bluuebunny/crossref_metadata_2025 huggingface dataset:
Membrane inflation of polymeric materials: Experiments and finite element simulations
Authors: Li Yong , Nemes James A. , Derdouri A. A.
Published: April 2004

A high‐speed optical measurement system, which is capable of measuring transient surface shape, is used in the polymer membrane inflation experiments. The accurate measurement data, which is an array of points, with known Cartesian coordinates and with respect to a fixed coordinate system, provides a source for further bubble shape analysis. Inflation pressure is correlated with each bubble shape measurement. The measured results reveal the importance of the thermal warpage and temperature gradient in the bubble inflation tests. Potential errors in the material parameter calculation, which are caused by assuming uniform temperature and zero thermal warpage, are pointed out. Consequently, a finite element analysis has been carried out to simulate the membrane inflation with/without thermal warpage and the temperature gradient. The material parameters obtained considering the thermal warpage and temperature gradient yield improved agreement with the experimental data. Although in this paper the measurement data is mainly used for the determination of the material parameters in the bubble inflation tests, they are also a source of validating other computer‐aided simulations as well as in the study of the thermal shrinkage of polymer products.
The vibration and hot‐tool welding of polyamides
Authors: Stokes Vijay K.
Published: April 2004

The weldabilities of polyamide 6 (PA‐6), polyamide 6,6 (PA‐6,6), 33 wt% glass‐filled PA‐6,6 (33‐GF‐PA‐6,6), and amorphous polyamide (PA‐A) are assessed through 120 Hz vibration welds. Weld strengths equal to those of the base resins can easily be obtained in vibration welds of both undried and dried PA‐6 and PA‐6,6. Relative weld strengths in the range of 54–57% are demonstrated for 120 Hz welds of 33‐GF‐PA‐6.6. Relative weld strengths in the range of 90–97% are demonstrated for dried PA‐A. The highest relative weld strengths obtained in hot‐tool welds of undried and dried PA‐6,6 are only 57% and 54% respectively.
Review: Recycling of nylon from carpet waste
Authors: Mihut Corina , Captain Dinyar K. , Gadala‐Maria Francis , Amiridis Michael D.
Published: April 2004

Large amounts of post‐consumer carpet are discarded every year. Most of this waste is currently landfilled, while a small percentage is incinerated. The face carpet fibers, consisting primarily of nylon 6 and nylon 6,6, represent the majority component in the carpet waste. Recent financial incentives and environmental constraints have motivated the industrial sector to develop recycling strategies for these fibers. Depolymerization into their constituent monomers is the most complex recycling route, but at the same time it produces the most valuable product. A second alternative involves the use of solvents for the extraction of carpet fiber components in their polymeric form. Finally, a third recycling option yields thermoplastic mixtures by melt blending the carpet waste. The recent literature on the recycling of nylon from carpet waste is reviewed in this paper. The paper also includes a section focusing on the current state of carpet recycling at the Industrial level.
A review on interface modification and characterization of natural fiber reinforced plastic composites
Authors: George Jayamol , Sreekala M. S. , Thomas Sabu
Published: April 2004

An Important aspect with respect to optimal mechanical performance of fiber reinforced composites in general and durability in particular is the optimization of the interfacial bond between fiber and polymer matrix. The quality of the fiber‐matrix interface is significant for the application of natural fibers as reinforcement for plastics. Since the fibers and matrices are chemically different, strong adhesion at their interfaces is needed for an effective transfer of stress and bond distribution throughout an Interface. A good compatibilization between cellulose fibers and non‐polar matrices is achieved from polymeric chains that will favor entanglements and interdiffiusion with the matrix. This article gives a critical review on the physical and chemical treatment methods that improve the fiber‐matrix adhesion and their characterization methods.
Measuring Tg in ultra‐thin polymer films with an excimer fluorescence technique
Authors: White C. C. , Migler K. B. , Wu W. L.
Published: April 2004

An excimer fluorescence technique has been applied to the measurement of Tg of ultra‐thin polystyrene films. This technique utilizes an excimer‐forming molecule with fluorescent emission in two wavelength bands. The intensity ratio of these bands is a sensitive measure of local viscosity. This technique has been applied to five polystyrene films in the thickness range of 25 nm to 200 nm supported on quartz substrates. The observed Tg for the five ultra‐thin polymer films was similar to the bulk Tg with no observed dependence upon thickness. Additionally, the Tg determined for each film did not show any dependence upon thermal history.
Rheology of blends of a thermotropic liquid crystalline polymer with polyphenylene sulfide
Authors: Han Minsoo , Kim Woo Nyon , Giles David W.
Published: April 2004

Blends of thermotropic liquid crystalline polymer (LCP) and polyphenylene sulfide (PPS) were studied over the entire composition range using Rheometrics Stress Rheometer, capillary rheometer, and differential scanning calorimeter. There is no molecular scale mixing or chemical reaction between the components, as evidenced by melting and crystallization points in the PPS phase. From the strain scaling transients test at low‐rate, LCP and the blends require approximately 60 strain units to obtain steady stale shearing results. The large recoveries in the strain recovery test, magnitude 3 to 3.3 strain unit, are likely the results of texture present in LCPs. With increasing PPS content in LCP/PPS blends, the total recovery declines. Scaling of the transient strain rate remains, but the magnitude of the transients is reduced. At low‐rate, when the LCP is added to the PPS, the pure melts have similar visosity: 500 Pa · s for LCP and 600 Pa · s for PPS, but the viscosity of the blends goes through a maximum with concentration that is nearly three times the viscosity of the individual melts. At high‐rate, a significant depression of the viscosity is observed in the PPS‐rich compositions and this may be due to the fibrous structure of the LCP at high shear rates.
Preparation and characterization of polyimide nanocomposites with different organo‐montmorillonites
Authors: Chang Jin‐Hae , Park Kwang Min , Cho Donghwan , Yang Hee Sam , Ihn Kyo Jin
Published: April 2004

Poly(amic acid) nanocomposites were synthesized from a dimethylacetamide (DMAc) solution with two organophilic montmorillonites (organo‐MMTs). It was then heated at various temperatures under vacuum, yielding 15–20 um thick films of polyimide/organo‐MMT hybrid with different clay contents (1–8 wt%). Dodecy‐lamine (C12‐) and hexadecylamine (C16‐) were used as aliphatic alkylamines in organo‐MMT. The ultimate strength monotonically increased with increasing clay content in the polymer matrix. Maximum enhancement in the initial modulus was observed for the blends containing 2 wt% clay with two kinds of organo‐clays, and values did not alter significantly with further increases in clay content. Additions of only 2 wt% C12‐ and C16‐MMT to the polyimide were shown to cause 94%‐95% reduction in oxygen gas permeability. This is caused by the barrier properties of the clay layers dispersed in the composite. In general, C16‐MMT is more effective than C12‐MMT in increasing both the tensile property and the gas barrier in a polyimide matrix. Intercalations of the polymer chains in clay were examined through wide‐angle X‐ray diffraction (XRD) and electron microscopies (SEM and TEM).
Crystallization kinetics by differential scanning calorimetry for PCL/starch and their reinforced sisal fiber composites
Authors: Cyras Viviana P. , Vázquez Analía , Kenny José M.
Published: April 2004

Calorimetric results obtained by differential scanning calorimetry (DSC) have been used to develop a kinetic model for the crystallization behavior of PCL/starch and their composites with sisal fibers. The model takes into account the effects of nucleation and crystal growth, and it is able to describe the isothermal and non‐isothermal conditions, especially for the low cooling rates. The effect of the sisal fiber has also been analyzed. The Avrami exponent was 2.0 for the crystallization of PCL/starch and sisal fiber reinforced composite. The activation energy of the crystallization process was 4.3 and 4.0 kJ/mol for PCL/starch and sisal composite, respectively. The induction time of the crystallization and the crystallization rate was not influenced by the presence of sisal fiber.
Thermoforming shrinkage prediction
Authors: Xu Haihong , Kazmer David O.
Published: April 2004

Most thermoforming product development processes rely on costly and time‐consuming forming trials to determine the adequacy of the mold and process. In this paper, an analytical method is developed for shrinkage predictions on the basis of a visco‐elastic constitutive material model with initial conditions from a commercial thermoforming simulation. The theoretical analysis has been developed to accommodate different sets of materials, process conditions, and mold geometry. The shrinkage model consists of a transient thermal analysis for temperature solution; a stretching phase analysis for Inflation‐induced stress estimation; a post‐contact analysis for thermal stress and relaxation; and a post‐molding strain analysis based on stress solution. The shrinkage prediction analysis has been developed and validated with a complex geometry thermoforming application. The results indicate that the shrinkage estimates provided by the analysis were within the objective tolerances of 0.1%, as measured in terms of absolute prediction error of part dimensions.
Viscoelastic simulation of film casting process for a polymer melt
Authors: Satoh Naoki , Tomiyama Hideki , Kajiwara Toshihisa
Published: April 2004

Numerical simulations of the film casting process were performed using a finite element method for Newtonian and viscoelasttc fluids. We simplified the governing equations by the assumption that the stress and velocity gradients in the thickness direction were negligible, and obtained the film thickness and mean value of stress and velocity components in the thickness direction as variables. Viscoelasticity was described by the Larson model with multiple relaxation times. Non‐isothermal conditions were considered by applying the time‐temperature superposition law. The simulation results for the several kinds of commercial low‐density polyethylenes wore compared to the experimental data for a laboratory‐scale process at l90°C and a commercial‐scale process at 310°C. The film width and film thickness distribution at chill roll, and the change of film width were in good agreement for the laboratory‐scale process, but the agreement for the commercial‐scale process was; not as good. In the simulation of the commercial‐scale process at high temperature, the value predicted by the use of the Viscoelasticity for the original pellet showed poor agreement owing to the change of Viscoelasticity in the process. The agreement was improved by the use of the Viscoelasticity for the processed resin, which was changed from the original one. Next, viscoelastic effects on neck‐in and edge bead phenomena were investigated. The neck‐in and edge bead phenomena were considered to be affected by both the uniaxial elongational viscosity and planar elongational viscosity.
Evaluation of the derivatives of the strain energy function with respect to strain invariants for carbon black–filled EPDM
Authors: Kakavas P. A.
Published: April 2004

The experimental and theoretical investigation of the mechanical properties of an ethylene‐propylene‐diene terpolymer (EPDM) elastomer reinforced with carbon black was examined. The material constants of the testing material were determined by plotting the stress‐strain experimental curve in a reduced stress versus the inverse stretch diagram. The Ogden equation was used for the strain energy function to fit uniaxial experimental stress‐strain curves. The characterization of the material was examined using the contour maps of ∂W/∂I1 and ∂W/∂I2, i.e., of the derivatives of strain energy function with respect to strain invariants I1 and I2.
NIR, DSC, and FTIR as quantitative methods for compositional analysis of blends of polymers obtained from recycled mixed plastic waste
Authors: Camacho Walker , Karlsson Sigbritt
Published: April 2004

Methods for the determination of the composition of two binary blends in mixtures of recycled polymeric materials were analyzed and compared. Recycled polypropylene/polyethylene (PP/HDPE) and recycled poly(acryl‐butadiene‐styrene) and polypropylene(ABS/PP) were used to develop and validate the methods. Diffuse reflectance near infrared spectroscopy (NIRS) offers high sensitivity and ease of operation and a possibility to perform multivariate data analysis. In comparison, differential scanning calorimetry (DSC) and Mid‐IR, which are commonly used for this purpose require certain sample preparation and are indeed time consuming. In addition, the low sensitivity of these two methods to concentrations lower than 1% wt makes their application in quality control of recycled polymers inappropriate. NIR can be used for estimating the composition of the recyclate on‐line in only a few seconds, no sample preparation is required, and high precision is achieved. We obtained a root mean square error of prediction (RMSEP) equal to 0.21% wt in the interval from 0‐15% wt of PP in HDPE and a RMSEP equal to 0.91% wt in the interval 0‐100%. For blends of PP/ABS a RMSEP of 0.74% wt in the range 0‐100% and 0.32% wt in the range 0‐15% wt PP was calculated. Most of the variation in the spectral data with respect to the polymer blend composition for all the studied blends were explained by two principal components (PC). The optimal number of factors (PC) was determined by cross‐validation analysis.
The effect of the feed section groove taper angle on the performance of a single‐screw extruder
Authors: Sikora Janusz W.
Published: April 2004

A new mechanism is described that allows adjustment of the groove geometry in grooved feed extruders. This mechanism enables efficient, continuous and independent change of the groove geometry during the extrusion process. The patented solution of the activated grooved feed section enables one to change the number of grooves, taper angle and, connected with it, groove depth. The paper contains the graphical presentation of the selected results of experimental studies of autothermal extrusion of a medium density polyethylene in an extruder with the grooved feed section in which the groove taper angle, and thus groove depth, was changed during the extrusion process. The influence of changing the groove taper angle in the range from 0 to 5.236 × 10−2 rad and screw speeds ranging from 177 to 279 rev/min on extruder output was studied. The energy efficiency of the extruder was studied as well.
Effect of molecular weight on crystallization and melting of poly(trimethylene terephthalate). 1: Isothermal and dynamic crystallization
Authors: Wang Xue‐Song , Yain Deyue , Tian Guo‐Hua , Li Xin‐Gui
Published: April 2004

The crystallization behavior of poly(trimethylene terephthalate) as a function of molecular weight was investigated under isothermal and dynamic cooling conditions using a differential scanning calorimeter (DSC) and polarized light optical microscopy (POM). THe overall rate of bulk crystallization increased with molecular weight. An Avrami analysis of the isothermal crystallization kinetics indicated that the crystallization rate constant increased with increasing molecular weight. The Avrami exponent, n, approached 2 and was nearly independent of both molecular weight and temperature. The modified Avrami analysis developed by Jeziorny and Ozawa was applied to the dynamic crystallization data. At the same cooling rate, higher molecular weight resulted in a narrower crystallization peak, higher onset crystallization temperature, and larger rate constant (Zt)1/n. Higher molecular weight resulted in larger cooling function of dynamic crystallization K(T) and lower Ozawa exponent m. For dynamic crystallization, the average value of the Avrami exponent varied from 3.4 to 3.8 and the average value of the Ozawa exponent changed from 2.3 to 2.6 as the number‐average molecular weight changed from 13,000 to 67,000. Morphology studies indicated that both the isothermal crystallization and the dynamic crystallization of PTT from the melt were thermal nucleation processes, and for a fixed temperature between 190°C and 210°C, the nucleation density increased with increasing the molecular weight.
Distributive mixing in a single‐screw extruder—evaluation in the flow direction
Authors: Rwei Syang‐Peng
Published: April 2004

