bluuebunny/crossref_metadata_2025 huggingface dataset:
The temperature‐dependence of some mechanical properties of a cured epoxy resin system
Authors: Gupta V. B. , Drzal L. T. , Lee C. Y.‐C. , Rich M. J.
Published: December 2004

The tensile mechanical properties and fracture toughness of a Bisphenol‐A type difunctional epoxy resin, cured with different amounts of metaphenylene diamine, using two cure cycles, were determined over a range of temperature. The tensile modulus in the glassy state was seen to be predominantly related to intermolecular packing, while in the rubbery state crosslink density was the important factor. Yielding appeared to be due to an increase in free volume as a result of dilatation during the tensile test and was related to a critical shear stress. The large strain properties like tensile strength, elongation‐to‐break, and toughness showed a more complex dependence on chemical structure, molecular architecture, intermolecular packing, and crosslink density. The roles played by the relaxation processes in determining mechanical properties are highlighted.
Impact strength and melt viscosity of bisphenol‐a polycarbonate and styrene‐maleic‐anhydride copolymer blends
Authors: Hansen Marion Glenn , Bland David G.
Published: December 2004

Mixtures of 90, 80, and 70 percent by weight bisphenol‐A‐polycarbonate (PC) and 10, 20, and 30 percent by weight styrene maleic anhydride (SMA) copolymer were melt‐blended in a single screw extruder. Differential scanning calorimetry (DCS) and scanning electron microscopy (SEM) were used to determine the miscibility of the blends. The viscosity, as a function of shear rate and temperature, was measured by an Instron capillary viscometer. The notched impact strength as a function of temperature was measured by an Izod impact tester.

The results of DSC showed two glass transition temperatures which merged slightly towards each other, indicating marginal miscibility of these blends. There was a decrease in viscosity as the fraction of SMA copolymer was increased. The most significant decrease occurred with the initial addition of SMA copolymer. The viscosity also decreased with increases in temperature. The impact strength of the blends was also dependent on SMA copolymer content. The blends showed six to ten times lower impact strengths at room temperature than the 100 percent polycarbonate. SEM analysis helped to determine the reason why the impact strength was lower for the blends. High magnification showed the presence of SMA copolymer inclusions dispersed throughout the PC matrix. These inclusions, which increased in size as SMA copolymer content was increased, acted as defects in the system.
Instrumented impact testing of glass reinforced polypropylene
Authors: Golovoy A.
Published: December 2004

The impact response of a glass fiber reinforced polypropylene was studied in a 3‐point drop‐weight impact test between −15 and 85°C and at a constant impact velocity of 2.2 m/s (5 mph). The response is a combination of tension and shear and can be expressed in terms of an apparent modulus,EA: 1.

WhereE11is the tensile modulus,G12: shear modulus,d: specimen thickness, andl: specimen length.

For a 40 weight‐percent glass reinforced polypropylene,E11was found to have a room temperature value of 5.8 GPa, and shear modulus of 0.43 GPa. Both decreased with temperature increase, with the shear modulus showing greater sensitivity to a temperature change. The fracture initiation and propagation energies were relatively independent of temperature. The fracture initiation energy per unit deformed volume was of the order of 1 MJ/m3. The total fracture energy was found to be sensitive tol/d: about 7 MJ/m3atl/dof 5.3 and about 1.7 MJ/ m3atl/dof 16.
Dynamic‐mechanical and transient testing of practical plastic specimens using a new servo‐hydraulic testing system
Authors: Yee A. F.
Published: December 2004

A servo‐hydraulic testing system which can simultaneously produce high loads and rapid response is described. This system allows the testing of relatively large plastic specimens, which makes it possible to perform dynamic‐mechanical and transient experiments on high modulus materials, specimens routinely molded for tensile testing, and specimens removed from actual processed articles. Such large specimens also permit the use of extensometers directly attached on the gage section, providing important data for the accurate calculations of material properties. Dynamic‐mechanical data on poly(methyl methacrylate), glass‐filled nylon, and talc filled polypropylene specimens removed from an injection‐molded dishwasher tub were obtained to demonstrate the capability of the system. Stress relaxation experiments in the nonlinear range were performed on polycarbonate to illustrate the transient testing capability of the system.
Phase behavior studies of the system polystyrene‐polybutadiene‐chloroform. I. Application of the flory‐huggins theory
Authors: Robledo‐Muniz J. G. , Tseng H. S. , Lloyd Douglas R. , Ward Thomas C.
Published: December 2004

The equilibrium phase behavior of the partially miscible system polystyrene‐polybutadiene‐chloroform was studied at 25°C and 1 atm pressure by using gel permeation chromatography to analyze the conjugate phases. Three narrow molecular weight distribution samples of each polymer were used to provide nine examples of the system for study. The Flory‐Huggins theory was used to determine the polymer‐polymer interaction parameter χ23, When literature values of the two polymer‐solvent interaction parameters χ12 and χ13 were used, the χ23 values generally were found to be negative and to show no distinct concentration dependence. No significant improvement was found when the literature value of only the polybutadiene‐chloroform interaction parameter was used to simultaneously generate values of χ23 and χ12. Values of χ23 at the critical point, χ23,cr, were found to increase with increasing polymer concentration.
A study on polymer blending microrheology: Part 1
Authors: Elmendorp J. J. , Maalcke R. J.
Published: December 2004

In order to achieve a better understanding of polymer blending processes some experimental work has been carried out on the deformation and break‐up behavior of liquid droplets in simple shearing matrices. For Newtonian systems good agreement was obtained with existing theories. For non‐Newtonian systems trends were established regarding the influence of fluid elasticity on droplet deformation and break‐up.
Studies of poly(2,6‐dimethyl‐1,4‐phenylene oxide) blends: 2. Poly(4‐methylstyrene)
Authors: Fried J. R. , Lorenz T. , Ramdas A.
Published: December 2004

Blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PMMPO) and poly(4‐methylstyrene) (P4MS) were found to be compatible from a variety of experimental methods including calorimetric, density, and mechanical property measurements. Blend property behavior was similar to that widely reported for PMMPO/polystyrene (PS) blends. For each blend composition studied, a single glass transition temperature (Tg) was detected by differential scanning calorimetry. The compositional dependence of blend Tg was equally well represented by the empirical inverse rule of mixtures or by the Couchman thermodynamic expression. Density measurements of molded films suggested a mild excess volume of mixing that was slightly smaller than that observed for blends of PMMPO and PS. As in the case for PMMPO/PS, densification in the solid state may be associated with the observed mechanical property behavior of the PMMPO/P4MS blends. Initial modulus at each blend composition was larger than would be predicted by a simple weighted average of component polymer values. Tensile deformation changed from a ductile to a brittle mode of failure with increasing P4MS composition. The yield stress for ductile compositions and ultimate stress of brittle samples were both higher than found for the corresponding unblended polymers and higher than would be predicted from a simple additive relationship of weighted component properties. Blend impact strength determined by small strain rate tensile tests rapidly decreased to low levels with increasing P4MS composition. This drop in impact strength became more composition sensitive at higher loading rates during multiaxial deformation in an instrumented dart impact tester.
Equilibrium phase compositions of heterogeneous copolymers
Authors: Bauer Barry J.
Published: December 2004

The products of random copolymerizations are heterogeneous in chemical composition, having a distribution of the fraction of each monomer in the copolymer. Polymer molecules with the same composition and molecular weight can be treated as separate components in a polymer blend. The spinodal limit is a simple function of chemical heterogeneity. The equilibrium number of phases, phase volumes, and average composition can be calculated from the condition that the chemical potential of a polymer species is equal in every phase. Phase diagrams are calculated for various hypothetical chemical distributions as well as a distribution characteristic of a random acrylonitrilebutadiene copolymerization to high conversion.
Theory of phase equilibria in block copolymer‐homopolymer mixtures
Authors: Whitmore Mark Douglas , Noolandi Jaan
Published: December 2004

A brief introduction to the theory of block copolymer/homopolymer mixtures is presented. All important effects, such as stretching of the polymer chains, changes in the conformational entropy at an interface, enthalpic and configurational effects, as well as connectedness of the blocks of the copolymer are included in the model.
Dynamic mechanical analysis of rubber toughened epoxy resins
Authors: Sanjana Z. N. , Kupchella L.
Published: December 2004

Dynamic mechanical analysis (DMA) was used to characterize cured epoxy resin formulations from −150°C to temperatures above their α transitions. The resins were aromatic amine and aliphatic amine cured and were modified with carboxylterminated acrylonitrile‐butadiene (CTBN) rubbers to improve their toughness, A DuPont 981 dynamic mechanical analyzer was used to measure the modulus and mechanical loss factor (tan δ) of the samples. Changes in the α and β transitions in the scan of tan δ as a function of temperature were related to changes in the formulation. Relations were also sought between changes in the DMA data and fracture and impact toughness of the cured formulations obtained using an instrumented impact test. Impact tests were performed at −196°C and at room temperature. Results indicate that fracture toughness and the dynamic mechanical properties are affected by the amount of rubber, the compatibility of the rubber and epoxy, and changes in the curing agent stoichiometry.
Tube flow of a particulate‐filled thermosetting polymer
Authors: Riccardi C. C. , Vazquez A.
Published: December 2004

The conservation equations of momentum, energy, and mass are numerically solved for the flow of filled thermosets reacting In a tube. The flow is assumed to be laminar and adiabatic with a constant volumetric flow rate. The critical radii are parameters that define the processability limits. The lower one is the value of the radius where an undesirable advance in the reaction extent takes place at the wall or where viscous heating leads to degradation. The upper critical radius is the radius where wall velocity is low and gelation takes place. The effects of filler volumetric fraction, wall slip velocity, and different inlet conditions are taken into account. Increasing wall slip velocity or filler fraction and decreasing inlet temperature or tube length amplify the processability zone.
Melt homogeneity in injection molding: Application of a ring‐bar device
Authors: Peischl G. C. , Bruker I.
Published: December 2004

A thermocouple ring‐bar device located between the nozzle and screw‐tip was used to study the thermal homogeneity of a shot formed during injection molding. Axial and radial melt temperature profiles thus observed under various processing conditions illustrated the importance of screw channel volume‐to‐short‐size ratio on melt homogeneity, Several methods of improving melt quality, as measured by this device, are demonstrated.
Melting mechanism in single screw extrusion
Authors: Bruker Izi , Balch Gary S.
Published: December 2004

Flow visualization experiments of polycarbonate and polystyrene resin extrusion were performed to observe the melting mechanism and the flow kinematics around the solid‐bed in the melting zone of a single screw extruder. The axial solids content and pressure profile calculations of the Tadmor melting model were modified as a result of variable solid‐bed velocity and solid‐bed temperature observations.
Simultaneous dielectric and dynamic mechanical analysis of thermosetting polymers
Authors: Gotro Jeffrey , Yandrasits Michael
Published: December 2004

This work presents a new method to measure simultaneously the dielectric loss factor and viscosity of thermosetting polymers during various cure cycles. A microdielectric sensor was mounted in the bottom plate of a parallel plate rheometer. Three types of high performance laminating resins were investigated. During non‐isothermal curing, dipole peaks were found to correspond to softening/devitrification, the maximum in the loss factor followed the same heating rate dependence as the minimum in the viscosity, and dipole peaks were observed to correlate with vitrification when the cure temperature was below the ultimate glass transition temperature of the resin.
Monitoring the cure of a composite matrix resin with microdielectrometry
Authors: Bidstrup Wayne W. , Senturia Stephen D.
Published: December 2004

This paper presents a study of the cure of glass and graphite fiber epoxy composites using dielectric monitoring techniques. Initial results reported here deal with the neat resin and the relationship between its conductivity and corresponding changes in glass transition temperature during cure.
Analysis of the Dielectric Response of Thermosets During Isothermal and Nonisothermal Cure
Authors: Nass Kirk A. , Seferis James C.
Published: December 2004

Using dielectric techniques to monitor thermoset properties on‐line during processing requires a mathematical relationship between the experimentally obtained signals and the physical state of the polymer. Such a relationship accounting for the dielectric response during both isothermal and dynamic cure experiments is developed in this study. Ionic conductivity changes with cure were described using the Keinle‐Race expression, while an approach taken by Lane, Bachmann, and Seferis for modeling dipolar relaxation during isothermal cure was extended to nonisothermal cure conditions. Both of these approaches were combined in this study, providing a complete description of the dielectric changes occurring in thermosetting systems resulting from cure. Experimental results for a model epoxy/amine system were predicted with the developed methodology for isothermal cure at 140°C, 150°C, 160°C, and 170°C and cure under dynamic heating conditions at 1°C per minute.
Glass transition temperature of a fluoroelastomer‐diluent system
Authors: Serbenski Francesca , Pezzin Giovanni , Ajroldi Giuseppe
Published: December 2004

The glass transition temperature has been measured carefully for the fluoroelastomer, Tecnoflon, a copolymer of vinylidene fluoride and hexafluoropropene, diluted with variable amounts of 2‐butanone. Of the several different theoretical treatments found in literature, that presented by Gordon and coworkers appears to give the equation that describes well the experimental results, without making use of adjustable parameters. Some features found at very high diluent content can be interpreted with a treatment based on free volume.
A novel sliding plate rheometer for molten plastics
Authors: Giacomin A. J. , Samurkas T. , Dealy J. M.
Published: December 2004

A novel sliding plate rheometer has been developed that is suitable for use with molten plastics, concentrated polymer solutions, raw elastomers, and other viscoelastic or thixotropic materials. It can generate steady shear rates from 0.05 to 500 s−1 and can also be used to measure linear viscoelastic properties. In addition, it can be used to measure a broad spectrum of nonlinear viscoelastic properties such as the nonlinear relaxation modulus and the shear stress growth coefficient. In order to measure these nonlinear properties it is necessary to generate large, uniform, transient deformations Involving high strain rates. Rotational and capillary melt rheometers are not capable of generating this type of deformation, and until now it was not convenient to use sliding plate rheometers for this type of application. However, the recent development of a reliable and robust shear stress transducer makes it very convenient to use the sliding plate geometry to carry out all of these tests. The new rheometer is described, and examples of the types of data it can generate are shown.
The effect of deformation history on the morphology and properties of blends of polycarbonate and a thermotropic liquid crystalline polymer
Authors: Kohli A. , Chung N. , Weiss R. A.
Published: December 2004

