摘要:

AbstractThe evolution of several structural characteristics during isothermal heat treatment of poly(p‐phenylene terephthalamide) was studied. In this work, heat treatment was interrupted after different treatment times, with the specimens immediately quenched to room temperature. These specimens were then characterized by tensile testing, wide‐ and small‐angle x‐ray scattering, and optical microscopy. Structural parameters obtained from these measurements relate to crystal perfection (via the paracrystalline axial distortion parameter), axial crystallite size, transverse crystallite size, degree of chain misorientation, and degree of pleating. Structural and mechanical parameters were then plotted against heat‐treatment time to obtain kinetic isotherms for each parameter. The kinetics of the removal of chain misorientation parallels that of tensile modulus increase under all conditions. Of the other structural parameters, only the kinetics of pleat removal mimics that of modulus change, indicating that pleat removal is the effective cause of increased chain alignment and thereby of increased axial stiffness. ©1995 John Wiley

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330101

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractIn order to obtain high‐performance polymer and products, processing of crystalline polymers below their softening temperature has been employed and studied in recent years. It has gathered attention, for example, in the area of producing high‐strength polymer rods and filaments of higher cross‐sectional area for special applications. Die drawing and extrusion techniques dominate the processes used to achieve these products. Extrusion is primarily achieved by forcing the polymer through converging dies of circular and other cross‐sections. The methods of solid‐state extrusion processing practiced are primarily ram extrusion and hydrostatic extrusion. In this study, we investigate the process of producing cylindrical rods by ram extrusion of plastics at room temperature. Instead of using a converging die, right angle dies of varying extrusion ratios are employed to extrude three commercial grades of polyethylene. A theoretical analysis is also performed to predict the forces required during extrusion. The theoretical analysis closely follows the methodology presented by Coates et al. for the circular extrusion of polymers below their softening temperatures. ©1995 John Wiley

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330102

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractMiscibility in blends of three styrene‐butadiene‐styrene and one styrene‐isoprene‐styrene triblock copolymers containing 28%, 30%, 48%, and 14% by weight of polystyrene, respectively, with poly(vinyl methyl ether) (PVME) were investigated by FTIR spectroscopy and differential scanning calorimetry (DSC). It was found from the optical clarity and the glass transition temperature behavior that the blends show miscibility for each kind of triblock copolymers below a certain concentration of PVME. The concentration range to show miscibility becomes wider as the polystyrene content and molecular weight of PS segment in the triblock copolymers increase. From the FTIR results, the relative peak intensity of the 1100 cm‐1region due to COCH3band of PVME and peak position of 698 cm‐1region due to phenyl ring are sensitive to the miscibility of SBS(SIS)/PVME blends. The results show that the miscibility in SBS(SIS)/PVME blends is greatly affected by the composition of the copolymers and the polystyrene content in the triblock copolymers. Molecular weights of polystyrene segments have also affected the miscibility of the blends. ©1995 John Wil

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330103

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractWe measured thermal diffusivity and heat capacity of polymers by laser flash method, and the effects of measurement condition and sample size on the accuracy of the measurement are discussed. Thermal diffusivities of PTFE films with thickness 200–500 μm were the same as those data that have been reported. But, the data for film thickness less than 200 μm have to be corrected by an equation to cancel thermal resistance between sample film and graphite layers for receiving light and detecting temperature. Thermal diffusivity was almost unaffected by the size of area vertical to the direction of laser pulse, because heat flow for the direction could be negligible. Specific heat capacity of polymer film was exactly measured at room temperature, provided that low absorbed energy (25 mg) were satisfied as measuring conditions. Thermal diffusivity curve of PS or PC versus temperature had a terrace aroundTg, whereas that of PE decreased monotonously with increasing in temperature untilTm. Further, we estimated relative specific heat capacity (RCp) by calculating ratios of heat capacities at various temperatures to the one at 299 K. RCpfor PS obtained by laser flash method was larger than that obtained by DSC method, whereas the RCpsfor PE obtained by the both methods agreed with one another untilTm(305 K). RCpfor PS decreased linearly, with increase in temperature after it increased linearly untilTg(389 K), showing similarity to temperature dependency of thermal conductivity. RCpfor PE also decreased untilTm, similar to thermal conductivity. ©1995 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330104

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe temperature dependence of steady‐shear viscosity and ionic conductivity were measured for a series of unreacted mixtures and partially cured, ungelled samples of diglycidyl ether of bisphenol‐A (DGEBA) and an amine cross‐linking agent, diamino diphenyl sulfone (DDS). Six stoichiometric ratios of epoxide groups to amine hydrogens were examined. Free volume expressions were used to model the temperature dependence of the conductivity and viscosity for the unreacted DGEBA‐DDS mixtures. In addition, these expressions were combined to successfully correlate changes in viscosity and conductivity during the DGEBA‐DDS polymerization prior to gelation. It also was demonstrated that the change in weight average molecular weight during polymerization could be interpreted from the dielectric data. Through studying variations in the stoichiometry, it was possible to examine the effects of changes in chemical structure and ion concentration on the fitted parameters in the free volume models. The inherent ion transport factor (ζ0) was found to be inversely proportional to the concentration of ions in the test samples. The fractional free volume for segmental motion (B) was found to increase with an increase in the glass transition temperature and to be a function of the rigidity of the polymer. ©1995 John Wile

