摘要:

AbstractThe transport property of chloroform in undeformed and stress‐whitened polypropylenes was studied. The rate of penetration of liquid chloroform in whitened samples prepared by uniaxial stretching was slower than that of the undeformed material. In the whitened region, the process appeared to be Fickian diffusion, while in the undeformed material, it was a combination of Fickian and Case‐II. The diffusivity (at 50°C) in the whitened region increased about 8 times as the strain rate of stretching decreased from 0.67 to 0.033/min. The temperature dependence of diffusivity (ε = 0.67/min) showed an activation energy of 10.16 Kcal/mole. The whitening effect was greatly reduced as chloroform was absorbed; the final residual whitening after desorption increased with the rate of stretching as determined by transmission densitometry. For the undeformed polypropylene, Case‐II type of matrix relaxation contributed significantly to the total flux. The transport process was relaxation controlled at the surface: it gradually changed to Fickian diffusion behavior toward the middle plane. The flux contribution of relaxation across the thickness increased with the sorption time, and that of diffusion decreased. These observations seem to indicate that cold drawing impeded the deformation by swelling stress from occurring at the penetratio

ISSN:0032-3888    

DOI:10.1002/pen.760262202

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThis paper studies the correlation of polymer structure and morphology and gas permeability. A scale of numerical values based on polymer cohesive energy density and fractional free volume has been devised to predict permeability and also to estimate diffusion and solubility properties.

ISSN:0032-3888    

DOI:10.1002/pen.760262203

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe sorption and diffusion of a series of liquids in a segmented polyurethane have been studied to determine how the behavior is affected by the choice of solvent and the heterophase nature of the polymer. The polyurethane was composed of methylene‐di‐para‐phenylene isocyanate (MDI) butanediol, and poly(tetramethylene oxide) (1000) with a mole ratio 3:2:1. Immersion experiments in n‐heptane liquid, a poor solvent, and incremental sorption experiments in n‐heptane vapor showed normal Fickian havior. In the set of liquids of increasing polarity, which included 1‐chloroheptane, three dichloroalkanes and orthodichlorobenzene, the swelling increased to very high levels. Effective values of the molecular weight between crosslinks computed from the Flory Rhener equation, assuming complete phase segregation, varied widely with the different liquids. Agreement could be improved by allowing 30 percent mixing of hard segments with the soft segment phase. The sorption and desorption curves for the highly swelling liquids showed various anomalies some of which might be the result of solvent induced relaxation of hard segm

ISSN:0032-3888    

DOI:10.1002/pen.760262204

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractA general‐purpose finite element program has been used to simulate the flow of nonshear‐thinning, highly elastic polymer solutions (Boger fluids). In particular, the creeping flow through an abrupt 4:1 circular and planar contraction is studied, as well as the flow at the exit of a capillary die for the determination of extrudate swell. Experimentally measured normal stress and viscosity data are included in a simple rheological model, based on the viscometric simplification of the CEF constitutive equation. Vortex size and intensity in the die entry and extrudate swell at the die exit increase rapidly, with elasticity level, in general agreement with experimental findings. It is shown that despite the limitations of the model, the viscometric approximation can be used to study the effect of normal stresses in cases where a main flow direction can unambiguously be defined. In die exit Flows, it can also provide an upper limit for the determination of extrudate swell, while Tanner's theory of elastic recovery provides the lower li

ISSN:0032-3888    

DOI:10.1002/pen.760262205

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe isothermal curing of an epoxy mixture of diglycidyl ether of bisphenol‐A and diglycidyl ether of 1,4 butanediol was monitored through the dynamic viscoelastic properties. Measurements were made at a frequency of 37.7 s−1using a Weissenberg Rheogoniometer Model R‐17 fitted with a piezoelectric load cell and interfaced with a microcomputer. Cures were conducted at four temperatures, 15.6 ± 0.2°C to 40.1 ± 0.2°C with the cure time varying from 35 to 11 hours, respectively. Additional measurements of the steady shear viscosity, up to three hours after cure initiation, were conducted using a Weissenberg Rheogoniometer Model R20. These results show that in the early stages of the cure cycle, the fluids show low elasticity and constant viscosity. Also, independent of temperature, the relationship, η′ = 0.05 η″, holds, although it is not maintained near the gel point. This implies that initially, the longest relaxation time is independent of the extent of reaction and

ISSN:0032-3888    

DOI:10.1002/pen.760262206

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThis paper reports results on the dielectric properties of carbon black filled crosslinked polyethylene composites. These systems are shown to follow percolative type models. The dielectric constant increases slowly, with carbon black concentration, up to roughly the percolation concentration and then increases rapidly over the whole concentration ranges studied. The dissipation factor‐concentration curves are bell‐shaped with maximum values at approximately the percolation concentration. The dielectric properties of these systems are discussed in terms of interfacial Maxwell‐Wagner polarization ef

ISSN:0032-3888    

DOI:10.1002/pen.760262207

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractDifferential scanning calorimetry (DSC) and the density gradient technique (DGT) were used to determine, both isothermally and dynamically, the crystallization kinetics of polyetheretherketone (PEEK). The data were analyzed by a model utilizing, for the first time, two crystal nucleation and growth processes which were observed experimentally in a typical Avrami plot of the isothermal data. Thus, by modeling the data as two separate Avrami type crystallization processes occurring in parallel, both isothermal and dynamic data could be predicted with the same model constants. The first process provided an Avrami exponent of 2.5 and an onset temperature of 320°C. The second process displayed an Avrami exponent of 1.5 and an onset temperature of 342°C. The validity of this dual mechanism crystallization model was proven in practice by predicting with best fit model constants, a wide range of crystallinities of both neat and carbon fiber‐reinforced PEEK samples that had been made at different cooling rates from the m

ISSN:0032-3888    

DOI:10.1002/pen.760262208

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractIn service, some plastics components are subjected to intimate mixtures of creep and fatigue loading, such that both have the potential to cause component failure. This paper examines, for the case of a single design of an injection molded fitting that comprised part of a polyethylene pipeline system, the response of that fitting to fatigue loading patterns that included significant elements of creep loading. The performance of the fitting was monitored and the data interpreted in terms of the concepts of fractional fatigue and fractional creep damage. The approach helps in identifying the design criteria to be used for components that are to be subjected to complex fatigue loadings. For the cases where significant creep‐fatigue interactions occur, such that the additive damage was nonlinear, the method can identify critical frequencies at which maximum damage occurs. This style of analysis will be most useful for plastics components that are used in critical applications where failure has to be avoide

ISSN:0032-3888    

DOI:10.1002/pen.760262209

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760262201

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY