Film formation from monodisperse acrylic lattices 2. Influence of drying temperature on the film formation process

The influence of drying temperature on the properties of latex films was investigated by gravimetry, turbidimetry (i.e., analysis of transmission spectra and interference), atomic force microscopy and measurement of water vapor permeability. Several pitfalls in the determination of water content of dried films that absorb water after being submerged in it have been proposed, such as fading boundaries, remaining water after drying and change of particle sizes. At moderately higher temperatures film formation is improved. This improvement follows from the formation of smoother film surfaces (AFM), lower water vapor permeabilities and smaller values for delta lambda(min). On the other hand, defects as cracks and channels also are created, especially at high temperatures. It appears, however, that these channels do not run from the one surface of a film to the other.     

Structure–property relationships of latex films: a special emphasis on viscoelastic behavior and water vapor permeability

The purpose of this work is to investigate the structure and related properties of polymer films obtained upon latex dehydration and coalescence of the particles. Coalesced latex films can be considered as cellular structures, in which the cell cores consist of the hydrophobic particle cores, while the array of interfacial membranes mainly contains hydrophilic species. The linear viscoelastic behavior of the films and their water vapor permeability properties are investigated using dynamic micromechanical analysis and vapor sorption, respectively. It is shown that both core and membrane have a strong effect on the film properties. The structure and viscoelastic behavior of polymer films obtained from sterically stabilized latexes are also studied and compared with that observed for films obtained from electrostatically stabilized ones.     

Addition of polysaccharides influences colloidal interactions during latex film formation along with film morphology and permeability

In this paper, the effect of two polysaccharides (chitosan and dextran) on latex film morphology and porosity is investigated with atomic force microscopy, and the water permeability of the films is examined as well. Furthermore, latex films formed with mixtures of dextran and poly(ethylene glycol), PEG, are investigated. The results show that latex films without added polymers have the most homogeneous and dense morphology. In films containing dextran the highest degree of flocculation is observed, while these films do not show the highest water permeability. The highest permeability is observed in films containing chitosan and film porosity and permeability correlate positively to increasing chitosan concentration. The permeability of the latex films containing dextran and PEG accelerates with time. Since addition of these polymers to latex suspensions give rise to different morphologies and film permeabilities, this approach has promising abilities for control of film properties and, thus, has potential within controlled drug release.     

引入三氟甲基侧基对对苯醚型聚酰亚胺薄膜吸水性及水蒸汽透过性的影响

合成了3种含三氟甲基的芳香二胺,进而与3,3′,4,4′-联苯四甲酸二酐(BPDA)缩聚,得到3种对苯醚型含氟聚酰亚胺薄膜,并由4,4′-二氨基二苯醚（4,4′-ODA）与BPDA缩聚得到聚酰亚胺薄膜。 对4种聚酰亚胺薄膜的水蒸汽透过率、吸水性和热学性能的测试结果表明,其中聚合物PI-1（2,2′-BTF-4,4′-BADE+BPDA;BTF：双三氟甲基;BADE：二氨基二苯醚）的水蒸汽透过率为7.70 g/（h·m2）,吸水率为0.67%,玻璃化转变温度为259.74 ℃,质量损失5%的温度为521.40 ℃,具有良好的水蒸汽透过性和低吸水性。     

Permeation through homopolymer latex films

The helium permeabilities of homopolymer films cast from polymer solutions and latex dispersions have been measured as a function of time. The permeability coefficients of most polymer latex films started off at a value which was considerably higher than that of the corresponding solvent-cast film, but then dropped at a rate dependent on the polymer concerned. The permeability coefficients levelled off at a value which was closer to, but still higher than that of the equivalent solvent-cast film. Solvent-cast film permeabilities remained constant for the period of several months over which time they were examined. The reduction in the permeability of latex films is attributed to ageing processes occurring within the film after casting. The fact that latex film permeability coefficients are always higher than those of solvent-cast films suggests that latex films never become completely homogeneous. The effect on permeability of the latex type and characteristics, and preparation and storage conditions has been examined. The polymer molecular weight, particle size, and surface-change density did not appear to exert any influence, within experimental error. However, the time-dependent permeability behavior was affected by the film preparation and storage temperatures.     

