摘要:

AbstractAn apparatus has been developed for the measurement of thermal conductivity of polymer melts. Based on the transient “line source method,” it is ideally suited to these materials because measurements can be made quickly, before the onset of thermal degradation. Also, little or no sample preparation is required. A number of commercial polymers have been tested, including some glass‐fiber filled compo

ISSN:0032-3888    

DOI:10.1002/pen.760300202

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractConditions are described for preparing blends of cellulose with nylon 6 (Ny6) and poly(ε‐caprolactone) (PCL) from solutions in N,N‐dimethylacetamide (DMAc)– lithium chloride (LiCl) by coagulation in a non‐solvent. The binary blend films of both series, obtained over a wide composition range (10/90–90/10) from mixed polymer solutions, were characterized by wide‐angle x‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and dynamic mechanical measurements. In the two series of cellulose blends the other component (Ny6 or PCL) was crystalline at every composition, but there was some degree of disproportional reduction of the crystallinity with an increase in cellulose content. From the dynamic Mechanical testing, the cellulose/Ny6 blends were found to be almost immiscible, although the possibility of a certain level of partial miscibility in the non‐crystalline regions was admitted at high cellulose concentrations (>80 wt%). For the cellulose/PCL blends, it was found that there was evidently an amorphous phase where a limited amount of cellulose could be well mixed with PCL. A relatively large shift of the midpoint in the PCL glass transition region to the higher temperature side was noted at the compositions containing 20 and 30 wt% cellulose. This effect is discussed in relation to the requirement of an optimum balance in the density of the interacting hydroxyl and ester groups, for obtaining true miscibility of cellulosics with PCL at the

ISSN:0032-3888    

DOI:10.1002/pen.760300203

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe physical behavior of the diglycidyl ether of bisphenol A, cured with different concentrations of 2‐ethyl‐4‐methylimidazole, was examined with dynamic mechanical and dielectric analyses, differential scanning calorimetry, and solvent extraction studies, ‘The network formation process was shown to depend strongly on the imidazole concentration’. At high imidazole concentrations, the gel point was characterized by a decrease in sol fraction, the crossover of the dynamic moduli and a rapid increase in viscosity. At low imidazole concentrations, the viscosity remained low until the sol fraction approached zero. For this system, the gel point, which occurred prior to the dynamic moduli crossover, was characterized by comparing the thermal properties of the network with the viscosity and dielectric behavior of the resin system du

ISSN:0032-3888    

DOI:10.1002/pen.760300204

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractRapid freezing of a polymethylpentene (PMP)/cyclohexane solution to −80°C gives a tough, flexible foam, in marked contrast to the weak, friable foams obtained by phase‐separation of PMP from other solvents. X‐ray diffraction and differential scanning calorimetry (DSC) data indicate that the isotactic PMP is in an amorphous state. The production of a flexible, robust foam tube from PMP/cyclohexane implies that this material could find applications as replacement parts for arteries and veins or as filter devices. In sheet form, this material seems ideally suited for use as light‐weight insulation for clothing because its open, microcellular structure permits moisture to escape as vapors, but retards air flow. This study demonstrates that process parameters, such as solvent composition, play an important role in determining the various microstructures and physical properties that can be obtained from a single

ISSN:0032-3888    

DOI:10.1002/pen.760300205

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractSudden changes of compressive strain‐rate on glassy poly(methyl methacrylate) lead to the conclusion that the post‐yield state under a constant stress is a state of steady flow in the polymer. Non‐linearity between the stress divided by temperature and the logarithm of strain rate for this steady plastic flow can successfully be analyzed using the Eyring equation with structural factors variable depending on stress and temperature. This analysis gives a unique functional relationship between the activation entropy and the activation enthalpy, which agrees fairly well with that for the melt derived from the WLF equation. This agreement provides a direct evidence verifying structural change of the glass into liquid‐like structure and enables us to recognize the conformational arrangement as an essential structural parameter controlling molecular mobility. Another experimental relation between the Eyring factors—the activation volume and the activation enthalpy—permits us to estimate the magnitude of an elementary volume for the molecular movement in the melt as a function of temperature. Moreover, the experimental finding of the steady flow in the glassy polymer motivated us to propose a transition mechanism from elastic deformation to plastic flow in which the internal viscosity or the activation volume is introduced as a single parameter representing the transient state of th

ISSN:0032-3888    

DOI:10.1002/pen.760300206

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractWe examine several practically important problems, related to the mechanical behavior of dual coated optical fibers: low temperature microbending, evaluation of spring constant due to coating layers, strength of the end portions of fibers clamped in terminal fixtures, and prediction of stresses caused by the misalignment of the openings in the frame and in the terminal fixture. The developed formulas are simple, easy‐to‐use, and clearly indicate the role of the major factors affecting the mechanical behavior of the fibers. The obtained results can be of help in physical design of dual coated fibers and optical interconnecti

ISSN:0032-3888    

DOI:10.1002/pen.760300207

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractAn apparatus was designed and assembled to study the solvent removal from solution‐cast thin polymer films. The computer interfacing of a thermogravimetric analyzer, spectrophotometer, electronic flowmeters, and control valves for the apparatus enabled the preprogramming of the carrier gas velocity, carrier gas solvent content, and temperature profiles to simulate the environment experienced in large parallel flow industrial driers. The apparatus has also been designed and operated to enable the visual observation of the drying film with an optical microscope. Initial experimental studies conducted with the apparatus involved the effect of temperature on solvent removal. The results indicate that high dryer gas temperatures can apparently cause skinning of the film surface resulting in slower solvent removal rates. The skin formation can be suppressed by higher solvent concentration in the carrier gas. The visual observations revealed the formation of standing waves in the film surface during drying at high gas velocities (>2OO cm/min). The wave formation at least partially overcomes the effect of skinning by increasing the surface area of the film, and may be the manifestation of flow instabilities involving circulation within the fil

ISSN:0032-3888    

DOI:10.1002/pen.760300208

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractRheological studies of an experimental liquid crystalline (LC) copolyester were carried out using a capillary rheometer and a cone and plate rheometer. Rheological characteristics of the polymer in the nematic state were observed. The nematic melt was found to be pseudoplastic and the degree of pseudoplasticity varied with shear rate. Melt viscosity was found to decrease with shear rate. Negative die swelling was observed at the exit of the capillary rheometer at temperatures marginally above the solid‐nematic transition temperature of the polymer and was also found to be a function of shear rate. The dynamic mechanical properties of the polymer were studied as a function of temperature. The activation energies of flow and of dynamic mechanical deformation were calculate

ISSN:0032-3888    

DOI:10.1002/pen.760300209

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe “Efficiency of Energy Absorption” (or “Efficiency”) and “Ideality” parameters were evaluated for several plastic foams and were found to be very useful in choosing an appropriate cushion for the protection of a specific product. The maxima in these parameters were found to be in the same range of stresses, when derived from dynamic measurements or from predicted stress‐strain curves based on previously proposed “Reference” and “Modified Boltzman Superposition” Models. For the rate independent foams the maxima in these parameters do not change with strain rate and can therefore be derived from slow, constant rate (“static”) experiments. For rate dependent foams however, the maxima from “static” measurements were found to be in a lower range of stresses than those derived from dynamic ones. As a result, slow rate compressive measurements do not predict well the behavior of the foams during impact and the use of the “Reference” and “Modified Boltzman Superposition” Models is required for good predictions. It was found that the suffer PS and PE foams attain maximum Efficiency and Ideality at higher stre

ISSN:0032-3888    

DOI:10.1002/pen.760300210

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760300201

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY