The mechanical behavior of latex films is governed by their macromolecular nature as well as by their origin from particles dispersed in an aqueous medium. When monomers of different polarity are copolymerized in emulsion copolymerization, a heterogeneous distribution of the polar groups in the latex and the film can occur, owing to the different water solubilities of the comonomers. Films from these latices in many cases show a two-phase morphology, first, consisting of the main polymer within the particles and, second, a phase which is concentrated in the interphase between the original particles and which has a strong influence on the mechanical properties of the films. Films from latices with crosslinked particles behave like homogeneous networks in the linear viscoelastic range, i.e. at small strains. Structured networks are found when latex films are interparticularly crosslinked during or after film formation, e.g. by polar bifunctional monomers or metal salts. Tensile tests of films show that the mechanical strength of latex films develops in the last stage of film formation by interdiffusion and entaglement formation across particle boundaries. 相似文献
In an attempt to eradicate many of the problems associated with outdoor and accelerated testing of polymeric formulations, an apparatus was constructed for the sensitive measurement of oxygen uptake into a polymer during its incipient stages of photooxidation. The photooxidation curves of certain HDPE and LDPE formulations demonstrate a first order asymptotic approach to a limiting value which corresponds to the initial number of reactive centers that are available in the material for oxygen attack. An equation for oxygen uptake as a function of time is derived which incorporates the asymptotic value together with a constant whose value reflects the rate at which the asymptote is approached. These parameters are used to calculate the value of the initial quantum yield for oxygen uptake, a quantity which is indicative of the relative photostability of a given formulation. The kinetics parameters obtained from analyses of certain photooxidative curves confirm that the initial rate of photooxidation is proportional to the concentration of polymer hydroperoxide species which are present in the material as a result of oxidation during processing. The removal of these by thermal treatment of the material in an inert atmosphere results in the appearance of an induction period in the photooxidative profile. The experimental results suggest that this method of determining and interpreting photooxidative curves has certain potential for assessing the relative photostabilities of polymeric formulations. 相似文献
The physical forces causing deformation of latex particles during the film formation process have been witley studied. However, the forces resisting particle deformation are still poorly characterized. It is clear that the extent of particle deformation is dependent on the viscoelastic nature of the polymer. In an emulsion, the latex particles will normally contain water, surfactants and “free” monomers which lead to plasticization of the polymer. Although this effect has been recognized, so far it has been studied only on films that had been dried and then partially or completely swollen by water. In this work, plasticization of the emulsion polymers by water and co-solvent has been quantified via differential scanning calorimetry investigation directly on the aqueous latex dispersions. More specifically, the plasticizing effect of water on VeoVa/vinyl acetate copolymer latices and its influence on minimum film-forming temperature (MFFT) has been studied. A linear correlation has been found between Tg and MFFT for the wet latices. This new direct method should help to improve our understanding of the forces resisting latex film formation. Additionally, the homogeneous distribution of the hydrophobic and hydrophilic monomers (VeoVa and vinyl acetate respectively) in the latex particles was verified via a 13C-NMR (nuclear magnetic resonance) study performed directly on the latices. This study confirmed that no significant core/shell type of morphology had influenced latex film formation. 相似文献
Predicting the weatherability of acrylic melamine coatings commonly used as enamel clearcoats requires a detailed understanding of each of the factors that influence photooxidation kinetics. Previous work1 has shown that the photooxidation rate in coatings can be written as the following function of hydroperoxide concentration: photooxidation rate = K[YOOH] + M. The existence of a measurable photooxidation rate in the absence of hydroperoxide (i.e. a non-zero value of the intercept, M) has been observed only in melamine crosslinked coatings. It has also been observed that the photooxidation rate in acrylic melamine coatings increases with increasing humidity. In contrast, for urethane crosslinked coatings the value of M is zero, and the photooxidation rate is independent of humidity. In this paper, infrared spectroscopic measurements of functional group changes (e.g. carbonyl growth and crosslink scission) are used to measure photooxidation rates in acrylic melamine coatings during UV exposures at different humidities. Comparisons of these rates to measured hydroperoxide concentrations for the same coatings and exposures reveal that the increase in photooxidation rate with humidity is due to the fact that the intercept M increases with increasing humidity. Since the intercept is zero under dry conditions, the chemical reactions responsible for the intercept in melamine crosslinked coatings must involve both UV light and moisture. These results confirm the importance of accurately controlling the humidity during UV exposure for predicting the weatherability of melamine crosslinked coatings. 相似文献
Latexes based on acrylic acid, acrylamide, ethyl methacrylate, and ethyl acrylate were synthesized via emulsion polymerization with different monomer compositions. The resultant latices were thickened with different molar ratios of NaOH to acrylic acid and were analyzed in terms of acid-basis titrimetry, turbidimetry, rheology, and tensiometry. Titrimetry, turbidimetry and rheometry were used to analyze factors such as carboxyl group availability and particle solubilization, tensiometry monitoring the influence of carboxyl neutralization on polymer-surfactant interactions. For the acrylic acid content used in this work (20 wt%), the results indicated that as carboxyl groups distribution became more homogeneous, the process of latex thickening became more effective. 相似文献
Crosslinked highly carboxylated acrylic latices with narrow particle size distributions were prepared by emulsion polymerization and characterized carefully by different AUC techniques (particle size distributions and particle density measurements). The acid form of those latices was neutralized with metal oxides like MgO, CaO, ZnO, or PbO in order to obtain the corresponding salt form of the latices which again were characterized carefully. The kinetics of the ion exchange between latex particles were studied by mixing, for example, the acid and the salt form of the latices monitoring the density distribution of the latex particles by density gradient ultracentrifugation. With all latices the hydrogen-metal ion exchange tends to be a complete one provided this process is given a sufficiently long exchange time. Theoretical models are provided which yield a qualitative explanation of the experimental data. 相似文献
Anionic and non-ionic copolymer latices with a hydrophobic core and hydrophilic shell were prepared using emulsifier-free emulsion polymerization. Styrene was used as the hydrophobic monomer; acrylic acid, acrylamide, and methacrylamide were employed as the hydrophilic monomers. The amount of chemically bound hydrophilic monomers in latex and unbound homopolymers in water were determined. The salt stability and redispersability of latices in water after spray-drying were also investigated. 相似文献
Four monodisperse core-shell latices were synthesized for small-angle neutron scattering (SANS) studies, differing by the acrylic acid content in the particle shell (1 or 4 wt%) and the T(g) of the acrylic core (around -40 or 10 degrees C). In a first part, the coalescence kinetics of the surfactant-free latices were studied. It was shown that coalescence was hindered by an increase in the acrylic acid content of the shell, pH of the latex, and Tg of the core. These results could be interpreted in terms of chain mobility in the shell and in the core. Upon coalescence, the hydrophilic phase was segregated in spherical, polydisperse domains with an average diameter of 110 nm. In a second part, labeled SDS was used to follow desorption of the surfactant during film formation. It was shown that desorption occurred early in the film formation process when the latex still contained around 20% of water. A small fraction of the surfactant remained irreversibly adsorbed at the particle surface. 相似文献
Copolymer latices of butylacrylate (BA) with acrylic and methacrylic acid (AA and MAA) were prepared by batch type emulsion polymerization, and, for comparison, copolymers with identical monomer composition were prepared by batch type solution polymerization.The distribution of the carboxylic monomers in the latex particles and the serum was studied by density gradient and sedimentation experiments with the analytical ultracentrifuge. Dynamic mechanical measurements of films of these copolymers were used to determine the storage and loss moduli as a function of temperature. From these measurements the position and extension of the glass transition range on the temperature scale is obtained. For heterogeneous emulsion copolymers with two glass transition temperatures the distribution of the carboxylic monomer units in the different copolymer phases can be determined. Electron microscopy of ultra thin cross-sections of stained films gave further insight into the film morphology.The combination of the results obtained with the different methods gives rise to the following clues: In the BA/AA latices about 40% (by weight) of the total AA used in the recipe are found in the serum as a water soluble polymer, about 50% are found to increase the glass transition temperatureTg of the bulk of the BA copolymer and, therefore, are thought to be incorporated into the interior of the latex particles, and the remaining 10% are, conclusively, located on the particle surface.In the BA/MAA latices no water soluble copolymer could be detected in the serum, about 90% of the MAA used is found in the bulk of the copolymer, and about 10% form a second hard phase on the surface of the latex particles.Dynamic mechanical measurements on the copolymer latex films show at least two phases with different glass transition temperatures: the bulk of the copolymer with a relatively low content of (M)AA units and a glass transition range at low temperatures, and a second (M)AA rich phase with a highTg.The latter phase forms a honeycomb-like structure surrounding the packed latex particles. That results in a three-dimensional network of polymer with a highTg extending throughout the latex film. In spite of the fact that this phase is built from a small fraction of the total copolymer only, it has a very pronounced influence on the performance behaviour of latex films.Dedicated to Professor Dr. R. Manecke on the occasion of his 70th birthday. 相似文献
The rheological behaviour of butyl acrylate/styrene/acrylic acid latices thickened with a hydrophobically modified ethoxylated polyurethane (HEUR) or hydrophobically modified alkali-soluble polyacrylate emulsion (HASE) was investigated. While the pseudoplastic character of frequency dependence of complex viscosity was similar for both thickeners, viscoelastic behaviour, expressed as the ratio of loss and storage moduli, significantly differed, indicating that the HEUR molecules, unlike swollen HASE particles, create a viscoelastic space structure. The increase in hydrophilicity of the particle surface, achieved by incorporation of 2-hydroxyethyl methacrylate (HEMA) monomer into the latex copolymer reduced the viscoelasticity of latices thickened with HEUR, but not of those thickened with HASE. This confirms that adsorption of hydrophobic end-groups on particle surface is important for thickening of latices with HEUR and that a physical network of latex particles interconnected by the thickener macromolecules is formed. To cite this article: O. Quadrat et al., C. R. Chimie 6 (2003).相似文献
Summary: Free radical emulsion polymerization of styrene (S) or butyl acrylate (BA) in the presence of latices of linear polyethylene (PE) prepared by catalytic emulsion polymerization affords colloidally stable multiphase latices. Coagulation of a PE/PS latex affords nanocomposites composed of small PE phases dispersed in a PS matrix, as evidenced by the large supercoolings of PE crystallization (by DSC). TEM of PE/PBA latices indicates a PBA phase around the PE particles under the emulsion polymerization conditions investigated. Films formed from these dispersions exhibit homogeneously dispersed PE particles.
Multiphase latices are obtained by free radical emulsion polymerization of butyl acrylate in the presence of latices of linear polyethylene (PE) prepared by catalytic emulsion polymerization. 相似文献
Vinyl acetate – Butyl acrylate (VAc-BuA) copolymer latices of various compositions were prepared by semicontinuous emulsion polymerization. The copolymer formed after removing the homopolymers was characterized by FTIR spectroscopy. Mechanical properties were studied by Universal Testing machine. Differential scanning calorimetry (DSC) study of copolymer showed single glass transition temperature (Tg) value confirming the absensce of graft and block copolymer. These copolymer latices were used as the binder in water based latex paint formulation. The paint prepared using 85/15 wt.% of VAc-BuA was found to give a better paint properties. Water based paints are generally easier to apply and clean up. The surface properties found to be superior compared to commercially used paint. 相似文献
Five poly(n-butyl methacrylate), PBMA, latex dispersions have been prepared, each incorporating a different fluorescent label, via a two-stage seeded emulsion polymerization. The resultant latices contain ca. 35% by weight total solids and are of 80 (+/-10) nm diameter as determined by photon correlation spectrometry. Luminescence spectroscopic techniques, namely fluorescence (and phosphorescence) excited state lifetime measurements in addition to time-resolved anisotropy experiments have provided useful information regarding the morphology, microviscosity and water permeability of the resultant particles. A picture of the PBMA colloid emerges of an interior which is highly viscous and water impermeable in nature. Indeed, the environment is protective enough to sustain room temperature stabilized phosphorescence from both an acenaphthylene and 9-phenanthrylmethyl methacrylate labeled dispersion through simple nitrogen purging of the solutions. However, the current spectroscopic measurements should be viewed with the knowledge that each luminescent label may fashion its own distinctive microenvironment within the latex during polymerization. 相似文献
The aim of this study is to determine the factors that contribute to the process of film formation of binder particles in drying aqueous dispersion coatings, based on acrylic polymers. It is known that concentrated latices of uniform size show iridescent, colored light patterns. These colors are caused by interparticle interference, and they are only present when the latex particles are ordered in a regular structure. The interparticle interference can be characterized by measuring the transmission as a function of wavelength of the incident light. It appeared that the changes of the interparticle interference of a drying latex film can be related to changes in the interparticle distance and displacement. It was also found that the interparticle distance becomes "negative" upon coalescence of the latex particles. This means that from this point on, the change in interparticle interference is directly related to the indentation or deformation of the latex particles. It became clear that the coalescence process differs from deformation mechanisms accepted in the literature. It seems that the deformation of the particles follows a biaxial mechanism. This means that the particles deform only in one direction, perpendicular to the film surface. Copyright 2000 Academic Press. 相似文献
Deposition of polymer latices on a grafted Nylon 6 fiber was studied as a function of pH and the degree of grafting. The latices were polystyrene (PS), styrene/acrylamide copolymer (P(St/AAm)) and styrene/acrylic acid copolymer (P(St/AA)). The deposition of the latices on the grafted fiber decreased in every case with increasing pH and no deposition was observed at alkaline pH. The grafting of fiber with acrylic and methacrylic acid reduced the deposition of P(St/AAm) and P(St/AA) latices but had no influence on the deposition of PS latex. The relation between the deposition rates and the interaction energy at acidic pH indicates that the deposition of PS latex on the grafted fiber mainly depends on the electrostatic interaction. These results suggest that the expansion of water-soluble polyelectrolyte layer on the surface of grafted fiber plays an important role on the deposition. 相似文献