摘要:

AbstractThe cure of an epoxy‐anhydride resin system used in pultrusion was characterized to develop an understanding of the cure behavior and to determine potential process controls parameters. Isothermal cures of neat resin formulations were monitored by differential scanning calorimetry (DSC), torsional braid analysis (TBA), and microdielectrometry (MDE). The processing conditions define a time/ temperature region in which monitoring would be applicable. Both DSC and MDE were found to yield useful information in this region, however, the events typically monitored by TBA either did not occur or occurred too quickly to be monitored. Significant ionic conductivity was observed in the fully cured resins at temperatures above the glass transition temperature and could possibly be used as a control parameter. This study revealed an apparent change in reaction mechanism with increasing cure temperature. DSC showed a change in activation energy with extent of reaction and a decrease in heat of reaction at the higher isothermal cure temperatures. The formation of a different network structure was indicated by a decreasing glass transition temperature of the cured resin with increasing cure temperature by both DSC and TB

ISSN:0032-3888    

DOI:10.1002/pen.760292202

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe influence of microstructure on dynamic mechanical behavior in the two phase blend of polycarbonate, (PC), with poly(styrene‐co‐acrylonitrile), (SAN), was studied by comparing the torsional response for injection and compression molded samples. A matrix component's glass transition (Tg) damping was only moderately altered by the presence of a dispersed phase although shifts inTg, assigned to the local maxima in tan delta, indicated partial miscibility. In compression molded samples the onset of a co‐continuous PC phase suppressed the damping characteristics of the SANTgon the high temperature side shifting the assignment of thisTgto lower temperatures. This suppression results from PC dominating the composite's response at temperatures above the SANTg. In injection molded samples the onset of PC co‐continuity only partially suppressed the damping of the SANTgsuch that a doublet results. Co‐continuity within the injection molded microstructure could be idealized as alternating sheets which, subsequently, in the dynamic mechanical measurement are arranged In series to a shearing stress during torsion. Above theTgof SAN the presence of such a series phase arrangement allows the composite to strain approximately to that extent which would be exhibited by pure SAN alone. The response of the composite is thereby approximately the response of SAN with the almost full extent of itsTgdamping process

ISSN:0032-3888    

DOI:10.1002/pen.760292203

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe gel melting temperature and crystallization kinetics of ultra‐high molecular weight polyethylene (UHMW‐PE)/decalin systems were investigated. Two methods were used to determine gel melting temperature; thermomechanical analysis (TMA) with a penetration probe and differential scanning calorimetry (DSC). The melting points determined from TMA and DSC were in good agreement, indicating that the crystallization of UHME‐PE is an essential step for gelation. The gel melting temperature increases with UHMW‐PE concentration. The change in gel melting temperature with composition results from interaction of the components in the amorphous phase. The gelation and crystallization rates increase with decreasing UHMW‐PE conc

ISSN:0032-3888    

DOI:10.1002/pen.760292204

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe optical properties of polyetherimide resin as described by the complex index of refraction, N = n ‐ ik, are derived by Kramers‐Kronig analysis of experimental absorption and reflectance data obtained in the range 40 μm ≥ λ ≥105 nm. Potential uses of this polymer as a printed circuit board material and as a packaging medium for microelectronic circuitry and the relevance of optical data in laser‐assisted processing schemes used in these and other applications are briefl

ISSN:0032-3888    

DOI:10.1002/pen.760292205

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA general kinetic model was developed to simulate the grafting of monomers such as unsaturated carboxylic acids and silanes to ethylene polymers. The polymers considered were ethylene‐co‐vinyl acetate (EVA), ethylene‐co‐butyl acrylate (EBA), and low‐density polyethylene (LDPE). Grafting was assumed to proceed by a free‐radical mechanism involving chain transfer. Organic peroxides having a strong tendency for hydrogen abstraction were selected as the source of primary radicals. The model simulated the grafting reaction as taking place in a single screw extruder. The residence time distribution in the extruder was experimentally determined by tracer analysis, according to which the extruder was a plug‐flow reactor connected to two mixed reactors in parallel. The model is able to predict the extent of grafting in terms of predefined parameters. Comparison of model predictions with available experimental data showed slight deviations, the possible causes of which are discussed. However, the kinetic behavior expected on the basis of the input parameters was observed, and, as such, the model allowed study of the effect of process variables on grafting kinetics and provided insight into the react

ISSN:0032-3888    

DOI:10.1002/pen.760292206

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe strain‐time response under tensile loading (creep tests) and the stress strain response under constant tensile stress rate (proportional loading tests) have been evaluated at 4 temperatures 20, 45, 55, and 65°C, for samples of cellulose nitrate. A time‐dependent constitutive equation (or stress‐strain relation) for the nonlinear visco‐elastic material is deduced from invariant theory with a hypothesis of a creep potential. The procedure for determining the seven material constants involved in the deduced constitutive equation is described for the creep and proportional loading tests and the variation of these constants with temperature is presented. The deduced constitutive equation gives good agreement with the actual observations for the creep and proportional loading tests, independent of the values of temperature, creep stress, or str

ISSN:0032-3888    

DOI:10.1002/pen.760292207

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractResults of studies on fatigue fracture in polystyrene are reported. Experiments were carried out on tension‐tension single edge notched specimens, 0.25 mm thick. Macroscopic studies involved the propagation of the crack and its associated active zone (or the so‐called process zone) evolution. Microscopic studies consisted of fracture surface examination and quantitative characterization of the crazing distribution along the trailing edge and within the active zone. The width and length of the active zone increased monotonically during the quasi‐static phase of crack layer growth. The crack growth kinetics followed an S‐shaped curve. Analysis of crazing distribution showed that; (i) the distribution of crazing along the trailing edge of the active zone is related by a scaling parameter, (ii) the average crazing density along the trailing edge as well as within the active zone is constant, (iii) the specific energy of crazing evaluated here compares well with previously reported data. The results of this work support the form of self similarity of damage evolution adopted by the crack layer model, and that the specific energy of damage is a material c

ISSN:0032-3888    

DOI:10.1002/pen.760292208

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper describes characterizations performed on two types of polyethylene T‐Joints as well as the starting resin from which they were manufactured. It was found that the melt flow rate of material taken from the two types of joints differed from that of the starting resin and differed from each other by as much as a factor of two. Investigation of the environmental stress‐crack resistance (ESCR) and uniaxial creep behavior of material from the two joints revealed further significant differences in behavior between the two joints. These observations lead to the conclusion that subtle differences in the processing conditions can result in significant differences in the long‐term mechanical beh

ISSN:0032-3888    

DOI:10.1002/pen.760292209

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractAn investigation of the effect of physical aging on excess enthalpy of compatible polymer blends was carried out. Poly(methyl methacrylate) (PMMA) and poly(styrene‐co‐acrylonitrile) (SAN) were chosen for this study. Blends of different ratios of PMMA and SAN were physically aged at different times and temperatures below their glass transition (Tg) and then subjected to enthalpy relaxation measurement in a differential scanning calorimeter (DSC). An improved procedure was developed and, employed to analyze the data. The error associated with the calculation of the normalized deviation in enthalpy, known as the “Φ” function, was below 4%. The relaxation was observed to proceed faster at higher aging temperature. It was also found that at higher aging temperatures ofTg– 20 andTg– 35°C, enthalpy relaxation in SAN‐rich blends proceeds faster than in PMMA rich blends, while at the low aging temperature ofTg– 50°C the rate of relaxation becomes independent

ISSN:0032-3888    

DOI:10.1002/pen.760292210

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractUsing an energy balance approach incorporating a Flory‐Huggins expression for free energy and the strain energy of the material, the solvent removal process in liquid‐based coatings was shown to depend on stress and temperature. An equilibrium is obtained between residual solvent content and stress in the coating at a given temperature. Such stress‐dependent solvent removal behavior was observed with a polyamic acid coating solution‐cast using N‐methylpyrr

ISSN:0032-3888    

DOI:10.1002/pen.760292211

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY