摘要:

AbstractRheologic, thermodynamic, and mechanical loss tangent properties of a binary polymeric mixture were studied. The system was a mixture of poly(vinyl acetate) (PVA) with ethylenevinyl acetate copolymer (EVC) with varying concentrations of the polymer components and filler. A correlation between the above characteristics of the PVA/EVC two‐phase mixture was found. This mixture was thermodynamically unstable (positive values of the interaction parameter, χ) practically over the entire range of compositions at temperatures of rehologic studies. The presence of a disperse filler raised the thermodynamic stability, that is, parameter χ decreased. Reversal of the sign of the temperature dependence of χ of a mixture with increasing concentration of filler was found. The variations of viscosity with the composition, temperature, and shear for the PVA/EVC mixture are ascribed to different levels of heterogeneity occurring in the process of the shear straining in the working unit of the rheometer. © 1993 John Wiley&Sons

ISSN:0021-8995    

DOI:10.1002/app.1993.070470601

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAn attempt to resolve the difficulties normally faced in preparing PVC‐dominant PVC/ENR blends with the Brabender plasticorder is discussed. As expected, it was found that the mechanical properties of PVC/ENR blends are greatly influenced by the mixing parameters, which are further reinforced with evidence from both dynamic mechanical analysis (DMA) and morphological studies. Both techniques showed the attainment of compatible 50/50/PVC/ENR blends, the former a single glass transition temperature (Tg) and the latter a single‐phase system, albeit their inherent properties are dependent on the blending parameters. By utilizing the correlation between mixing temperature and rotor speed derived, good PVC/ENR blends can be easily procured. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070470602

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe use of on‐line densimetry to monitor conversion in batch emulsion polymerization reactors are investigated. Some characteristics of the sampling circuit connecting the reactor to the densitometer, which allow one to obtain reliable on‐line estimations of monomer conversion in the whole range of conversion, are discussed in detail. Moreover, the amount of collected data provides a practically continuous monitoring of the system evolution in time, which allows one to estimate directly the rate of conversion as a function of time. The technique has been applied both to homopolymerization systems [i.e., styrene (STY) and methyl methacrylate (MMA)] as well as to copolymerization systems [i.e., STY–MMA, acrylonitrile (ACN)–MMA, vinyl acetate (VAC)–MMA]. In the latter case, the density measurements are combined with a reliable model which provides for polymer composition as a function of conversion, in order to obtain accurate measurements of monomers conversion. © 1993 John Wiley

ISSN:0021-8995    

DOI:10.1002/app.1993.070470603

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractGrafting of methyl methacrylate onto polyacrylonitrile was carried out using benzoyl peroxide as initiator and dimethylformamide as solvent. The occurrence of grafting was confirmed by IR spectroscopy and SEM analysis. Effects of various parameters such as reaction time, reaction temperature, initiator concentration, and monomer concentration on rate of polymerization, percentage grafting, and grafting efficiency were studied. The graft copolymers were found to have the similar thermal and structural properties like virgin polyacrylonitrile. Decreasing extent of swelling was observed for the polymers of higher percentage graft in polar solvents. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070470604

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWet filament winding processing for unidirectional composites uses specific reactive systems with low viscosity and long‐pot life. This work describes improvement of toughness of an epoxy/anhydride matrix using, first, the increasing of the average molecular weight of the diepoxy prepolymer and, second, the introduction of a functionalized elastomer. Thermomechanical behaviors (glass transition temperature, elasticity, plastic, and fracture properties) are discussed in terms of (1) the increase of the average molecular weight between crosslinks in the first case and(2) the amount of elastomer dissolved in the matrix in the second case. Dynamic mechanical spectroscopy confirms that phase separation occurred, during curing, between the epoxy system and the elastomer. A good correlation is obtained between matrix toughness and fatigue behavior of unidirectional composites. © 1993 John Wiley&Sons, I

ISSN:0021-8995    

DOI:10.1002/app.1993.070470605

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe acid hydrolysis method is usually utilized to separate acrylic polymer chains grafted onto amylopectin (AMP). The hydrolysis with the HCl acid has been found to be appropriate when we grafted hydroxyethyl methacrylate (HEMA) and hydroxypropyl methacrylate (HPMA). Using the perchloric acid method, various secondary reactions appear falsifying the grafting yields. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070470606

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractA statistical mechanical description of the gas takeup or sorption in polyimides below their glass transition temperature is proposed. The model treated is formally similar to Fowler's early model of monolayer adsorption of gases on solid surfaces. It is expected to be appropriate for polymers exhibiting a significant degree of crystallization, e.g., the aromatic polyimides at temperatures well below their glass transition temperature. The model assumes that the penetrant gas molecules bind to a spectrum of states characterized by a distribution of binding energies. If it is assumed that the penetrant molecules bind to the polymer with only two well‐defined interaction energies, namely, zero as well as some particular finite value, a “dual‐mode” expression for sorption is obtained. It is pointed out that this “dual‐mode” or “two‐state” model is not consistent with some recent data obtained on carbon dioxide sorption in a polyimide. Two other simplified models are examined, a “uniform‐density‐of‐states” model and a “three‐state” model. The present treatment yields explicit expressions for the temperature dependence of the sorption parameters. This dependence reflects the thermodynamic redistribution of penetrant molecules among the available fixed density‐of‐states as the temperature is varied. It is pointed out that the temperature dependence of the Langmuir capacity constant obtained from nonlinear least squares fitting the standard “dual‐mode” sorption expression to the polyimide sorption data may lead to an erroneous inference concerning the decrease in “unrelaxed volume” as the temperature is increased from well below the glass transition temperature of the polymer. The “three‐state” model yields sorption isotherms that parallel the data of Sada et al. closely. This suggests the presence of multiple carbon dioxide bind

ISSN:0021-8995    

DOI:10.1002/app.1993.070470607

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractCured adhesive layers produced from ethyl‐(ECA), allyl‐(ACA), and allyloxyethyl‐(AOECA) 2‐cyanoacrylates were studied by means of thermogravimetry and differential scanning calorimetry. Polymer films of ECA‐based adhesive compositions comprising various amounts and types of 2‐cyano‐2,4‐pentadienoic acid (CPDA) esters were also examined. The influence of the modifier type, as well as the chemical structure of the cyanoacrylates used, was followed upon the glass transition temperatures (Tg) and the rates of thermal degradation of the corresponding polymers. In the case of cured adhesive mixtures containing unsaturated CPDA esters and when poly(ACA) and poly(AOECA) were studied, a significant increase of their heat resistance was established, as compared with poly(ECA). This fact was explained with the formation of three‐dimensional structure of the polymer film due to crosslinking reactions. A different course and character of these reactions were found comparing the thermal behavior of poly(ACA) and cured compositions containing unsaturated CPDA esters. A good agreement was found between data from the thermal analyses and the tensile shear and impact strength tests. It was shown that the modification of ECA with unsaturated CPDA esters is a possible way of increasing the heat resistance of the basic adhesive. © 1993 Jo

ISSN:0021-8995    

DOI:10.1002/app.1993.070470608

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractPoly(methyl methacrylate) (PMMA) was photolyzed with monochromatic light of wavelengths 260, 280, 300, 320, 400, and 500 nm in vacuo by the use of the Okazaki Large Spectrograph. UV spectral changes, the quantum yields of main‐chain scission (ϕcs), and effects of wavelength were investigated. UV spectral changes around 280 nm were observed with irradiation at 260 nm. The ϕcshas a maximum value in case of irradiation with 300 nm light. It turned out that photodegradation of PMMA took place by irradiation of 260–320 nm light but did not by irradiation with the light longer wavelength than 340 nm. The average values of ϕcsobtained in this work were 0.84 × 10−4, 1.06 × 10−4, 4.21 × 10−4, 1.23 × 10−4, 0, and 0 for irradiations at 260, 280, 300, 320, 400, and 500 nm, respectively. It was found that the photo‐induced side‐chain scission initiates the main‐chain scission of PMMA by irradiation of 260 and 280 nm light. ©

ISSN:0021-8995    

DOI:10.1002/app.1993.070470609

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe diffusion and permeation coefficients for He, H2, D2, O2, and N2in a variety of elastomers were measured by simple manometric methods. The elastomers studied were butyl rubber; Hypalon® 40 and 45; Viton® E60 and GF; Hydrin® 100 and filled Hydrin® 100; Kraton® G, FG, and KG VTEOS; EPDM; epoxidized natural rubber; and neoprene. Consistent with earlier studies, elastomers with higher glass transition temperatures exhibited lower diffusion coefficients. The ratio of diffusion coefficients of the hydrogen isotope pair differed from the purely molecular‐weight‐based prediction. Deuterium's slightly smaller size relative to hydrogen is consistent with observed deviations from the molecular‐weight‐based diffusion coefficient ratio. © 1993 John Wi

ISSN:0021-8995    

DOI:10.1002/app.1993.070470610

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY