摘要:

AbstractThis is a two‐part theoretical and experimental study on the estimation of kinetic parameters associated with the curing of a thermoset epoxy resin. In Part I, the estimation procedure is presented. This estimation procedure is based on a method referred to as the Box‐Kanemasu method, which involves the minimization of a least squares function, and it represents a new application of this method. The kinetic parameters under consideration were the Arrhenius constants associated with two rate constants in a kinetic model used to describe the curing rate of an amine epoxy resin. The use of differential scanning calorimetry (DSC) and dielectric data assuming isothermal and dynamic experimental conditions was first investigated in a sensitivity study. It was determined that the degree of cure should be treated as the dependent variable and that data from isothermal experiments should be used. The estimation procedure was then used to estimate the Arrhenius constants from simulated degree of cure data with added errors. These results compared favorably with those found using a linear regression met

ISSN:0032-3888    

DOI:10.1002/pen.760331802

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThis is a two‐part theoretical and experimental study on the estimation of the kinetic parameters associated with the curing of a thermoset epoxy resin. In Part II, the kinetic parameters associated with the curing of the bisphenol‐A‐diglycidylether/meta‐phenylenediamine (BADGE/mPDA) resin were estimated from both differential scanning calorimetry (DSC) and dielectric experimental data using a new estimation procedure described in Part I. The kinetic parameters estimated were the Arrhenius constants associated with a kinetic model used to describe the degree of cure. Isothermal experiments were performed using both experimental techniques at four different curing temperatures. The resulting estimates of the kinetic parameters were compared with results obtained from the same data using a linear regression method. The magnitude of the confidence intervals of the estimated parameters and the standard deviation of the model (based on the residual errors between predicted values of the degree of cure and experimental values) were used as criteria in the comparison of the results. From this comparison, it was concluded that the parameters estimated from DSC data using the new estimation procedure provided the estimates with the least variability and, consequently, the smallest errors associated with the kineti

ISSN:0032-3888    

DOI:10.1002/pen.760331803

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe mechanical hysteresis of a polyether polyurethane thermoplastic elastomer was studied as a function of temperature, percent strain, and deformation energy. Hysteresis values remained small at low temperatures when the extent of the sample deformation did not disrupt the glassy matrix. This was readily evident at temperatures below the glass transition temperature,Tgof the polymer where the material did not formally yield. At temperatures above theTgof the polymer, hysteresis remained small even at substantial strains levels and demonstrated the capabilities of the hard segment domains to act as physical crosslinks. At elevated temperatures, percent hysteresis increased as the hydrogen‐bonded hard segment domains weakened. When mechanical hysteresis was considered on the basis of constant deformation energies, hysteresis values reached a maximum in the vicinity of theTgof the polymer. These maxima existed as a consequence of two opposing trends: the decreasing resiliency of the polymer as it becomes a glass and the increase in the resistance of that glass to undergo deformations sufficient to cause plastic flow. Finally, a hysteresis response surface constructed as a function of deformation energy and temperature was found to be sensitive to both the strain‐induced crystallization of the rubbery soft segment matrix and to the strain‐induced yielding of the glassy soft segment m

ISSN:0032-3888    

DOI:10.1002/pen.760331804

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractResin flow and fiber spreading during the prepregging process were investigated experimentally using a scale‐down version of a commercial hot‐melt prepregger with bismaleimides and carbon fibers as model systems. Specifically, several dimensionless parameters such as the Prepreg Flow Number, fractional resin uptake, resin distribution function, fractional width change, and prepregging efficiency were defined to characterize the prepregging process as well as the quality of the prepreg. Fiber spreading during the prepregging process was observed to be a viscoelastic phenomenon depending on the impregnation temperature. For resin impregnation into collimated fiber tows, all the experimental data points obtained at different operating conditions were superimposed onto a single line showing a temperature‐pressure‐velocity superposition for the prepregging process as predicted by the definition of the Prepreg Flow Number (PFN). Finally, three fundamental steps of the prepregging process were identified and confirmed with cross‐sectional micrographs of unaged prepregs produced at different tem

