聚硅氧烷-醋酸乙烯酯共聚乳液的研究

采用功能性聚硅氧烷 (PMS)、醋酸乙烯酯 (VAc)及羟甲基丙烯酰胺 (NMA)进行乳液聚合 ,得到了PMS -VAc共聚乳液胶粘剂。讨论了PMS用量对聚合反应转化率、乳液流变性、冻融稳定性及耐水性的影响。结果表明 :该共聚物乳液具有良好的粘接强度、耐低温性能和耐水性     

Dynamic mechanical properties of hydroxyapatite-ethylene vinyl acetate copolymer composites

Dynamic mechanical thermal analysis (DMTA) was carried out to explore the dependence of temperature on the viscoelasticity of composites consisting of synthetic hydroxyapatite (HAP) particulate filled ethylene vinyl acetate copolymer (EVA). Two forms of HAP, differing in their surface characteristics and particle size, were used for the study. The freeze-dried HAP (FDHAP) had a mean particle size of 49.18 μm and an irregular surface morphology. In the contrary the spray dried form of HAP (SDHAP) had a mean particle size of 5.84 (m and a spherical morphology. The dynamic mechanical analysis of the composites showed that both, particle size and morphology, had a significant effect on viscoelastic properties. A tremendous increase of the storage modulus was noted with the addition of HAP. Above the T_g of the polymer matrix, the values were marginally higher for the composites containing FDHAP than for those with SDHAP. The damping (tan δ) was found to decrease with the inclusion of HAP. A marginal upper shift in the value of the glass transition temperature (T_g) was observed for the composites fabricated from SDHAP indicating a slightly strong interaction between this HAP and the EVA matrix.     

Thermal conductivity of ethylene vinyl acetate copolymer/nanofiller blends

To reduce weight and increase mobility, comfort, and performance of future spacesuits, flexible, thermally conductive fabrics and plastic tubes are needed for the Liquid Cooling and Ventilation Garment. As an approach to raise thermal conductivity (TC) of an ethylene vinyl acetate copolymer (Elvax^™ 260), it was compounded with carbon based nanofillers: multi-walled carbon nanotubes (MWCNTs), vapor grown carbon nanofibers (CNFs), and expanded graphite (EG) as well as metallized CNFs, nickel nanostrands, boron nitride, and powdered aluminum. Ribbons and tubing of the nanocomposites, in which the nanofillers were aligned in the direction of flow, were extruded. Compression molding was used to fabricate nanocomposites in which the nanofillers were randomly oriented. TC of the samples was measured in the direction of, and perpendicular to, the alignment direction and significant improvement in TC (up to 24-fold) was observed when measurements were made in the direction of alignment.     

Preparation of ethylene vinyl acetate copolymer latex by flow induced phase inversion emulsification

Ethylene vinyl acetate (EVA) copolymer was emulsified in the melt state using hydrophobically modified water soluble polymers (HMWSPs) as surfactants and the flow induced phase inversion (FIPI) emulsification technique. The history of the emulsification and emulsion structure were monitored using a process rheometer and off-line scanning electron microscopy and particle size measurements. It was shown that low molecular weight surfactants could not be used to emulsify the polymer melt. When HMWSPs were used, the emulsion characteristics were strongly influenced by the molecular structure of the surfactant. Water-in-polymer melt emulsion was phase inverted to polymer melt-in-water emulsion at 20% water phase volume. When this emulsion was allowed to cool after further dilution (30% water) while mixing, a second phase inversion took place to obtain a water-in-polymer dispersion which has the consistency of a powder. When this dispersion was re-heated, while mixing, a third phase inversion occurred and a multiple emulsion system was obtained. Upon the solidification of the polymer, the structure of the dispersion was revealed as (water-in-polymer)-in-water. Water continuous latex from the first phase inversion and the powdery emulsion from the second phase inversion can be used in coating applications while the third phase inversion produces micro-porous polymer.     

Controlled drug release for oral condition by a novel device based on ethylene vinyl acetate (EVA) copolymer

The application of drug delivery systems in oral environment is relatively a new area of research with the exception of release of fluoride ions from polyalkenoate cements and their predecessor silicate cements. The present study addresses development of a novel device based on ethylene vinyl acetate copolymer (EVA), a biocompatible material which enables constant drug release over several days to treat oral infections. Drugs incorporated in EVA included tetracycline, minocycline and nystatin together with combinations (C) of nytatin-tetracycline (1 : 1) and nystatin-minocycline (1 : 1). Polymer casting solutions were prepared by dissolving EVA and the drugs in the ratio of 10 : 1 in 70 ml of dichloromethane at 38 °C for 6 h. Thin square films of 3×3 cm and 1 mm thickness were cut from the dry sheet obtained by solvent evaporation. Drug loaded samples were extracted for a minimum of 15 days in 10 ml medium (water or water/ethanol (1 : 2) or 0.9% saline solution) which is replaced daily. Spectral measurements were made to follow changes in optical densities (OD) during release kinetics. Analysis of the data revealed that among all the drugs tested tetracycline exhibited the highest release rate (56.15ug/cm²/day) and % cumulative release (27.92).The observed enhanced values may be interpreted as due to the channels formed due to changes in free volume (microvoids). In case of nystatin-minocycline combination, the observed increased values of release rates and percent cumulative release, may be attributed to the swelling component or channels or relative hydrophobic interactions. Initial burst effects due to liberation of surface-bound drug molecules were observed with reference to all the three drugs and the combinations of drugs studied. Among all the drugs, minocycline exhibited the least burst effect suggesting that the drug is more homogeneously distributed in the copolymer. Drug loaded EVA thermoplastic copolymer may provide a favorable therapeutic material for the development of a novel, local treatment for oral, mucosal and periodontal infections.     

Stability and release of antiviral drugs from ethylene vinyl acetate (EVA) copolymer

The use of polymer based drug delivery systems in dentistry is a relatively new area of research with the exception of the inhibition of secondary caries by the release of fluoride ions from polyalkenoate cements and their predecessors silicate cements. The present study was to test on orally biocompatible material, ethylene vinyl acetate copolymer (EVA), for release of antiviral drugs at oral therapeutic levels over extended periods of time. We also determined their stability during film casting and release. Materials studied include gancyclovir (GCY), acyclovir (ACY), dichloromethane (DCM), and ethylene vinyl acetate (EVA). The square films (3 × 3 × 0.1 cm) were prepared from the dry sheet obtained by solvent evaporation of polymer casting solutions. These solutions were made of EVA and the drug (40:1) in 70 ml of dichloromethane at 38^∘C. Then drug release characteristics from the drug loaded films were examined at 37^∘C for a minimum of 14 days in 10 ml medium (ddwater) replaced daily. Kinetics of drug release were followed by spectral measurements using previously determined λ_max values (GCY = 250 nm; ACY = 253 nm). A minimum of three samples was tested and reproducible results were obtained. Drug stability (ACY) during film casting and its release was determined using ¹H NMR spectrometer (Bruker DRX-500 and 400). Rate of drug release was determined from the part of the curve (rate vs. time) after the onset of the “burst.” Although GCY has a larger molecular weight (255) than ACY (225), GCY exhibited about three times higher rate of release than ACY. This difference in rate values may be explained due to its relatively greater solubility in EVA, facilitating faster diffusion of the molecules through the channels present in EVA. This is consistent with the observation that the rate at which drug molecules diffuse through the channels of the polymer, can be increased by decreasing the molecular weight. In the case of ACY, the molecules may be undergoing molecular associations, perhaps dimerization or trimerization in addition to its lower solubility in EVA. The diffusion of ACY tends to be slower under these circumstances compared to GCY resulting in lower rate value than in the case of GCY. Biological studies revealed that ACY exhibited a remarkable decrease in a number of viral organisms present in virus infected cell culture system using real-time polymerase chain reaction (RT-PCR). NMR analysis indicates that the chemical structure of the drug remains stable during film casting process and release.     

LDPE/EVA/蒙脱土熔融插层纳米复合体系稳态剪切流变行为

用平行板和毛细管流变仪测定并研究了具有剥离结构的低密度聚乙烯(LDPE)／乙烯-醋酸乙烯共聚物(EVA)／蒙脱土纳米复合材料熔体的稳态剪切流变行为。研究结果表明,蒙脱土含量较低的复合物熔体,在低剪切速率下,即出现剪切变稀现象；而在较高剪切速率下,填充物浓度对体系熔体的剪切粘度影响较小；与基体树脂相比较,蒙脱土的加入,使其熔体的非牛顿指数降低,粘流活化能略有增加。     

通过微弧氧化和水热处理在钛上沉积羟基磷灰石

在含有0.04mol/L β-甘油磷酸钠(β-GP)和0.10mol/L醋酸钙(CA)电解液中对Ti进行微弧氧化.结果发现:微弧氧化方法适合于Ti在甘油磷酸钠和醋酸钙电解液中形成富含有Ca和P的氧化膜.氧化膜粗糙多孔,电流密度和最后电压分别为200A/m2和430 V形成的氧化膜主要由锐钛矿型TiO2,金红石型TiO2和非晶相组成.低温下进行水热处理,羟基磷灰石晶体在氧化膜的表面沉积.用扫描电镜、能谱仪、X射线衍射、X射线光电子能谱对氧化膜进行了研究.     

四氟乙烯-全氟甲基乙烯基醚共聚物的研究进展

作为可熔融加工且性能接近于聚四氟乙烯的全氟聚合物,PFA(四氟乙烯-全氟烷基乙烯基醚聚合物)得到了很快的发展并已形成了两个系列的商品.其中四氟乙烯-全氟丙基乙烯基醚共聚物(PFA-P)已经为人们熟悉,而另一类品种即四氟乙烯-全氟甲基乙烯基醚共聚物(PFA-M)却少有文献介绍.本研究对PFA-M的结构、性能、加工以及应用进行了综述.     

不同蒙脱土对Al(OH)_3/乙烯-醋酸乙烯酯复合材料力学性能和阻燃性能的影响

对比研究了钙基蒙脱土(Ca-MMT)和有机改性的钠基蒙脱土(Na-MMT)对Al(OH)_3/乙烯一醋酸乙烯醋(EVA)复合材料的力学性能、热稳定性和阻燃性能的影响。采用熔融插层法制备MMT-Al(OH)_3/EVA复合材料。用XRD和TEM进行微观结构表征。结果表明:两种MMT在复合材料中均表现为一定程度的剥离分散状态,其中Ca-MMT的剥离片层相对尺寸更小。测试显示,Ca-MMT-Al(OH)_3/EVA的拉伸强度、热稳定性均高于Na-MMT-Al(OH)3/EVA;在燃烧过程中,加入Ca-MMT的Ca-MMT-Al(OH)_3/EVA复合材料热释放更低,形成的炭层隔热效果更好,表现出更优异的阻燃性能;同时火灾性能指数(FPI)提高,火灾危险性明显降低。分析原因是Ca-MMT中的Ca~(2+)在燃烧成炭中具有促进作用。     

Morphology of the poly(vinyl alcohol)–poly(vinyl acetate) copolymer in macrodefect-free composites: a 13C magic-angle-spinning nuclear magnetic resonance and 1H spin-diffusion study