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330105

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractDynamic viscosity and ionic conductivity were measured simultaneously during the cure of a digylcidyl ether of bisphenol‐A (DGEBA) epoxy resin with diamino‐diphenyl sulfone (DDS) by mounting a microdielectric sensor into the plates of a rheometer. Two different cure temperatures were examined. Periodically, throughout the cure, samples were removed from the plates of the rheometer, quenched, and analyzed for the glass transition temperature and epoxide conversion. The relationship between conductivity and viscosity appeared to be independent of cure temperature. A linear relation with a slope of −1 was observed between the natural logarithms of conductivity and viscosity during the cure up to approximately 85% cure conversion. It was hypothesized that the reaction rate was hindered by diffusion at this stage in the polymerization. A free volume relationship was used to successfully correlate conductivity with viscosity up to the diffusion limited region. ©1995 John Wiley&Son

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330106

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractDetermination of the orientational order of morphological components in polyethylene terephthalate (PET) is sought through quantitative application of two‐dimensional rotor synchronized magic angle spinning (ROSMAS)13C NMR technique. Previous study in our laboratories had established a procedure for resolution of the carbonyl carbon (CA) and glycol ethylene carbon (GE) resonances into those corresponding to four morphological components.1Due to paucity of sidebands in the GE resonances, the focus has been on the CA resonances in this attempt to obtain orientation distributions. A set of PET fibers possessing a broad range of crystalline and orientational order has been used to infer the meaning of NMR‐based orientation measurements vis‐a‐vis other techniques. A surprising finding of this study is the observation that the orientational orders of the broad component in the13C CP/MAS spectrum and the narrow component are very similar in these fibers. ©1995 John Wiley&S

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330107

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe viscosities of dilute solutions of poly(p‐phenylene terephthalamide), PPTS, in dimethylacetamide, water, and their mixtures were determined. The reduced viscosity plot in dimethylacetamide shows a negative slope. When the water content in the mixed solvent in 90% or higher, there is an upswing in the reduced viscosity values at concentrations below 0.1 g/dL. The latter behavior suggests a “polyelectrolyte” effect. However, an association model was found to be able to explain the viscosity behaviors in both solvents. ©1995 John Wiley&Son

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330108

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractPositron Annihilation Lifetime Spectroscopy (PALS) measurements were conducted on polycarbonate subjected to either thermal expansion or to tensile and compressive strains. It was found that thermal expansion affected both the nanometer hole size and the hole number density, whereas mechanical stress affected mainly the size of existing holes, and did not generate or eliminate holes in the quasielastic deformation region. The effect of stress on yield and postyield behavior of this glassy material was also investigated. The deduced hole volume fraction of this polymer at 25°C was 6.8 ± 0.5% from the thermal expansion experiment and 7.2 ± 1.2% from the mechanical loading experiment. When the specimen was under compression, the hole volume fraction was found to continuously decrease. This can be considered as evidence of the inability of the free volume concept in explaining the yield behavior of glassy polymers. ©1995 John Wiley&Sons,

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330109

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe ferroelectric and piezoelectric properties of a new class of polymer ferroelectric and piezoelectric materials, nylon 11/polyvinylidene fluoride (PVF2) bilaminate films, prepared by a co‐melt‐pressing method, is presented. The bilaminate films exhibit typical ferroelectricD‐Ehysteresis behavior with a remanent polarization,Pr, of about 75 mC/m2, which is higher than the value of 52 mC/m2observed for PVF2or nylon 11 films measured under the same conditions. The coercive field,Ec, of the bilaminate films is ∼ 78 MV/m, which is higher than that of either PVF2or nylon 11 films. Measurements of the temperature dependence of the piezoelectric strain coefficient,d31, and the piezoelectric stress coefficient,e31, were also carried out. The bilaminate films exhibit a piezoelectric strain coefficient,d31, of 41 pC/N at room temperature, which is significantly higher than the PVF2films (25 pC/N) and the nylon 11 films (3.1 pC/N). When the temperature is increased to 110°C,d31of the bilaminate films reaches a maximum value of 63 pC/N, more than five times that of PVF2(11 pC/N) and more than four times that of nylon 11 (14 pC/N) at the same temperature. The piezoelectric stress coefficient,e31, of the bilaminate films shows a value of 109 mC/m2at room temperature, almost twice that of the PVF2films (59 mC/m2) and about 18 times that of the nylon 11 films (6.2 mC/m2). Measurement of the temperature dependence of the hydrostatic piezoelectric coefficient,dh, of the bilaminate films also shows an enhancement with respect to the individual components, PVF2and nylon 11. ©1995 John Wiley&

ISSN:0887-6266    

DOI:10.1002/polb.1995.090330110

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY