bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of a mold‐cooling process for gas‐assisted injection molded parts designed with a top rib on the gas channel
Authors: Chen Shia‐Chung , Hu Sheng‐Yan , Chao Sher‐Meng , Chien Rean‐Der
Published: April 2004

The same CAE model used for the filling and packing stage in the gas‐assisted injection molding (GAIM) process simulation was also applied to simulate the cooling phase. This was made possible by using the line source method for modeling cooling channels. The cycle‐averaged and cyclic transient mold cavity surface temperature distribution within a steady cycle was calculated using the three‐dimensional modified boundary element technique similar to that used in conventional injection molding. The analysis results for GAIM plates of a semicircular gas channel design attached with a top rib are illustrated and discussed. It was found that the difference in cycle‐averaged mold wall temperatures may be as high as 10°C, and within a steady cycle, part temperatures may also vary by about 15°C. The conversion of the gas channel into equivalent circular pipe and further simplification into two‐node elements using the line source method not only affects the mold wall temperature calculation very slightly but also reduces the computer time by 93%. This indicates that it is feasible to achieve an integrated process simulation for GAIM under one CAE model, resulting in great computational efficiency for industrial application.
Relationship between isothermal and dynamic cure of thermosets via the isoconversion representation
Authors: Atarsia A. , Boukhili R.
Published: April 2004

This study deals with the cure of thermoset resins used in the pultrusion of fiber reinforced composites. The objective was to predict the degree of cure under non‐uniform time‐temperature profiles. A simple procedure using differential scanning calorimetry results was developed for predicting the degree of cure vs. time under isothermal conditions from dynamic DSC tests and vice versa. The principal feature of the procedure is the transformation of the degree of cure vs. time curves obtained under isothermal or dynamic DSC conditions into isoconversion curves as time vs. temperature or time vs. heating rate diagrams. The proposed procedure is validated with isothermal and dynamic DSC results from epoxy and polyester resin formulations used in the pultrusion of fiber reinforced composites. The agreement between predictions and experiments was very good and the extension of the procedure for predicting the cure under non‐uniform temperature profiles as in pultrusion seems to be feasible.
Fatigue crack growth in polyethylene: Material dependence. II: Effects of time “off‐load”
Authors: Harcup J. P. , Duckett R. A. , Ward I. M. , Capaccio G.
Published: April 2004

Fatigue crack growth rates have been determined for a series of polyethylenes through the application of various periodic loading and unloading programs in which the load was held constant for tON seconds and unloaded to a lower constant value for tOFF seconds in each cycle. The crack growth rate, da/dN, was given by

where the parameters γ, k, β and n are material dependent and β and n are also geometry dependent. It was found that β and n described the closure of the crack during the unloaded period as well as the kinetics of the increase in crack growth rate. It is proposed that this equation is consistent with a mechanism in which the crack growth rate increases because of damage sustained by the craze during the unloaded period as it closes and is compressed under the recovery of the surrounding material.
Correlation and modeling of the occurrence of different crystalline forms of isotactic polypropylene as a function of cooling rate and uniaxial stress in thin and thick parts
Authors: Choi Cheol‐Ho , White James L.
Published: April 2004

A study of structure development in thin melt spun isotactic polypropylene filaments is described, which is then applied to the prediction of the behavior of thick parts. Conditions under which different crystalline forms of polypropylene are obtained as a function of cooling rate and spinline stress were investigated. Continuous cooling transformation (CCT) curves are developed. This also allows us to develop a map of crystalline form as a function of these variables. We have applied the CCT curves and this map to predict the development of cross‐sectional variation structure in thick filaments and rods. This is applied in particular to the quenching of a cylindrical rod and the structural characterizations observed through the cross section are compared with predictions from the CCT curves and solutions of Fourier's transient heat conduction equation.
Dynamic mechanical modeling of PEI/dicyanate semi‐IPNs
Authors: Kim Yu‐Seung , Min Hyun‐Sung , Choi Woo‐Jin , Kim Sung‐Chul
Published: April 2004

The dynamic mechanical behavior of polyetherimide(PEI)/dicyanate semi‐interpenetrating polymer networks (semi‐IPNs) was analyzed by using the conventional Takayanagi model for the sea‐island morphology (PEI content of 10% or below) and a polyhedron model, which we developed for the dicyanate nodular structure (PEI content of 20% or above). The model parameters for the Takayanagi model were determined by the volume fraction of the PEI dispersed phase and Kerner's equation, while the model parameters for the polyhedron model were simply calculated by introducing a phase continuity factor. Both models correlate well with the morphology revealed in the micrographs except near the transition temperature of the PEI‐rich phase. The additional shift toward higher temperature found in the nodular structure was due to the intermixed phase composition, and the effect was quantified by measuring the calorimetric transition temperature. The dynamic mechanical modeling for the dual‐phase morphology (PEI content of 15%) and for the semi‐IPNs showing a morphology spectrum were also successfully accomplished by combining the Takayanagi model and the polyhedron model.
Polyurethane and unsaturated polyester hybrid networks: Chemorheological and dielectric study for the resin transfer molding process (RTM)
Authors: Maazouz A. , Dupuy J. , Seytre G.
Published: April 2004