A study was made of the macrodefect-free (MDF) composite based on aluminate cement and a poly(vinyl alcohol)–poly(vinyl acetate) (PVAc) copolymer by ¹³C cross-polarization magic-angle-spinning nuclear magnetic resonance. The spectra were run on both the copolymer and the MDF composite in order to observe the atomic environments of the carbon nuclei. An analysis of the intramolecular hydrogen bonds showed a stronger modification in the sample containing CaAl₂O₄ (CA) than in that containing Ca₃Al₂O₆ (C₃A). From the spectra, it was seen that deacetylation had occurred, and that there was interaction between acetate groups and the calcium and aluminium ions. Proton relaxation times both in the laboratory frame, T ₁(H), and in the rotating frame, T1ρ(H), were exploited for the study of the dimension of the polymer matrix in MDF composites. An extended interphase was identified in the composite containing CA. A comparison with the behaviour of the composite based on silicates Ca₃SiO₅–PVAc highlights the better mixing of the phases in the MDF composites containing CA. This revised version was published online in November 2006 with corrections to the Cover Date.     

Cyclodextrin microencapsulated ammonium polyphosphate: Preparation and its performance on the thermal,flame retardancy and mechanical properties of ethylene vinyl acetate copolymer

Cyclodextrin microencapsulated ammonium polyphosphate (MCAPP) was prepared by the reaction between cyclodextrin (CD) and toluene-2,4-diisocyanate (TDI) with the goal of improving the water durability of APP and preparing a novel functional flame retardants. The Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS) results indicated MCAPP were successfully prepared, and the water contact angle (WCA) results indicated that cyclodextrin resulted in the transformation of hydrophilic to hydrophobic of the flame retardant surface. The MCAPP was then incorporated into the ethylene vinyl acetate copolymer (EVA) system and the effects of the MCAPP on the mechanical, combustion, thermal, interfacial adhesion and flame-retardant properties of EVA cable were investigated and compared by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), limiting oxygen index (LOI), mechanical test, cone calorimeter and UL-94 test. The characterization for the various properties of EVA composites demonstrated that cyclodextrin microencapsulation technology could enhance the interfacial adhesion, resulting in the improved mechanical, thermal stability, combustion properties and flame-retardant properties compared with those of EVA/APP/CD system. Furthermore, the water resistance experiments results demonstrate that EVA/MCAPP composites have good water durability due to the hydrophobic property of MCAPP. Above all, the microencapsulation of APP with cyclodextrin developed in this study may be a promising formulation for combining the acid source, the carbonization agent and the blowing agent in one flame retardant, and the MCAPP can solve the water resistance and the compatibility problem of the flame retardant during the industrial application.     

离子液体中淀粉颗粒接枝醋酸乙烯酯的研究

以离子液体1-乙烯基-3-甲基咪唑氯盐([AMIM]Cl)为溶剂,以过硫酸铵为引发剂,制备了木薯淀粉接枝醋酸乙烯酯共聚物.研究了引发剂浓度、醋酸乙烯酯单体与淀粉的配比、反应温度以及反应时间等因素对淀粉接枝醋酸乙烯酯共聚参数的影响,并对淀粉接枝产物进行了红外光谱、XRD、SEM分析.结果表明,在[AMIM]Cl中淀粉接枝...     

Time-domain dielectric relaxation in polyamide 6, poly(vinyl chloride), ethylene-vinyl acetate copolymer and poly(vinylidene fluoride)

The time-domain dielectric responses of polyamide 6 (PA6), poly(vinyl chloride) (PVC), ethylene-vinyl acetate copolymer (EVA) and poly(vinylidene fluoride) (PVDF) to a voltage step were measured at different temperatures. From the variation of the sample capacitance,C, with time, the ratioF _d/C was determined, whereF _d = (dC/dlnt)_max is the maximum (inflexion) slope of the capacitance versus log(time) dipole response curve, and C is the difference between the initial and the extrapolated equilibrium capacitance values. A modified KohIrausch-WiIIiams-Watts (stretched exponential) function provided a good fit to the measuredC(t) data. For low temperatures, typically below – 20°C,F _d/C, is about 0.1, characteristic of highly cooperative relaxation, while at higher temperatures the ratio approaches 1/e, characteristic of nearly independent (Maxwellian) relaxation. This is in contrast to corresponding analyses of mechanical relaxation in solids for which the constant is almost always near 0.1 at room temperature.     