Film formation from pure and mixed latices; transient fluorescence study

A fast transient fluorescence technique was used to study latex film formation induced by organic solvent vapor. Mixtures of pyrene (P)- and naphthalene (N)-labeled and/or pure naphthalene-labeled latex films were prepared separately from poly(methyl methacrylate) (PMMA) particles. Then these pure and mixed latex films were exposed to vapor of various chloroform-heptane mixtures in seven different experiments. In both films, fluorescence lifetimes from N were monitored during vapor-induced film formation. It was observed that N lifetimes decreased as the vapor exposure time is increased. A Stern-Volmer kinetic analysis was used for low quenching efficiencies to interpret the decrease in N lifetimes. A Prager-Tirrell model was employed to obtain back-and-forth frequencies, nu, of reptating PMMA chains during latex film formation induced by solvent vapor. In both pure and mixed latex films, nu values were found to be correlated with the chloroform content in the vapor mixture. It was observed that polymer interdiffusion obeyed a t1/2 law during film formation.     

紫外光固化的聚氨酯－丙烯酸酯－纤维素复合膜

再生纤维素膜(甘蔗渣浆制)表面直接用紫外光固化聚氨酯-丙烯酸酯制备出防水性复合膜。由红外光谱和扫描电镜研究了复合膜的结构。同时,测定了膜的防水性、力学性能、水汽透过性和尺寸稳定性。实验结果表明,当聚氨酯：丙烯酸酯为40:55(质量比),在400W紫外光下固化5min制得的复合膜具有致密的表面结构和较好的性能,该膜经水浸泡后其断裂强度可达干膜的90%,浸水收缩率和膨胀率均小于2.5%,水汽渗透量仅为再生纤维素膜的1/4.由此表明复合膜的防水性和尺寸稳定性明显提高。此外,该复合膜在可见光区的透光率在80%～90%之间,而且对紫外光有屏蔽作用。     

The gas barrier coating of 3-aminopropyltriethoxysilane on polypropylene film

Nonporous films were formed on polypropylene (PP) films using 3-aminopropyltriethoxysilane (APTEOS) as the only precursor. The PP film was modified by corona-plasma treatment to provide appropriate adhesion between coating layer and substrate. Gas permeation properties of coating films were evaluated, and the influences of water ratio and film storing time on the gas permeability were investigated. Structural and surface properties of coating layers were characterized by ²⁹Si-NMR, FT-IR, and contact angle analyzer. The APTEOS coating films exhibit much higher barrier properties than PP film. The permeability coefficient of APTEOS coating film with water ratio of 3 is 0.011Barrer for nitrogen, 0.044Barrer for oxygen, and 0.002Barrer for carbon dioxide, while each permeability coefficient of PP bare film is 0.233, 0.858, and 2.886Barrer, respectively. The gas permeability coefficient is increased slowly along with storage time. Although additionally formed siloxane network may lead to a higher inorganic network density, the enhancement of gas permeability during storing period is largely attributed to film-swelling effect by the water vapor from atmosphere.     

Fast transient fluorescence technique (FTRF) for studying vapor-induced latex film formation

A fast transient fluorescence (FTRF) technique was used to study latex film formation induced by organic solvent vapor. Seven different films with the same latex content were prepared separately from poly(methyl methacrylate) (PMMA) particles and exposed to vapor of various chloroform-heptane mixtures in seven different experiments. Latex films were prepared from pyrene (Py)-labeled latex particles and fluorescence lifetimes of Py were monitored during vapor-induced film formation. It was observed that pyrene lifetimes decreased as vapor exposure time increased. A Stern-Volmer kinetic analysis was used for low quenching efficiencies to interpret the decrease in pyrene lifetimes. A Prager-Tirrel model was employed to obtain back-and-forth frequencies, nu, of the reptating PMMA chains during latex film formation induced by solvent vapor. nu values were found to be correlated with chloroform content in vapor mixture. It was observed that polymer interdiffusion obeyed a t(1/2) law during film formation. The results of optical transmission experiments were found to support these findings.     

