聚醋酸乙烯乳液保护胶体的改性

介绍了聚醋酸乙烯乳液保护胶体改性的一些现状和进展。包括聚乙烯醇的缩醛化、酰基化、烷基化、醋酸乙烯共聚物皂化、添加剂改性等方法以及其他保护胶体的应用。     

高分子量聚醋酸乙烯酯的醇解研究

探讨了催化剂浓度、醇解温度和反应时间等对高分子量聚醋酸乙烯酯醇解的影响,得出高分子量聚醋酸乙烯酯醇解的适合条件。     

Manufacturing and characterizations of flexible poly(dimethylsiloxane)/poly(vinyl acetate)/polythiophene ternary composite films

ABSTRACT

In this study, polythiophene and poly(dimethylsiloxane)/poly(vinyl acetate)/polythiophene ternary composites were synthesized. The new ternary composites obtained in powder and film forms were characterized using various techniques. Magnetic properties of all the materials were analyzed by Gouy balance measurements, and it was found that their conductivity mechanism is of polaron nature. The surface structure, surface roughness, and thermal properties of the prepared samples were identified by Scanning Electron Microscopy, Atomic Force Microscopy, and Thermogravimetric Analysis, respectively. The tensile-tension test studies were performed for mechanical properties. The PDMS/PVAc/PT (6%) composite demonstrated about 50% of the maximum strain value (%) of vulcanized natural rubber.     

Studies on the miscibility and phase structure in blends of poly(epichlorohydrin) and poly(vinyl acetate)

The miscibility of atactic poly(epichlorohydrin) (aPECH) with poly(vinyl acetate) (PVAc) was examined under two different conditions: (i) in dilute solution, using vicometeric measurements and (ii) as cast films, using differential scanning calorimetric (DSC) and FT-infrared spectroscopy. Phase separation on heating, i.e. lower critical solution temperature (LCST) behavior of the aPECH/PVAc blends was examined by the measurement of transmitted light intensity against temperature. From viscosity measurements, the Krigbaum-Wall polymer-polymer interaction (ΔB) was evaluated. The DSC results show that the aPECH/PVAc blends are miscible as evidenced by the observation of a single composition-dependent glass-transition temperature (T_g) which is well described by the Couchman and Gordon Taylor models. The Flory-Huggins interaction parameter (χ₁₂) calculated from the T_g-method was negative and equal to −0.01, indicating a relatively low interaction strength. The FT-IR results match very well with those of DSC. The cloud point phenomenon is thermodynamically driven but phase separation, once taken place, is diffusion controlled in normal accessible time.     

Miscibility and hydrogen bonding in blends of poly(vinyl acetate) with phenolic resin

The miscibility of phenolic resin and poly(vinyl acetate) (PVAc) blends was investigated by differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FT-IR) and solid state ¹³C nuclear magnetic resonance (NMR). This blend displays single glass transition temperature (T_g) over entire compositions indicating that this blend system is miscible in the amorphous phase due to the formation of hydrogen bonding between hydroxyl groups of phenolic resin and carbonyl groups of PVAc. Quantitative measurements on fraction of hydrogen-bonded carbonyl group using both ¹³C solid-state NMR and FT-IR analyses result in good agreement between these two spectroscopic techniques. According to the proton spin-lattice relaxation time in the rotating frame (T_1ρ^H), the phenolic/PVAc blend is intimately mixed on a scale less than 2-3 nm. Furthermore, the inter-association equilibrium constant and its related enthalpy of phenolic/PVAc blends were determined as a function of temperatures by infrared spectra based on the Painter-Coleman association model.     

The thermal degradation of poly(vinyl acetate) measured by thermal analysis-Fourier transform infrared spectroscopy

The elimination process which occurs during the thermal degradation of poly(vinyl acetate) has been studied using thermal analysis-Fourier transform infrared spectroscopy. It was found that elimination of acetate groups initially began slowly, but increased as degradation proceeded due to an additional process. The increase in rate was found to depend on the concentration of unsaturated groups in the polymer chain. The activation energy for the initial step was found to be 190 kJ mol⁻¹, while that for the additional process was 130 kJ mol⁻¹. The additional process of elimination was considered to be due to a four-membered transition state, activated by double bonds adjacent to the acetate unit.     

Grafting and adsorption of poly(vinyl) alcohol in vinyl acetate emulsion polymerization

Poly(vinyl alcohol) is often used in vinyl acetate emulsion polymerization as a protective colloid, but its role is complex and controversial since it partakes in grafting reactions with the monomer, influencing process mechanisms, and affecting the colloidal properties of the latex. Furthermore, in industrial operations, the wide scatter of macromolecular properties of the commercial types of poly(vinyl alcohol) causes process irreproducibilities. In this work different types of polyvinyl alcohol were used to perform a series of polymerizations, and their kinetics were compared. A selective solubilization procedure was applied to separate the three fractions of poly(vinyl alcohol) in the final latex: free in the water phase, physically adsorbed onto the polymer particles and chemically grafted. These results were compared with those obtained from pure adsorption measurements of polyvinyl alcohol onto ‘emulsifier-free’ polyvinyl acetate dispersions. The rheological behavior of the different latexes was also compared, and the results were used to formulate an hypothesis on the interaction mechanisms acting in these systems.     

Hansen solubility parameter: from polyethylene and poly(vinyl acetate) homopolymers to ethylene–vinyl acetate copolymers

The Hansen solubility parameters (HSPs ) of two ethylene–vinyl acetate (EVA ) copolymers (with 18 and 33 wt% of vinyl acetate) and their corresponding homopolymers (polyethylene, PE , and poly(vinyl acetate), PVAc ) have been studied at various temperatures, employing the previously obtained Flory–Huggins parameters. From these latter values, a procedure based on the Hansen solubility spheres theory was employed to determine the HSPs , as well as the radius of interaction. The procedure was validated with literature data, with deviations of around 3%. The HSP values (dispersion, polar and association terms, respectively, all in MPa^{1 /2}) at 333.15 K are 14.84, ?3.88 and 1.78 for PE , 17.65, ?1.24 and 2.76 for EVA410 (with 18 wt% of vinyl acetate), 17.52, 0.15 and 3.61 for EVA460 (with 33 wt% of vinyl acetate) and 19.45, 10.59 and 5.76 for PVAc . The main characteristic of the obtained HSP values is that the high polar term of PVAc tends to increase the solubility character of the pure PE , and thus the EVA copolymers, allowing them to solubilize dispersion and polar compounds. Finally, it was also demonstrated that it is possible to predict the HSPs of EVA copolymers using the vinyl acetate content and the HSPs of pure PE and PVAc as input data. © 2017 Society of Chemical Industry     

Drying of semicrystalline polymers: mathematical modeling and experimental characterization of poly(vinyl alcohol) films

A mathematical model was developed to predict the drying mechanism of semicrystalline polymers involving multiple solvents. Since drying of semicrystalline polymers can be accompanied by changes in polymer degree of crystallinity, the model integrates crystallization kinetics and the Vrentas-Duda diffusion model to provide a better understanding of the mechanism. The model considers the effect of external conditions such as temperature, film shrinkage and diffusion and evaporation of multiple solvents during drying. Poly(vinyl alcohol) (PVA)/water/methanol was chosen as a test system. The drying kinetics of PVA films swollen in water and methanol were investigated using gravimetric techniques. The model predicts that higher temperatures, lower film thicknesses and lower methanol to water ratios increase the drying rate. The model predictions were compared with experimental data and showed good agreement.     

Diffusion of solvents in poly(vinyl acetate) and partially and fully hydrolyzed poly(vinyl alcohol)

Diffusivities of methyl acetate, methanol and water in poly(vinyl acetate) and fully and partially hydrolyzed poly(vinyl alcohol) have been measured by capillary column inverse gas chromatography and/or gravimetric sorption. Data from the literature have been used when available for comparison. Overall the diffusivities show good consistency in terms of their temperature and concentration dependences. The free‐volume model has been applied to all the data with excellent results. In most cases the dramatic changes in diffusivities with temperature and concentration can be captured using only a few experimental data points and two regression parameters. This demonstrates that the free‐volume theory is a valuable tool for the design of equipment for processing and devolatilization of polymer ? solvent systems. © 2013 Society of Chemical Industry     

乳液聚合法合成高相对分子质量聚醋酸乙烯酯的研究

采用过硫酸铵/亚硫酸氢钠氧化还原体系低温引发醋酸乙烯酯乳液聚合,合成出分子量为1.07×106、分子量分布为2.75的聚醋酸乙烯酯。讨论了聚合温度、单体用量、十二烷基硫酸钠(SDS)用量、过硫酸铵用量、亚硫酸氢钠用量等因素对聚醋酸乙烯酯黏均分子量的影响,并用GPC法对其进行表征。     