The effect of deformation history on the morphology and properties of liquid crystalline polymers (LCP) blended with polycarbonate resin was assessed. The addition of an immiscible LCP phase was found to improve the melt processability of the host thermoplastic polymer. In addition, by employing a suitable deformation history, the LCP phase may be elongated and oriented such that a microfibrillar morphology can be retained in the solid state.
A study on polymer blending microrheology: Part 5 deformation of purely elastic particles in an elongational flow field
Authors: Van Der Reijden C. , Van Heel A. S. , Sára A. , Schut J.
Published: December 2004

The deformation of purely elastic spheres in steady and unsteady elongational flow has been studied. Experiments were carried out in a four roller apparatus (steady elongational flow) and in the time dependent elongational flow of a converging channel. The existing theory which gives a first order approximation of the deformation of elastic spheres is extended to the non‐steady elongational flow in the cone. Both in steady and unsteady elongational flow, the theory describes the deformation of the spheres satisfactorily and under certain conditions even for higher deformations than expected.
Physical basis for a pressure‐dependent yield criterion for polymers
Authors: Lyon Richard E.
Published: December 2004

A previously empirical pressure‐dependent yield criterion for polymeric solids is derived from linear thermoelasticity and equilibrium thermodynamics. The assumption of a critical value of the mechanical component of the internal energy density at the onset of plastic deformation leads to an explicit expression for the yield condition in terms of the stress invariants and thermomechanical properties of the material. Order of magnitude agreement between the linear theory and published experimental data is obtained for a variety of polymers, suggesting a possible physical basis for pressure‐dependent yielding.
A fundamental study of polymer melt devolatilization. IV: Some theories and models for foam‐enhanced devolatilization
Authors: Lee S. T. , Biesenberger J. A.
Published: December 2004

Some model experiments on polymer melt devolatilization (DV) conducted in our laboratories have been previously reported. Here, we examine some theories and propose some mathematical models in pursuit of an explanation of these experimental observations. Included are bubble nucleation and free volume theories as well as continuum models for bubble growth in quiescent fluids and fluid flow in rolling pools without bubbles. A modification of Harvey's cavity model seems to explain the behavior of foam formation in DV, at least qualitatively. Denson's cell model for bubble growth fits the separation data under vacuum. A simple exponential model for overall separation fits the separation data at atmospheric pressure (entrained DV).
Poly(t‐BOC‐styrene sulfone)‐based chemically amplified resists for deep‐UV lithography
Authors: Tarascon R. G. , Reichmanis E. , Houlihan F. M. , Shugard A. , Thompson L. F.
Published: December 2004

The unique ability of the tert‐butoxycarbonyl protecting group (t‐BOC) to be removed by a catalytic amount of strong acid has intensified the search towards new chemically amplified resist systems based on this chemistry. A series of new copolymers of t‐BOC‐styrene and sulfur dioxide have been prepared by free radical polymerization. These polysulfones function as chemical amplification positive resists for deep‐UV lithography when mixed with either 2,6‐dinitrobenzyl tosylate or triarylsulfonium salt acid precursors. The lithographic characteristics of 2:1 and 3:1 polysulfones have been evaluated. The new positive deep‐UV photoresists are aqueous base developed and are capable of 0.5 μm resolution. Even though the photoresists containing 2,6‐dinitrobenzyl tosylate are less sensitive than the onium salt formulations, they displayed greater contrast values. For example the poly(t‐BOC‐styrene sulfone) (2:1) 15 wt % tosylate resist formulation exhibits a sensitivity of 26 mJ/cm2and a contrast of ∼20.
Factors controlling the etching rate and etching profile in the O2reactive ion etching pattern transfer step in multilevel lithography
Authors: Jurgensen Charles W. , Shaqfeh Eric S. G.
Published: December 2004

Physical bombardment plays a dominant role in the O2reactive ion etching (RIE) pattern transfer step in multilevel lithography. Etching rates are determined by the flux and energy distribution of the bombarding ions and energetic neutrals (charge transfer products), while anisotropy is determined by their directionality. Measurements of the sheath thickness and voltage drop may be used to estimate flux, energy distribution, average energy, and angular distribution of ions and the energetic neutral products of charge transfer collisions. The estimated flux of bombarding particles allows measured etching rates to be converted into yields. The trends for the etching rate as a function of pressure, bias voltage, and other system variables reflect a single fundamental trend for the yield as a function of bombardment energy. Etching rates of an organic novolac polymer are proportional to the energy flux from bombarding particles while the yield per bombarding particle is proportional to its energy. These kinetics are combined with angular distribution and interface evolution models to predict etching profiles in multilevel lithography.
Photochemical free‐volume generation in poly(methyl methacrylate) photoresists
Authors: Limm William , Winnik Mitchell A. , Smith Barton A.
Published: December 2004

The dissolution rates of poly(methyl methacrylate) [PMMA] thin films on quartz substrates are studied by a combination of laser interferometry and fluorescence quenching methods. In this way one can monitor the penetration, rate of the solvent (2‐butanone, 2‐pentanone) into the film. When these films were prepared containing 2 to 8 percent Meldrum's diazo (1) as a dopant, the dopant acted as a mild retarder of film dissolution. Upon irradiation at 254 nm, 1 is converted to CO, N2 + acetone, and this process leads to a pronounced acceleration' of the PMMA film dissolution rate.
Dissolution inhibition mechanisms of naphthoquinone diazides
Authors: Koshiba Mitsunobu , Murata Makoto , Harita Yoshiyuki , Yamaoka Tsuguo
Published: December 2004

Dissolution inhibition mechanisms of naphthoquinone diazides in novolak based positive photoresists were investigated from three different aspects:

• Dipolar interaction.

