摘要:

AbstractThe following models describe the effect of temperature and shear rate on the viscosity of polyisoimide solutions.\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} \tau & = & {\beta _O \gamma ^{\beta 1} \exp (\beta _2 /T)} & {(1)} \\ \tau & = & {\beta _O \gamma ^{\beta 1 + \beta 3T} \exp (\beta _2 /T)} & {(2)} \\\end{array} $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} \beta & = & {{\rm fitted coefficient}} \\ \tau & = & {{\rm shear stress, N/m}^{\rm 2} {\rm or }1b_f /ft^2 } \\ T & = & {{\rm temperature (K of R)}} \\ \gamma & = & {{\rm shear rate, S}^{{\rm - 1}} } \\\end{array} $$\end{document}Data was obtained for 20, 30, and 40% polyisoimide solutions in 20:80 tetrahydrofuran/diglyme and for a 30% solution in N‐methyl‐pyrrolidone at temperatures of 25°, 35°, 55°, and 75°C. The measurements were taken on a Brookfield cone and plate viscometer at shear rates ranging from 9.59 to 383.4 reciprocal seconds. Experimental data fits model (1) reasonably well. In some cases, model (2) provides a better fit. This model accounts for temperature dependencies in the power law shear‐thinning exponent.The coefficients β depend on the material lot that is being tested even though the lot molecular weights are very close. Slight differences in acid functional group concentrations for this particular material are a possible e

ISSN:0032-3888    

DOI:10.1002/pen.760291802

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractPolyester blends may undergo transesterification during processing, resulting in molecular rearrangements, transient properties, and eventually, degradation. To suppress transesterifcation, the use of organophosphites has been suggested in the patent and technical literature. The effectiveness of organophosphites, however, is variable and sometimes inconsistent. Our recent studies suggest a clue to the inconsistent behavior and provide a simple way to enhance the effectiveness of these stabilizers. Using solid state31P NMR it was shown that for bis(2,4‐di‐t‐butylphenyl)pentaerythritol diphosphite a conversion of the phosphite group to a phosphonate, via hydrolysis, is a prerequisite for an effective inhibition of transesterification. This conversion occurs readily during melt compounding if the polymers are not completely dry. However, if rigorous drying is employed and phosphite conversion does not occur, then transesterification is not arrested. It was also found that over a period of time the conversion of the phosphite to a phosphonate may take place at room temperature as well. After aging for about a year in the laboratory, the originally ineffective compound, has become a very effective inhibitor of transesterification in blends containing poly(ethylene terephthalate), poly(butylene terephthalate), polycarbonate, and polyarylate. Thus, a simple way to enhance the phosphate effectiveness is to expose it to a humid environment prior to ble

ISSN:0032-3888    

DOI:10.1002/pen.760291803

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe slip phenomenon through capillaries has been analyzed experimentally using solutions of polyacrylamide and xanthan gum. These polymeric solutions present macromolecules with different conformations in flow. Attention was given to the influence of molecular conformation of those polymeric solutions upon the slip velocity. Considerable variations on the slip velocity were observed when the ionic strength of the xanthan solution was increased and also when the material of the capillaries was changed. Measured magnitudes were much larger in the xanthan solutions than those observed in the polyacrylamide solution.

ISSN:0032-3888    

DOI:10.1002/pen.760291804

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA novel process for the formation of biaxially balanced films of poly(p‐phenylene terephthalamide) was developed. The liquid crystalline sulphuric acid solution is extruded through a slit die on a flat plate. The optically anisotropic to isotropic transition is generated by controlling the temperature and/or the water content in sulphuric acid before coagulation. The wet gel films are dried while holding their width and length constant. The films thus produced are transparent and biaxially oriented. Young's modulus of 12 GPa, tensile strength of 450 MPa, and elongation at break of 25% were obtained in the plane of the film. Such films which possess high dimensional and thermal stabilities are expected to be useful for new practical uses under severe condition

ISSN:0032-3888    

DOI:10.1002/pen.760291805

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractChanges in the crystalline morphology and thermal behavior of amorphous poly(etheretherketone) (PEEK) films have been effected by irradiation with a continuous wave CO2laser. At high laser scan rate and power, PEEK films melt and requench into amorphous transparent films. At a scanning velocity of 14 μm/s and incident intensities ≥ 4.8 W/cm2and a Gaussian beam radius of 1.63 mm, PEEK films crystallize “completely” aboveTgon laser annealing. Irradiation of PEEK films on a quartz substrate reduces the cooling rate, allowing slower and more perfect recrystallization. Similar changes are effected by reducing the laser scan velocity or by increasing the laser power. Depending on the experimental conditions, laser induced recrystallization may occur on annealing aboveTgor on cooling from th

ISSN:0032-3888    

DOI:10.1002/pen.760291806

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe recently developed mathematical technique for studying the parametric sensitivity of reactors is extended to include chain polymerization systems exhibiting the gel and glass effects, as well as physical property variations. The sensitivities of the two temperature maxima with respect to various parameters are computed. It is found that, for a sample system, poly(methyl methacrylate), all the sensitivities of the gel effect induced temperature peak attain their maxima at the same conditions—this leads to a generalized temperature sensitivity constraint applicable to reactor design or operation. This sensitivity boundary is associated with high conversions and high molecular weights. The analysis shows that the dimensionless propagation activation energy,ϵp, and the dimensionless initiation activation energy,ϵd, are the two most important parameters governing the system performance. Sensitivities of the gel effect‐induced number average chain length peak with respect to various parameters are also obtained. Again, all of these chain length sensitivities show maxima at the same condition, leading to the concept of a generalized chain length sensitivity criterion of constraint. Most importantly, the temperature and chain length sensitivity boundaries are virtually iden

ISSN:0032-3888    

DOI:10.1002/pen.760291807

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe crystallization behavior of poly(ethylene terephthalate) (PET) was studied by the methods of small angle light scattering, depolarized light intensity and density measurements. Spherulite growth rates and the overall rates of crystallization were determined at various temperatures. A detailed analysis of the crystallization course has been made with special emphasis on the early stages of crystallization. The results indicate that a significant amount of crystallization takes place in the extraspherulitie material during isothermal crystallization.

ISSN:0032-3888    

DOI:10.1002/pen.760291808

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractPrimary normal stress difference data of some 32 different polymer solutions have been examined and correlated to the shear stress by a simple power‐law model. The normal stress at constant shear stress is shown to increase with the molecular weight of the polymer, but decreases with the polymer concentration. The method proposed by Abdel‐Khalik,et al., for predicting the primary normal stress difference from viscosity data for these polymer solutions is inadequate. The FENE‐P dumbbell model is used to obtain master curves combining normal stress and viscosity data as a function of a dimensionless shear rate. It is found that this presents several drawbacks. It predicts shear‐thinning effects with a power‐law slope of −2/3, which is found to be too restrictive. The model fails to predict shear‐thinning effects for dimensionless shear rates λEγ lower than approximately 0.5. It also fails to predict satisfactorily the low shear rate value of the dimensionless combination of viscosity and first normal stress coefficient Ψ1/λE(η − ηs). An empirically modified correlation is proposed. The fit for a series of polyacrylamide (Dow Separan AP‐30) solutions is very good. In the case of a series of monodisperse polystyrene solutions, the fit is not as good, as the data show a more pronounced effect of polymer concentrat

ISSN:0032-3888    

DOI:10.1002/pen.760291809

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe effects of physical aging on dynamic mechanical and transient stress‐relaxation properties of a high performance thermoplastic, polyetheretherketone (PEEK), are reported in this study. The aging effects are shown to be physical effects (and not chemical degradation) by establishing thermoreversibility of the aging process. The unique aspect of the present study is the simultaneous investigation of both dynamic and transient properties in the same mode of loading, namely, in shear. The influence of continuous dynamic deformation on the aging process is also reported. The results for the aging rate, obtained from dynamic and transient testing under shear load, agree with one another and verify the equivalence of dynamic and transient viscoelastic properties. However, these results differ significantly from the aging rate results reported in an earlier study for tensile loading. A possible explanation for the difference has been proposed in terms of the volume change that accompanies tensile creep deformatio

ISSN:0032-3888    

DOI:10.1002/pen.760291810

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe curing conditions determine the rheological changes in the resin during the lamination of prepregs into multilayered circuit boards. In order to specify the optimum curing conditions during lamination, it is necessary to understand the rheology of the resin as it cures. In this study, the chemorheological behavior of two commercial epoxy resins and one cyanate‐based resin was characterized using an engineering model for the resin viscosity. A linear regression technique was used to evaluate the model parameters from the conditions at the minimum viscosity obtained during resin cures at constant heating rates. The technique was extended to predict the minimum viscosities reached by the resins when subjected to temperature conditions commonly encountered during lamination. The utility of the technique for specifying the curing conditions necessary to have a desired resin flow during lamination and for selecting resin systems for lamination based upon chemorheology has been demonstrate

ISSN:0032-3888    

DOI:10.1002/pen.760291811

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY