bluuebunny/crossref_metadata_2025 huggingface dataset:
Reversible optical data storage on poly(ethylene terephthalate)
Authors: Buckley G. S. , Roland C. M.
Published: April 2004

A desirable feature of optical data storage processes is that they provide high contrast between the image and background. Thermal marking techniques are inherently advantageous in this regard, because of the nonlinearity of the response. A thermal method for lithography on polymer films has been developed based on selective exposure of the films to infrared laser radiation passing through a mask. Radiation induced crystallization, melting and ablation have been demonstrated with the processes prevailing at different levels of radiation intensity. These methods are capable of producing high resolution images with excellent edge acuity and minimal interference from diffraction. The absence of diffraction effects is due to the nonlinear response of the polymer film to the radiation. The best resolution obtained to date (submicron) is limited by the size of the smallest features present on the masks used to create the pattern. The ultimate resolution achievable by these methods is presently unknown.
Chemorheology of poly(urethane/isocyanurate) formation
Authors: Sun Xiudong , Toth James , James Lee L.
Published: April 2004

Poly(urethane/isocyanurate) is a major resin used in the structural reaction injection molding (SRIM) process. In this study, the kinetics and viscosity changes of a poly(urethane/isocyanurate) resin were investigated by the adiabatic temperature/viscosity rise method and differential scanning calorimetry. The effect of the catalyst concentration and the volume ratio of isocyanate to polyol was investigated. It is found that isocyanate trimerization depends on the diffusion effect resulted from the urethane formation. A kinetic model including the diffusion effect is developed, which is able to predict the experimental results. The reaction induced viscosity rise depends on the concentration and the molecular weight of the formed polymer. The measured adiabatic viscosity rise correlates well with the calculated molecular weight growth using the recursive method.
The structure and morphology of syndiotactic polystyrene injection molded coupons
Authors: Evans A. M. , Kellar E. J. C. , Knowles J. , Galiotis C. , Carriere C. J. , Andrews E. H.
Published: April 2004

The structure and morphology of syndiotactic polystyrene (sPS) injection molded coupons have been investigated using wide angle X‐ray scattering (WAXS), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), light microscopy, and laser Raman spectroscopy (LRS). By sectioning the samples at approximately 200 μm increments, profiles across “hot molded” (oil heated to 140°C) and “cold molded” (water heated to 104°C) coupons, could be built up. Using DSC and WAXS, variations in crystallinity and polymorphic phases were observed. The crystallinity was found to remain fairly constant in the “hot molded” samples, whereas the cold molded samples had a pronounced “amorphous” skin, before becoming more uniform towards the center of the specimen. Characterization of the polymers' microstructure, in the molded plaques, was achieved by optical birefringence. The surface of the plaques were successfully etched with an acid/permanganate solution, prior to SEM studies, to reveal their morphology. Overall, the coupons showed very little orientation effects and the structure appeared to be consistent with that of a semicrystalline polymer, crystallized under relaxed conditions.
Synthesis and characterization of epoxy resins containing arsenic acrylate
Authors: Anand M. , Srivastava A. K.
Published: April 2004

The properties of epoxy resins containing arsenic acrylate have been compared with that of a blank epoxy resin (DGEBA). The values of epoxide equivalent, hydroxyl content, hydrolyzable chlorine content, and specific gravity increased, whereas refractive index decreased in the epoxy resins containing arsenic acrylate (AsA3). This is attributed to a complex formation between an As and an oxygen atom in the resin, as evidenced from IR spectroscopy. The reaction is first order (ER3) with an activation energy of 53 kJ/mole. The epoxy resin with As cured with polyamide at 30°C, showed chemical resistance and excellent thermal stability compared with blank epoxy resin (epoxy resin without As).
Effect of processing on weld line strength in five thermoplastics
Authors: Seldén R.
Published: April 2004

Weld line strength has been measured in five engineering thermoplastics. The effect of processing parameters was studied using experimental design. Four parameters–holding pressure, injection velocity, melt temperature, and mold temperature–were varied in two levels. For each parameter setting the weld line strength was measured and compared with the bulk strength via a weld line factor (WL‐factor), defined as: strength of specimens with weld line/strength of specimens without weld line. Results from flexural tests on both filled and unfilled materials showed that the weld line factors for cold weld lines varied between 0.25 and 0.98 depending on material and parameter setting. Highest WL‐factors were obtained for unfilled materials and using high melt temperature, high holding pressure, and low mold temperature. Results from instrumented falling weight impact tests on weld lines sometimes showed a WL‐factor higher than 1.0. There was generally a poor correlation between results from impact tests and results from flexural tests.
Use of surface modified recycled rubber particles for toughening of epoxy polymers
Authors: Bagheri R. , Williams M. A. , Pearson R. A.
Published: April 2004

