ISSN:0021-8995    

DOI:10.1002/app.1990.070410101

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

年代:1990

数据来源: WILEY

ISSN:0021-8995    

DOI:10.1002/app.1990.070410102

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe dielectric relaxation behavior of 1,2‐polybutadienes is analyzed in terms of the experimental data and master curves. The dielectric measurement data were fitted to the empirical relaxation time distribution model of Havriliak and Negami over a frequency range from 100to 1012Hz. The constants of the WLF equation,C1andC2, were evaluated withTgat 100 kHz as a reference temperature for some samples, and the master curve of a sample was constructed. The dynamic mechanical measurements for a series of 1,2‐polybutadienes with different chain structure were performed over a temperature range from −150 to 50°C. A qualitative comparison of the dielectric and dynamic mechanical behaviors of 1,2‐polybutadienes has b

ISSN:0021-8995    

DOI:10.1002/app.1990.070410103

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

年代:1990

数据来源: WILEY

摘要:

AbstractAs a part of continuous study, annular extrudate swell phenomena was investigated using a finite element method. For a Newtonian fluid, gravitational force and surface tension effects are considered. For non‐Newtonian fluids, power‐law fluid and second‐order fluid were considered. Some interesting results were found for non‐Newtonian fluids. For highly shear thinning fluid, thickness was contracted instead of swelling. For second‐order fluid, the analysis was confined only to weak elastic fluid. Explanations are presented for high Weisenberg number

ISSN:0021-8995    

DOI:10.1002/app.1990.070410104

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

年代:1990

数据来源: WILEY

摘要:

AbstractPolyurethane (PU) films were prepared by solution casting using a three‐component system consisting of a low molecular weight fraction of softwood kraft lignin (KL), polyethylene glycol (PEG) of various molecular weights, and crude diphenylmethane diisocyanate (MDI) as starting materials. All films were prepared using a constant NCO/OH ratio. The effects of KL content, PEG content, and molecular weight of PEG on the tensile, thermal, and swelling properties of the PUs were studied. The results showed that the crosslink densityTgand tensile properties were essentially unaffected by variations in the sequence length of the soft segment at a given PEG content. The properties of the PUs were found to depend mainly on the soft/hard segment ratio. The behavior of the glass transition temperature upon changes in the PU composition indicated that the soft and hard segments were extensively mixe

ISSN:0021-8995    

DOI:10.1002/app.1990.070410105

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn solid catalyzed olefin polymerization, equilibrium sorption plays a key role in determining the local monomer concentration (s) in the semicrystalline polymer shell which surrounds the active sites of the catalyst surface. Modelling based on polymer solution thermodynamics indicates that crystallinity and reactor environment have a major effect on this local monomer concentration. The model is used to explain well known experimental trends seen in the literature, such as observed differences in gas phase and diluent slurry polymerization rates, and enhanced α‐olefin incorporation in gas phase copolymerizati

ISSN:0021-8995    

DOI:10.1002/app.1990.070410106

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

年代:1990

数据来源: WILEY

摘要:

AbstractStress relaxation of unattached chains of acrylonitrile–butadiene copolymer in TDI end‐linked acrylonitrile–butadiene copolymer has been studied. The advantage of this system is that the polar nature of the TDI crosslinking agent in end‐linked acrylonitrile–butadiene copolymer can be compensated if an unattached acrylonitrile–butadiene copolymer with moderate acrylonitrile content is selected. It was found that with increasing unattached chain content, the position of the relaxation spectra transitions shifted to shorter times. The frictional resistance for the relaxation of networks containing unattached chains was proportional to the amount of crosslinked components. This means that crosslinked components not only bear load but also resist the relaxation of unattached chains. The relaxation moduli contribution from unattached chains first increased and then decreased with increasing amount of crosslinked components. This can be explained by the presence of two kinds of entanglements, i.e., those between unattached chains themselves and those between unattached chains and crosslinked components, which in turn depend on the amount of unattached chains. At lower concentrations of unattached chains, relaxation of unattached chains requires that molecules pass only through obstacles formed by one kind of entanglement; this results in lower relaxation modulus. With increasing unattached chain content, the relaxation of those chains require molecules reptation through both kinds of entanglements, which results in higher relaxation modulus. Therefore, the enhancement of mechanical properties for networks containing unattached chains originates not only from load‐bearing of crosslinked components but also from the relaxation of unat

ISSN:0021-8995    

DOI:10.1002/app.1990.070410107

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

年代:1990

数据来源: WILEY

摘要:

AbstractAcid–base interactions were used to enhance the miscibility of blends of polystyrene and oligomeric poly(alkylene oxide). The polystyrene was modified by sulfonation of less than 5% of the styrene rings. The poly(alkylene oxides) were low molar mass polyethylene oxide chains (M= 900 and 6000) that were end capped with propyl amine groups. Blends of the poly(alkylene oxide) diamines with polystyrene were immiscible. Blends with the sulfonated polystyrenes were miscible due to proton transfer from the sulfonic acid groups to the basic amino groups of the functionalized poly(alkylene oxide). This was confirmed by FTIR. DSC and dynamic mechanical analyses were used to verify the one‐ or two‐phase nature of the b

ISSN:0021-8995    

DOI:10.1002/app.1990.070410108

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

年代:1990

数据来源: WILEY

摘要:

AbstractA series of high molecular weight, linear polyamide samples have been subjected to various solution spinning techniques, such as gel, wet, and dry spinning, in an attempt to produce high‐tenacity filaments. The spinning experiments involved polyamide 6, polyamide 12, and copolymers thereof, with a molecular weightMwin the range of 105−106kg/kmol. Filaments with a tenacity of 100 cN/tex have been obtained. Their draw ratio never surpassed a value of six, which may also be reached after conventional melt spinning. Apparently, the drawability of polyamides cannot be improved via solution spinning techniques, although a favorable molecular topology for accomplishing high draw ratios has most likely been realized. This behavior is in sharp contrast with the highly increased drawability after solution spinning of less polar polymers, such as polyethylene or polyvinyl alcohol. A semiempirical equation is now proposed that relates the maximum drawability of flexible chain polymers with their polarity, being expressed in terms of cohesive energy. A preassumption underlying this equation is that drawability is not limited by a high entanglement density as is, e.g., the case after melt process

ISSN:0021-8995    

DOI:10.1002/app.1990.070410109

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

年代:1990

数据来源: WILEY

摘要:

AbstractDirect current and radiofrequency plasma treatment of different durations were given to polyester fabric to impart soil resistance. The soil repellency increased with increasing time of treatment. The possible mechanism of soil repellency is outlined. The evaluation of soiling has been made from CIE brightness variableYwith sourceD65using Minolta Chromameter Reflectance II. This was well in agreement with the conventional reflectance measurement method using spectrophotometer. The plasma treatment system has the advantage of energy and floor space savings and pollution‐free atmosphe

ISSN:0021-8995    

DOI:10.1002/app.1990.070410110

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

年代:1990

数据来源: WILEY