• Interfacial chemical reactions.

• Chemical structures of naphthoquinone diazides.

The results suggest that there exists a hydrogen bonding interaction between the compounds with the matrix novolak resin and that naphthoquinone diazides would crosslink the resin in contact with an alkaline developer, both of which contribute to dissolution inhibition mechanisms. However, there seems to exist another dissolution inhibition mechanism; namely, 1,2‐naphthoquinone diazide does not inhibit dissolution of the matrix novolak resin at all while a clear dissolution inhibition effect Is observed for its derivatives containing sulfonyl groups. In the present paper, three dissolution inhibition mechanisms of naphthoquinone diazides will be proposed.
Novel photoresist design based on electrophilic aromatic substitution
Authors: Reck B. , Allen R. D. , Twieg R. J. , Willson C. G. , Matuszczak S. , Stover H. D. H. , Li N. H. , Fréchet J. M. J.
Published: December 2004

A new approach to resist materials that exhibit chemical amplification is based on systems comprised of three structural units at least one of which is polymeric: (a) an aromatic moiety such as poly(4‐hydroxystyrene), Novolac, or other aromatic compounds which are susceptible to electrophilic aromatic substitution; (b) a latent electrophile which may be polyfunctional and, in the case of this study, is a carbocation precursor; (c) a material which generates strong acid upon irradiation. Exposure of a film containing these three structural components affords a latent image of acid dispersed in the polymer matrix. In a subsequent baking step, the photogenerated acid reacts with the latent electrophile releasing a very reactive carbocationic species which becomes bound to the aromatic moiety. As one of the components of the resist is polymeric and multifunctional, the result is a rapid increase in molecular weight due to branching and crosslinking of the chains. In terms of imaging, this process translates into the formation of a negative image of the mask although under some conditions a positive image may also be produced. The system shows a very high sensitivity and can provide high resolution images devoid of distortion due to the absence of swelling during development.
Melt transformation coextrusion. I.
Authors: Perez M. A. , Collier J. R.
Published: December 2004

Using the Melt Transformation Coextrusion process it is possible to enhance the mechanical and thermal properties of polymeric extrudates directly from the melt and maintain continuous production rates. This adaption of melt transformation extrusion has significantly enhanced line speed compared to the precursor process. The required operating pressures in both processes are low enough to allow for the usage of commercial plasticating extruders as the polymer melt sources. Molecular orientation necessary to produce property enhancement is induced in the converging section of specially designed dies and retained by the core layer of the extrudate by imposing a steep temperature gradient in the land section of the die. Mechanical properties (i.e. tensile strength and modulus) and melting point elevation observed for the polypropylene core/polyethylene skin extrudates were functions of extrusion pressure. The highest values of these properties noted were: tensile modulus, 9.37 × 105 psi; tensile strength, 2.10 × 104 psi; and melting point elevation in excess of 10 K. The levels of property enhancement seem to be bound in their lower limit by a metastable liquid crystalline form. The upper theoretical limit of property enhancement should correspond to a fully extended chain morphology.
Melt transformation coextrusion. II: Flow analysis
Authors: Perez M. A. , Collier J. R.
Published: December 2004

Melt Transformation Coextrusion for power law fluids was analyzed with particular attention being paid to the influence of the die's geometrical shape on flow patterns, and to skin layer effect on the velocity profile and shear stress at the interface between layers in a three‐layered system. Volumetric flow rate expressions were also generated for the aforementioned system, and stream and potential functions were derived for a free boundary converging film geometry. Newtonian as well as non‐Newtonian fluids were considered for this analysis in which the streamline shape changes their convergence downstream into the land section. Also, a finite element solution technique was utilized to reveal shear stress profiles that arise from the flow of high density polyethylene at 200°C in a converging fixed boundary geometry.
Numerical simulation and experimental investigation of injection mold filling with melt solidification
Authors: Chen B. S. , Liu W. H.
Published: December 2004

A two‐phase model is presented for simulating the injection mold filling process including the effect of transient melt solidification, i.e., the phase change effect. The liquid region is governed by Hele‐Shaw flow for a non‐Newtonian fluid using a modified Cross model to describe viscosity under non‐isothermal conditions. Further, the energy equation of the solid phase is dominated by a transient condition. The interfacial energy balance equation is also proposed to predict the solidified layer thickness and temperature profile. Two well‐characterized semicrystalline materials, polypropylene and polyethylene, were used in the present work. Good agreement is obtained between the predicted results and experimental observations from this study and the previous literature concerning the thickness of solid layer, the shape of, advancing melt front, and the pressure traces. In particular, the predicted pressure based upon the two‐phase model is higher than that in terms of the single‐phase model by about 13 percent. Finally, the semicrystalline structure of the frozen skin layer and the central core were investigated with a scanning electron microscope to verify the two‐phase model.
Reaction and thermal analysis for SMC (sheet molding compound) molding in complicated geometries
Authors: Lee Ching‐Chih
Published: December 2004

A finite element technique has been developed for coupled reaction and heat transfer analysis in which mass diffusion is negligible. The temperature unknowns are located at nodal points, while the reaction variables (species concentrations, reaction rates) are at the Gauss points in each element. With a mechanistic kinetic model, the SMC (sheet molding compound) cure in 2‐D and 3‐D geometries was analyzed. The results for plate‐and‐rib configurations show the progression of cure and heat transfer and the influence of geometry on the progression. The analysis for a flat sheet of SMC in a mold with localized heating using bubblers indicates the thermal interaction between the mold and the curing SMC. Temperature and reaction profiles are given for each case.
A nonisothermal differential scanning calorimetry study of the curing kinetics of an unsaturated polyester system
Authors: Ng H. , Manas‐zloczower I.
Published: December 2004

Nonisothermal differential scanning calorimetry (DSC) measurements were used to estimate the kinetic parameters for the curing reaction of a commercial unsaturated polyester resin. The reaction rate expression was derived from a mechanistic kinetic model based on the concept of free radical polymerization, accounting also for the diffusion controlled reaction. The total heat of reaction was evaluated in experiments run at very low scan speeds and using high amount of initiator. The kinetic parameters were found to show no dependency on the heating rate nor on the initiator concentration. Dynamic DSC measurements provide reliable kinetic data over a broad range of temperatures that is mostly significant for process simulations.
Gradient‐Index polymer materials and their optical devices
Authors: Koike Yasuhiro , Tanio Norihisa , Nihei Eisuke , Ohtsuka Yasuji
Published: December 2004

A gradient‐index (GRIN) plastic optical fiber was prepared by a heat‐drawing process of the GRIN preform rod obtained by a new interfacial‐gel copolymerization technique. The attenuation loss of the GRIN fiber was 179 kB/km at 650‐nm wave‐length and its numerical aperture was 0.20‐0.25. To attain low loss and highly dense integrated circuits, steric radial‐GRIN optical waveguide components such as GRIN branching, star coupler, multi‐coupler, and a 2‐D GRIN lens array, were monolithically fabricated by this technique. A novel spherical GRIN sphere lens, whose index function is symmetrical about the center of the sphere, with a low spherical aberration, was prepared by a modified suspension polymerization technique. A W‐shaped GRIN sphere has been newly proposed to further reduce the spherical aberration, compared with the parabolic GRIN sphere previously proposed.
Control of transesterification in polyester blends
Authors: Golovoy A. , Cheung M.‐F. , Carduner K. R. , Rokosz M. J.
Published: December 2004

Polyester 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 state 31P 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 blending.
Crystallization behavior of poly(ethylene terephthalate)
Authors: Jabarin S. A.
Published: December 2004

The 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.
Adhesive bonding of polymer composites
Authors: Vinson Jack R.
Published: December 2004

In structures composed of polymer matrix composite materials, components must be joined such that the overall structure retains its structural integrity while it is performing its, intended function which can include both mechanical loads (static and dynamic) and environmental loads (temperature and humidity). The use of composite materials in complex structures almost always reduces the number of components in the structures compared to the use of metallic alloys for the same structure. Thus, using composite materials not only results in great savings in weight, but also through a reduced number of joining operations, results in significant savings in assembly, inspection, parts storage, and movement, resulting in increased reliability and lower cost. Yet joining is still required. Joining metallic structures is a mature technology involving riveting, bolting, welding, glueing, brazing, soldering, and other methods. However, for most polymer matrix composites only adhesive bonding and mechanical fastening can be utilized. Attention has been given recently, however, to localized welding of thermoplastic polymer matrix composites, and this will be discussed briefly later. Inherently, adhesive bonding is preferable to mechanical fastening because of the continuous connection, whereas in drilling holes for bolts or rivets, fibers or other reinforcements are cut, and large stress concentrations occar at each discrete fastener hole. The following is a review of much of the literature dealing with adhesive bonding of polymer matrix composite structures. It is Intended not only to be a review, but also a background for detailed study of the referenced and other documents, and a catalyst for future research.
Mechanical fastening of polymer composites
Authors: Vinson Jack R.
Published: December 2004

In structures composed of polymer materials and polymer matrix composite materials, components must be joined such that the overall structure retains its structural integrity while it is performing its intended function which can include both mechanical loads (static and dynamic) and environmental loads (temperature and humidity). The use of composite materials in complex structures almost always reduces the number of components in the structures compared to the use of metallic alloys for the same structure. Thus, using composite materials not only results in great savings in weight, but also through a reduced number of joining operations, results in significant savings In assembly, inspection, parts storage, and movement, resulting in increased reliability and lower cost. Yet joining is still required. Joining metallic structures is a mature technology involving riveting, bolting, welding, glueing, brazing, soldering, and other methods. However, for most polymer matrix composites only adhesive bonding and mechanical fastening can be utilized. Attention has been given recently, however, to localized welding of thermoplastic polymer matrix composites. Inherently, adhesive bonding is preferable to mechanical fastening because of the continuous connection, whereas in drilling holes for bolts or rivets, fiber or other reinforcements are cut, and large stress concentrations occur at each discrete fastener hole. However, in many structures, it is necessary to employ mechanical fasteners in order to remove components or to have access to the interior of the structure. Hence, both adhesive bonding and mechanical fastening are important in joining structural components of polymer or polymer matrix materials. The following is a review of much of the literature dealing with mechanical fastening of polymer matrix composite structures. Hopefully, it provides an overall introduction for detailed study of the referenced documents as well as others, and a catalyst for further research.
Welding of polymer interfaces
Authors: Wool R. P. , Yuan B.‐L. , McGarel O. J.
Published: December 2004

Studies of strength development at polymer‐polymer interfaces are examined and applications to welding of similar and dissimilar polymers are considered. The fracture properties of the weld, namely, fracture stress, σ, fracture energy, GIc, fatigue crack propagation rate da/dN, and microscopic aspects of the deformation process are determined using compact tension, wedge cleavage, and double cantilever beam healing experiments. The mechanical properties are related to the structure of the interface via microscopic deformation mechanisms involving disentanglement and bond rupture. The time dependent structure of the welding interface is determined in terms of the molecular dynamics of the polymer chains, the chemical compatibility, and the fractal nature of diffuse interfaces. Several experimental methods are used to probe the weld structure and compare with theoretical scaling laws, Results are given for symmetric amorphous welds, incompatible and compatible asymmetric amorphous welds, incompatible semicrystalline and polymer‐metal welds. The relevance of interface healing studies to thermal, friction, solvent and ultrasonic welds is discussed.
Fatigue crack propagation of rubber‐toughened epoxies
Authors: Hwang J.‐F. , Manson J. A. , Hertzberg R. W. , Miller G. A. , Sperling L. H.
Published: December 2004

Epoxies containing epoxy‐terminated butadiene acrylonitrile rubber (ETBN) or amino‐terminated butadiene acrylonitrile rubber (ATBN) were prepared and studied in terms of fatigue crack propagation (FCP) resistance and toughening mechanisms. Rubber incorporation improves both impact and FCP resistance, but results in slightly lower Young's modulus andTgAsTgincreases, the degree of toughening decreases. Rubber‐induced shear yielding of the epoxy matrix is believed to be the dominant toughening mechanism. Decreasing fatigue resistance with increasing cyclic frequency is observed for both neat and rubber‐toughened epoxies. This result may be explained by the inability of these materials to undergo possible beneficial effects of hysteretic heating. FCP resistance is linearly proportional toMc1/2, whereMcis the apparent molecular weight between crosslinks determined on the rubber‐toughened material. FCP resistance also increases with increasing static fracture toughnessKIC. ATBN‐toughened epoxies demonstrated better fatigue resistance than ETBN‐toughened systems.
Phenolic triazine (PT) resins. I. Gelation phenomenon studied by calorimetric, mechanical, and dielectric techniques
Authors: Khanna Y. P. , Kumar R. , Das S.
Published: December 2004

Gelation phenomenon in thermoset polymers is an area of extreme importance from the processing point of view. Gel point (GP) has traditionally been detected using rheological and mechanical techniques. We wish to report the use of dielectric and especially calorimetric techniques for detecting GP. Using a particular thermoset system, we have compared the calorimetric, dielectric, and mechanical techniques and shown how to define GP in terms of time and temperature. As a matter of convenience, we have briefly defined the gelation phenomenon in thermosets, its significance and measurement, and a critical evaluation of the techniques for detecting GP.
Structure development in biaxially stretched polystyrene film: Part I. Property‐orientation correlation
Authors: Choi Kyung‐Ju , Spruiell Joseph E. , White James L.
Published: December 2004

A study of orientation development in polystyrene film by biaxial stretching is described. Stretch ratios up to 7.2 × 7.2 were used. Mechanical properties of polystyrene films were correlated with the level of molecular orientation developed by uniaxial or biaxial stretching. Sensitivity of the mechanical properties to change due to development of orientation varied as follows: Yield strength < Young's modulus < Tensile strength < Elongation to break. Brittle to ductile transition phenomena were observed at certain orientation values in the orientation triangle diagram. The transition occurs whenf×f∼ 0.0025 for biaxially oriented andf∼ 0.015 in the machine direction for uniaxially oriented films. SEM photomicrographs show that the fracture surfaces of ductile failures exhibit many fibrils while brittle failures exhibit no fibrils.
Optical properties of simultaneous biaxially stretched poly(ethylene terephthalate) films
Authors: Cakmak Mukerrem , White James L. , Spruiell Joseph E.
Published: December 2004

We offer a detailed study on the anisotropic optical properties in uni and simultaneous biaxially stretched Poly(ethylene terephthalate) (PET) films. Cast amorphous sheets of PET were stretched to a series of extension ratios in two mutually perpendicular directions at 80, 90, and 100°C. Additionally, 0selected films were subsequently “heat‐set” by annealing with their width and lengths constrained. The principal refractive indices at sodium D wavelength of these, asstretched and heat‐set films were obtained using a modified Abbe refractometer. The changes in the principal refractive indices with the processing history were correlated with the orientation of PET chains and phenyl plane normals, which were determined independently by wide angle X‐ray (WAXS) pole figure technique.
The joining of biaxially oriented polyethylene pipes
Authors: Atkinson J. R. , Ward I. M.
Published: December 2004

Die‐drawing techniques recently developed at Leeds University make it possible to produce oriented polymer tubes with both axial draw and hoopwise expansion. These products have increased axial stiffness, improved barrier properties, and excellent resistance to chemical reagents. Normally mechanical methods are used to join such tubes in order to preserve their orientation: however we show that electrofusion techniques produce joints of strengths such that in tensile tests, failure always occurs in the fittings, not at the joint interfaces. Optical and electron microscopy reveal different zones in the welds and indicate that only 20 percent of the wall thickness is affected by the electrofusion process. The pipe studied was biaxially drawn medium density polyethylene of outside diameter 63 mm with draw ratios of 4 in the axial direction and 2, inner hoop. Optimum welding conditions were determined using socket and saddle electrofusion fittings. The joints did not fail in a standard crush test. Careful control of welding parameters is essential in butt fusion welding when the maximum weld strength exceeds that of the undrawn polymer.
Two‐Dimensional thermal analysis of resistance welded thermoplastic composites
Authors: Jakobsen Tom B. , Don Roderic C. , Gillespie John W.
Published: December 2004

A transient two‐dimensional thermal model for resistance welding of thermoplastic composites is presented. A parametric study is conducted that yields insight into the welding process enabling some critical process and material parameters to be identified. Time to melt is predicted by the model and is successfully compared to experimental observations. Local heating and meltthrough can also be explained by the transient thermal model in agreement with experimental observations. Mode I fracture toughness of unidirectional graphite reinforced poly(etheretherketone) resistance welded double cantilever beam specimens are conducted under various process conditions. Experimental results indicate that under optimum process conditions, the interlaminar fracture toughness of the bulk compression‐molded thermoplastic composite material can be achieved using resistance heating as a joining technique.
Thermal behavior of transparent poly(etheretherketone)(PEEK) film
Authors: Gupta Hemant , Salovey R.
Published: December 2004

The thermal behavior of poly(etheretherketone)(PEEK) film heated in an open differential scanning calorimetry (DSC) pan at 20°C/min is distorted by relaxation of the strained film. PEEK film in a closed pan or quenched PEEK in open or closed pans shows a glass‐transition temperature (Tg) around 144°C, cold crystallization (∼22 J/g) at 177°C, melt‐temperature (Tm) peaking at 335–340°C, with an enthalpy of fusion of 32–34 J/g, and recrystallization on cooling at 285°C, with a crystallization exotherm of about 40 J/g. The enthalpy of fusion decreases with increasing heating rate from 2–100°C/min and approaches the enthalpy of cold crystallization. With increasing heating rate, further crystallization of PEEK during the DSC scan is suppressed. With increasing cooling rate, PEEK melt crystallizes at larger supercoolings to a lesser extent. Crystallization on cooling the melt was more complete than cold crystallization and annealing on heating.
Dielectric and magnetic properties of random and segregated ferrite polystyrene composites
Authors: Yacubowicz J. , Narkis M. , Kenig S.
Published: December 2004

The dielectric and magnetic properties of polystyrene composites containing barium or nickel‐zinc ferrites were studied as function of the ferrite concentration and field frequency. The composites were prepared by methods yielding a random distribution of the ferrite particles or segregated structures. Barium ferrite‐poly‐styrene composites exhibited a typical insulator behavior, and only above 60% ferrite were high values of the dielectric properties noted at the lower frequencies, decreasing gradually with frequency to the low values typical of the higher frequencies. The mode of barium ferrite particle distribution did not affect the dielectric properties. The nickel‐zinc ferrite systems demonstrated a conductor type behavior. An apparent insulator‐conductor transition was observed, having lower values for segregated than for random distributions. The magnetic permability of barium ferrite‐polystyrene composites above 10% ferrite increases with the ferrite concentration, whereas the magnetic dissipation factor steeply increases with concentration above 40% ferrite.