This study investigates distributive mixing in the flow direction for a single‐screw extruder. WIth a custom‐designed transparent extruder, an Image Analysis System, and a newly defined parameter, i.e., distribution index, the distribution mechanism is thoroughly examined with respect to various processing conditions or screw designs. Experimental results indicate that the longitudinal distribution can be enhanced with an increasing RPM, a longer metering section, or a decreasing diameter of the die. However, a plateau region occurs when an optimum condition exists for the RPM and the length of the metering section. In addition, an extruder modified with a barrier, pin‐elements, or high helix angle performs better in the longitudinal mixing than the conventional one. Our results further demonstrate that leakage flow significantly enhances mixing in the flow direction.
The application of an integral type constitutive equation to numerical flow analyses of viscoelastic fluid in unsteady flow
Authors: Shiraishi Yutaka , Narazaki Norio , Kikutani Takeshi
Published: April 2004

The applicability of the Wagner model to numerical flow analyses of the injection molding process is investigated under the following approximations: the strain and stress histories of the molten polymer before the injection is negligible, and the flow field in a mold cavity is treated as Hele‐Shaw flow. A comparison between the results for simple step‐strain‐rate flow calculated with the Wagner model and that calculated with the Leonov model suggests that the Wagner model is superior to the Leonov model for unsteady flow because of its stability and accuracy. Therefore, numerical flow analysis software of a viscoelastic fluid in the injection molding process is developed using the Wagner model. For the analysis, the velocity profile of a Newtonian fluid is used instead of that obtained through iterative calculation. The validity of the developed program is confirmed through a comparison of the results of the computation for two simple flow velocity histories with the analytical results from the Wagner model. Furthermore, the computation time of the developed software is only 1.4 times greater than that of the previous numerical flow analysis of a viscous fluid.
Characterization of anisotropic structure in poly(phenylene vinylene) films
Authors: Ou Runqing , Samuels Robert , Wang Xingwu , Gregory Richard
Published: April 2004

The evolution of the anisotropic structure in poly(phenylene vinylene) (PPV) films was studied using three nondestructive characterization techniques: prism waveguide coupling, infrared dichroism, and X‐ray diffraction. The anisotropic PPV films were thermally converted from precursor drawn films at fixed length. The three‐dimensional refractive indices, infrared dichroic ratios, crystal alignment, and orientation function were determined from each film. The results show that converted cast PPV film has a highly planar structure with a tendency for the PPV chains to orient parallel to the film surface. The a axis of the crystal unit cell is normal to the film plane. One‐way stretching converts the film from a planar structure to a uniaxial structure.
Adhesion enhancement of evaporated copper on HDPE surface modified by plasma polymerization of glycidyl methacrylate
Authors: Zou X. P. , Kang E. T. , Neoh K. G.
Published: April 2004

Surface modification of high‐density polyethylene (HDPE) surfaces by plasma polymerization of glycidyl methacrylate (GMA) (the pp‐GMA‐HDPE surfaces), in the absence and presence of Ar plasma pre‐activation of the HDPE substrates, was carried out to enhance the adhesion of the polymer with evaporated copper. THe FTIR and X‐ray photoelectron spectroscopy (XPS) results suggested that the epoxide functional groups on the pp‐GMA‐HDPE surfaces had been preserved to various extents, depending on the RF power used during plasma polymerization. Ar plasma pre‐activation of the HDPE surface led to the strong interaction of the pp‐GMA layer with the HDPE substrate. GMA plasma polymerization at low RF powers and in the presence of Ar plasma pre‐activation was shown to be an effective method for enhancing the adhesion of HDPE with the evaporated Cu. An optimum adhesion strength of about 16 N/cm was achieved between the evaporated Cu and the pp‐GMA‐HDPE surface prepared by plasma polymerization of GMA at 5 W, 100 Pa, 20 sccm for 5 s on the HDPE surface pre‐activated by Ar plasma at 35 W, 100 Pa 20 sccm for 20 s. The adhesion enhancement of the Cu/pp‐GMA‐HDPE assemblies in the presence of Ar plasma pre‐activation of the HDPE substrate was attributed to the covalent bonding of the plasma‐polymerized GMA (pp‐GMA) layer with the HDPE surface, the preservation of the epoxide functional groups in the pp‐GMA layer, and the spatial interactions of pp‐GMA chains with the evaporated Cu matrix.
Epoxy + montmorillonite nanocomposite: Effect of composition on reaction kinetics
Authors: Butzloff Peter , D'Souza Nandika Anne , Golden Teresa D. , Garrett David
Published: April 2004

The objective of this investigation is to determine the effects of montmorillonite layered silicates on the curing kinetics of an epoxy resin. Differential scanning calorimetry was used to probe the changes in reactivity due to the presence of montmorillonite and due to the diamine hardener. The enthalpy of polymerization was strongly affected at compositions greater than 5% (wt) montmorillonite for epoxy + montmorillonite reactions. On introduction of the hardener, epoxy + amine kinetics dominate the reaction for all compositions except for a montmorillonite concentration of 2.5 wt%. X‐ray diffraction was used to determine if the reacted system was exfoliated. The results show a strong montmorillonite composition dependence on the exfoliated state. Transmission electron microscopy of the cured epoxies confirmed a mixed intercalated and exfoliated dispersion at compositions having montmorillonite greater than 2.5 wt%.
The effects of specimen size and testing conditions on fracture toughness evaluation of polypropylene homopolymer
Authors: Santarelli Edgardo , Frontini Patricia
Published: April 2004

