摘要:

AbstractNonisothermal crystallization kinetic data obtained from differential scanning calorimetry (DSC) for a poly(ethylene terephthalate) are corrected for the effects of temperature lag between the DSC sample and furnace using the method of Eder and Janeschitz‐Kriegl which is based on experimental data alone without resort to any kinetic model. A method is presented for shifting the corrected nonisothermal crystallization kinetic data with respect to an arbitrarily chosen reference temperature to obtain a master curve. The method is based on experimental data alone without reference to any specific form of kinetic model. When the isothermal crystallization kinetic data for the same material are shifted with respect to the same reference temperature, a master curve is also obtained which overlaps to a large extent the corresponding master curve from nonisothermal data. It follows that nonisothermal DSC measurements provide the same crystallization kinetic information as isothermal DSC Measurements, only over a wider range of temperatures. The shift factors obtained from experimental data alone are compared in turn with the corresponding values calculated from the Avrami equation, the Hoffman‐Lauritzen expression, and the Nakamura equation as a means of evaluating these models individually. It is concluded that the Avrami equation is very good at describing isothermal crystallization kinetics, the Hoffman‐Lauritzen extrapolation of the limited isothermal data to a wide range of temperatures is quite good, and the Nakamura equation yields reliable crystallization kinetic information over a narrower range of temperatures than nonisothermal data alone without using any specific

ISSN:0032-3888    

DOI:10.1002/pen.760350902

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractFor a science‐based design of the Powder Injection Molding (PIM) process, it would be desirable for designers to have a numerical analysis tool capable of predicting the PIM filling process as a design aid. In this regard, the present study is aimed at developing a numerical analysis system to simulate the PIM filling process based on a new physical modeling taking into account rheological characteristics of powder/binder mixtures, namely the yield stress and the apparent slip phenomena. In particular, two different slip models were employed to represent the apparent slip phenomena. In accordance with the new physical modeling, the numerical simulation of the PIM filling process was accomplished by combining a finite element method and a finite difference method. It was found that the slip layer plays a role of not only a lubricating layer but also a thermal insulation layer. In this aspect, the slip layer model seems to represent the apparent slip phenemena better than the slip velocity model with regard to both the momentum and the thermal transport phenomena. The present paper presents the physical modeling, numerical scheme, and some numerical analysis results showing the effect of the yield stress and slip phenomen

ISSN:0032-3888    

DOI:10.1002/pen.760350903

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe effect of hot curing of unsaturated polyester resin on the dynamic relaxation time was studied using dielectric measurements along with two dynamic mechanical measurement methods. It was found that the dynamic response during cure was a material frequency dependent property and did not depend on the measurement method. All relaxation times, measured during cure, by all three measurement methods used, converged to a single equation: τ(t)av=atbwheret= curing time,a, b=constants. The increase of the relaxation time during cure followed the same trend as a friction factor, which was found to increase with conversion. The crosslinking density was found to increase slowly with conversion, while the relaxation time increased exponentially. These two different modes of behavior during cure explain the high resolution of dynamic measurements as a cure monitoring tool, which can easily detect small curing changes. This behavior of the relaxation time was explained by the sharp rise of activation energy due to a parallel decrease of free volume at high conversion

ISSN:0032-3888    

DOI:10.1002/pen.760350904

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractTwo numerical approaches have been applied to examine the possibility of adding shims to conventional extrusion dies such as T‐dies and coat‐hanger dies to produce multiple stripes. The first numerical approach is based on a one or two‐dimensional lubrication approximation and the second one is the three‐dimensional finite element simulation. Both approaches are applicable, but the lubrication approximation is accurate and much simpler to use. The extruded stripes are assumed to obey a non‐Newtonian power‐law model. It has been found that the T‐die with a shim can produce multiple stripes of acceptable uniformity, irrespective of the strip numbers and widths and the power‐law index. The coat‐hanger die with a shim did not deliver multiple stripes with good uniformity. Adding an outer manifold to the coat‐hanger die can serve as an effective means to reduce f

ISSN:0032-3888    

DOI:10.1002/pen.760350905

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractA versatile transient network theory has been used as a framework for the interpretation of large amplitude oscillatory behavior of polyolefin melts in terms of their entanglement kinetics. The model reasonably describes all previously published measurements of the large amplitude oscillatory shear behavior on melts. Seven polyolefins are examined, three new materials and four previously studied. A qualitative difference in the nonlinear behavior in large amplitude oscillatory shear has been identified between the polyethylenes examined and the two other polyolefins, polystyrene and polyisobutylene.

ISSN:0032-3888    

DOI:10.1002/pen.760350906

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper investigates the effect of matrix ductility on toughness in a carboxyl‐terminated butadiene‐acryionitrile copolymer (CTBN) toughened diglycidyl ether of bisphenol‐A (DGEBA)‐piperidine system. Two kinds of epoxides were blended separately into this system to change the matrix ductility. One was a rigid and polyfunctional 4,4′‐diaminodiphenol methane (MY720), and the other was a flexible diglycidyl ether of propylene glycol (DER732). The matrixTgwas significantly changed, but without alteration of the microstructure of the dispersed rubbery phase. The result of fracture energy tests reveals that the toughness of the neat epoxy resins increases slightly with the increase in the resin ductility. The toughness of the rubber‐modified epoxy resins increases strongly with matrix ductility. Studies on the morphology of the toughened systems and their fracture surfaces indicate that the size of the plastic deformation zone under constant rubbery‐phase morphology is determined by the multiple but localized plastic shear yielding. Increasing matrix ductility increases the size of the plastic deformation zone by inducing more extensive shear yielding. In addition, fracture surfaces reveal that as the matrix rigidity is increased, an increasing proportion of the fracture energy is dissipated by rubber cavitation during c

ISSN:0032-3888    

DOI:10.1002/pen.760350907

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractA method to determine viscoelastic changes in medium density polyethylene (MDPE) pipe specimens associated with the crack tip during fatigue crack initiation (FCI) and propagation (FCP) experiments is described. The load‐displacement curves are analyzed to obtain the phase angle, δ. Changes in δ are related to the number of cycles of crack initiation of three different MDPE copolymers: hexene (H), butene (B), and methyl pentene (MP) copolymers. These changes are related to craze formation and growth at the notch tip, leading to crack initiation and to the irreversible work,Wi, expended on them. Within a given material, step wise increments in δ distinguish the onset of crack initiation and the brittle‐to‐ductile transition in crack growth. The magnitudes of tan δ andWiare noted to be in quantitative agreement with the resistance of the three copolymers to FCI and brittle propagation that rank in the order: isobutyl (MP)>ethyl (B)>butyl (H). Similar crystallinity of the three copolymers insinuates a hypothesis that variance in the nature of chain entanglements associated with the respective branch type might be accountable for the observed differences in viscoelastic character. The final stage of failure by ductile tearing is dominated by large scale plastic flow that seemingly overshadows the material differences governing time dependent brittle

ISSN:0032-3888    

DOI:10.1002/pen.760350908

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760350901

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY