摘要:

AbstractThe mechanical properties andin vitrodegradability of poly(L‐lactide) fibers with different average molecular weights, prepared by a dry spinning–hot drawing process from CHCI3solutions, were studied in relation to the γ‐irradiation dose. In the range of molecular weight of 1.6−3.6 × 105, no differences were found in the relative decrease of tensile strength after irradiation of 25 kGy. Changes of the elongation at break are discussed in terms of a network solution theory.In vitrodegradation of the fibers is also discussed in network solution theory terms. Regardless of the courses of degradation curves, it may be stated that all prepared fibers could be sterilized by γ‐rays and the rate of degradation was not affected by the irradiation dose. © 1993 John Wi

ISSN:0021-8995    

DOI:10.1002/app.1993.070500101

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

年代:1993

数据来源: WILEY

摘要:

AbstractUtilization and conservation of raw materials are two of the main thrusts of our research. Several plasticized woods have been prepared from sawdust in our laboratory. They possess unique thermal, mechanical, and viscoelastic properties. In this study, benzylated wood was used to blend with polystyrene to prepare a wood/plastic composite. Its dynamic processability and viscoelastic properties were evaluated. The mixtures with different blending ratios (benzylated wood/polystyrene) were prepared by mixing them in an intensive mixing device. The specific energy required to do the processing work decreased with the increase of benzylated wood in the composite. The mixture can be molded or extruded easily. The study of the viscoelasticity of the compression‐molded composite products using a dynamic mechanical thermal analyzer (DMTA) revealed, regardless of the mixing ratios, a single damping peak (tan δ). This suggested good compatibility between the two polymers. The glass transition temperature and the storage modulus of these composites decreased as the amount of benzylated wood increased. A composite with comparable mechanical properties of polystyrene was obtained from those composites with mixing ratios (benzylated wood/polystyrene) ranging from 0.4 to 0.6. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070500102

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe preparation of membranes of nylon 4,6 by diffusion‐induced phase separation (DIPS) using formic acid as a solvent and water as a nonsolvent was studied. Nylon 4,6 is a semi‐crystalline polymer; phase separation from a solution can occur by solid–liquid (s–l) de‐mixing as well as by liquid–liquid (l–l) demixing. Upon quenching films of solutions with low polymer concentration (<17 wt %) in a nonsolvent bath containing water, the morphology of the membranes show a foam‐like structure typical for l–l demixing. When phase separation is induced by water vapor a transition in structure occurs from the cellular type to a morphology typical for s–l phase separated films. At higher polymer concentrations membranes exhibit structures consisting of spheres or smaller crystal‐like units resulting from an s–l phase separation process. The addition of 2 wt % or more of water to polymer solutions with low concentration (up to 15 wt %) resulted in s–l demixing as well. In a DIPS process s–l demixing is kinetically competitive with l–l demixing if nuclei are already present in the starting solutions (heterogeneous nucleation), or if a relatively long time is available for crystal nuclei to be formed. The morphology resulting from s–l demixing is a result of spherulitic crystallization. A certain concentration of nuclei or of precursor particles already present results in a small nucleation density during precipitation and thus large spherulites can be grown; at higher polymer and/or water concentrations the nucleation density increases resulting in an axialitic morphology of the membran

ISSN:0021-8995    

DOI:10.1002/app.1993.070500103

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

年代:1993

数据来源: WILEY

摘要:

AbstractStudies on cellulose III solubility have been conducted in 8.5% NaOH solution with and without the presence of added substances, such as acrylamide, acrylic acid, acrylonitrile, and thiourea. The highest value of cellulose III solubility was obtained as a result of the introduction thiourea and acrylamide in a 5% ratio of NaOH into NaOH solution. Moreover, dissolving conditions proved to be of great importance. Cellulose III introduced into NaOH solution and repeatedly frozen and unfrozen three times dissolved 50% (dissolving with 5% thiourea). The soluble cellulose fraction showed significantly lower molecular mass in comparison with its insoluble fraction. Comparative studies on cellulose crystallinity using the CP / MAS13C‐NMR method showed a satisfactory compatibility of results with determinations obtained from the X‐ray method. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070500104

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe swelling of five types of Sephadex that are either nonionic (G) or possess one of four different ionic groups [sodium carboxymethyl (CM), sodium sulfopropyl (SP), diethyl‐aminoethyl chloride (DEAE), diethyl ‐ (2‐hydroxypropyl) aminoethyl chloride (QAE)] in the same skeleton of the molecule has been studied by picture analysis and by calorimetry. Inducing dissociation of the ionic group in the polymer skeleton increased the water swelling. By the addition of sodium chloride, the maximum swelling volume of nonionic Sephadex was only slightly decreased. However, that of ionic polymers was considerably decreased. The variation of the apparent first‐order rate constant of the swelling and that of the maximum swelling volume show the same tendency. The maximum heats of swelling were 93.2 ± 7.1 J g−1for G, 128.8 ± 9.1 J g−1for CM, 92.3 ± 8.0 J g−1for SP, 68.8 ± 10.5 J g−1for DEAE, and 67.0 ± 7.2 J g−1for QAE and did not depend on the concentration of sodium chloride. From the results obtained, we conclude that the nonionic Sephadex swells only by hydration but that ionic Sephadexes swell mainly by the osmotic pressure due to the counterions of the ionic groups and that the swelling ratio is not dependent on the kinds of ions but on the ionic concentration. Most of the water in the gels of ionic Sephadexes is free water that does not interact with the Sephadexes. © 19

ISSN:0021-8995    

DOI:10.1002/app.1993.070500105

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe critical micelle concentration and various acoustic parameters of chromium soaps (myristate, palmitate, and stearate) in a mixture of benzene and dimethyl formamide (4 : 1 v/v) have been determined by ultrasonic velocity measurements. The results showed that the ultrasonic velocity, specific acoustic impedance, molar sound velocity, and molar sound compressibility increase, while intermolecular freelength, adiabatic compressibility, and available volume decrease with increasing concentration and chain length of the soap. The results show that there is a significant interaction between soap and solvent molecules in dilute solutions and the soap molecules do not aggregate appreciably in dilute solutions. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070500106

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe main objective of this study was to measure the crystallinity, particle size, and mechanical properties of fibers and to assess their relationship in 18 Egyptian and American cotton cultivars. Remarkable variations in crystallinity were found, ranging between 49 and 90%, whereas the range of differences in particle size was somewhat narrow, and so its effect on mechanical properties was not detectable. The cotton cultivars that have higher values of crystallinity are characterized by higher values of tenacity at either\documentclass{article}\pagestyle{empty}\begin{document}$ \frac{1}{8} $\end{document}in. or zero gauge and stiffness and by reduced elongation. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070500107

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe tensile strain rate effect in tensile strength and elongation at break for a series of filled dummy hydroxy‐terminated polybutadiene (HTPB) propellant binders was studied. The data were obtained at various tensile strain rates from 10−4to 10−1s−1on two types of specimens at room temperature. The “high velocity ductility” behaviour, which is qualitatively similar to those of unfilled elastomers, was revealed. This means that the breaking strain increases markedly at elevated strain rates. For “Bukkon‐type” and rod‐shaped specimens, test results are consistent with each other. The fact that the increased filled solids level leads to a decreased breaking elongation capability and an increased tensile strength was obviously found. © 1993

ISSN:0021-8995    

DOI:10.1002/app.1993.070500108

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe main α and sub β relaxations in bisphenol A‐based epoxides cured by two kinds of aliphatic diamines were examined in wide temperature and frequency ranges by using middle‐frequency dynamic, dielectric, and ultrasonic measuring systems. The obtained temperature–frequency correlation maps revealed an Arrhenius‐type behavior for the β relaxation with apparent activation energy of 16 kcal/mol. For the α relaxation, the maps were in good agreement with the W.L.F. equation. Owing to the similarity of structure in these resins, both maps showed the same tendencies. © 1993 John Wil

ISSN:0021-8995    

DOI:10.1002/app.1993.070500109

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

年代:1993

数据来源: WILEY

摘要:

AbstractRadical‐induced copolymerization of styrene and butyl methacrylate was studied. The effects of the initiator (benzoyl peroxide) concentration, reaction temperature, and poly(vinyl alcohol) amount on the rate of reaction and final product quality are also measured. Kinetics studies and optical microscopy of the reaction mixture indicate that the reaction exhibits autoacceleration behavior, which could be suppressed by reducing the reaction temperature.1H‐NMR of the intermediate and final product samples reveals the monomer sequencing. The monomer reactivity ratios at various temperatures are estimated from the experimental data. The reaction is mathematically modeled by a Monte‐Carlo simulation, and the results of this analysis are compared with observed data. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070500110

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

年代:1993

数据来源: WILEY