The objective of this research is to investigate the feasibility of using surface treated recycled rubber particles for toughening of epoxy polymers. These particles are obtained through grinding of scrap tires followed by oxidizing the surface of the particles in a reactive gas atmosphere. Surface treated recycled rubber particles with a nominal particle size of approximately 75 μm and a commonly used reactive liquid elastomer, CTBN, have been incorporated in a DGEBA epoxy resin. It has been shown that the recycled rubber particles are not as effective as CTBN in toughening of the epoxy matrix. However, blending of the two modifiers results in a synergistic toughening. Microscopy reveals that, when used alone, recycled rubber particles simply act as large stress concentrators and modestly contribute to toughening via crack deflection and microcracking. In the presence of micron size CTBN particles, which cavitate and induce massive shear yielding in the matrix, however, the recycled particles “stretch” the plastic deformation to distances far from the crack tip. This mechanism causes plastic zone branching and provides an unexpectedly high fracture toughness value. This study, therefore, provides a practical approach for manufacturing engineering polymer blends utilizing the surface modified recycled rubber particles.
Biaxial orientation of linear polyethylenes using the compressive deformation process
Authors: Prins A. J. , Kortschot M. T. , Woodhams R. T.
Published: April 2004

The tensile properties of three grades of linear polyethylene were enhanced by a factor of as much as 15 using a melt/solid phase compressive deformation process that produced equi‐biaxial planar orientation in the sheet. Ultra high molecular weight polyethylene with planar isotropy and an in‐plane modulus of 10 GPa and a tensile strength of 330 MPa was produced using this method. It was found that the molecular weight had a significant influence on the optimum processing temperature, the ultimate biaxial deformation ratio and hence the ultimate tensile properties. High density polyethylene processed under ideal conditions had a tensile modulus of 2.3 GPa and a tensile strength of 250 MPa. The tensile strength increased linearly with increasing biaxial deformation ratio and the tensile modulus increased non‐linearly with increasing biaxial deformation ratio. The deformation rate and the dwell time did not have a significant effect on the tensile properties. Shrinkage tests showed that biaxial deformation was less effective than uniaxial deformation in inducing orientation of the polymer chains, however differential scanning calorimetry results were consistent with the presence of extended chain crystals in very highly oriented ultra high molecular weight polyethylene sheets.
Flow analysis of natural rubber in a capillary rheometer. 1: Rheological behavior and flow visualization in the barrel
Authors: Sombatsompop N. , Tan M. C. , Wood A. K.
Published: April 2004

Capillary rheometers have been widely used in the study of the rheological behavior of thermoplastics but their application to rubber has so far been limited. An investigation was therefore carried out to determine the effect of mastication and temperature on the rheological properties of natural rubber using a capillary rheometer. The flow of the rubber in the barrel of the capillary rheometer was observed at various test conditions such as die geometry, piston speed, and test temperature using layers of pigmented rubber compound, this involving the use of a split barrel system. It was found that the flow patterns in the barrel of the capillary rheometer used were very complex and were a function of piston displacement.
Flow analysis of natural rubber in a capillary rheometer. 2: Flow patterns and entrance velocity profiles in the die
Authors: Sombatsompop N. , Wood A. K.
Published: April 2004

An investigation was carried out to determine the effect of variations in test conditions, such as die geometry, for example die entry angles, on the flow patterns observed in the die of a Davenport Extrusion Rheometer. In addition, the velocity profile near the die entrance was determined for different piston displacements. The results indicate that the velocity profile generated in the capillary near the die entrance was parabolic in form. However, there appeared to be a non‐zero velocity at the capillary wall. Melt fracture was observed, this being linked with the appearance of a disturbance in the flow along the capillary, the disturbance being of a converging helical form.
A three‐dimensional analysis of coextrusion
Authors: Gifford W. A.
Published: April 2004

The coextrusion of two polymers in a square channel is presented in this paper. Fluids are fed into the channel through different passages with a plane separating them partway through the channel. Downstream of the separation plane, the streams merge forming an interface between them, which is normally distorted before reaching the exit of the channel. These results show that the degree of distortion depends upon factors in addition to the ratio of the viscosity of the two fluids. The ratio of the flow rates in addition to the shape and location of the separation plane are also important.
Mechanical properties of hand‐cast and reaction injection molded polyurethane and vinyl ester resin interpenetrating polymer networks
Authors: Fan Lian Hua , Hu Chun Pu , Ying Sheng Kang
Published: April 2004

A series of simultaneous interpenetrating polymer networks (SINs) composed of polyurethane (PU) and vinyl ester resin (VER) was prepared from different rigid phase components, where the pendent hydroxyl groups of VER were retained or capped, and through different molding processes, i.e., hand‐casting or reaction injection molding (RIM). It was recognized that the occurrence of chemical binding between PU and VER networks through the reaction of the diisocyanate and the pendent hydroxyl groups of VER played an important role in determining the mechanical properties of these SINs. The hand‐cast SINs, with VER containing pendent hydroxyl groups as the rigid phase component and with these pendent hydroxyl groups counted for the metering of diisocyanate besides that due to polyether polyol and chain extender of PU phase, behaved like the hybrid polyester matrix. For the RIM‐molded SIN samples, an obvious reinforcing effect of VER network, whose pendent hydroxyl groups were capped with acetyl groups, upon PU network was observed. These results correlated well with the knowledge of polymerization kinetics and morphology development of these PU/VER SINs.
Structure and strength of a polyethylene pipe grade containing glass spheres and low‐molar‐mass linear polyethylene
Authors: Tränkner T. , Hedenqvist M. , Gedde U. W.
Published: April 2004

The resistance to slow crack growth and to internal over‐pressure of pipes based on a commercial polyethylene gas pipe grade (BPE; 0.6 mol% butyl branches and M̄W = 197,000 g/Mol) blended with both an injection molding grade linear polyethylene (LPE;M̄W = 42,000 g/mol) and 0.5 ± 0.1 mm glass spheres was studied. The blends and the pure polymer components were characterized by density measurements, differential scanning calorimetry, small‐angle X‐ray scattering, and transmission electron microscopy. The fracture properties of extruded pipes were measured using hydrostatic pressure testing and notched uniaxial testing on samples cut from the pipe wall. The polymer components were macroscopically uniformly blended and differential scanning calorimetry indicated the occurrence of partial co‐crystallization between the branched and linear components. Transmission electron microscopy showed molar mass segregation on a 100 nm level. Notched uniaxial testing showed that the slow crack growth resistance of pure BPE was considerably higher than that of the LPE/BPE blend with 30% LPE. Fractography indicated that the fracture‐initiating particles were larger in pipes failing after shorter period of time in the hydrostatic pressure testing. The lifetimes of hydrostatic pressure tested pipes based on the BPE grade containing glass spheres were similar to those of pipes based on the LPE/BPE blend with 30% LPE.
On‐line ultrasonic monitoring of the injection molding process
Authors: Wang H. , Cao B. , Jen C. K. , Nguyen K. T. , Viens M.
Published: April 2004

On‐line ultrasonic monitoring of injection molding of a simple polymer box is studied using pulse‐echo techniques. The flow front of molten polymers inside the mold has been probed by a multiple‐channel probing system with a time resolution of 2 ms. This information can be used to control the plunger movements. The gap development, because of the shrinkage of the part in the mold, is also monitored. This information, which is important for the understanding of the part's cooling process, has been found to be superior than that measured by a conventional pressure probe. The relation between the gap formation time and the packing pressure has been investigated at various part locations characterized by different thicknesses. The velocity and the amplitude variations of ultrasonic waves, in a reflection as well as in a transmission configuration, have also been measured in the part's material during its solidification. The behavior of these ultrasonic parameters contributes to the interpretation of the solidification process.
Injection and compression molding of polystyrene/high‐density polyethylene blends—phase morphology and tensile behavior
Authors: Bureau M. N. , El Kadi H. , Denault J. , Dickson J. I.
Published: April 2004

Processing and compatibilization effects on the phase morphology and the tensile behavior of blends of polystyrene and high‐density polyethylene (PS/HDPE) were investigated. As predicted by theory, high shear rates encountered during extrusion blending led to efficient minor phase emulsification in immiscible PS/HDPE blends for which the viscosity ratio approaches unity. Consequently, the emulsifying effect of a styrene/ethylene‐butylene/styrene (SEBS) compatibilizer was found to be negligible. In the subsequent molding process, disintegration, shape relaxation and coarsening of the minor phase domains were found to be responsible for the morphological evolution. In the compression molding process, morphological observations showed that the rate of minor phase coarsening followed the predictions of the Ostwald ripening theory, in agreement with the rheological analysis. In the injection molding process, minor phase coarsening was attributed to shear coalescence. Tensile tests performed on compression molded and injection molded blends showed that the mechanical behavior of PS/HDPE blends depend strongly upon the matrix orientation as well as the dispersed phase morphology and orientation. In both postforming operations, compatibilization effects on the morphological stability and the tensile behavior of PS/HDPE blends were found to be dependent upon the composition and the rheological behavior of the blend. Evidence of adhesion between the PS and HDPE phases was observed in the presence of SEBS in HDPE‐rich blends.
Predicting the migration of endocrine disrupters from rigid plastics
Authors: Berens Alan R.
Published: April 2004

Previous studies of the diffusion of gases and organic vapors at low concentrations in glassy polymers have established the applicability of Fickian kinetics, the correlation of diffusion coefficients with the dimensions of the diffusing molecules, and the impracticality of experimentally measuring the diffusivities of molecules larger than C6 hydrocarbons. The diffusivities of the suspected endocrine disrupters, p‐nonyl phenol, bisphenol‐A, and tetrachlorodioxin, have been estimated by extrapolation of the established correlations of diffusivity with mean molecular diameter. Estimated diffusivities of these substances in glassy polystyrene, poly(vinyl chloride), and poly(methyl methacrylate) at 30°C range from 10−17 to 10−26 cm2/sec. Calculations of desorption rates, based on Fick's law, show that it would take from several hundred to millions of years for even 1% of the initial content of an endocrine disrupter to migrate from a glassy polymer sheet 1 mm thick. It therefore seems that migration from rigid polymer products should not be considered a significant source of endocrine disrupters in the environment.
Nonlinear mechanical response of high density polyethylene. Part II: Uniaxial constitutive modeling
Authors: Zhang Chuntao , Moore Ian D.
Published: April 2004

Based on the experimental data presented in Part I, two uniaxial constitutive models are constructed. The first, a nonlinear viscoelastic (NVE) model, is formulated using the mechanical analogy consisting of one independent spring and six Kelvin elements in series. Creep data are used to determine the model parameters. The second model, a viscoplastic (VP) formulation, is developed using the viscoplastic theory proposed by Bodner to characterize the uniaxial viscoplastic behavior of metals. Inelastic strain rate is introduced into the state variable in addition to inelastic work to depict the strong rate dependent behavior of HDPE. Experimental data from constant strain rate tests are employed to construct the material functions of the model. Limitations in the application of each model are discussed in conjunction with possibilities for future work.
Processing parameters of the diethylenetriamine and unsaturated aldehyde resin
Authors: S̆ebenik Anton
Published: April 2004

The dependence of processing parameters of the reaction between diethylenetriamine (DETA) and crotonaldehyde (CR) or cinnamaldehyde (CA) on reaction time were followed by calorimetric and viscosity measurements. Resins with molecular weights up to 800 g/mol and content of unreacted monomers under 1% were formed. The most reactive were the amino and aldehyde groups. The aldehyde groups are five times more reactive than double bonds. NHCHOH, CH2NH, CHNH, and NCH groups were formed. The rates of the reactions and the rate constants decrease with increasing molar ratio between DETA and unsaturated aldehydes. The heat of the addition of DETA to CR was up to 54 KJ/mol and the total heat of reaction was up to 71 KJ/mol. The heat of addition of DETA to CA was up to 32 KJ/mol and the total heat of reaction was up to 61 KJ/mol. For DETA and CR the activation energy of condensation were 57.3 KJ/mol, and 42.0 KJ/mol for DETA and CA. The viscosity of the final products increased up to hard resins.
Prediction of the stress distribution in an elastic pancake using a neo‐hookean strain energy function
Authors: Kakavas P. A.
Published: April 2004

The aim of this article is to evaluate the axial stress of a thin cylindrical rubber specimen bonded between two steel cylindrical plates. The thickness of the rubber with respect to its diameter is small. It was assumed that the rubber is described by a Neo‐Hookean strain energy function. A theoretical equation was developed to correlate the diametral contraction η with respect to strain ε within the sample. The equilibrium equations of motion and the incompressibility constraint with the free stress condition of R = A were used to determined the axial stress state.
In‐process control of epoxy composite by microdielectrometric analysis
Authors: Stéphan F. , Fit A. , Duteurtre X.
Published: April 2004

The curing of an epoxy prepolymer based on the diglycidyl ether of bisphenol A (DGEBA) with dicyandiamide (DDA) as the hardener and imidazole as the catalyst agent was analyzed using microdielectrometry, differential scanning calorimetry, viscosity measurements, and insolubles in THF for gel‐point detection. Interpreting dielectric data with respect to chemorheology continues to be the subject of scientific discussion. The focus of this issue is to give an industrial point of view on the collected on‐line dielectric measurements during an epoxy/fiber glass composite cure. Hence, isothermal polymerizations of DGEBA/DDA/imidazole resin were examined and dielectric properties such as ionic conductivity were related to the cure kinetics by conversion through an experimentally established equation. This mathematical model was used to predict reaction advancement of epoxy processing under nonisothermal cure conditions. This model is shown to be able to forecast both isothermal and nonisothermal cure data of unaged resin. According to these results, cure monitoring was carried out on prepregs. Whereas some deviations of the law were observed at the time of the last stage of the cure, good correlation was obtained for the reaction rate during the in‐mold process curing time.
Experimental study of the thermoforming of a blend of styrene‐butadiene copolymer with polystyrene
Authors: Stephenson M. J. , Ryan M. E.
Published: April 2004

Material characterization and thermoforming studies were completed using a blend of a styrene‐butadiene copolymer with polystyrene used commercially for the production of cups and dishes. This composition was thermoformed between 135 and 152°C. Studies consisted of forming 30‐mil and 46‐mil sheets at 130, 140, and 150°C at three evacuation rates in an aluminum cylindrical mold. The mold was instrumented with a pressure transducer to follow the change in pressure during forming and two Linear Voltage Displacement Transducers, which served as mold wall contact sensors. The results indicated that the process is extremely rapid (0.25–0.60 sec) for the high and medium evacuation rates. The process was found to require a low pressure differential for forming (typically <4 psi). The final part thickness distribution and extension ratio data indicated that the material stretches into the approximate shape of a spherical segment, contacts the bottom/ center of the mold, contacts the sides, and finally stretches into the corners. The tensile strength and modulus of elasticity measurements of the final part were slightly less than the original sheet properties for samples measured in the machine direction but slightly greater for samples taken in the transverse direction. However, the percent elongation at break increased significantly in both the machine and transverse directions.
Evaluation of data on the kinetics of isothermal polymer crystallization: Part II
Authors: Lambrigger Markus
Published: April 2004

The kinetic crystallization model of Avrami is generally accepted as a starting point for the analysis of isothermal polymer crystallization. In a previous communication, the author has shown that data of isothermal crystallization experiments can be evaluated together with the help of Avrami master curves, if the Avrami index n is larger than one. These Avrami master curves have been obtained by scaling the three‐parameter Avrami equation functions θ(t) with the time‐values of its inflection points. In this work, alternative Avrami master curves will be displayed; they are obtained by scaling θ(t) with the mean‐time t̄ = ∫ t dθ. These alternative Avrami master curves can be constructed for every Avrami index n > 0.
Laminar morphology development and oxygen permeability of LDPE/EVOH blends
Authors: Lee Sang Young , Kim Sung Chul
Published: April 2004

Morphology and oxygen barrier properties of LDPE/EVOH blends have been studied. Laminar dispersion of ethylene‐vinyl alcohol copolymer (EVOH) with high oxygen barrier properties was obtained in the matrix of low density polyethylene (LDPE) when extruded through an annular blown film die. Various laminar morphologies were observed and the main factors determining the morphology of the blends were viscosity ratio of the components, processing conditions, and compatibilizer level. Oxygen permeation tests have shown that thinner and longer EVOH layers in larger numbers were more effective in reducing the oxygen permeability. The oxygen permeability of the compatibilized blend having 6 phr of LLD‐g‐MAH was reduced by a factor of 740. The correlation between morphology and oxygen permeability was explained as a function of the EVOH layer size (L × R) and the number of EVOH layers (N), which were closely related to the predeformed domain size (Lo × Ro). The high Weber number (resulted from large Lo × Ro and low interfacial tension) and low viscosity ratio yielded large L × R. However, small Lo × Ro produced high N. Experimental results of oxygen permeability were well correlated with (L × R) × N.
Biofiber‐reinforced polypropylene composites
Authors: Karnani Rajeev , Krishnan Mohan , Narayan Ramani
Published: April 2004

Biofibers, natural lignocellulosics, have an outstanding potential as a reinforcement in thermoplastics. This study deals with the preparation of lignocellulosic composites by reactive extrusion processing in which good interfacial adhesion is generated by a combination of fiber modification and matrix modification methods. PP matrix was modified by reacting with maleic anhydride and subsequently bonded to the surface of the modified lignocellulosic component, in‐situ. The fiber surface was modified by reacting it with a silane in a simple and quick aqueous reaction system, similar to that employed for glass fibers. The modified fibers are then extruded with the modified polymer matrix to form the compatibilized composite. The various reactions between the lignocellulosic fiber/filler and modified polymer chains, is expected to improve the interfacial adhesion significantly as opposed to simple mixing of the two components, since new covalent bonds between the fiber surface and matrix are created in the former case. These composite blends were then injection molded for mechanical characterization. Typical mechanical tests on strength, toughness and Izod impact energy were performed and the results are reported. These findings are discussed in view of the improved adhesion resulting from reactions and enhanced polar interactions at phase boundaries.
Kinetics of isothermal and nonisothermal crystallization of novel poly(arylene ether ether sulfide)s
Authors: Srinivas Srivatsan , Babu J. R. , Riffle J. S. , Wilkes Garth L.
Published: April 2004

The kinetics of crystallization have been studied for a series of novel poly(ether ether sulfide)s based on a biphenyl moiety in the backbone (Mn = 14.3K, 19.1K), referred to as biphenyl sulfide (Tg = 142°C, Tm = 347°C) and phenyl moieties in the backbone (Mn = 8.1K, 19.9K, 34K), referred to as phenyl sulfide (Tg = 100°C, Tm = 243°C). Isothermal melt crystallization kinetics were analyzed based on the Avrami equation. Avrami exponents close to three were obtained for the phenyl sulfides, independent of molecular weight or crystallization temperature, which implies growth of three‐dimensional spherulitic superstructures following heterogeneous nucleation. For the biphenyl sulfides, values closer to 2 were obtained for the exponent, also independent of molecular weight or crystallization temperature, which could imply the incomplete development of three‐dimensional superstructures following heterogeneous nucleation. Nonisothermal crystallization kinetics were also studied by cooling from the melt; in all cases studied, the Ozawa analysis could not well describe the evolution of crystallinity, probably because of the inapplicability of some of the inherent assumptions in this type of analysis. The data were analyzed using the conventional form of the Avrami equation, which yielded good fits. This semiquantitative method of analysis yields a reduced rate constant that was found to increase with increasing cooling rate and decreasing molecular weight. The results of the isothermal and nonisothermal crystallization studies carried out on the poly(ether ether sulfide)s have been compared wherever possible to the results available for PPS and PEEK.
Mathematical modeling and computer simulations of the flow, nematic phase orientation, and heat transfer in thermotropic liquid crystalline polymers
Authors: Lekakou C.
Published: April 2004

This study includes a mathematical analysis and computer simulations of the injection molding of thermotropic liquid crystalline polymers (LCPs). The particular area of interest is the modeling and numerical evaluation of the orientation of the rigid rods in the nematic phase of LCPs during the filling stage of injection molding. The model is based on a continuum mechanics approach in order to derive the orientation distribution function of rigid rods for different orientation angles. Numerical distributions of average orientation factors are also derived. Computer simulations have been conducted in case studies that investigate the effects of changes in the processing conditions.
Aromatic copolyester thermosets: High temperature adhesive properties
Authors: Frich Dan , Economy James , Goranov Konstantin
Published: April 2004

The adhesive properties of a new family of crosslinkable aromatic copolyester resins are described in this paper. A unique method for forming an adhesive bond in the solid state through high temperature interchain transesterification reactions (ITR) between cured thin films of these copolyester thermosets is indicated. Bonds formed via this procedure yield average lap shear strengths of roughly 13 MPa to titanium adherends and invariably exhibit failure at the polymer‐metal interface and not within the polymer. Various procedures to increase the strength of the bond at the interface between the polymer and the metal were tested such as the effect of surface pretreatments, primers, fillers, and the role of bondline thickness on the lap shear strength of the joints. Of these, the use of surface pretreatments and thinner bondlines has the greatest effect, raising the observed average lap shear strength of the joints to 16.5 and 20.7 Mpa, respectively. Some of the adhesive properties pertaining to the use of this new thermoset as a matrix in a graphite fiber composite are also presented.
Finite element analysis for the flow characteristics along the thickness direction in injection molding
Authors: Lee Ho‐Sang
Published: April 2004

A numerical simulation of the filling stage along the thickness direction is proposed by combining the free‐surface boundary condition with the relevant governing equations. The mathematical model is based on the equations of continuity, momentum, and energy along with the inelastic power‐law model and relevant boundary conditions. Because of the significant implications for microstructure development in the product, the fountain effect at the advancing free surface is explicitly taken into consideration in the simulation. The model yields data on free‐surface shape and velocity, pressure, temperature, and shear stress distributions within the mold cavity. The rearrangement of the velocity and temperature profiles in the vicinity of the melt front is considered in detail.
Nonisothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone)
Authors: Liu Tianxi , Mo Zhishen , Wang Shanger , Zhang Hongfang
Published: April 2004

Analysis of the nonisothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone) (PEEKK) was performed by using differential scanning calorimetry (DSC). The Avrami equation modified by Jeziorny could describe only the primary stage of nonisothermal crystallization of PEEKK. And, the Ozawa analysis, when applied to this polymer system, failed to describe its nonisothermal crystallization behavior. A new and convenient approach for the nonisothermal crystallization was proposed by combining the Avrami equation with the Ozawa equation. By evaluating the kinetic parameters in this approach, the crystallization behavior of PEEKK was analyzed. According to the Kissinger method, the activation energies were determined to be 189 and 328 kJ/mol for nonisothermal melt and cold crystallization, respectively.
Simulation of thermal degradation, peroxide induced degradation, and maleation of polypropylene in a modular co‐rotating twin screw extruder
Authors: Kim Byoungjoo , White James L.
Published: April 2004

The characteristics of thermal degradation, peroxide induced degradation, and maleation of polypropylene have been modeled in a modular intermeshing twin screw extruder for a range of screw configurations and screw speeds. The models use the Akro‐co‐Twin Screw® formulation and account for starvation and fully filled pressurized regions including the effects of viscosity reduction along the screw axis by both degradation and viscous heating. The results are compared with experiments.
Numerical analysis of injection molding of glass fiber reinforced thermoplastics. Part 1: Injection pressures and flow
Authors: Greene Joseph P. , Wilkes James O.
Published: April 2004

Numerical calculations of flow and injection pressures during injection molding of fiber‐filled thermoplastics are compared to experimental measurements. The flow is modeled as a 2–D, nonisothermal, free‐surface flow with a new viscosity model dependent upon temperature, pressure, and fiber concentration. The steady‐state viscosity model is developed to account for the fiber‐concentration and shear‐thinning viscosities of the polymer based upon combining the Dinh‐Armstrong fiber model with the Carreau viscosity model. The new model has four parameters, three from the Carreau model and one from Dinh‐Armstrong for fiber concentrations. The new model calculates reasonably well the steady‐state viscosity of fiber‐filled polypropylene over the shear rate range of 0.01 s−1to 20 s−1. The numerical work successfully describes the flow of fiber‐filled polymers during injection molding using finite‐difference solutions for the transport equations and marker particles to track the flow front. The comparisons between the calculated and measured pressure drops for an injection molded part were reasonable for the unfilled and fiber‐filled polypropylene materials. The pressure drop comparison is very good for slow fill of a base case resin, Himont polypropylene, but not as good for fast fill of the resin. The pressure drop comparison is very good for fast fill of glass‐filled resin, DSM polypropylene with 10% and 20% short fibers, but not as good for slow fill of the resin and resin plus fibers.
Properties of poly(butylene terephthalate)/functionalized polyolefin blends
Authors: Kang Tae‐Kyu , Kim Yang , Kim Guehyun , Cho Won‐Jei , Ha Chang‐Sik
Published: April 2004

The object of this study was to investigate the physical properties and morphology of melt‐mixed blends containing poly(butylene terephthalate) (PBT) with several functionalized polyolefins such as ethylene/vinyl acetate copolymer (EVA), EVA‐g‐maleic anhydride (EVA‐g‐MAH), EVA‐g‐ACID, EVA‐g‐ACID/ACRYLATE, ethylene methacrylate‐g‐MAH (EMA‐g‐MAH), ethylene/ethyl acrylate copolymer (EEA) and an ethylene ionomer. Special focus was made on PBT/EVA‐g‐MAH and PBT/EMA‐g‐MAH blends compared with PBT/EVA and PBT/EMA blends. Blends were prepared in a counter‐rotating twin‐screw extruder. Mechanical and thermal properties, glass transition temperature and morphology were examined using a tensile testing machine, differential scanning calorimeter (DSC), dynamic mechanical analysis and Scanning Electron Microscope (SEM). PBT/EVA‐g‐MAH and PBT/EMA‐g‐MAH blends exhibited better impact strength than PBT/EVA and PBT/EMA blends because of the larger interfacial adhesion of EVA‐g‐MAH and EMA‐g‐MAH with PBT than EVA and EMA.
Simulation of linear viscoelastic flow behavior in the Buss Kneader
Authors: Lyu Min‐Young , White James L.
Published: April 2004

Viscoelastic flow in a Buss Kneader in which the screw has both rotating and oscillating motions is simulated. Linear viscoelastic responses are considered using both the Maxwell model and the Boltzmann superposition model. Calculations are made first in a basic screw element and subsequently in Kneader screw modules where we consider leakage flows through the interrupted screw flights. Our study includes filled length variation in the crosshead screw extruder, screw characteristics of Kneader screw elements, and pressure profiles along the modular Kneader machine.
The effect of temperature on the interfacial tension of polycarbonate/polyethylene blends
Authors: Pham H. T. , Carriere C. J.
Published: April 2004

Controlling interfacial tension during the processing of blends is critical to developing morphologies that will yield consistent and acceptable mechanical properties. Determination of the interfacial tension is important in developing a predictive understanding of the effects of processing conditions on the morphology and the physical properties of multicomponent systems. The focus of the research reported herein was to investigate the temperature dependence of the interfacial tension for blends composed of polycarbonate (PC) and polyethylene (PE). The effects of temperature were characterized by direct measurements of the interfacial tension using the imbedded fiber retraction (IFR) method. The interfacial tensions of PC/PE were measured at 210, 220, 230, and 240°C. The temperature dependence of the interfacial tension was found to be −0.018 ± 0.006 dyn/cm‐°C. In general, the interfacial tension, evaluated for low‐viscosity simple fluids, is commonly a weak function of temperature (on the order of 0.01 dyn/cm‐°C). The results found in this study are in accord with those findings.
Interferometric measurement of the apparent longitudinal electrostrictive effect in isotactic polypropylene
Authors: Kloos Gerhard
Published: April 2004

By the application of high electric fields, small dilatations are induced in samples of polypropylene. These strains are detected at double frequency using a Michelson interferometer. This corresponds to the measurement of the proportionality factor between strain and the square of the electric field strength. Experimental results and a macroscopic discussion based on thermodynamics are presented. From X‐ray experiments it is concluded that the majority of the investigated polymers can be regarded as isotropic, while two polymers show a slight anisotropy. With the exception of one material, the different isotactic polypropylenes show quite similar electrostrictive behavior. The purpose of the thermodynamic considerations is to study how the viscoelastic response of polymeric materials might influence the observed values.
Polymer flow length simulation during injection mold filling
Authors: Buchmann M. , Theriault R. , Osswald T. A.
Published: April 2004

The maximum flow length of a polymer for a given set of processing conditions is important in injection molding to avoid incomplete mold filling. Experimental analysis, using various processing conditions, can generate the actual influence of processing conditions on the maximum flow length. However, the experimental determination of the flow length for all known industrial polymers would be time consuming and expensive. A non‐Newtonian, nonisothermal model of mold filling was developed to evaluate the flow length without requiring large amounts of computation time. The model implements the use of both a temperature and shear rate–dependent viscosity as well as viscous heating. This paper presents the model and its numerical implementation, followed by simulation results. The model is compared with other simulation programs and experimental results using both an amorphous Styron 484‐27 polystyrene and a semicrystalline 640I polyethylene in a spiral mold geometry. Good agreement between the three is observed.
A review of the electrofusion joining process for polyethylene pipe systems
Authors: Bowman Jeremy
Published: April 2004

Electrofusion joining is now an essential and widely used method to assist in the creation of polyethylene pressure pipe systems. The process of electrofusion joining is reviewed by examining the experimental and some computer simulation literature relating to the temperature and melt pressure changes during the fusion process, and on how varying fusion time and pipe/fitting gap influences the strength of electrofusion joints. From this literature review, four key stages in the joining process are identified. First, an incubation period where the joint has no strength. Second, a joint formation and consolidation stage where an increasing joint temperature aids molecular diffusion to both increase the joint strength and promote a more ductile mode of failure. A plateau region then follows where the joint strength, and ductility, remain reasonably constant despite the fusion time increasing. This plateau is thought to allow some welding variables, such as gap, to have only a small influence on joint strength (for gap maintained within reasonable limits). Finally there is a cooling stage where the joint bridging “tie molecules” become locked into either side of the joint. It is these tie molecules that give the joint its ductility and strength. The concluding section of the review notes some of the important on‐site practices that, if followed, allow electrofusion joints to acquire their good strength properties, and hence give polyethylene pressure pipe systems of a high integrity.
Cross‐thickness vibration welding of polycarbonate, polyetherimide, poly(butylene terephthalate), and modified polyphenylene oxide
Authors: Stokes Vijay K.
Published: April 2004

In vibration welding of thermoplastics, frictional heat generated by vibrating two parts under pressure, along their common interface, is used to effect welds. In the normal, well‐understood mode, the vibratory motion is along the weld seam, which is at right angles to the thickness direction for straight boundaries. But in many applications, such as in the welding of closed seams of box‐like parts, this vibratory motion occurs in the part‐thickness direction, so that a portion of the molten layer along the seam is exposed to the ambient air during each vibratory cycle. The resulting reduction in temperature can affect weld quality. The process phenomenology and the weld strengths of such cross‐thickness vibration‐welded butt joints are investigated for four neat resins. Weld amplitudes and weld pressures are shown to affect the strengths of 120‐Hz welds differently. It is shown that strengths on the order of the strengths of the neat resins can be achieved in 250‐Hz butt welds.
Microwave welding of high density polyethylene using intrinsically conductive polyaniline
Authors: Wu Chung‐Yuan , Benatar Avraham
Published: April 2004

The use of intrinsically conductive polymers in welding of plastics and composites offers the possibility of developing new welding methods. Intrinsically conductive polyaniline (PANI) composite gaskets were used to microwave weld high density polyethylene (HDPE) bars. Two composite gaskets were made from a mixture of HDPE and PANI powders in different proportions. Adiabatic heating experiments were used to estimate the internal heat generation and electric field strength in the gasket. During welding, the effects of heating time, heating pressure and welding pressure were evaluated. It was found that increasing the heating time and the welding pressure increased the joint strength. The maximum tensile joint strength was achieved using a 60 wt% PANI gasket with a heating time of 60 sec and a welding pressure of 0.9 MPa; this resulted in a tensile weld strength of 24.79 ± 0.34 MPa, which equals the tensile strength of the bulk HDPE.
Threaded joints in glass fiber reinforced polyamide
Authors: Dratschmidt Frank , Ehrenstein Gottfried W.
Published: April 2004

Threaded joints can be used to join different polymers or polymers to metals at high loads. Design with self‐threading screws or threaded inserts requires dynamic mechanical properties. Results are presented on threaded joints of glass fiber reinforced polyamide 6 under static and dynamic loads. Dynamic load limits are determined by using the hysteresis measurement method with stepwise load increment experiments and single load level experiments. The failure and fatigue behavior of threaded joints is characterized by several parameters calculated from the hysteresis loop. These parameters change in a characteristic manner as a function of load and time. Significant changes exhibited by the damping and stiffness curves in stepwise load increase experiments can be used to determine the loss of preload on the screw and the beginning of screw pull out. Specially designed self threading screws for threaded joints capable of bearing high dynamic loads are discussed. These joints can attain a life in the endurance range (106 cycles) without loss of preload. In comparison with S‐N curves, the dynamic load limits for threaded joints can be determined more quickly by the hysteresis measurement method.
Numerical analysis of promoted polyester and vinylester reinforced composites in RTM molds
Authors: Yousefi A. , Lafleur P. G. , Gauvin R.
Published: April 2004

This article presents a one‐dimensional simulation of the post‐filling period in the resin transfer molding (RTM) process. In this work, transient heat conduction and kinetic of cure equations were solved simultaneously using the Galerkin finite element method. The kinetic models employed in this study were developed with regard to the effects of additives frequently used in the formulation of composite parts (e.g., promoting agents and reinforcements). These specialized kinetic models enabled us to predict the influence of incorporated reinforcement on the process variables, e.g., gel time and demold time, and on the distributions of temperature and extent of cure in through‐the‐thickness direction of the polyester‐based and vinylester‐based composites. It was shown that in the case of vinylester, the incorporation of glass fibers gave rise to a severe inhibition of the cure reactions at high conversions. The inhibiting effect of glass fibers in polyester‐based formulation was found less significant, and the delay in the exotherm temperature peak was mainly attributed to the thermal effects induced in the presence of glass fibers. The numerical predictions were compared with the experimental data obtained in a heated mold for a reinforced polyester part.