摘要:

AbstractPolystyrene and its various alkyl and halo derivatives have been studied as homoelectrets and their stabilities under different environmental conditions determined. The stabilities of the homoelectrets prepared from these polymers depended on their volume resistivities, glass transition temperatures, and interactions with electron‐acceptor impurities. Excellent stabilities were exhibited by the homoelectrets prepared from polystyrene, poly(vinyltoluene), poly(chlorostyrene), and poly(t‐butylstyrene). It is postulated that the charged particles are trapped by the π‐orbitals of the phenyl rings present in these polymers and that they are adversely affected by the presence of electron‐acceptor compounds that generally from charge‐transfer complexes with the phe

ISSN:0021-8995    

DOI:10.1002/app.1982.070270401

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

年代:1982

数据来源: WILEY

摘要:

AbstractGraft copolymerization of vinyl monomers such as methacrylate, acrylamide, and acrylic acid on cellulose using the peroxyacetic acid–ferrous ion redox initiator system was studied. Filter paper was chosen as cellulosic material. The effect of the experimental conditions on grafting ratio, grafting efficiency, total conersion and number of branches, and other factors was studied by varying the concentration ratio of peroxyacetic acid to ferrous salt, reaction time, reaction temperature, the addition of disodium ethylenediaminetetraacetate (EDTA), pH, and so on. It was found that there is an optimum range of initiator concentration, that at a higher temperature the copolymerization proceeds more rapidly and more efficiently, and that the addition of EDTA enables the copolymerization to proceed at a higher p

ISSN:0021-8995    

DOI:10.1002/app.1982.070270402

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

年代:1982

数据来源: WILEY

摘要:

AbstractRates of the MgCl2‐catalyzed reaction between cellulose and 4,5‐dihydroxy‐1,3‐bis(hydroxymethyl)‐2‐imidazolidinone were measured at 70, 90, and 110°C. The rate constants were determined by curing the resin for various times, extracting the unreacted resin, and determining its concentration by liquid chromatography. The energy of activation was calculated from the rate data. This work confirms the pseudo‐first‐order behavior

ISSN:0021-8995    

DOI:10.1002/app.1982.070270403

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

年代:1982

数据来源: WILEY

摘要:

AbstractThe swelling behavior of water in a poly(ethylene–vinyl alcohol) copolymer (70 mol % vinyl alcohol) has been characterized at 25°C by vapor and liquid sorption experiments over a range of water activities. The activity of the vapor phase has been varied by incrementing the pressure of the water vapor in the sorption cell. Alternatively, for the liquid phase experiments, aqueous sodium chloride solutions of different concentrations have been used to vary systematically the activity of the water in the salt solution and to introduce various concentrations of salt into the copolymer films. Relaxation‐controlled sorption and Fickian diffusion have been observed as limiting cases of the water sorption behavior at high and low water activities, respectively. The effects of sorbed sodium chloride on water vapor sorption kinetics and equilibria were determined independently. A second salt phase forms within the previously homogeneous and seemingly single phase polymeric system, upon contacting the salt‐loaded film with a water vapor activity above a threshold value corresponding to the activity of water in the salt solution used to introduce the salt into the films. The water and salt solubilities in the ethylene–vinyl alcohol copolymer have been measured systematically to describe the complex sorption equilibria associated with this three‐component, multiph

ISSN:0021-8995    

DOI:10.1002/app.1982.070270404

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

年代:1982

数据来源: WILEY

摘要:

AbstractSeveral nonreinforced and reinforced crosslinked polyester formulations were prepared and investigated. Solid glass microspheres, with and without coupling agent, were used as reinforcement. All samples were exposed to various cyclic hygrothermal fatigue patterns, differing from one another by the temperature and duration of a cycle. Dynamic mechanical measurements were used to evaluate the effect of hygrothermal fatigue on the mechanical properties of all formulations. Fatigue induced changes in the glass–matrix interphase led to the appearance of relaxation peaks (β′ and β″) in the temperature range between −50°C and −10°C. Electron microscopic evidence was obtained for the existence of nodular morphology on all fracture surfaces. The character of nodular morphology was described in terms of an inhomogeneous ther

ISSN:0021-8995    

DOI:10.1002/app.1982.070270405

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

年代:1982

数据来源: WILEY

摘要:

AbstractSorption of pure anhydrous ammonia and pure sulfur dioxide in Kapton polymide has been measured at 30 and 35°C at subatmospheric pressures using a McBain quartz spring balance. The sulfur dioxide sorption and desorption was well described by the Fickian transport model; however, the ammonia sorption exhibited significant deviations from Fickian behavior. A substantial fraction of the initially sorbed ammonia remained in the film after extended periods under vacuum at 35°C. Infrared analysis of the treated film revealed the presence of new carbonyl and nitrogen–hydrogen stretching peaks characteristic of primary and secondary amides. These observations suggest that the ammonia reacts chemically with some of the imide linkages. Based on infrared analysis of the ammonia‐exposed Kapton, heating the sample under vacuum at 120°C caused re‐formation of most of the orginally disturbed imide structures, with attendant evolution of ammonia as a condensation

ISSN:0021-8995    

DOI:10.1002/app.1982.070270406

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

年代:1982

数据来源: WILEY

摘要:

AbstractA polymer with high aromaticity and/or cyclic ring structures chain backbone usually has high heat, thermal, and flame resistance. Two diglycidyl ethers of bisphenols were prepared from 4,4′ isopropylidenediphenol (DGEBA) and 9,9‐bis(4‐hydroxyphenyl) fluorene (DGEBF) for evaluation. Four boroxines—trimethoxyboroxine (TMB), triethoxyboroxine (TEB), triisopropoxyboroxine (TIPB) and triphenoxyboroxine (TPB)—were used as the curing agents. DGEBA and DGEBF cured with various boroxines indicate that the trend for their respective glass transition temperature (Tg's), degradation temperatures (Td's), and gel fractions are TMB‐cured epoxy ≈ TEB‐cured epoxy

ISSN:0021-8995    

DOI:10.1002/app.1982.070270407

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

年代:1982

数据来源: WILEY

摘要:

AbstractThis study presents experimental results on the preparation and characteristics of high‐density phenol–formaldehyde foams and compares their characteristics with the available patent literature. An extrapolation of the data has been used to identify the relevant process parameters used for the preparation of lower‐density foams. The effect of catalyst combination and phenol formaldehyde molar ratio on the ease of foaming and its ultimate strength has been investigated. A total solids refractive index correlation has been developed for following the reaction. The effect of foaming temperature on the density and strength of the foam was also st

ISSN:0021-8995    

DOI:10.1002/app.1982.070270408

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

年代:1982

数据来源: WILEY

摘要:

AbstractA series of asphalt–polyurethane composites was prepared by means of polyurethane synthesis in asphalt and carried out in melt. The applied materials were asphalts of differentiated group components content, polyester polyols of chain structure from linear to strongly branched, 2,4‐tolylene diisocyanate, 4,4‐methylenebis(phenyl isocyanate), and tinorganic catalyst. The asphalt components react with isocyanates to a minimal degree. The influence of the applied substrates, temperature, and polyurethane content in the system on the basic kinetic relations characterizing the process is presented. Polyurethane synthesis in asphalts does not differ in a fundamental way from the obtaining of polyurethanes, especially when their content in the composition is significant, 20 wt % and

ISSN:0021-8995    

DOI:10.1002/app.1982.070270409

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

年代:1982

数据来源: WILEY

摘要:

AbstractAn experimental study of the relationships between foaming variables and foamed structures of expanded ethylene–propylene terpolymer (EPDM) is reported. The study was carried out using EPDM composition containing azobisformamide blowing agent. The compositions were expanded and cured in hot air into a foamed structure consisting of dense skin and foamed core. The results showed that the foam density, skin thickness, average cell size, and number of cells of the expanded rubbers can be controlled closely by the foaming variables such as residence time, foaming temperature, and blowing agent concentratio

ISSN:0021-8995    

DOI:10.1002/app.1982.070270410

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

年代:1982

数据来源: WILEY