The kinetic, rheological and dielectric behavior of a polyurethane‐unsaturated polyester hybrid system was studied with a view to control the RTM process. The kinetics of the polyurethane reaction (which governs the viscosity evolution during injection) was satisfactorily modeled with a simple second order model. The rheological study enabled complex viscosity and gelation time (tanδ crossover) at different curing temperatures to be obtained. Furthermore, dielectric data and viscosity measurements have been interpreted with respect to kinetics. It was shown that the modified percolation law equation suggested by Macosko et al. can be used to describe the viscosity as a function of temperature and extent of reaction by using a temperature and conversion dependent critical exponent. Dielectric properties such as ionic conductivity were related to viscosity with a Stockes based equation, and to conversion with an empirical equation.
Numerical simulation of double‐layer flow from tube‐in‐orifice spinnerets
Authors: Watanabe Haruhiko , Kihara Shin‐Ichi , Funatsu Kazumori
Published: April 2004

Numerical simulations of double‐layer flow from tube‐in‐orifice spinnerets have been carried out using a differential constitutive equation. The streamline‐upwinding finite element method with 4 X 4 sub‐elements on stress components and over‐relaxation method for equation of motion were used. In addition, the extrudate swell and interface shape have been experimentally observed for PVP(polyvinyl‐pyrrolidone) aq./water system to check the validity of numerical results and to relate the flow geometry to the extrudate swell and interface shape. It was found through both numerical predictions and experiments that extrudate swell shape is strongly dependent on the location of the center tube edge in a tube‐in‐orifice spinneret. In particular, the minimum of the outer diameter swell was found when the center‐tube edge was flush with the outer‐orifice edge. These results give useful information for choosing the optimal design of a tube‐in‐orifice spinneret.
Calculating morphology development of polymer blends in extruders on the basis of results of boundary and finite element simulations using the sigma simulation software
Authors: Potente H. , Bastian M.
Published: April 2004

Models have been developed for binary, incompatible polymer blends that can be used to estimate the morphology development that takes place in drops of the second component that are dispersely embedded in the matrix. The calculations are based on the results of flow simulations using the boundary element (BEM) and finite element (FEM) methods and, more particularly, on an analysis of the stresses that act on fluid particles over their trajectories as a function of the residence time. The models formulated are converted into algorithms, which can then be implemented in the SIGMA simulation software for designing and simulating the process behavior in tightly intermeshing co‐rotating twin‐screw extruders. In this way, it is possible to estimate the morphology development that takes place in incompatible polymer systems by describing the mean drop size and the drop size distribution as a function of the material properties, the geometry of the barrel and the screw, and the process parameters.
Solid state complexes of poly(L‐lysine) with metal chlorides from the 1st row of the d‐block
Authors: Belfiore Laurence A. , McCurdie Mary Pat
Published: April 2004

Solid state characterization of poly(L‐lysine)hydrobromide was obtained via differential scanning calorimetry, thermogravimetric analysis, optical microscopy and infrared spectroscopy. The glass transition temperature of poly(L‐lysine)hydrobromide is 178°C. This thermal transition has not been reported previously. Poly(L‐lysine)'s Tg decreases when complexes are produced with the following divalent transition metal chlorides; cobalt chloride hexahydrate, nickel chloride hexahydrate, copper chloride dihydrate and anhydrous zinc chloride. At 10 mol% salt, nickel, chloride decreases Tg by 45°C, and the general trend is Ni2+Co2+Zn2+Cu2+. The depression of poly(L‐lysine)'s Tg correlates well with ligand field stabilization energies for pseudo‐octahedral and pseudo‐tetrahedral dn complexes (n = 7, 8, 10) from the 1st row of the d‐block. However, d9 copper(II) complexes cannot be included in this empirical correlation. Infrared spectroscopic evidence suggests that Co2+, Ni2+ and Zn2+ coordinate to the carbonyl oxygen in the main chain of the polymer. When transition metal ions coordinate to CO, the network of hydrogen bonded amide groups is disrupted, which lowers the glass transition. The amide I region of the infrared spectrum reveals a hydrogen bonded CO stretch @ 1655 cm−1 that is characteristic of poly(α‐amino acid) random coil conformations, and a metal‐ligand coordinated CO stretch @ 1625 cm−1 in complexes with divalent cobalt, nickel and zinc. The amide II region of the infrared spectrum near 1550 cm−1 is also sensitive to the formation of coordination complexes with these d‐block metal chlorides.
Surface topography and gloss of polyolefin blown films
Authors: Wang Lei , Huang Tao , Kamal M. R. , Rey Alejandro D. , Teh Joo
Published: April 2004

Atomic Force Microscopy (AFM) was used to obtain a comprehensive characterization of the surface roughness of polyethylene blown films based on a variety of resins. The quantitative description of surface roughness was achieved using a number of statistical parameters. Surface gloss of the sample films was calculated using the general Kirchhoff solution for rough surfaces. The calculated gloss values showed good agreement with experimental measurements. The quality of the correlation suggests the utility of AFM in characterization of surface roughness. It also suggests that the proposed mathematical and statistical description of roughness is a useful tool for the estimation of surface gloss.
Environmental stress cracking of poly(vinylidene fluoride) in sodium hydroxide. Effect of chain regularity
Authors: Maccone Patrizia , Brinati Giulio , Arcella Vincenzo
Published: April 2004

Three commercial samples of poly(vinylidene fluoride) (PVDF) homopolymers with different crystallinity degree have been evaluated for chemical stress cracking behavior in 30 wt% sodium hydroxide solution. The polymers were submitted to thermal and mechanical analyses before environmental experiments. These were carried out at 23°C on 3‐mm‐thick PVDF sheets, using three different levels of constant strain applied (3%, 5%, 7%). The time for crack appearance decreases with the increase of the degree of crystallinity. This behavior has been related to the presence of head‐to‐head VDF additions (defect “a”), as well as to the overall chain regularity. The head‐to‐head sequences inhibit the degradation mechanism because of the dehydrofluorination reaction activated by alkaline media. The less crystalline PVDF polymer, with the higher content of head‐head VDF additions and a limited number of chain‐branching defects, presents the best crazing resistance.
Effect of blending sequence on the morphology and impact toughness of poly(ethylene terephthalate)/polycarbonate blends
Authors: Wu Jingshen , Xue Pu , Mai Yiu‐Wing
Published: April 2004

The morphology of PET/PC/E‐GMA‐MA blends made by different mixing sequences was studied by transmission electron microscopy (TEM). The results suggest that migration of the E‐GMA‐MA copolymer from the PET phase to the PC phase occurred during the mixing of the (PET/E‐GMA‐MA) pre‐blend with the PC at 10% copolymer content. As a result of the migration, the E‐GMA‐MA particles are located in the PC phase rather than in the PET phase. This finding is not in agreement with the prediction made previously by others based on the possible reaction between the epoxy group of GMA and carboxyl group of PET. Core‐shell (PC/E‐GMA‐MA) particles formed in situ during blending and the size of the core‐shell particles was controlled by the blending sequence used. Mechanical properties of the ternary blends were tested at various temperatures. Although the blending sequence does not have a noticeable effect on the yield strength and modulus of the blends, it has a strong influence on the morphology formed, which determines the impact toughness. For blends made under optimum processing conditions, the brittle‐ductile transition occurred at a lower temperature and lower elastomer content. A study of the toughening mechanism suggested that the major toughening events were cavitation plus matrix shear yielding. It is postulated that the very high impact toughness found with the (PC/E‐GMA‐MA)/PET blend (at 10% E‐GMA‐MA) originated from the bimodal particle size distribution of the core‐shell particles formed in situ.
Constitutive equations in nonlinear viscoelasticity of glassy polymers based on the concept of traps
Authors: Drozdov Aleksey D.
Published: April 2004

Constitutive equations are derived for the nonlinear viscoelastic response of amorphous polymers. The model treats a glassy polymer as an ensemble of independent relaxing regions that randomly hop in their cages being thermally activated. Rearrangement occurs when a flow unit reaches some liquid‐like state. Stress‐strain relations are verified using experimental data in tensile relaxation tests for polyester resins with two types of flexibilizers. Fair agreement is demonstrated between observations and results of numerical simulation.
Numerical and experimental studies on the ejection of injection‐molded plastic products
Authors: Wang H. , Kabanemi K. K. , Salloum G.
Published: April 2004

Numerical and experimental studies have been conducted on the ejection stage of plastics injection molding process. A numerical approach is proposed to predict the ejection force from the mold‐part constraining and friction forces as the product cools in the mold cavity up to the moment of ejection. The finite element thermoviscoelastic solidification analysis has taken into account the stress and volume relaxation behavior of polymers under the cavity‐constrained condition. The predicted ejection force and its distribution over ejector pins are validated by injection molding experiment of rectangular boxes using a polycarbonate resin. Different cases of the ejector pin layout are evaluated to examine the effect of the number, location and dimension of ejector pins, so as to identify the balanced layout causing minimum stress and deformation to the product. The approach is also applied to another product geometry which shows complex distribution of the mold‐part constraining and friction forces and involves multi‐step operations in the demolding stage.
Effects of particle size of Al(OH)3 on electrical properties of EPDM compounds
Authors: Lee Cheol Ho , Kim Sang Wook , Nam Jin Ho , Suh Kwang S.
Published: April 2004

Effects of particle size of Al(OH)3 (ATH) filler on electrical properties of ethylene propylene diene terpolymer (EPDM)/ATH compounds were studied. It was found that tracking and erosion resistance of EPDM/ATH compounds decreased while dielectric properties and 90°C water resistance were improved with the increase of particle size. Homocharge accumulates in the compounds, which increases first and then decreases with the increase of particle size. This was explained by the change of particle‐to‐particle distance due to filler size.
Separation, size reduction, and processing of XLPE from electrical transmission and distribution cable
Authors: White C. C. , Wagenblast J. , Shaw M. T.
Published: April 2004

The recycling of power transmission cable insulated with crosslinked PE (XLPE) was investigated by using different methods of separation and reprocessing. Separation was attempted by thermo‐chemical, thermo‐mechanical and microwave‐mechanical means, the latter being the most successful. A mechanism encompassing all of these was formulated. Compression molding, extrusion, and injection molding with and without preheating of the material were also investigated. It was found that by preheating the XLPE and injection molding under high injection pressure, the neat XLPE could be formed into shapes with tensile strengths equal to that of the original insulation. In view of available observations, possible mechanisms for the flow and reconsolidation of XLPE crumb are proposed and discussed.
Viscoelastic predictive laws of linear polyurethane: Rheological changes during bulk polymerization
Authors: Cassagnau P. , Michel A. , Aulagner‐Revenu P. , Carrot C. , Guillet J.
Published: April 2004

The rheological behavior during the bulk polymerization of urethane systems made from diphenyl methane 4,4′ diisocyanate (MDI) and poyether macro diol was studied in connection with the kinetics of the reaction. The linear viscoelastic behavior in the terminal zone has been reasonably predicted using the molecular weight distribution obtained from size exclusion chromatography (SEC) and owing to only a few rheological parameters, namely, the scaling law relating the zero shear viscosity to the average weight molecular weight and the plateau modulus. These parameters were previously determined from oscillatory shear experiments performed on model samples of various molecular weights. The combination of this predictive model together with a reasonable kinetic scheme for such systems, enables to calculate the evolution of the viscoelastic parameters (storage and loss moduli) during bulk polymerization. The overall calculation was shown to give a reasonable depiction of the viscosity function. However, some discrepancies were noted as far as the elasticity of the melt is concerned. This was attributed to an additional relaxation mechanisms in the earliest stage of the polymerization connected to hydrogen bonding. Nevertheless, the procedure remains fundamental for apprehending some aspects of the viscoelastic changes of the material during a reactive processing technique such as extrusion for example.
Experimental validation of numerical simulations of the kneading disc section in a twin screw extruder
Authors: Jaffer Shaffiq A. , Bravo Victor L. , Wood Philip E. , Hrymak Andrew N. , Wright Joseph D.
Published: April 2004

A comparison of the results of a 3D model for the simulation of flow in the kneading disc region of a fully intermeshing twin screw extruder has been done against particle image velocimetry (PIV) experimental data. Experimental results using a geometry with an extended first and last kneading disc to capture the simplified inlet and outlet boundary conditions, are in good qualitative agreement for low flow rates. The results showed good agreement at flow rates less than 5 mL/s and rotation speeds of 60 rpm, while above that there was poor agreement. These results highlight the importance of the use of appropriate boundary conditions for the accurate prediction of the flow field. The flow field within the kneading discs with forward conveying elements placed before and after the kneading discs was also measured. For a flow rate of 8.5 mL/s and 60 rpm, results showed good agreement when conveying elements were deployed before and after the kneading blocks whereas for lower flow rates there was poor agreement.
Structure development in melt spinning filaments from polybutylene terephthalate based thermoplastic elastomers
Authors: Li Hang , White James L.
Published: April 2004

Structure development in polybutylene terephthalate (PBT) and thermoplastic elastomers (TPEs) based on PBT during the melt spinning process was investigated. Melt spun filaments were examined using wide angle X‐ray diffraction and birefringence. Crystalline orientation was characterized in terms of Hermans‐Stein orientation factors. Crystalline orientation and birefringence were found to correlated with spinline stress better than drawdown ratio. Crystalline orientation development was strongly dependent on spinline stress. The TPEs with low PBT content had low birefringence although the crystalline orientation was often high.
Scratch resistance of mineral‐filled polypropylene materials
Authors: Chu J. , Xiang C. , Sue H.‐J. , Hollis R. Damon
Published: April 2004

Pigmented mineral‐filled polypropylene (PP‐PMF) is marketed as a potential alternative to acrylonitrile‐butyldiene‐styrene (ABS) and Polycarbonate/ABS for automotive interior components. PP‐PMF is more easily damaged by surface scratch/mar, thus limiting its acceptance for such applications. This study focuses on investigating the scratch/mar mechanisms of PP‐PMF having different mineral fillers and additives. A new method is introduced to characterize the scratch visibility by image analysis. A correlation is found between scratch visibility and scratch hardness measured by interferometer. It is found that Wollastonite filler imparts higher scratch/mar resistance. Addition of an interface modifier and a lubricant can further improve scratch/mar resistance. It is also found that Talc‐filled PP‐PMF has poor scratch/mar resistance, irrespective of the addition of an interface modifier or a lubricant.
Mechanical studies on poly(vinylidene fluoride) based polymer electrolytes
Authors: Jacob M. M. E. , Arof A. K.
Published: April 2004