Development of PE/PCL Bilayer Films Modified with Casein and Aluminum Oxide

The studied samples were prepared from polyethylene (PE) polymer which was coated with modified polycaprolactone (PCL) film in order to obtain bilayer films. Thin PCL film was modified with casein/aluminum oxide compound to enhance vapor permeability as well as mechanical and thermal properties of PE/PCL films. Casein/aluminum oxide modifiers were used in order to achieve some functional properties of polymer film that can be used in various applications, e.g., reduction of water vapor permeability (WVTR) and good mechanical and thermal properties. Significant improvement was observed in mechanical properties, especially in tensile strength as well as in water vapor values. Samples prepared with aluminum oxide particles indicated significantly lower values up to 60%, and samples that were prepared with casein and 5% Al₂O₃ showed the lowest WVTR value.     

Oxygen and water-vapor diffusion through biaxially oriented poly(ethylene terephthalate)

The gas barrier properties of a wide range of biaxially oriented polyethylene terephthalate films have been investigated. The permeability and diffusion coefficients for oxygen and water vapor transmissions were determined for films prepared by both simultaneous and sequential biaxial stretching. The effect of annealing was also studied and a comparison made with previous results for uniaxially oriented films. It was found that the permeability correlated well with the density of the sample, but that the dependence on the gauche/trans conformer ratio shown for uniaxial material was not so clear. A good empirical correlation was also obtained between permeability and a proposed measure of molecular orientation obtained from refractive index measurements. A more detailed interpretation, based on infrared measurements of orientation, showed that there is a systematic reduction in permeability as the planes of the terephthalate residues become parallel to the film surface.     

Action of gaseous ammonia and water on neodymium diphthalocyanine

The method of flow injection into the gas flow with detection of current resistance of the film was used to investigate the action of ammonia and water vapor on neodymium diphthalocyanine film. The value and sign of the electrophysical response are reversible at 18–22°C. When the film contacts with vapor, the current is changed within a few seconds, whereas the relaxation to the initial value when vapor is removed occurs within tens of seconds. The response parameters are suitable for developing effective sensors based on resistant films. No optical changes in the absorption spectra of the films were observed in the 400–800 nm region under the action of ammonia and water vapor. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1446–1447, July, 1998.     

Spontaneous film formation from a polymer solution

An unusual continuous film formation process of lateral pentyloxy substituted poly(p-phenylene terephthalate)s (s-PPPT) and poly(carbonate) (PC) is observed. A liquid film of polymer solution creeps over the surface of water dropped into the polymer solution. By vaporization of the solvent a solid polymer film is formed on the water surface and can be removed. The driving force for the film formation mechanism is assumed by the reduction of the surface tension of water. Experiments verify this mechanism by increasing the film formation speed using a gas stream, by reducing the formation speed through lowering the surface tension by rinsing agents, and by lowering the solubility of the polymer. As expected, no effects are found by variation of the pH-value of water. Necessary conditions for the film formation process are: good solubility of the polar polymers in organic solvents having a high vapor pressure, complete phase separation, solution density higher than water density, and a surrounding gas phase unsaturated with solvent vapor.The thickness of the mechanically stable films is less than 0.5 m. The films are amorphous by microscopical, FT-IR, x-ray, and DTA investigations.     

氧化石墨烯增强卡拉胶复合膜的制备与性能

在Hummers法基础上制得了氧化石墨烯(GO), 采用流延法制备了氧化石墨烯/κ-卡拉胶(GO/κ-Car)复合膜材料. 结合红外光谱、 扫描电子显微镜及热重分析对其结构进行表征. 探讨了不同条件所得膜的成膜性、 溶解性、 透气性和力学性能, 得到性质稳定GO/κ-Car复合膜的制备条件为15.0 g 3%的κ-Car溶液、0.040 g GO粉末及5.0 g 8%的PVA溶液于75 ℃搅拌混合5 h后, 流延铺平, 于30 ℃烘干6.5 h. GO质量分数为5%的GO/κ-Car复合膜的最大负荷、 拉伸强度及杨氏模量分别是对照组κ-Car膜的1.5倍、 1.5倍和1.6倍. 同时, GO/κ-Car复合膜具有较强的透气性能, 且保留了κ-Car清除羟基自由基的生物性能.     

Modified whey protein coatings for improved gas barrier properties of biodegradable films

As a result of environmental concern, there is an increasing interest in the development of biodegradable polymers for packaging with suitable properties, as an alternative to the synthetic petroleum‐based polymers. However, such biodegradable polymers are prevented for use in wide industrial and commercial packaging because of their limited gas and vapor barrier properties. This obstacle urges innovative strategies to achieve enhanced gas barrier properties using “bio‐layering” technologies. Whey protein isolate (WPI), a by‐product of the cheese industry, has quite promising properties for packaging purposes. It possesses good oxygen, aroma, and oil barrier properties; however, its permeability to water vapor is high. In this study, several WPI coatings were obtained, adding polyvinyl alcohol and pectin to improve the coated film properties; in addition, nanoclays were used to improve water vapor barrier properties. Comparison of neat poly (lactic acid) film versus poly (lactic acid) coated with WPI presented advantage of the later: improvement of about 90% in the oxygen barrier properties and about 27% in the water vapor barrier properties. Copyright © 2016 John Wiley & Sons, Ltd.     

Water-Resistant Films and Coatings Based on Cross-Linking Styrene-Acrylate Latex Copolymers

Water-resistant films and coatings were prepared from latexes of copolymers of styrene, n-butyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, and methacrylic acid. The degree of cross-linking of the copolymers in the course of film formation and the water resistance of the films and coatings, associated with this parameter and evaluated by the water absorption and mechanical properties of wet films, were studied in relation to the gross composition of the latex copolymer, conditions of its synthesis, distribution of functional groups responsible for cross-linking in a latex particle, and temperature of film formation.     

Thermal crystallization kinetic and electrical properties of partly crystallized amorphous indium oxide thin films sputtering deposited in the presence or the absence of water vapor

Partly crystallized amorphous indium oxide thin films were deposited under water vapor atmosphere by magnetron sputtering. XRD analysis revealed that appropriate water vapor could suppress the film’s crystallinity. In situ thermal crystallization process was monitored by high-temperature XRD. The crystallization data were analyzed using the Kolmogorov–Johnson–Mehl–Avrami equation. The kinetic exponent n is determined to be approx. 1/2 and 3/2 for film deposited in the absence and the presence of water vapor, respectively. The activation energy of crystallization for film deposited under 1 × 10^?5 Torr water vapor pressure was determined to be 30.7 kJ mol^?1, which is higher than 18.9 kJ mol^?1 for film deposited in the absence of water vapor. The increased activation energy caused by the chemically bonded hydrogen and embedded O–H bonds from the water vapor resulted in the suppression of crystallization. Introduction of appropriate water vapor during the deposition decreased the resistivity because of the increase of Hall mobility. The resistivity of the films after annealing increased due to the evaporation of water vapor resulted in crystal defects.     

Sorption isotherms, sorption enthalpies, diffusion coefficients and permeabilities of water in a multilayer PEO/PAA polymer film using the quartz crystal microbalance/heat conduction calorimeter

Sorption isotherms, sorption enthalpies, and diffusion coefficients for water in an 11 μm thick PEO/PAA multi-layer film have been measured at 30, 40, and 60 °C for relative humidities between 0 and 70%. All quantities were measured on the same film using the quartz crystal microbalance/heat conduction calorimeter. Water diffusion coefficients in the film are several orders of magnitude lower than in the separate components. Sorption isotherms are of type III at 30 and 40 °C and linear at 60 °C. Water vapor permeabilities are calculated as the product of Henry's law solubility and diffusion coefficient. The permeability of the PEO/PAA multilayer film is exceedingly low compared to other polymer films used as membranes. The enthalpy of water sorption determined from the sorption isotherms using the van’t Hoff relation is 32.9 ± 0.3 kJ/mol. Calorimetric enthalpies of water sorption range from 42 to 34 kJ/mol at 30 and 40 °C over the humidity range studied. The change in motional resistance, a quantity proportion to the loss compliance of the film, has also been recorded at all three temperatures, and a common trend is an increase in loss compliance with increasing relative humidity, indicating plasticization of the film by water.     

Chemical heterogeneity in emulsion copolymers of carboxylic monomers

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 temperatureT _g 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 highT _g.The latter phase forms a honeycomb-like structure surrounding the packed latex particles. That results in a three-dimensional network of polymer with a highT _g 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.     

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.