The results of an experimental test program performed to investigate the influence of specimen dimensions and testing rate conditions on room temperature fracture toughness of PP homopolymer are presented. The material displayed nonlinear load‐displacement behavior and exhibited small amounts of slow crack growth (ductile tearing) prior to cleavage instability, which invalidates the direct application of the current standards for the determination of KICin polymers. Data points were considerably scattered consistently with typical ductile‐brittle transition patterns. The resulting load‐displacement diagrams were analyzed in terms of KQ, KMAX, and the ratio PMAX/PQ. THe fracture toughness at instability, JC, was also computed and plotted against the amount of stable crack growth in order to construct J‐R curves as a function of size and strain rate. From these curves an alternative critical fracture parameter, KJIC, was calculated. Weibull statistics were used as a tentative approach for treating the scatter of fracture toughness of polypropylene homopolymer in large samples, which exhibited restricted ductile tearing. The significance of each of these methods and the validity and size independence of the corresponding parameters are discussed.
Wall thickness distribution in thermoformed food containers produced by a Benco aseptic packaging machine
Authors: Ayhan Zehra , Zhang Q. Howard
Published: April 2004

Effects of process parameters such as forming temperature, forming air pressure and heating time on wall thickness distribution in plug‐assist thermoformed food containers using multilayered material were investigated. Multilayered rollstockbase material formed into containers by thermoforming process using a Benco aseptic packaging machine. Forming temperatures in the range of 131–170°C, airforming pressures of 2, 3, 3. 5 and 4 bars, and heating times of 66, 74, 84, 97 and 114 seconds were used in the thermoforming process. Analysis of wall thickness data obtained for the thermoforming parameters used in this study showed that wall thickness was significantly affected by forming temperature, pressure and heating time at 0.05 significance level. Besides the processing parameters, wall location, container side, and their interactions significantly affected wall thickness. Forming temperature was found to be the principle parameter influencing wall thickness distribution in a plug‐assist thermoforming operation. The optimum operating conditions of the packaging machine for the thermoforming process are: 146–156°C for forming temperature, 2–4 bars for air‐forming pressure and 74–97 seconds for heating time.
Effect of elongational viscosity on axisymmetric entrance flow of polymers
Authors: Gupta Mahesh
Published: April 2004

A finite element simulation of the flow in a channel with an abrupt contraction is presented. The effects of the shear and elongational viscosities of a polymer on the entrance flow are analyzed employing a truncated power‐law model. The power‐law index and the strain rate characterizing the transition from Newtonian to power‐law behavior for the elongational viscosity are treated as being independent of the values of these two parameters for the shear viscosity. The effect of flow rate on entrance flow is also analyzed. It is confirmed that the Trouton ratio is important in determining the recirculating vortex and the extra pressure loss in entrance flow. Extra pressure loss and vortex length predicted by a finite element simulation of entrance loss are compared with the corresponding predictions from Binding's approximate analysis.
Conductive composites of UHMWPE and ceramics based on the segregated network concept
Authors: Bouchet J. , Carrot C. , Guillet J. , Boiteux G. , Seytre G. , Pineri M.
Published: April 2004

The manufacturing of composites of ultra high molecular weight polyethylene and ceramics with conductive properties has been investigated. Attention has been focused on the lowering of the amount of filler necessary to achieve low resistivity. Using segregated networks, mixing large polymer particles and submicron metal or conductive ceramic particles may be an interesting route, provided that the processing method enables to generate the desired structures. Because sintering avoids the intimate blending of the components, it is a suitable technique for this aim. The combined effects of temperature, pressure and sintering time have been investigated. The influence of the blending of the solids on the covering of the polyethylene particles before the sintering has also been pointed out. The typical features related to the concept of a segregated network are discussed in connection with the morphologies of the polymer and ceramic particles. The successful application of the reduction of the percolation threshold by a segregated network in conductive composites of polymer and metallic particles is described.
Dispersity improvement in solvent casting particle/polymer composite
Authors: Schruben Dale L. , Gonzalez Perla
Published: April 2004

The standard solvent casting method for preparing particle/polymer composites is reviewed. Unless extraordinary conditions are used, the standard process is restricted to thin films because of difficulties (blistering) that occur during the solvent removal. These thin films have better dispersion and less clustering of the metal particle loading than if comparable materials were made by adding metal powder into a polymer melt. However, the best dispersion is obtained in a new process where thin films in the standard process go through a redissolving step (or steps) described herein. Characterization by the large particle end of the particle size distribution confirms the reduced clustering tendency of particles in the new process.
Effects of the shape of the energy director on far‐field ultrasonic welding of thermoplastics
Authors: Chuah Yew Khoy , Chien Liang‐Han , Chang B. C. , Liu Shih‐Jung
Published: April 2004