The mechanical strength of the poly(vinylidene fluoride) (PVDF) based polymer electrolyte deteriorates with increasing salt content. For a salt concentration of 2 wt% the Young's modulus is 10−5 Pa. The Young's modulus reduces by 60% when the salt concentration increases five‐fold. The decrease in mechanical strength of the polymer electrolyte by the incorporation of the salt is attributed to the intramolecular interaction between the chains of the polymer and the salt. The mechanical strength of the polymer electrolyte was also analyzed for different plasticizer content. The plasticizer used was ethylene carbonate (EC). The Young's modulus of the plasticized polymer electrolyte decreased with increased in EC content, but the elongation of the material and the energy at break increased with EC content, showing increased flexibility.
A model study for the recovery of polymides using the dissolution/reprecipitation technique
Authors: Papaspyrides C. D. , Kartalis C. N.
Published: April 2004

A model dissolution/reprecipitation process is studied for the recycling of both polyϵ‐caprolactam (PA 6) and polyhexamethyleneadipamide (PA 6 6). This process comprises dissolution of each of the aforementioned polyamides in an appropriate solvent, reprecipitation by addition of a nonsolvent and finally recovery of the polymers through washing and drying. Dimethylsulfoxide/methyl‐ethyl‐ketone (DMSO/ MEK) proved to be the most suitable solvent/nonsolvent system for the recovery of PA 6, while formic acid/methyl‐ethyl‐ketone was used as a potential pair of solvent/ nonsolvent in the case of recovering PA 6 6. The recycled polyamides were evaluated in terms of the following characteristic properies: molecular weight (based on end‐group analysis and intrinsic viscosity determination), crystallinity and grain size analysis. In all cases, the recycled materials present excellent retention of the properties studied. Finally, the solvent mixtures involved are separated by distillation for reuse.
Application of the essential work of fracture concept to high temperature deformation in polyoxymethylene
Authors: Plummer C. J. G. , Scaramuzzino P. , Kausch H.‐H. , Steinberger R. , Lang R. W.
Published: April 2004

Essential Work of Fracture (EWF) tests have been carried out on double edge notched samples machined from injection molded sheets of commercial grades of polyoxymethylene homopolymer with different molecular weight averages. Most of the measurements were made at 1000C and over a range of test speeds in which polyoxymethylene is anticipated to undergo a macroscopic ductile‐brittle transition with decreasing strain rate. The results reflect both the existence and the molecular weight dependence of this transition, and are argued to be valid in terms of the European Structural Integrity Society's EWF draft test protocol under certain test conditions. However, it is shown that the applicability of the test method used here becomes highly questionable for test speeds in the immediate vicinity of the transition, owing to the influence of the initial ligament length on the crack tip deformation mechanisms.
Water transport in crosslinked 2‐hydroxyethyl methacrylate
Authors: Chou K. F. , Lee Sanboh , Han C. C.
Published: April 2004

Water transport in crosslinked 2‐hydroxyethyl methacrylate (HEMA) was investigated. Crosslinked HEMA was irradiated by gamma ray in vacuum for this study. The sorption data of de‐ionized water transport in crosslinked HEMA subjected to various gamma ray dosages are in excellent agreement with Harmon's model which accounts for Case I, Case II, as well as the anomalous transport processes. The diffusion coefficient for Case I transport and velocity for Case II transport satisfy the Arrhenius equation for all dosages. The transport process was exothermic and the equilibrium‐swelling ratio satisfied the van't Hoff plot. The pH value of de‐ionized water after the sorption/de‐sorption treatment of the irradiated crosslinked HEMA specimen was analyzed. The transmittance of irradiated crosslinked HEMA treated by de‐ionized water was also studied. The effect of irradiation on the polymer chains was revealed by the measurement of glass transition temperature and the quantitative determination of water structures in crosslinked HEMA hydrogel. The UV cut‐off wavelength of crosslinked HEMA shifted to longer wavelength side with increasing irradiation dosage, but the trend of transmittance after water treatment was opposite. The effect of specimen thickness on water transport was also studied.
The effect of calcium chloride dihydrate on the optical properties and mass transport of methanol in poly(methyl methacrylate)
Authors: Chou K. F. , Lee Sanboh
Published: April 2004

