Effect of crosslinking on the surface free energy and surface reorganization of waterborne fluorinated polyurethane

To endow waterborne fluorinated polyurethanes (WFPUs), films with stable lower surface free energy and lower surface reorganization after the films contacted with water, a series of crosslinked WFPUs (CWFPUs) emulsions were prepared by adjusting the content of aziridine (AZ). The effect of crosslinking on the surface free energy, glass-transition temperature (T _g), water absorption, and surface composition of dry/hydrated WFPUs and CWFPUs films were studied by CAs test, dynamic mechanical analysis, water absorption measurements, and X-ray photoelectron spectroscopy. When the fluorine content was 0.5%, the surface free energy of the CWFPUs films modified by 0.4% AZ content (CWFPU-6-0.5-CK0.4) reached to the lowest value of 15.76 mN m⁻¹ which almost equaled to the surface free energy (15.45 mN m⁻¹) of the dry uncrosslinked films (WFPU-6-0.5). With the increasing of AZ content, the T _{g, hard} of hard segments of the CWFPUs films increased and the water absorption of the CWFPUs films decreased, which suggested the formation of the crosslinked network structures. The studies of the surface elements and groups composition of dry/hydrated WFPUs and CWFPUs both confirmed that the surface reorganization and the migration of fluorinated side chains were restricted by the crosslinked network structures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47167.     

Glass-transition temperature of a polyacrylate latex film and its water whitening resistance

Polyacrylate latex materials have become a hot area recently in China due to its environmental friendliness. However, the water whitening resistance of the polyacrylate latex products in the market is largely unsatisfactory, which seriously affects the appearance and performance of the latex products. In this work, the effect of glass-transition temperature (T_g) of a polyacrylate latex film on its water whitening resistance was investigated. The light transmittance measurement showed that the higher the T_g of the latex film, the better the water whitening resistance. Atomic force microscope, surface element analysis, static water contact angle measurement, and attenuated total reflection–Fourier transform infrared were used to characterize the accumulation of the emulsifier on the surface of the latex film. It was found that the amount of emulsifier migrated to the surface of the latex film increased with the increase of the T_g of the latex film, that is, the amount of emulsifier remained inside the latex film decreased, thereby reducing its affinity to water. In addition, the higher the T_g of the latex film, the lower the water absorption, also reducing the affinity of the latex film to water. Both work together to improve the water whitening resistance of polyacrylate latex film with higher T_g. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48361.     

Reactive polymers, 49. Changes in the porous structure of macroporous copolymers due to successive effects of solvents and temperature

By drying at 78°C, the macroporous terpolymer 2,3-dihydroxypropyl methacrylate-co-sodium methacrylate-co-ethylene dimethacrylate with a water retention of 3.78 g H₂O/g loses porosity which is renewed by reswelling. Drying of this terpolymer at 0–25°C by which water or methyl alcohol is removed does not disturb its porosity. Less swelling copolymers such as 2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate with a water retention of 1.71 g H₂O/g do not lose its permanent porosity when dried. Inversion gas chromatography has made possible the determination of the glass transition temperature of these macroporous terpolymers (T_g = 45°C) by using heptane and methyl alcohol as retention acids. With respect to this, and using scanning electron microscopy the loss of porosity due to drying was interpreted as sintering of macroporous copolymers whose polymer networks swell to a higher degree on heating above T_g.     

Development of cantaloupe (Cucumis melo) pulp powder using foam-mat drying method: Effects of drying conditions on microstructural of mat and physicochemical properties of powder

In this study, the effects of drying conditions on moisture content, water activity (a_w), dissolution time, solubility, hygroscopicity, β-carotene, color, glass transition temperature (T_g), and sticky point temperature (T_s) of foam-mat-dried cantaloupe pulp powders and microstructure of dried cantaloupe pulp foams were investigated. Drying was performed in three temperatures (40, 55, and 70°C) on 3- and 5-mm thicknesses. The analysis of scanning electron microscopy micrographs with grey-level co-occurrence matrix showed that there is wide porous structure of dried foams at higher speeds drying. The temperature increase reduced moisture content and a_w, and increased hygroscopicity, and thickness rise increased moisture content and a_w and consequently decreased powders’ hygroscopicity under the same thickness and drying temperature, respectively. Increase in drying temperature would increase the reconstitution speed of powders into water and therefore the dissolution time decreased. In addition, results showed that the powder produced at 40°C have higher β-carotene content than those of produced at 55 and 70°C. With increasing drying temperature from 40 to 70°C, Lightness parameter (L) was increased while redness parameter (a) was decreased. The T_g and T_s were compared by plotting them in a graph against moisture content. For all drying processes the T_s was higher than the T_g. The drying conditions at 70°C (higher drying temperature) and 3?mm (lower thickness) led to a shorter drying time and consequent lower energy demand to produce a powdered cantaloupe pulp with high stability (low moisture content, a_w, and high T_g and T_s) and reconstitution speed of powder into water.     

Development of VOC-free, high-T g latex binders by a high-temperature water-extended latex technology

The potentiometric titration of carboxylated methyl methacrylate latexes prepared with varying amounts of methacrylic acid showed that only very small amounts of their total acids copolymerized were neutralized at room temperature until the acid level was well above 10%. However, it was found that all the acids copolymerized were completely titrated either in a 50/50 water/ethanol mixture at room temperature or in water at high temperatures near their backbone polymer T _gs, regardless of their acid contents, as predicted from the existing theories on the alkali-swelling of carboxylated latexes. It was also found that these high-temperature alkali-swollen latex particles remained in the swollen state even after they were cooled down to room temperature and became film-forming at much lower temperatures. This discovery led to a new technology coined as a high-temperature water-extended latex technology. This new technology enabled us to develop VOC-free water-extended latexes of high-T _g polymers that would exhibit good film formation at ambient temperature and turn into hard and non-blocking latex films and latex-bound pigmented coatings upon drying. Particularly, when fugitive bases were used for neutralization at high temperatures, the resulting water-extended latexes became hard, non-blocking, and water-resistant binders upon drying.     

Effect of acrylic acid on water-whitening resistance of polyacrylate latex films and its mechanism

Two groups of polyacrylate latexes with higher (21 ~ 35 °C) or lower (−33 ~ −43 °C) glass transition temperatures (T_g) were prepared by adjusting the monomer ratio of butyl acrylate (BA) and styrene (St), and the effect of acrylic acid (AA) on water-whitening resistance of these latex films was investigated. It was found that the water-whitening resistance of the two groups of latex films was different. With the increase of AA content, the water whitening resistance of the latex films with higher T_g continued to improve, while that of the latex films with lower T_g increased first and then decreased. A series of characterizations, such as light transmittance, water whitening, water absorption, static water contact angle, surface morphology, and optical microscope test of the latex film, and so forth, showed that the reason for this difference was that under higher AA content (≥5%), compared with the polyacrylate latex films with lower T_g, the latex films with higher T_g could reach the saturation state of water absorption quickly, and water in these latex films exhibited continuous and large area distribution, rather than formation of many so-called micro- or nano-scale water sacs that can scatter light as found in the latex films with lower T_g.     

Influence of particle surface properties on film formation from precipitated calcium carbonate/latex blends

The surface properties of films prepared from a blend of precipitated calcium carbonate pigment (PCC) and poly(n‐butyl methacrylate‐co‐n‐butyl acrylate) [P(BMA/BA); T_g = 0°C] latex were investigated in terms of the surface characteristics of the PCC and P(BMA/BA) latex particles. It was found that the presence of carboxyl groups on the P(BMA/BA) latex particles significantly improved the uniformity of the distribution of the PCC particles within the P(BMA/BA) copolymer matrix and the gloss of the resulting films. This phenomenon could be explained by an acid‐base reaction between the PCC particles and the carboxylated P(BMA/BA) latex particles. Studies on the influence of the composition of PCC/P(BMA/BA) latex blends on the gloss and transparency of the films were also performed, which led to the determination of the critical pigment volume concentration (CPVC) of this system, which was found to be 42 vol %. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 891–900, 2002     

A simple approach to fabricate morphological gradient on polymer surfaces

This paper presents a novel and feasible approach for fabrication of morphological gradient surfaces based on the film-formation of nanocomposite polymer latex. In this method, when the polymer latex with relatively low glass transition temperature (T_g) was blended with colloidal silica and then dried at certain temperatures, a morphological evolution with deeper pores from the center to the edge could be directly obtained on polymer surface. Neither careful control of experimental conditions nor any complex processes are needed. The T_g of polymer, the silica content, the solvent and the drying temperature have significant influences on this surface morphology. The film-formation mechanisms at different drying temperatures are also discussed.     

Preparation of transparent Bi2O3-ZnO-B2O3 glass by conventional sintering at low temperatures

Glass components fabricated by the sintering route have wide-ranging applications. However, one issue is that the crystallization tendency of glass powders often leads to residual pore-glass interfaces and crystal-glass interfaces, thereby causing strong light scattering and rendering the sintered glass opaque. This issue is particularly pronounced in glasses with a low glass transition temperature (T_g) due to their weak bonding and thus high crystallization tendency. In the present study, a Bi₂O₃-ZnO-B₂O₃ glass with a low T_g of 364°C was fabricated using the conventional sintering method to explore whether transparent glass materials can be obtained. The temperature range of crystallization of the glass powders was analyzed using differential scanning calorimetry. X-ray diffraction was employed to analyze the crystalline phases formed in the sintered glasses. The microstructure of the sintered glasses was examined using scanning electron microscopy. The optical transmittance of the sintered glasses was measured using ultraviolet-visible spectroscopy. The results show that transparent sintered glasses with the highest transmittance of 54% at the wavelength of 650 nm can be obtained by using a coarser initial particle size, lower forming pressure, and an appropriate sintering temperature/time (430°C/30 min). It is suggested that this combination of processing parameters can suppress glass crystallization while maintaining a low glass viscosity during sintering.     

Effects of ultrasonic pretreatments on thermodynamic properties,water state,color kinetics,and free amino acid composition in microwave vacuum dried lotus seeds

Abstract

Ultrasonic pretreatments were applied to lotus seeds at acoustic energy densities of 0.29, 0.40, and 0.51?W mL^?1 for 10?min. After pretreatments, lotus seeds were subjected to microwave vacuum drying (MVD). Parameters of glass transition temperature (T_g), gelatinization temperature (T_p), water state, color kinetics, and free amino acid content of microwave vacuum dried lotus seeds were determined. With increasing acoustic energy density, MVD elevated the T_g values appreciably by decreasing the content of cytoplasmic bulk water in lotus seeds tissues. The T_p had a positive relationship with the relaxation times of cytoplasmic bulk water (T₂₂), while T_g had a negative relationship with T₂₂. Color kinetics were analyzed by the divisional method during MVD due to different browning reactions, which failed to appear with ultrasonic pretreatment. Free amino acid content ranged from 517.65 to 666.13?mg/100?g dry weight at 0.51?W mL^?1.     

How the infrared radiation affects the film formation process from latexes?

In this study, the effect of the infrared radiative heating (IRH) was investigated on the film formation from composites of polystyrene (PS) latex particles and poly vinyl alcohol (PVA). The films were prepared as a pure PS and a mixture of PS and PVA particles at equal compositions at room temperature and they were annealed at elevated temperatures above the glass transition temperature (T_g) of PS for 10 min by using IRH technique. Identical experiments were performed by using standard convectional heating technique in oven as comparison. It was shown that the activation energy for the film formation from PS latex particles decreased considerably in IRH annealing technique. Photon transmission (PT) and steady state fluorescence (SSF) techniques were used to monitor the film formation process at each sintering step. Minimum film formation temperature, T_o, and healing temperature, T_h, were determined by the data obtained from the SSF and the PT measurements for each heating processes. The film formation was modeled as a void closure and as an interdiffusion stage below and above T_h, respectively. Scanning electron microscopy (SEM) was used to examine the variation in morphological structure of annealed composite films. It was observed that IRH heating causes more homogenous and more flat film surface than films annealed in the oven. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43289.     

Energetic studies on epoxy–polyurethane interpenetrating polymer networks

A blend system prepared from epoxy resin (EP) and polyurethane (PU) was investigated in terms of glass-transition temperature (T_g), contact angle, mechanical interfacial, and mechanical properties. Deionized water and diiodomethane were chosen as the angle testing liquids. In this work, the models of Owens–Wendt and Wu, using a geometric mean, were studied to analyze the surface free energy of the EP/PU blend system. Fourier transform infrared (FTIR) spectroscopy was employed to investigate the intermolecular hydrogen bonding and functional group changes. The impact test was carried out at room and cryogenic temperatures to determine the low-temperature performance of PU. As a result, mechanical interfacial and mechanical properties give a maximum value at 40 phr of PU, and the deviation of T_g of EP/PU was the closest at 40 phr of PU. Thus it is concluded that EP and PU have the best compatibilities at this ratio. Furthermore, the specific (or polar) component of the surface free energy of the blend system was largely influenced on the addition of the PU, resulting in increasing the critical stress intensity factor (K_IC) and the impact strength for the excellent low-temperature performance. These results could be explained by means of improvement of hydrogen bonding between the hydroxyl group in EP and isocyanate group in PU. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 775–780, 2001     

Dry sintering of latex particles in pigmented coatings. I. Influence on coating structure and properties