An energy director is widely used in ultrasonic welding to increase the welding speed and quality. In the present work, three different types of energy directors were studied—namely, a triangular, a rectangular, and an innovative semicircular energy director. Experiments were performed using far‐field test samples made of amorphous‐type (ABS) and semicrystalline‐type (PE) thermoplastics. It was found that the weld time is an important parameter of ultrasonic welding for the three types of energy directors studied. Weld pressure has different effects for the types of plastics tested. Increasing the weld pressure will decrease the welding efficiency for ABS. But for PE, increasing the weld pressure to four bars will increase the welding efficiency. The shape of the energy director was found to significantly affect the welding efficiency. In comparison, a semicircular shape was found to yield the highest welding efficiency under the same welding conditions and the triangular shape the lowest. Temperature measurements at the triangular energy director during the welding process indicate that the energy director absorbed 48.5% of the welding energy for ABS and 21.1% for PE. The different energy absorption rates are probably due to the difference in elasticity and viscosity between amorphous (ABS) and semicrystalline (PE) plastics.
Mixing mechanism of three‐tip kneading block in twin screw extruders
Authors: Yoshinaga Makoto , Katsuki Shingo , Miyazaki Masaru , Liu Lijie , Kihara Shin‐Ichi , Funatsu Kazumori
Published: April 2004

In recent years, twin screw extruders have been applied to various kinds of polymer processing. It has been important to find their optimum geometrical configurations and operational processing conditions for the best performance of extrusions and products. Many engineers have been evolving numerical and the experimental methods to characterize the mixing performance for twin screw extruders. We have carried out three‐dimensional flow simulations of kneading blocks in intermeshing co‐rotating twin screw extruders by using the finite element method to quantify their ability in distributive and dispersive mixing. We discuss their performance in distributive mixing for three different type of kneading blocks in terms of the residence time distribution and the nearest distance between markers at various periods of time, by using the marker tracking method. Those numerical techniques and applications of mixing indices have enabled us to quantify and evaluate their abilities in distributive mixing of kneading blocks in twin screw extruders.
Boron nitride as a processing aid for the extrusion of polyolefins and fluoropolymers
Authors: Rosenbaum Eugene E. , Randa Stuart K. , Hatzikiriakos Savvas G. , Stewart Charles W. , Henry Donald L. , Buckmaster Marlin
Published: April 2004

The influence of a new processing additive (fine particles of boron nitride) on the processability of polyolefins and fluoropolymers in extrusion is studied. The equipment used includes an Instron capillary rheometer with two types of dies, namely capillary dies and special annular dies (Nokia Maillefer wire coating crosshead) attached to the rheometer, and an extruder. Two metallocene polyethylenes and several Teflon® fluoropolymers were tested using these two pieces of equipment. The additive had a significant effect on the extrudate appearance of polyethylene and fluoropolymer particularly in the crosshead dies. It was found to eliminate surface melt fracture and to postpone the critical shear rate for the onset of gross melt fracture to significantly higher values depending on resin type, temperature, and additive concentration (typically 0.005% to 0.5%). To explain the possible mechanism for the effect of the additive on the processability of the resins, rheological measurements using both parallel‐plate and sliding‐plate rheometers were carried out. The rheology of the resins did not seem to change significantly with the addition of boron nitride except for the low‐shear‐rate (low‐frequency) range, where the behavior of the filled resin was found to be similar to that of a crosslinked polymer or a phase‐separated entangled blend. Practical wire coating and tubing extrusion studies for these resins were also carried out.
The brittle‐ductile transition temperature of polycarbonate as a function of test speed
Authors: Gaymans R. J. , Hamberg M. J. J. , Inberg J. P. F.
Published: April 2004

The fracture behavior of polycarbonate was studied as a function of temperature (−80°C to +80°C) and test speed (10−5 to 10 m/s) using an instrumented, singleedged, notched tensile test (SENT). SENT tests give information on the fracture stress, fracture displacements, and fracture energies of polycarbonate, and from these data the average crack speeds were calculated and the brittle‐ductile transitions were determined. The fracture stress and the fracture energies of ductile fracturing samples increased with increasing test speed. The fracture surfaces were studied by scanning electron analysis, and sometimes a mixed mode fracture, part ductile and part brittle, could be seen. At high test speeds, a sharp brittle‐ductile transition was observed, while at low test speeds the transition was more gradual, via a mixed mode region. This mixed mode region decreased in size with increasing test speed and was absent at the higher test speeds. The average crack speeds in the ductile region were directly related to the test speeds. The brittle‐ductile transition temperature increased with the logarithmic of the test speed.
Carboxyl terminated polyamide 12 chain extension by reactive extrusion using a dioxazoline coupling agent. Part I: Extrusion parameters analysis
Authors: Chalamet Yvan , Taha Mohamed , Vergnes Bruno
Published: April 2004

