摘要:

AbstractA new method to investigate the mechanical degradation of polymers in solution is described that uses size exclusion chromatograms of the initial polymer and of the degraded sample. The incipient parts of these chromatograms are analyzed to obtain kinetic data about degradation at the level of infinitesimal fractions. The procedure is based on the fact that mechanical degradation of the polymers is a first‐order reaction and macromolecules are cleaved mostly in their central region. The rate constant and the variation in the rate constant with molecular weight are determined in a single experiment, avoiding additional fractionation steps. Moreover, the slope of the size exclusion chromatographic calibration curve is derived, opening new ways to determine polydispersities or even to make rapid calibration for unknown polymers. To verify the method, the rate constant and the molecular weight dependence of the rate constant were determined for the sonic degradation of polystyrene in toluene. The rate constant is found to vary with the square of the molecular weight, and its value is in good agreement with results reported using much more laborious methods. © 1993 John Wiley&Sons, I

ISSN:0021-8995    

DOI:10.1002/app.1993.070501201

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe esterification of cellulose by a poly(carboxylic acid) proceeds in two steps: the formation of a 5‐membered cyclic anhydride intermediate by the dehydration of two carboxyls, and the reaction between cellulose and the anhydride intermediate to form an ester. Sodium hypophosphite is the most effective catalyst for the esterification. The effect of sodium hypophosphite on the esterification of cotton cellulose was studied by Fourier transform infrared spectroscopy (FTIR). It was found that sodium hypophosphite accelerates both the formation of the cyclic anhydride intermediate and the reaction between the anhydride intermediate and cellulose. The chief role of sodium hypophosphite is possibly the acceleration of the esterification of cellulose by the anhydride intermediate. © 1993 John Wiley&Sons, I

ISSN:0021-8995    

DOI:10.1002/app.1993.070501202

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe present investigation was aimed at understanding the role of chemical compatibilizers like carboxy‐terminated nitrile rubber, amine‐terminated nitrile rubber, liquid carboxylated nitrile rubber, etc. in the reactive processing of a dynamically vulcanized 50 : 50 nylon/ HNBR blend. The interfacial parameters for a bilayer specimen of nylon and rubber and structure parameters during the processing were determined. The interfacial thickness (λ) increased from 48 to 70–80 nm and the interfacial tension (γ∞) decreased from 0.240 to 0.209–0.198 mN/m, depending on the nature and concentration of the compatibilizer. There was, however, an optimum level of the compatibilizer beyond which the thickness did not change significantly. For the ionomeric compatibilizer, λ decreased after the optimum concentration. The increase in λ is ascribed to the formation of a graft copolymer of nylon and rubber and the compatibilization reactions. Structure parameters were dependent upon the sequence of mixing of the compatibilizer. If the compatibilizer and the cross‐linker were added in the rubber and the mixture was then added to nylon, the mean radius of the dispersed particle was smaller over the range of mixing times. The compatibilizers also reduced the particle size at the early stage of mixing due to reduced interfacial tension. In general, the particle size decreased with mixing time, attained a minimum, and then increased. The volume fraction of the interface was also very large for compatibilized systems. The particles were larger, however, when the compatibilizer was first mixed in nylon. SEM studies indicated that the compatibilizer in the latter case was not acting as a surfactant. © 1993 John

ISSN:0021-8995    

DOI:10.1002/app.1993.070501203

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe action of methacrylic acid onto tetraglycidyl methylene dianiline, tetraglycidyl sulfone dianiline, triglycidyl triphenylmethane (TACTIX), and epoxy novolac resins was performed using different catalysts. In each case, a comparative study of these catalysts was investigated depending upon the polarity of the solvent and of the temperature. Chromium complexes are better in low polar solvents. The reactions were monitored by1H‐NMR, by epoxide titration, and by size exclusion chromatography (SEC), and the reactivity of these resins could be compared. Finally, the study of these materials obtained after radical and photochemical cross‐linking, especially by dynamic mechanical analysis (DMA), shows that these materials exhibit highTg's (200°C for methacrylated TACTIX) compared to those of the corresponding multiepoxides cured by diamines. © 1993 John Wiley&Sons

ISSN:0021-8995    

DOI:10.1002/app.1993.070501204

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

年代:1993

数据来源: WILEY

摘要:

AbstractExperimental specific volume data as a function of temperature (30–269°C) and pressure (0–2000 bar) are presented for two semicrystalline polymers, namely, poly(vinylidene fluoride) and polyamide‐11. Data for the melt state were used to determine the characteristic parameters for six theoretical equations of state as well as the empirical Tait equation. The theories employed were the cell models of Flory–Orwoll–Vrij, of Prigogine et al., and of Dee and Walsh, the latticefluid theory of Sanchez and Lacombe, the hole theory of Simha and Somcynsky, and the semiempirical model of Hartmann and Haque. Solid‐state data were also fit using the Hartmann–Haque and Tait equations. © 1993 John

ISSN:0021-8995    

DOI:10.1002/app.1993.070501205

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

年代:1993

数据来源: WILEY

摘要:

AbstractDiscrete small‐angle X‐ray scattering (SAXS) has been used as an analytical tool to study the development of crystalline morphology in a series of blow‐extruded high‐density polyethylene (HDPE) films. Processing parameters, take‐up ratio (TUR) and blow‐up ratio (BUR), were the primary variables used in this investigation. Results from SAXS have led to the consideration of a new microstructural model for crystallite development in blown films. The model incorporates row‐nucleated lamellae, where crystalline morphology is sensitive to TUR and BUR. Increasing TUR results in an increase in the number of lamellae in a particular stack, a decrease in fluctuations of amorphous and crystalline thickness distributions, a flattening out of undulations of crystal surfaces, and an increase in the lateral dimensions of lamellae. Increasing BUR did not significantly influence any of the SAXS parameters studied; this can be attributed to the low BURs at which the films were made. © 1993 John W

ISSN:0021-8995    

DOI:10.1002/app.1993.070501206

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

年代:1993

数据来源: WILEY

摘要:

AbstractA method to predict the permeability coefficients of gases in nylons at different relative humidities was proposed. The model was tested for Nylon 6 and 6,6 with oxygen as a permeant. Very good agreement between the predicted and experimentally determined values was found. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070501207

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

年代:1993

数据来源: WILEY

摘要:

AbstractCellulose thiocarbonate was prepared by reacting cotton cellulose fabric with carbon disulphide in the presence of sodium hydroxide. The treated fabric formed, with pentavalent vanadium ion, an effective redox system capable of initiating grafting of methyl methacrylate (MMA) and other monomers no+o the cotton fabric. The dependence of grafting on vanadium concentration, pH of the polymerization medium, temperature and duration of grafting, nature and concentration of monomer, and solvent/water ratio was studied. The results indicated that increasing the pentavalent vanadium (Vv) concentration up to 60 mmol/L was accompanied by enhancement in the rate of grafting; the latter was not affected by further increase inVvconcentration. Maximum grafting yield was achieved at pH 2; grafting fell greatly at higher pH. The rate of grafting followed the order: 70°>60°>50°C. The graft yield increased significantly by increasing the MMA concentration from 0.5 to 5%. Of the solvents studied,n‐propanol and isopropanol enhanced the grafting rate provided that a solvent/water ratio of 5 : 95 was used; a higher solvent ratio decreased the magnitude of grafting. Other solvents, namely, methanol, ethanol,n‐butanol, and acetone, in any proportion, decreased the rate of grafting. With the monomer used, the graft yield followed the order: methyl methacrylate>methyl acrylate>methacrylic acid>ethyl methacrylate>acrylic acid. Also reported was a tentative mechanism for vinyl‐graft copolymerization onto cotton fabric using cellulose thiocarbonate‐Vv. © 1993 John Wile

ISSN:0021-8995    

DOI:10.1002/app.1993.070501208

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

年代:1993

数据来源: WILEY

摘要:

AbstractAssignment of C13NMR bands to important sites of polymeric flavonoid tannin extracts produced industrially for production of tannin–formaldehyde resins is reported. Five different tannin extracts were studied. The C13NMR bands' position and relative intensities allowed us to qualitatively explain comparative differences in the five tannins' structural features and properties that are of importance for tannin adhesives applications. The five tannins could be divided into two classes (1) mimosa and quebracho tannins and (2) pecan nut, pine, and gambier tannins. Properties of relevance that varied considerably among the five tannins and that could be detected by13C NMR were: the relative proportions of fisetinidin/robinetinidin units in relation to catechin/gallocatechin units; differences in number average degree of polymerization; the extent of open heterocycle forms present; branching; and relative proportion of pyrogallol versus catechol B‐rings in the flavonoid repeating units. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070501209

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

年代:1993

数据来源: WILEY

摘要:

AbstractA procedure to verify the identity of hydraulic fluids (HF) type C and D U is described. Different gel filtration systems were tested to separate the constitutive components. After fractionation of the mixture, IR and NMR spectroscopy were tried for their suitability in verifying the identity of the different constituents. The combination of aqueous gel filtration chromatography and IR spectroscopy was found suitable to separate and identify the different components of HFC fluids. For HFD U fluids, a modified gel filtration system was used and NMR spectroscopy was necessary to give a decisive answer about their identity. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070501210

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

年代:1993

数据来源: WILEY