the latex emulsion processing and its role in morphology and performance in paints

This article explores the influence of process variation and neutralization of itaconic acid (IA) on polymer properties and paint performance. The study elaborated how the reaction pathway changes the acid distribution in the latexes. The study also investigated the influence on paint performance of degree of neutralization of IA before its incorporation into emulsion. The acid distribution study was done through the conductometric titration method. Latex film properties were studied through differential scanning calorimeter (DSC) and minimum film forming temperature (MFFT). These latexes were formulated in the corresponding paint and study was done using scanning electron microscopy (SEM), which was further correlated with the performance properties of the paint such as scrub, gloss, whiteness and contrast ratio.

Structural Reorganization of a Polymeric Latex Film During Dry Sintering at Elevated Temperatures

Structural rearrangement in a latex powder during dry sintering at temperatures higher than the minimum film formation temperature was investigated by means of synchrotron small-angle X-ray scattering. Two major effects were identified: (1) Deformation of latex particles leads to a closure of voids between them and an extensive perfectioning of the face centered cubic colloidal crystalline ordering. Such an improvement of the colloidal crystalline structure involves preferential crystal growth along certain crystallographic directions as was evidenced by the measured unmatched relative diffraction intensity distribution of the crystallographic (111) and (220) planes. (2) Interdiffusion of polymeric chains between adjacent particles promotes a nanometer sized aggregation of nonpolymeric materials previously located in the interstices between particles. Size and size distribution of the aggregates at different dry sintering conditions were evaluated by using a model considering spheres dispersed in the system.

New additives to offer freeze–thaw stability and increase open time of low/zero VOC latex paints

With increasing pressure from regulations to reduce VOC in waterborne coatings and the push toward low odor coatings, coalescing aids are being taken out of the formulations. As film forming properties need to remain identical, binder polymers that exhibit low minimum film formation temperatures (MFFT) are being developed and utilized for formulating coating with the expectation that the resulting products exhibit the same if not better performance as the traditional ones containing significant amounts of solvents. However, this change of binder, has a negative impact on a number of properties including freeze–thaw stability – due to destabilization of the latex during transport, storage and application through cold climate – and open time. New additives, Additive FT-100 and Additive OTE-500 were designed as novel solutions to these issues. These additives are added either to the resin or to the paint formulation to provide a finished coating formulation that exhibits five cycles of freeze–thaw stability as well as significant extension in open time. Other paint properties, such as gloss, scrub resistance, stain resistance, etc., were also improved when Additive FT-100 or Additive OTE-500 products were incorporated. An extensive comparison between formulations with and without these additives will be discussed.

An ESEM investigation of latex film formation in cement pore solution

Environmental scanning electron microscopy (ESEM) and complementary methods were employed to study the time dependent film formation of a latex dispersion in water and cement pore solution. First, a model carboxylated styrene/ n-butyl acrylate latex dispersion possessing a minimum film forming temperature (MFFT) of 18 °C was synthesized in aqueous media via emulsion polymerization. Its film forming property was at a temperature of 40 °C, studied under an ESEM. The analysis revealed that upon removal of water, film formation occurs as a result of particle packing, particle deformation and finally particle coalescence. Film formation is significantly retarded when the latex dispersion is present in cement pore solution. This effect can be ascribed to adsorption of Ca 2+ ions onto the surface of the anionic latex particles and to interfacial secondary phases. This layer of adsorbed Ca 2+ ions hinders interdiffusion of the macromolecules and subsequent film formation of the latex polymer.

Synthesis and characterization of latexes based on copolymers BA\\MMA\\DAAM and BA\\MMA\\VEOVA-10\\DAAM and the corresponding 1K crosslinkable binder using the adipic acid dihydrazide as crosslinking agent

In this study stable latexes of butyl acrylate (BA)/methyl methacrylate (MMA)/diacetone acrylamide (DAAM) copolymers and BA/MMA/vinyl neo-decanoate (VeoVa-10)/DAAM copolymers were synthesized by a modified semi-continuous microemulsion copolymerization. Ammonium persulfate was used as initiator and a redox system for post-polymerization to reduce the free monomers content. Methacrylic acid (MMA), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), acrylic acid (AA) and various “green” industrial anionic, non-ionic and anionic polymerizable surfactants free of alkylphenol ethoxylates (APEO free) were tested as a stabilizing system. The resulting latexes, their corresponding self-1K crosslinkable binder using the adipic acid (ADH) dihydrazide as crosslinking agent and their films were characterized with rotational viscometer, dynamic light scattering, gloss, dynamic mechanical analysis, minimum film forming temperature (MFFT), water resistance and swelling in methyl ethyl ketone measurements. The experiments showed that BA\\MMA\\VEOVA-10\\DAAM latexes prepared with methacrylic acid and a polymerizable surfactant showed zero coagulation during polymerization. Their corresponding 1K crosslinkable binder with ADH were stable over 6 months storage time and showed good all around properties that makes them suitable for use in friendly to the environment coatings.

Evolving Stresses in Latex Films as a Function of Temperature

Latex films were dried on a flexible substrate, and the substrate deflection was monitored over time to give an averaged film stress-evolution profile. Films were dried at various temperatures below and above the minimum film-formation temperature of the latex dispersion. The effect of polymer rheology, which is a temperature-dependent parameter, on film formation, was investigated. The reliability of the Stoney model in predicting film stress from substrate curvature was also examined and compared to the Euler-Bernoulli model. It was shown that the linearized Stoney model was unsuitable for the larger measured stresses.