Condensation reaction between a carboxyl terminated polyamide 12 (CTPA) (Mn = 2000 g mol−1) and a dioxazoline [2,2′‐(1,3‐phenylene)‐bis(2‐oxazoline)] (OO) was achieved by reactive extrusion. Extrusion parameters effects on the process were analyzed through residence time distribution (RTD) and conversion distribution (CD) evolutions. RTD was measured using ultraviolet and ultrasonic detectable tracers. RTD measured along the extruder screws showed a decrease of the dimensionless variance (σ) with the reaction progress. Comparing measured molar masses and dispersity with those calculated using CD, competition between condensation and chain scission was detected. Effects of barrel temperature, screw profile, rotation speed and viscous dissipation on the reactive system evolution were analyzed and used for the process optimization. It was shown that a polyester amide with a Dpn 12 can be obtained using this dioxazoline coupling agent by reactive extrusion.
Kinetic parameters estimation for unsaturated polyester‐styrene systems
Authors: Lin Chao‐Ming , Weng Cheng‐I , Ho Cheng‐Ter
Published: April 2004

A model modified from the traditional kinetic model is proposed for the determination of the kinetic parameters describing the autocatalytic reaction of polyesterstyrene systems. The proposed method utilizes three experimental data values from the \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{d\alpha }}{{dt}} $\end{document} vs. α curve—the initial value, the peak value, and the maximum value—to solve the kinetic parameters. The curing reaction of a thermosetting polyester was investigated by using the isothermal and dynamic techniques of differential scanning calorimetry (DSC). The results show that the reaction orders m, n and the ultimate conversion are not constant, and instead are functions of temperature. The estimated kinetic curves agree well with the experimental DSC data.
Characterization of UV irradiated space application polymers by spectroscopic ellipsometry
Authors: Bungay Corey L. , Tiwald Thomas E. , Devries Michael J. , Dworak Brad J. , Woollam John A.
Published: April 2004

Materials deployed on long‐duration space missions such as the Hubble Space Telescope (HST) and the proposed International Space Station (ISS) are subject to high ultraviolet (UV) radiation fluences. Some UV radiation present in space has photon energy high enough to dissociate organic polymer molecular bonds. Induced chemical structure modifications can cause changes in optical, structural, and thermal properties. The present work investigates UV radiation effects on DuPont Kapton® H polyimide, polyarylene ether benzimidazole (PAEBI), and DuPont Teflon® fluorinated ethylene‐propylene (FEP). UV irradiated polymers were characterized with in situ and ex situ spectroscopic ellipsometry (SE). Ellipsometric data acquired on UV modified polymers were best modeled as an exponentially graded layer, as opposed to a single layer or linearly graded layer model. Because photon intensity decays exponentially as a function of depth into absorbing materials, an exponentially graded model should be the most physically realistic. Ellipsometric data provided information about changes in UV absorption spectra, depth of damage, and growth trends in the damaged layer.
On the effect of crystallinity on the elastic properties of semicrystalline polyethylene
Authors: Doyle Michael J.
Published: April 2004

The small strain elastic response of a semicrystalline polyethylene has been simulated with a simple finite element model comprising a composite microstructure of alternating amorphous and crystalline layers arranged in a multi‐layered spherical shell structure. The crystalline lamella is modeled as an isotropic solid having the experimentally determined modulus properties of bulk linear polyethylene and extrapolated to 100% crystallinity. The amorphous layer is modeled as an elastomeric solid with the modulus that of molten linear polyethylene extrapolated to room temperature. Assuming constancy of these phase properties, the finite element calculations of elastic modulus versus crystallinity fit quite well the experimental data of Crist for linear polyethylene above 55% crystallinity. At lower crystallinity the experimental modulus data, which are for copolymers, fall below the model calculations. Two possible causes are discussed: the loss of deformation constraint in lamellae of finite and decreasing width as crystallinity declines, and an expansion of the crystal lattice as a result of the crowding of the comonomer units excluded from the crystal lamella. Either effect would reduce both the modulus and the yield stress as is observed.
Modeling of peroxide initiated controlled degradation of polypropylene in a twin screw extruder
Authors: Berzin F. , Vergnes B. , Dufossé P. , Delamare L.
Published: April 2004

In this work, experimental and theoretical studies of the free‐radical initiated molecular weight degradation of polypropylene in a modular self‐wiping corotating twin screw extruder have been investigated. Our objective was to build a model that would be able to predict the evolution of the average molecular weight along the screws, in relation to the processing conditions and the geometry of the twin screw extruder. Modeling the process involves resolving interactions occurring between the various flow conditions encountered in the extruder, the kinetics of the reaction and the changes in viscosity with changes in molecular weight. We have studied the influence of operating parameters such as the initial peroxide concentration, the feed rate and the screw speed on the degradation reaction. Good agreement was found between theoretical results and experimental values obtained by size exclusion chromatography measurements.
Correlation of thermally stimulated current and blow molding condition in poly(ethylene terephthalate) bottles
Authors: Satoto Rahmat , Hama Takashi , Morikawa Junko , Hashimoto Toshimasa
Published: April 2004

Thermally stimulated current (TSC) was used to study molecular relaxations in polyethylene terephthalate (PET) bottles. Unstretched PET film, which was used as a model for the bottle preform, exhibited two peaks at 77 and 90°C that correspond to the α and ρ relaxation processes, respectively. The bottles exhibited only the ρ relaxation, which is located within the temperature range for blow molding PET bottles. The α peak is associated with the main glass transition temperature (Tg) and the ρ peak may be associated with a second Tg. The second Tg is attributed to a “constrained state,” which shows dipolar behavior. Heat‐shrinkage behavior was examined at 90°C. The maximum TSC (Im) of the ρ peak decreased with increasing heat set temperature, and with decreasing shrinkage. Bottles blown at 113°C showed a lower Im and shrinkage than those blown at 103°C for equivalent heat set temperatures. The higher blowing temperature allowed a higher stretch speed that produced higher crystallinity bottles with self‐heat generation during rapid deformation. A relationship between the shrinkage mechanism and the dipole relaxation was proposed.
Continuous production of solid polystyrene in back‐mixed and linear‐flow reactors
Authors: Chen Chi‐Chin
Published: April 2004

A mathematical model has been developed to predict the steady state performance of a continuous bulk styrene polymerization process with catalytic initiation for solid polystyrene. The polymerization section contains one boiling CSTR, followed by multiple linear‐flow reactors. The devolatilization section consists of two polymer pre‐heaters and two high‐solids flashes. The polymer moment equations were solved simultaneously with the reactor modeling equations. The non‐linear algebraic equations were solved by a Newton‐Raphson iteration technique to give the steady‐state styrene monomer weight fraction in a CSTR. The coupled, non‐linear ordinary differential equations were numerically integrated using a single‐step, 4th‐order Runge‐Kutta technique, followed by a multi‐step Adams‐Moulton technique. The resulting computer simulation model is capable of evaluating how the production rate and product quality are affected by feed composition, temperature, initiator type, initiator concentration, and residence time. Several case studies were given for commercially important crystal‐clear and impact‐resistant resins. A binary initiation system gives a good balance of monomer conversion, polymer molecular weights, and rubber grafting compared to a single initiation system. The styrene dimer/trimer occur in low concentrations but can be substantially reduced with a low temperature initiator. The ideal mean residence time is approximately one minute or less in a shell‐and‐tube devolatilization pre‐heater. Low flash chamber vacuum is more effective than high polystyrene melt temperature to reduce the volatile content of the final product. The water injected to the low volatile melt shows promising improvement in the second‐stage polystyrene devolatilization.
Polyurethane/poly[bis(carboxylatophenoxy)phosphazene] blends and their potential as flame‐retardant materials
Authors: Reed Carey S. , Taylor Jonathan P. , Guigley Kevin S. , Coleman Michael M. , Allcock Harry R.
Published: April 2004

A functionalized polyphosphazene, poly[bis(carboxylatophenoxy)‐phosphazene], was blended with a structural polyurethane via reactive mixing of the polymer with diisocyante and diol prepolymers. The thermal stabilites of the resultant foams were analyzed by thermogravimetric analysis (TGA). The char yields at both 400°C and 600°C increased relative to the pure polyurethane upon increasing the amount of polyphosphazene from 5 wt% to 20 wt%. At higher incorporations, the char at 400°C remained the same, but the char at 600°C continued to increase. The combustion behavior of these foams was analyzed both qualitatively, by a horizontal flame test, and quantitatively, by oxygen index (OI) measurements. Both of these tests indicated an increase in flame resistance at loadings of 20 wt% and above.
Optimizing the impact strength of rotationally molded parts
Authors: Liu Shih‐Jung , Lai Cheng‐Chih , Lin Shun‐Tien
Published: April 2004

Rotational molding of thermoplastics has become an important process in industry. However, the optimization of this technique has been essentially based on a trial‐and‐error process. In this report, an L'16 experimental matrix design based on the Taguchi method was conducted to optimize the impact strength of rotationally molded parts. Oven temperature and oven time were found to be the principal factors affecting the impact property of rotationally molded thermoplastics. Density and melt flow index measurements were also employed to identify the material and structural parameters. The part density increased with increasing total energy transmitted into the molding system. The melt flow index provides an easy indication of the mechanical properties of rotationally molded parts.
Dynamic slip and nonlinear viscoelasticity
Authors: Lan Seon Keat , Giacomin A. Jeffrey , Ding Fan
Published: April 2004

Several significant problems arise when film is fabricated on a large scale. One of these is the appearance of irregularities on the extrudate surfaces when the polymer melt is extruded at high rates. These irregularities vary in intensity and form and are generally known as sharkskin melt fracture. This phenomenon, which occurs when the wall shear stress exceeds a critical value, is a limiting factor for production rates in many industrial extrusion operations such as film blowing of polyethylene. We used a sliding plate rheometer incorporating a shear stress transducer to study slip in both steady and unsteady flows. By combining a dynamic slip model with a nonlinear viscoelastic constitutive model, we determined the slip model parameters for LLDPE film resin with and without a fluoropolymer sharkskin suppressant. The models give good prediction of our slip data in steady shear but show insufficient gap dependence in exponential shear. Our own film blowing studies demonstrated the efficiency of the sharkskin suppressant; it has more than doubled the throughput in our laboratory setup. The fluoropolymer additive was found to profoundly affect both the steady and dynamic slip parameters. Hence, the sharkskin suppressant alters how the LLDPE remembers its past slipping motions.