摘要:

AbstractA critical account has been presented of the recent investigation on the chemical modification of lignocellulosic sisal fibers. The molecular structure of the paracrystalline cellulose, which forms the major constituent of the fiber, was studied by x‐ray diffraction technique. Scanning electron microscope examination of the multicellular structure, surface topology, and fracture morphology of the fiber was carried out. The mechanical properties of the sisal ultimate cell and the “technical” fiber have been investigated by means of a microextensometer and an Instron tensile tester, respect

ISSN:0021-8995    

DOI:10.1002/app.1976.070201101

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

年代:1976

数据来源: WILEY

摘要:

AbstractBy measuring tack energy using a modified probe tack testing procedure, the interrelation of bulk energy and surface energy effects in pressure‐sensitive adhesives was studied. Tack energy was strongly influenced by the solvent used in the preparation of the adhesive film. A procedure was empirically derived which reduced the number of variables to a single variable, yielding a single master curve in which the independent variable was the speed of probe withdrawal expressed on a logarithmic scale. The form of the curve was a simple exponential function,y=Aexp (mx), whereAandmare constants andyandxare the dependent and independent variables, respectively. The constantmwas found to be a unique function of the type of adhesive used. A theoretical interpretation of the devised procedure was based on bulk viscoelastic effects and a combined activation energy–free volume concept of adhesive bonding. The wider implications of this are briefly discus

ISSN:0021-8995    

DOI:10.1002/app.1976.070201102

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe surface areas of dyed and undyed secondary cellulose acetate fibers have been determined using low‐temperature nitrogen gas adsorption by the method of Brunauer, Emmett, and Teller. The results confirmed earlier work usingp‐nitrophenol, in which it was shown that there is a marked change of surface area of dyed fiber in the region corresponding to a theoretical monolayer adsorption of the

ISSN:0021-8995    

DOI:10.1002/app.1976.070201103

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe thermal stability of poly‐ϵ‐caprolactone samples obtained by ring‐opening polymerization in the presence of different metal alkoxides has been investigated. A significant degradation of the polyesters is observed under isothermal conditions at 120°C. The degradation is related to the nature of the endgroup, the presence of catalyst residues, and the presence of molecular oxygen. The hydroxyl endgroups play a determinant role in the process. They probably give rise, under the influence of catalyst residues, to hydroperoxides which are responsible for the polymer degradation by a radical reaction. It is shown that this is clearly different from the change in molecular weights distribution due to the well‐known ester interchange reaction (transesterification equilibrium). Resulting methods for the polymers stabilization are

ISSN:0021-8995    

DOI:10.1002/app.1976.070201104

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

年代:1976

数据来源: WILEY

摘要:

AbstractBromostyrene was used as partial replacement of styrene for crosslinking polyester resins. The oxidative stability of the polymer was studied and the performance in standard flammability tests was tested. It was shown that flame retardation increased linearly with the Br content. Under certain conditions, self‐extinguishing polyesters were obtaine

ISSN:0021-8995    

DOI:10.1002/app.1976.070201105

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe partial replacement of styrene by bromostyrene in polyesters, in order to achieve fire‐retardant resins, raised the need to explore the effect of the bromine on the mechanical performance of these resins and of their glass fiber composites. The present study reveals that under combined humidity and uv radiation conditions, the mechanical performance of the bromine‐containing resin surpasses that of the original re

ISSN:0021-8995    

DOI:10.1002/app.1976.070201106

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

年代:1976

数据来源: WILEY

摘要:

AbstractA practical method for the overall performance evaluation of a GPC system (columns) is described. System performance is defined as the ability of the system to give experimental M̄nand M̄wvalues (uncorrected for instrumental spreading and other distorting factors) which agree with the theoretical values, and it is expressed as the per cent deviation between the theoretical and experimental values. The method consists of running blends of monodispersed polystyrene standards of known compositions through the GPC system to be evaluated. From the resulting chromatograms, their M̄nand M̄wvalues are calculated (experimental). The theoretical M̄nand M̄wvalues of the same standards are also calculated from the formulas\documentclass{article}\pagestyle{empty}\begin{document}$$ \bar M_n = \frac{{\Sigma M_i N_i }}{{\Sigma N_i }}{\rm and }\bar M_w = \frac{{\Sigma M_i ^2 N_i }}{{\Sigma M_i N_i }} $$\end{document}on the basis of their composition. By plotting the per cent difference of the experimental values from the theoretical values versus the theoretical values on a semilog scale, the overall performance of the GPC system under investigation is pictorially depicted. Results indicate that performance under experimental conditions can vary significantly from system to system. Results also indicate that performance of a system can be improved and optimized by proper column selection and system modifica

ISSN:0021-8995    

DOI:10.1002/app.1976.070201107

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

年代:1976

数据来源: WILEY

摘要:

AbstractA new method for predicting elastic moduliMof heterogeneous polymer compositions is proposed. It is based on a phenomenological adjustment between parallel and series models for upper and lower bound moduliMUandML. Thus,\documentclass{article}\pagestyle{empty}\begin{document}$$ M = \phi _H ^n (n\phi _S + 1)(M_U ‐ M_L ) + M_L $$\end{document}where ϕHis the volume fraction of hard phase, ϕSis the volume fraction of soft phase, andnis the only adjustable parameter since the upper and lower bound moduli are given by\documentclass{article}\pagestyle{empty}\begin{document}$$ M_U = \phi _H M_H + \phi _S M_S $$\end{document}and\documentclass{article}\pagestyle{empty}\begin{document}$$ M_L = (\phi _H /M_H + \phi _S /M_S )^{ ‐ 1} $$\end{document}whereMHandMSare the moduli of the pure hard and soft phases, respectively. Predicted values ofMare in agreement with measured values in a number of systems which include polyblends and composite materials of fixed morphology. The significance ofnis discussed relative to concentrations in the area of a phase transition for the polyblendsorrelative to phase morphology in the case of fixed morphology compositions. Interestingly, the relationship, by analogy, is in agreement with measured values of polyblend melt viscositie

ISSN:0021-8995    

DOI:10.1002/app.1976.070201108

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

年代:1976

数据来源: WILEY

摘要:

AbstractDrag reduction data of poly(ethylene oxide) obtained in turbulent pipe flows were analyzed. A cutoff molecular weight for drag reduction was determined by correlating the drag reduction effectiveness with polymer molecular weight. Based on a time‐correlation onset concept, this critical molecular weight was found to depend on the pipe diameter and Reynolds number. This effect is examined using available experimental dat

ISSN:0021-8995    

DOI:10.1002/app.1976.070201109

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

年代:1976

数据来源: WILEY

摘要:

Abstract13C NMR has been found to be useful in elucidating the structure of a complex condensation product. Study of a divinylbenzene–p‐cresol oligomer mixture has shown structural units consisting of approximately 85% 2,6‐substitutedp‐cresol, 5–10% 2,5‐substitutedp‐cresol, and 5–10% 2‐substitutedp

ISSN:0021-8995    

DOI:10.1002/app.1976.070201110

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

年代:1976

数据来源: WILEY