The effect of calcium chloride dihydrate on optical properties and the mass transport of methanol in poly(methyl methacrylate) (PMMA) has been investigated. The solvent transport was analyzed based on the Harmon model accounting for Case I, Case II, and anomalous diffusions. Both Case I and Case II transports satisfy the Arrhenius equation. Calcium chloride dihydrate depresses Case I diffusion and enhances Case II diffusion. From the mass transport data, the equilibrium solvent content of methanol with various concentrations of calcium chloride dihydrate in PMMA is obtained and satisfies the van't Hoff plot. A comparison of movement of sharp front and mass transport is made. The increase of UV transmittance of specimens treated with a mixture of methanol and calcium chloride dihydrate is attributed to the reduction of the carbonyl group. The critical solvent content to change transmittance from a slow increase to a fast increase occurs when the sharp fronts meet at mid‐plane. The decrease of transmittance in UV range is due to void creation for a large amount of solvent. The visible light transmittance of the specimen with small solvent content is the same as that of the specimen without solvent treatment. The visible wavelength dependence of transmittance of specimens with large solvent content is attributed to the void of which the size is smaller than the wavelength of visible light. The void is enlarged during the mass uptake, then it is fully closed after desorption of a small solvent amount and shrinks to a small size after desorption for a large solvent content.
Surface modification of plasma‐pretreated high density polyethylene films by graft copolymerization for adhesion improvement with evaporated copper
Authors: Ng C. M. , Oei H. P. , Wu S. Y. , Zhang M. C. , Kang E. T. , Neoh K. G.
Published: April 2004

Surface modification of Ar plasma‐pretreated high density polyethylene (HDPE) film via UV‐induced graft copolymerization with glycidyl methacrylate (GMA) and 2‐hydroxyethylacrylate (HEA) was carried out to improve the adhesion with evaporated copper. The surface compositions of the modified HDPE surfaces were characterized by X‐ray photoelectron spectroscopy (XPS). The adhesion strengths of evaporated copper with the graft‐copolymerized HDPE films were affected by the Ar plasma pretreatment time, the monomer concentration used for graft copolymerization, and the graft concentration. Post‐treatments, such as plasma post‐treatments after graft copolymerization and thermal treatment (curing) after metalization, further enhanced the adhesion strength of the Cu/HDPE laminates. The T‐type peel strengths of the laminates involving the graft‐modified and plasma posttreated HDPE films were greater than 15 N/cm. The enhanced adhesion strength resulted from the strong affinity of the graft chains for Cu and the fact that the graft chains were covalently tethered on the HDPE surface. XPS characterization of the delaminated surfaces of the Cu/HDPE laminates revealed that the failure mode of the laminates with T‐peel adhesion strengths greater than 5 N/cm was cohesive in nature.
Interfacial instabilities in coextrusion flows of low‐density polyethylenes: Experimental studies
Authors: Tzoganakis Costas , Perdikoulias John
Published: April 2004

A fundamental investigation into the interfacial instability phenomenon was performed. Coextrusion experiments were carried out using well‐characterized low‐density (LDPE) resins in an effort to gain a better understanding of interfacial instability phenomena. The resins used were chosen carefully and included materials of high and low viscosity as well as broad and narrow molecular weight distributions (MWD). The experiments involved the coextrusion of either the same material in both layers or various combinations of the four materials and the focus of the work was to elucidate the effects of flow rates, molecular weight (MW) and MWD on interfacial instability. The effect of the geometry at the point where the materials merged was also investigated. It was concluded that there are essentially two types of interfacial instabilities and that the MW had the strongest effect on the occurrence of the “zig‐zag” instability due to high interfacial stress while the breadth of the MWD had a strong effect on the appearance of the “wave” instability. Broad MWD materials had a greater tendency to exhibit interfacial instability, which is more due to layer ratio than processing conditions or die geometries. The results suggest that the origin of the “wave” type of interfacial instability is due to an extreme extensional deformation of the minor layer at the merge point and that the viscoelastic properties of adjacent layers determine the instability development.
Experimental study on extrudate swell and die geometry of profile extrusion
Authors: Lee Woei‐Shyong , Ho Hsueh‐Yu
Published: April 2004

The objective of this study was to determine the die swell behavior of a polymer melt and to design a die for forming a polymeric extrudate with a desired shape using profile extrusion. Polystyrene pellets were chosen to perform the profile extrusion experiments. First, the polystyrene pellets were melted and pushed through a quarter ring profile. The profile of the swelled extrudate agreed with the numerical predictions. A modified die was designed to produce a quarter ring profile extrudate based on the direct extrusion problem (DEP) prediction. Polystyrene pellets were also melted and pushed through the modified die. The experimental results were close to the computational results. The melting temperature, die length, and melting residence time affect die swell behavior. The die swell ratio becomes smaller as the melting temperature and melting residence time are increased. As the die length is increased, the die swell ratio is lowered. According to the die geometry predictions, an extrudate with the desired profile can be made precisely.
The effects of kneading block design and operating conditions on distributive mixing in twin screw extruders
Authors: Shearer Gifford , Tzoganakis Costas
Published: April 2004

A mixing limited interfacial reaction between polymer tracers was used to directly measure the distributive mixing performance of a co‐rotating twin screw extruder during melt‐melt blending of polypropylene. The reaction between the polymer tracers, which are low molecular weight succinic anhydride and primary amine terminally functionalized polymer chains, was followed using Fourier‐Transform Infrared Spectroscopy (FT‐IR). Experiments were completed to determine the effects of flow rate, screw speed, and kneading block design on the distributive mixing performance and the residence time distribution (RTD). The only RTD variable that was significantly affected by the experimental factors was the average residence time. Distributive mixing with neutral and reverse kneading blocks was controlled by the average residence time, the fully filled volume, and the shear rate. Conversely, the mixing performance of a forward kneading block did not follow the same trends.
In‐line monitoring of polyethylene density using near infrared (NIR) spectroscopy
Authors: Nagata Takefumi , Ohshima Masahiro , Tanigaki Masataka
Published: April 2004

Density and melt index are two key properties in grading commercial polyolefin polymers. For quality assurance, these properties must be controlled as accurately as possible in the production plant. However, the lack of suitable in‐line sensors for these properties makes feedback quality control difficult. In this study, an in‐line density sensor using near infrared (NIR) spectroscopy is developed. The NIR spectra of molten polyethylene in flow are collected by a fiber‐optic device attached to a single screw extruder. By the ratio of the absorption intensity at 1170 nm to that at 1213 nm, the densities of 14 grades of polyethylene were successfully measured. The results were very promising for quality control in the polyethylene production process.
Kinetic study of the degradation of a new aromatic polyethersulfone
Authors: Abate L. , Pappalardo A. , Recca A.
Published: April 2004

The degradation of a new thermoplastic polyethersulfone containing more than one SO2 group in the repeating unit was carried out in both dynamic and isothermal heating conditions, under N2 flow and in a static air atmosphere. The experiments indicated that the polymer degraded by initial random chain scission, followed by branching and crosslinking in an inert atmosphere and complete degradation in an oxidative environment. Apparent activation energy values associated with the first degradation stage were calculated and suggested that the first degradation stage was not affected by the experimental conditions. Results indicated for the investigated polymer a thermal stability higher than those of some previously investigated polyethersulfones containing only one SO2 group in their repeating units.
Single and double bubble tubular film extrusion of polyethylene 2, 6‐naphthalate (PEN)
Authors: Song Kwangjin , White James L.
Published: April 2004

An experimental study of film formation and structure development of polyethylene 2,6‐naphthalate (PEN) in single and double bubble tubular film extrusion is presented. PEN was largely stable in film blowing. The films produced were characterized with wide angle X‐ray diffraction, DSC, and Abbe refractometer techniques. The structure and orientation in the films varied substantially with process and film formation history. Single bubbles exhibited polymorphs with considerable levels of orientation, while double bubbles possessed only the extended α‐modification. With increasing planar strain, the naphthyl rings on the chain backbone became increasingly aligned parallel to the film surface. The mechanism of structure evolution in PEN was related to its behavior during the inflation period and compared with that found in polybutylene terephthalate (PBT) and polyethylene terephthalate (PET).
Blends of linear and branched polyethylenes
Authors: Lee Heon Sang , Denn Morton M.
Published: April 2004

We employ rheological measurements of polyethylene blends in the melt and solid state, together with thermal analysis, to infer phase behavior. Partial‐miscibility in the melt is characterized by use of the double‐reptation model to define the complex modulus of the continuous phase for input into the emulsion model for the blend; this approach introduces a new fitting parameter, the fraction of the minor component contained in the continuous phase. The results on binary systems suggest the use of HDPE as a compatibilizer for LLDPE/LDPE blends, apparently creating a fully miscible ternary system.
Blending of immiscible polymers in a mixing zone of a twin screw extruder—effects of compatibilization
Authors: Franzheim O. , Rische T. , Stephan M. , MacKnight W. J.
Published: April 2004

The dependence of the morphology development of physical as well as of reactive compatibilized polypropylene/polyamide 6 (PP/PA6) blends in a mixing zone of a co‐rotating twin screw extruder on blend composition and screw rotational speed was investigated. A special process analytical set‐up based on a co‐rotating twin screw extruder was used, which allowed melt sampling from different positions along the operating extruder in time periods less than 10 seconds. It has been shown that the disperse particle sizes in physical blends depend crucially on the blend composition because of the increasing influence of coalescence with an increasing concentration of the disperse phase. Furthermore, the morphology of physical PP/PA6 blends depends strongly on their rheological properties. In contrast, the influence of the screw rotational speed on the morphology is minor. The resulting particle size in a mixing zone is achieved already after a short screw length. The particle size of compatibilized blends is significantly smaller than in physical blends because of the better conditions for drop break‐up and the suppression of coalescence effects. Due to this, compatibilization has a stronger influence on the blend morphology than a variation of process or rheological conditions with physical blends. Furthermore, the compatibilization leads to a concurrent crystallization of the PA6 phase with the PP phase.
Co‐injection molding: Effect of processing on material distribution and mechanical properties of a sandwich molded plate
Authors: Seldén R.
Published: April 2004

The effect of molding parameters on material distribution and mechanical properties of co‐injection molded plates has been studied using experimental design. The plates were molded with a polyamide 6 (PA 6) as skin and a 20% glass fiber‐reinforced polybutyleneterephtalate (PBTP) as core. Five molding parameters—injection velocity, mold temperature, skin and core temperature, and core content—were varied in two levels. The statistical analysis of the results showed that three parameters—Injection velocity, core temperature, and core content—were the most significant in affecting skin/core distribution. A high core temperature was the most significant variable promoting a constant core thickness, while core content was the most significant factor influencing a breakthrough of the core. Mechanical properties, such as flexural and impact strength showed a high correlation with the skin/core distribution. The slight increase in falling weight impact strength of the sandwich molded plates, compared to similar plates molded from PBTP only, could be explained from the failure process, which initiates in the brittle core and propagates through the ductile skins.
Post‐yield behavior of thermoplastics and the application to finite element analysis
Authors: Fesko Donald G.
Published: April 2004

This report delineates the rate sensitivity of three commodity thermoplastics and assesses the appropriateness of assuming simple rate dependence in finite element analysis. Polycarbonate does indeed show simple rate dependence in the plastic region with very rapid adjustment from one rate to the next; thus, a rate dependent model is an accurate representation. Acrylonitrile/Butadiene/Styrene (ABS) does not exhibit such large plastic strains and is a bit more complex with a process of craze formation leading to more variable necking and failure. It also shows a rapid transition from one rate to another, but superimposed failure processes impart considerable variability. Assuming simple rate dependence is a reasonable approximation and directionally correct. An impact‐modified polypropylene exhibits craze formation, a very low Poisson's ratio to large extensions and simple rate dependent behavior before failing. At elevated temperature, it draws and forms a stable neck and again shows simple rate dependence. However, the processes of failure and transition to necking are not simply rate dependent and this will keep this assumption from being generally valid.
An experimental matrix design to optimize the weldline strength in injection molded parts
Authors: Liu Shih‐Jung , Wu Jun‐Yu , Chang Jer‐Haur , Hung Shiu‐Wan
Published: April 2004

The forming of weldlines wherever polymer flow fronts meet is one of the problems that confound the overall success of injection molding technology. In this study, an L'18 experimental matrix design based on the Taguchi method was conducted to optimize the weldline strength of injection molded thermoplastics. Experiments were carried out on a 4.1 oz injection molding machine. A plate cavity with an obstacle at the center was used to create a weldline. After molding, the weldline strength of the parts was measured with a tensile tester. Of the factors selected in the main experiments, melt temperature and mold temperature were found to be the principal factors affecting the weldline property of injection molded thermoplastics. Weldline strengths of injection molded parts increase with the size of the obstacles.
Non‐isothermal crystallization kinetics of PET
Authors: Piccarolo S. , Brucato V. , Kiflie Z
Published: April 2004

The crystallization kinetics of poly(ethylene terephthalate) was studied using constant cooling rate, isothermal and quenching experiments. A non‐isothermal crystallization kinetics equation based on a single mechanism was used to analyze the data. Different mechanisms of crystallization at low, intermediate, and high cooling rates were hypothesized based on deviation of the experimental data from the single mechanism model.
Cavity balance for plastic injection molding
Authors: Lam Y. C. , Seow L. W.
Published: April 2004

Cavity balancing is the process of altering the flow front within a cavity through thickness and design changes such that a desired fill pattern is achieved. This paper reports the preliminary research undertaken in developing an automated method for cavity balancing of two‐dimensional cavities. The aim of the automated cavity balancing routine is to reduce product development time and to improve product quality. This will lower the level of prerequisite expert knowledge necessary for successful mold and part design. The automated cavity balancing routine has been developed using the concept of flow paths. The hill‐climbing algorithm was employed on the cavity fill pattern for generation of the flow paths. Replacing the flow paths generated using the straight flow path assumption in previous work, this method was found to be more versatile and suitable to automation. No special considerations or routines were required to overcome the presence of inserts within the cavity. The method has been implemented in a computer program running as an external loop to the Moldflow software. The models analyzed demonstrate that the proposed method is viable and robust.
On mechanical properties of sago starch/poly(ε‐caprolactone) composites
Authors: Odusanya O. S. , Ishiaku U. S. , Azemi B. M. N. , Manan B. D. M. , Kammer H. W.
Published: April 2004

Four types of sago starch were incorporated into a poly(ε‐caprolactone) (PCL) matrix, native, predried, thermoplastic starch (TPS) granules and TPS. All systems were found to be phase‐separated. Tensile properties were obtained after formulation of various mixtures and processing of suitable test specimens. It was found that elongation at break of composites comprising native starch and thermoplastic starch decreases almost linearly with volume fraction of starch whereas tendencies to nonlinear dependencies were observed for predried and thermoplastic starch granules. Except for composites containing native starch, tensile strength was found to decrease linearly with volume fraction of starch. However, statistical analysis of the corresponding regression coefficients shows that the coefficients ruling the compostion dependence of tensile properties are not significantly different for the four starch types. One may conclude that in all cases, tensile properties decrease almost linearly with volume fraction and maximum volume fraction of starch loading is around 0.6. Scanning electron micrographs of fracture surfaces revealed weak interfacial adhesion between sago starch and the polymer matrix.