When a clay–latex coating, dried below the minimum film-forming temperature (MFT) of the latex, was subsequently heated above the MFT, its opacity and brightness were considerably enhanced. The improvement in optical properties was optimum in the latex content range of 20–40 parts per 100 parts of clay. The sintering of the latex particles, brought about by the thermal treatment, increased the average size of the microvoids to a diameter that is optimum for the scattering of light, without significantly affecting the total void content. Data on light-scattering coefficient, porosity, gloss, brightness, and oil permeability are discussed and compared to those of conventional coatings, i.e., of coatings dried above the MFT of the latex. Similar improvements in optical properties were obtained when coalescence of the latex particles was induced by exposure to a solvent.     

Self‐Healing Latex Containing Polyelectrolyte Multilayers

Self‐healing paints would have the potential benefit of protecting the underlying substrate and extending the coating's service life. As a step toward those types of coatings, this work examines layer‐by‐layer films of branched poly(ethylene imine)/poly(acrylic acid) with the inclusion of various types of latex particles with different T_g and different compositions. Due to high mobility of the polyelectrolyte chains when plasticized with water, water enabled self‐healing of these films is demonstrated, as well as steam enabled self‐healing. The films with various latex particles show different swelling ratios, surface hydrophilicity, as well as varying ability to self‐heal scratches. This self‐healing property is studied as a function of temperature. Also, the mechanical properties such as hardness and modulus of the films are measured.     

Preparation and dynamic mechanical properties of poly(styrene‐b‐butadiene)‐modified clay nanocomposites

Polybutyl acrylate (PBA) was intercalated into clay by the method of multistep exchange reactions and diffusion polymerization. The clay interlayer surface is modified, and obtaining the modified clay. The structures of the clay‐PBA, clay‐GA (glutamic acid), and the clay‐DMSO (dimethyl sulfoxide) were characterized using X‐ray diffraction (XRD). The new hybrid nanocomposite thermoplastic elastomers were prepared by the clay‐PBA with poly(styrene‐b‐butadiene) block copolymer (SBS) through direct melt intercalation. The dynamic mechanical analysis (DMA) curves of the SBS/modified clay nanocomposites show that partial polystyrene segments of the SBS have intercalated into the modified clay interlayer and exhibited a new glass transition at about 157°C (T_g3). The glass transition temperature of polybutadiene segments (T_g1) and polystyrene segments out of the modified clay interlayer (T_g2) are about ?76 and 94°C, respectively, comparied with about ?79 and 100°C of the neat SBS, and they are basically unchanged. The T_g2 intensity of the SBS‐modified clay decreases with increasing the amounts of the modified clay, and the T_g3 intensity of the SBS‐modified clay decreases with increasing the amounts of the modified clay up to about 8.0 wt %. When the contents of the modified clay are less than about 8.0 wt %, the SBS‐modified clay nanocomposites are homogeneous and transparent. The T_gb and T_gs of the SBS‐clay (mass ratio = 98.0/2.0) are ?78.39 and 98.29°C, respectively. This result shows that the unmodified clay does not essentially affect the T_gb and T_gs of the SBS, and no interactions occur between the SBS and the unmodified clay. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1499–1503, 2002; DOI 10.1002/app.10353     

Mechanical properties of films prepared from model high‐glass‐transition‐temperature/low‐glass‐transition‐temperature latex blends

The mechanical properties of films prepared from model high‐glass‐transition‐temperature (T_g)/low‐T_g latex blends were investigated with tensile testing and dynamic mechanical analysis. Polystyrene (PS; carboxylated and noncarboxylated) and poly(n‐butyl methacrylate‐co‐n‐butyl acrylate) [P(BMA/BA); noncarboxylated] were used as the model high‐T_g and low‐T_g latexes, respectively. Carboxyl groups were incorporated into the PS latex particles to alter their surface properties. It was found that the presence of carboxyl groups on the high‐T_g latex particles enhanced the Young's moduli and the yield strength of the PS/P(BMA/BA) latex blend films but did not influence ultimate properties, such as the stress at break and maximum elongation. These phenomena could be explained by the maximum packing density of the PS latex particles, the particle–particle interfacial adhesion, and the formation of a “glassy” interphase. The dynamic mechanical properties of the latex blend films were also investigated in terms of the carboxyl group coverage on the PS latex particles; these results confirmed that the carboxyl groups significantly influenced the modulus through the mechanism of a glassy interphase formation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2788–2801, 2002     

Limiting surface tension by gas chromatography

The change in retention mechanism at the glass transition temperature (T_g) of a polymer stationary phase from surface adsorption below T_g to bulk sorption above T_g allows for a separate determination of the magnitude of the solute interaction with both the bulk and the surface of the polymer. As a result, the limiting surface tension of the polymer-probe solution can be obtained from the corresponding partition coefficients. Examples of such determinations are given for several polymer-solute systems.     

Effect of vinylidene chloride content on film-formation property of vinylidene chloride-methyl acrylate copolymer latex

Minimum film-formation temperature (MFFT) of vinylidene chloride (VDC)-methyl acrylate (MA) copolymer latexes prepared by batch emulsion polymerization with various compositions from 20 to 97 wt % of VDC were measured. For latexes with VDC content below 90 wt %, MFFT was similar to polymer T_g. As VDC content increased beyond 90 wt %, the MFFT curve plotted against VDC content rose sharply, in contrast with the T_g curve that descended smoothly. Measurements of infrared absorption of latexes in the dispersed state, and X-ray diffraction and infrared absorption of lyophilized polymers were conducted on 40 : 60, 80 : 20, and 95 : 5 VDC-MA specimens. These observations indicated that only 95 : 5 VDC-MA specimens were highly crystalline. It was therefore believed that film-formation property of latex with high VDC content was significantly affected by polymer crystallinity of particles in the dispersed state. Morphology and oxygen gas transmission rate of heat-treated and non-heat-treated coatings of 95 : 5 VDC-MA latex were investigated. Heat treatment of coatings beyond the temperature at which crystalline polymer began to melt induced effective particle coalescence, resulting in reduced oxygen gas transmission rate. This supported our belief that film-formation property of VDC-MA latex with high VDC content was significantly affected by polymer crystallinity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 565–572, 1998     

Suppression of phosphor‐glass reactions in YAG:Ce phosphor‐embedded glasses

For high‐power white LED applications, YAG:Ce‐based yellow phosphors were embedded in a low‐T_g Bi₂O₃–B₂O₅–ZnO–Sb₂O₅ glass (BiG) by sintering route. A high‐T_g silicate glass (SiG) was also used for comparison. Dense (porosity<2%) phosphor‐glass composites were obtained after sintered at 800°C (for SiG) and 325°C (for BiG). XRD quantitative analysis indicates that the loss of phosphor content is in the range of 2.5%‐22%, caused by partial dissolution of phosphor particles into the glass matrix during sintering. The element distribution across the interface and within the reaction zone between phosphor and glass was analyzed by TEM/SEM‐EDS. The intrinsic emission characteristic of YAG:Ce is nearly not altered, possibly resulted from the slight modification of the YAG phase during sintering. Thus the final emission intensity of the sintered body is mainly determined by the residual amount of the YAG:Ce phase. Replace the high‐T_g SiG glass by the low‐T_g BiG glass, prenitridize the YAG:Ce phosphor, and change the sintering atmosphere from air to N₂ suppress the loss of phosphor during sintering. Therefore, the resulting loss of emission intensity of the phosphor‐embedded glass material can be reduced to only about 1.8%.     

Study on reconstruction mechanism at the surface of a glassy polymer

The introduction of hydrophilic functional groups at various depths in the functionalized interfacial region of poly(4-methylstyrene) (P4MS) provided a system for studying the surface reconstruction mechanism of this glassy polymer. The degree of surface reconstruction (RD) and the rate of surface reconstruction (1/t_1/2) were employed to compare the surface reconstruction behavior for various samples. The results showed that 1/t_1/2 decreased with increase of the depth in the functionalized interface region at a temperature below T_g of poly(4-methylstyrene). By studying the relation of water contact angles and the surface free energy of the samples with temperature, it was found that surface reconstruction of surface-oxidized P4MS samples took place in two steps when the samples were heated in air. The first step took place below 80 °C, in which polar side groups turned into the bulk, leaving a relatively nonpolar backbone projecting out of the surface to form a “hydrophobic conformation”. The second step occurred above the P4MS T_g (110 °C), in which P4MS molecular chains migrated to the surface in order to minimize the interfacial free energy between surface-oxidized P4MS film and air, since oxidized P4MS molecules containing carbonyl groups have higher surface free energy than the unmodified P4MS molecules. As the depth of the functionalized interfacial region increases, a longer time is needed for the polar side groups to reorient (the first step) and for unoxidized P4MS molecules to migrate to the surface (the second step), which resulted in the sample with deeper functionalized region having lower reconstruction rate and RD using the same treatment condition.