Miscibility and interactions in poly(methylthiomethyl methacrylate)/poly(vinyl alcohol) blends

Poly(methylthiomethyl methacrylate) (PMTMA) is miscible with poly(vinyl alcohol) (PVA) over the whole composition range as shown by the existence of a single glass transition temperature in each blend. The interaction between PMTMA and PVA was examined by Fourier transform infrared spectroscopy, solid-state nuclear magnetic resonance spectroscopy and X-ray photoelectron spectroscopy. The interactions mainly involve the hydroxyl groups of PVA and the thioether sulfur atoms of PMTMA, and the involvement of the carbonyl groups of PMTMA in interactions is not significant. The measurements of proton spin-lattice relaxation time reveal that PMTMA and PVA do not mix intimately on a scale of 1-3 nm, but are miscible on a scale of 20-30 nm. In comparison, we have previously found that PMTMA is miscible with poly(p-vinylphenol) and the two polymers mix intimately on a scale of 1-3 nm.     

Preparation and characterization of high loading porous crosslinked poly(vinyl alcohol) resins

Porous crosslinked poly(vinyl alcohol) resin beads have been prepared by a two-step pathway involving a pre-crosslinking reaction followed by a reverse suspension crosslinking reaction with epichlorohydrin as crosslinker. The reaction conditions have been optimized for the two steps in order to obtain resins with various pores sizes. The crosslinking density of these resins was calculated from their swelling properties by a modified Flory equation. High loading of hydroxyl groups is one of the important characteristics of these resins (attaining ca. 17 mmol/g). The porosity, pore volume, pore structure and the swelling behavior in water of these resins have been studied.     

Studies on the characterization of partly hydrolysed derivatives of poly(vinyl acetate) and their red iodine complex

Three samples of poly(vinyl acetate) 36% hydrolysed, respectively, by saponification, transesterification and acid-equilibrium have been characterized through the refractive indices and light-scattering properties of their solutions in 10% aqueous methanol at 25°C. The original poly(vinyl acetate) sample and its iodine/iodide complex have been similarly characterized, respectively, in methanol at 5°C and in 9.1% methanolic water over the range 5–15°C. The apparent weight-average molecular weights of the vinyl polymers show that the three hydrolytic processes degrade the 130 000 average molecular weight of the original poly(vinyl acetate) macromolecules hardly at all. It is suggested that values of the apparent second virial coefficient might be used as criteria for the characterization of hydrolysed poly(vinyl acetate) specimens which have otherwise identical degrees of hydrolysis and blockiness of their residual acetate groups, but contrasting polydisperse characteristics and surface-active properties. The apparent average root-mean-square radius of gyration of the poly(vinyl acetate) macromolecules is reduced to ≈33% or less of its value on formation of the complex. The characteristics and structure of such complexes are discussed.     

Miscibility Studies of Poly (vinyl acetate) and Cellulose Acetate

Polymer blends of poly (vinyl acetate) (PVAc) with cellulose acetate (CA) have been prepared by solution blending, and their miscibility has been investigated by using physical techniques. Viscosity, density, and ultrasonic velocity for blend solutions at different percentages of the blend composition have been measured at 30°C. The results are discussed.     

Fabrication of poly(vinyl alcohol)s (PVAs) nanotubes through the fusion of nanocapsules composed of PVAs multilayer films

Poly(vinyl alcohol) (PVA) nanocapsules were fabricated by the deposition of PVA multilayer films onto the surface of silica particles followed by the removal of the silica cores. When a water dispersion of PVA nanocapsules was dried on a substrate, PVA nanotubes were formed through the one-dimensional fusion of the nanocapsules. This fusion behavior of the PVA nanocapsules was strongly affected by the molecular weights and acetylation degrees of PVA, the capsule film thickness of the PVA nanocapsules and the temperature to dry a water dispersion of the nanocapsules. When nanocapsules composed of 20 layered films of acetylated PVA with a 14% acetylation degree were used, nanotube formation via the fusion of these nanocapsules occurred effectively upon drying the water dispersion at 20 °C.     

Fibrous membranes of cellulose acetate and poly(vinyl pyrrolidone) by electrospinning method: Preparation and characterization

Fibrous membranes of cellulose acetate (CA), poly(vinyl pyrrolidone) (PVP) and composite membranes of these polymers, were obtained by the electrospinning method. Using systematic method, the optimal conditions for preparation of fibrous membranes were found. Both CA and PVP a concentration of 8% weight was found. The CA was dissolved in a acetone:water solution, volume ratio 80 : 20 and the PVP is dissolved in ethanol:water solution, ratio volume 85 : 15. The flow rate for both polymers was 1.5 mL h^?1. The same applied voltage value and the distance between the needle and collection plate were for polymer both, 15 kV and 15 cm respectively. The morphology of fibrous membranes and composite membranes were evaluated by scanning electron microscopy (SEM). The CA fibers showed ribon morphology, while the PVP fibers were cilindric, in both cases with diameters in the micrometer range. Thermogravimetric analysis showed that CA had a complete degradation to 445°C, while the fibrous membranes PVP required a value of temperature for degradation of up to 571°C. Fibrous composite membrane PVP/CA/PVP shows a higher value of strain at break (%), and a lower value of tensile strength (MPa) compared to CA/PVP/CA. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

超临界二氧化碳-共溶剂体系与聚醋酸乙烯酯相互作用

采用多尺度模拟和实验结合研究了乙醇、丙酮、正庚烷等共溶剂的加入对超临界二氧化碳（CO₂）溶剂体系的影响,通过改善溶剂-溶剂和溶剂-溶质相互作用增强聚醋酸乙烯酯（PVAc）与CO₂的相容性。量子力学从头算结果表明,3种共溶剂中乙醇与CO₂的相互作用最强,丙酮次之,正庚烷最弱。分子动力学模拟也表明在相同共溶剂含量下,乙醇对溶剂体系溶解度参数的改善最为明显,超临界CO₂-乙醇体系与PVAc链的相互作用更强,有助于提高PVAc与溶剂的相容性。这是由于乙醇本身的溶解度参数较大,且与CO₂形成氢键作用,从而大幅增强了其与CO₂的相互作用。浊点压力实验证实了共溶剂的加入增强了超临界CO₂体系与PVAc的相容性,乙醇的加入对PVAc浊点压力的降低最为有效,且随着共溶剂含量的增加,PVAc在溶剂中的溶解能力增强。     

Study of heat shrinkability of crosslinked low‐density polyethylene/poly(ethylene vinyl acetate) blends

In this study, the heat‐shrinkage property in polymer was induced by first compounding low‐density polyethylene/poly(ethylene vinyl acetate) (LDPE/EVA) blends with various amounts of peroxide in a twin‐screw extruder at about 130°C. The resulting granules were molded to shape and chemically crosslinked by compression molding. A process of heating–stretching–cooling was then performed on the samples while on a tensile machine. Shrinkability and effective parameters were also investigated using thermal mechanical analysis. The results showed that the gel fraction was higher for the sample of higher EVA content with the same amount of dicumyl peroxide (DCP). A decrease in the melting point and heat of fusion (ΔH_f), as determined from DSC, was observed with an increase in the DCP content. Studies on the heat shrinkability of the samples showed that samples stretched above the melting point had a higher shrinkage temperature than those stretched around the crystal transition temperature. The results showed that by increasing the peroxide content, the shrinkage temperature was decreased. These could be attributed to the formation of new spherulites as well as changes in the amount and the size of crystals. Furthermore, in samples elongated at 120°C (above the melting point), the rate of stretching had no effect on the shrinkage temperature. The results showed that the extent of strain had no effect on the temperature of shrinkage, but rather on the ultimate shrinkage value. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1389–1395, 2004     

Crosslinking of poly(vinyl acetate) nanolatices by gamma and UV radiation

Poly(vinyl acetate) PVAc, in nanolatices with 10% polymer content, prepared by microemulsion polymerization was crosslinked by gamma and UV radiation. PVAc colloidal nanoparticles (average diameter, Dp = 58 nm) had M_w = 562,000 g/mol and about 95% conversions. PVAc nanolatices irradiated by gamma rays (1–13 kGy) at room temperature without crosslinking agent and by UV light (30–300 s exposure times) in the presence of divinylbenzene and allyl methacrylate showed crosslinking of up to 96% (high gel content), Dp < 100 nm and did not degrade as shown by FTIR spectroscopy. DSC and TGA characterization of irradiated PVAc samples indicated that T_g temperatures increased from 28°C for PVAc to 42°C and 39°C for UV and gamma rays crosslinked PVAc, respectively, whereas 10% weight losses occurred at 261°C for uncrosslinked PVAc and at 320 and 313°C for UV and gamma rays crosslinked PVAc. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012