Effect of stabilizer on the mechanical,morphological and thermal properties of compatibilized high density polyethylene/ethylene vinyl acetate copolymer/organoclay nanocomposites

In this work, the effects of a phosphate containing stabilizer on the mechanical, morphological and thermal properties of a compatibilized high density polyethylene (HDPE)/ethylene vinyl acetate (EVA) blend containing an ammonium quaternary salts modified montmorillonite were studied from both statistical and experimental aspects. According to the results obtained from simultaneous implementation of analysis of variance (ANOVA) and mean effect assessment, the formulations designed based on the optimized coupling of stabilizer into organoclay/compatibilizer system exhibited the highest tensile properties among the prepared samples. From experimental point of view, the d-spacing measurements and microscopy observations through X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively, revealed that the stabilizer not only favored the penetration of the polymeric chains between the silicate layers but also contributed to provide finer dispersion of the minor phase in the matrix. Thermal characterizations using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the stabilizer could play a role in prevention of the organic modifier of the nanoclay to undergo thermo-oxidative degradation by hindering the SN₂ nucleophilic substitution reactions between alkyl ammonium chains and oxygen molecules. This, we believe, is responsible for the properties enhancement, since the protective role of stabilizer might inhibit the formation of destructive degradation products which could collapse the organoclay tactoids and also deactivate the anhydride groups of the compatibilizer.     

邻甲苯胺与醋酸乙烯酯的化学氧化共聚

通过化学氧化聚合法制备了一系列不同单体配比的邻甲苯胺/醋酸乙烯酯共聚物。研究了聚合反应过程中聚合体系的开路电位和溶液温度的变化,并提出了邻甲苯胺与醋酸乙烯酯的共聚反应机理。采用红外光谱和热重分析对共聚物进行了结构表征。     

Chemistry of removal of ethylene vinyl acetate binders

The research presented herein has focused on debinding of an ethylene copolymer from a SiC based moulded ceramic green body within an inert atmosphere. Upon heating, the pure polymer undergoes a two-stage thermal degradation process. In the first stage, acetic acid is the only degradation product formed. The effect of the introduction of high surface area powder on the chemistry and kinetics of this first stage reaction was examined. The effluents were captured and analysed in a gas chromatograph/mass spectrometer. The product of the reaction was not altered by introduction of the ceramic powder. However, the kinetics of the reaction were altered. The kinetics of the reaction were determined with the use of thermogravi metric analysis (TGA). The mechanism of mass transport during binder removal was determined by monitoring dimensional changes during binder removal. It was found that one unit volume of shrinkage corresponded with one unit volume of binder removed, indicating that no porosity developed. The escaping acetic acid effluents must diffuse through the liquid polymer filled pores to escape. Bloating was observed in certain conditions and was attributed to the concentration of acetic acid exceeding a critical value, resulting in bubbling.     

Emulsion polymerization of vinyl acetate: safe optimization of a hazardous complex process

Fast and exothermic discontinuous emulsion polymerization processes are particularly difficult to optimize from both safety and productivity point of view because of the occurrence of side undesired reactions (e.g. chain transfer to monomer, backbiting, propagation of tertiary radicals, termination by disproportion, etc.) and the hazards of boiling phenomena and stable foam formation under atmospheric pressure. Moreover, the relevant number of loading, heating and cooling steps, required before starting the monomer addition (that is, the desired reaction), makes a strict product quality reproducibility very difficult to obtain. Under these operating conditions, it is necessary to employ a suitable combined theoretical and experimental procedure able to detect the optimum process dosing time at both the laboratory and the industrial scale. In this work, it is shown how to use the topological criterion theory together with proper adiabatic calorimeter and RC1 experimental data to safely optimize the synthesis of polyvinyl acetate through the radical emulsion polymerization of vinyl acetate by the means of an indirectly cooled isoperibolic semibatch reactor.