ISSN:0032-3888    

DOI:10.1002/pen.760331805

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractStress analysis around a three‐dimensional craze and a three‐dimensional craze containing a penny‐shaped crack has been made. The craze is treated as a transversely isotropic, oblate spheroid embedded in an isotropic glassy polymer. The craze is assumed to consist of primary fibrils and cross‐tie fibrils, such that a penny‐shaped crack may form at the central regime of the craze. The craze surface stress, the stress field near the craze tip outside the craze region, and the stress intensity factor in the crack tip are determined by using Eshelby's equivalent inclusion method. Numerical values of the fracture toughness and the stress needed to sever a craze fibril at the crack tip are calculated and the results appear to be in good agreement with the data given in the l

ISSN:0032-3888    

DOI:10.1002/pen.760331806

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effects of added polyisoprene homopolymer (PI) and polyisoprene‐blockstyrene diblock copolymer (SI) on the viscoelastic properties of a polystyrene‐block‐polyisoprene‐block‐polystyrene triblock copolymer (SIS) having a spherical domain morphology have been examined. The former two species are used to model the effects of imperfections in structures that result from triblock copolymers missing, respectively, two or one polystyrene end blocks. The results indicate that the loss modulus and tangent delta in the plateau region can be dominated by imperfections in the copolymer structure. The interpretation of viscoelastic data in the rubbery plateau region as an indication of interface structure in block copolymers is therefore greatly complicated. Small angle X‐ray scattering (SAXS) and rheological tests were also used to determine the order‐disorder transition temperature for an SIS triblock copolymer and its blend with an SI diblock. The SAXS data are consistent with Han's rheological criteria for determining the order‐disorder transition temperature. However, the complex viscosity does exhibit Newtonian behavior for low rates at the highest temperatures, even though the domain morphology persists. Stress relaxation and dynamic modulus data at high temperatures clearly show a secondary “rubbery” plateau at long times, and we offer a qualitative explanation for this feature based on a proposed r

ISSN:0032-3888    

DOI:10.1002/pen.760331807

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe role of water and other contaminants like salt water, iso‐octane, and ethylene glycol on neat resin, composites, and friction materials have been investigated. The maximum solvent uptake and the diffusion coefficient of the solvent in these systems were determined and the experimental data was fitted to a Fickian model. The nature of the diffusion process was determined in each case and deviations from Fickian behavior were accounted for. For the neat resin and the composites, the diffusion coefficients of the liquids were of the order of 10−10cm2/s. After exposure to these contaminants, mechanical properties of all the systems were determined and a general degradation in properties was found. The flexural strength and fracture toughness showed reduction in values while the flexural modulus was not affec

ISSN:0032-3888    

DOI:10.1002/pen.760331808

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA study of the progress of the synthesis of unsaturated polyesters, based on anhydrides of phthalic and maleic acid and propylene glycol without added catalysts was done. The reaction was carried out on a laboratory and industrial scale. The acid number and molecular weight distribution were determined. In the laboratory synthesis the, amount of water produced during the reaction was also measured. Two steps in the reactions were observed. The first is the reaction of anhydrides with glycol producing monoester which is followed by step‐growth polymerization reaction producing polymer. The kinetics of step‐growth polymerization reaction was found to be third order with an activation energy ofEa= 54.3 kJ mol−1andko= 15.2 kg2mol−2s−1. The kinetic model was prepared and compared with results obtained from reactions carried out on an industrial scale. A method is presented for determining a heating program based on a limited reaction rate and a maximal reaction temperature for a particular system. The MWD of polyester resin was determined and disagreement was found compared to the “most pr

ISSN:0032-3888    

DOI:10.1002/pen.760331809

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA constitutive equation for small strain viscoelastic response is considered in which stress relaxation. occurs faster as strain increases. The constitutive equation is of single integral type and has a psuedo‐ or material time function which is calculated from a strain dependent shift function. First, it is shown that such a constitutive equation can account for yield as observed in polymers for a number of different stress and strain histories. Next, the constitutive equation is used in the analysis of the problem in which a hollow cylinder is fixed at its inner surface and a moment history is applied to its outer surface. This causes the cylindrical surfaces to rotate about the central axis, thereby inducing a radial shear strain distribution. It is shown that there is a time when the material near the inner support begins to yield and a layer of large shear strain gradient begins to grow rapidly. It is also shown that the stress or strain history at a material element will generally not be one of the standard histories used to study yiel

ISSN:0032-3888    

DOI:10.1002/pen.760331810

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760331801

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY