bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal and mechanical properties of a hydroxyl‐functional dendritic hyperbranched polymer and trifunctional epoxy resin blends
Authors: Ratna D. , Simon G. P.
Published: April 2004

Curing characteristics of blends of a hydroxyl‐functionalized dendritic hyperbranched polymer (HBP) and a triglycidyl p‐amino phenol (TGAP) epoxy resin have been studied. THe HBP strongly enhances the curing rate owing to the catalytic effect of the hydroxyl groups. THe thermal and dynamic viscoelastic behavior of the blends of various compositions (HBP content 0–20%) have been examined and compared to the neat TGAP matrix. THe glass transition temperature (Tg) gradually decreases with increase in HBP concentration. The blends show a higher impact strength compared to neat TGAP. Scanning electron microscopy analysis indicates a single‐phase morphology.
Coating window for double layer extrusion slot coating of poly (vinyl‐alcohol) solutions
Authors: Lu Shih‐Yuan , Lin Yu‐Ping , Liu Ta‐Jo
Published: April 2004

The expansion of coating windows for low‐viscosity poly(vinyl‐alcohol) (PVA) solutions is achieved via utilization of a higher viscosity PVA solution as the stabilizing carrier layer. It is found that PVA solutions of higher viscosities possess a higher degree of processability than those of lower viscosities, and can serve as a stabilizing carrier layer when coating lower viscosity PVA solutions. The stabilizing effect of the carrier layer enhances with increasing viscosity of the carrier layer, but reaches a saturation state at a high enough viscosity. It is further found that the coating defects occurring at lower maximum coating speeds are dominated by the lower, carrier layer, while those at higher maximum coating speeds are controlled by the upper, carried layer. Consequently, there exists an optimal layer flow rate ratio at which the coating window is the largest. A new type of coating defect, called spreading failure, is observed for coating situations involving a thin and much less viscous upper layer.
Influence of initial sheet temperature on ABS thermoforming
Authors: Lee Je Kyun , Virkler Terry L. , Scott Chris E.
Published: April 2004

Understanding the effects of material and processing parameters on the thermoforming process is critical to the optimization of processing conditions and the development of better materials for high quality products. In this study we investigated the influence of initial temperature distribution over the sheet on the part thickness distribution of a vacuum snap‐back forming process. The linear viscoelastic properties along with the Wagner two parameter nonlinear viscoelastic constitutive model were utilized for numerical simulation of the thermoforming operation. Simulations of pre‐stretched vacuum thermoforming with a relatively complex mold for a commercial refrigerator liner were conducted. THe effects of temperature distribution over the sheet on the part thickness distribution were determined to examine process sensitivity and optimization. Effects of the temperature distribution on the material rheology and polymer/mold friction coefficient are primarily responsible for the changes in the thickness distribution. We found that even small temperature differences over the sheet greatly influenced bubble shape and pole position during the bubble growth stage and played a critical role in determining the part thickness distribution. These results are discussed in terms of rheological properties of polymers such as elongational viscosity and strain hardening.
Processing of short‐fiber reinforced polypropylene. I. Influence of processing conditions on the morphology of extruded filaments
Authors: Barbosa Silvia E. , Kenny José M.
Published: April 2004

An experimental investigation of the processing of glass fiber reinforced polypropylene is presented. Final fiber orientation distribution, fiber distribution in filament sections, rheological properties, final fiber length distribution and surface morphology were analyzed. This analysis was done taking into account the quantity of fibers and their interactions and flow conditions. The final fiber orientation increased when shear rate increased and fiber concentration decreased. Moreover, inhomogeneities in fiber distribution increased as the concentration of fibers decreased. The density profile showed a significant variation with fiber concentration, but it was not dependent on the shear rate applied. The viscosity showed a linear dependence with shear rate. The average fiber length and the breadth of this distribution decreased with the increasing fiber concentration and extrusion rate. The extruded filament surface showed minor roughness when the shear rate increased or when the fiber concentration decreased. The results of this experimental characterization give useful information to determine the influence of the processing variables on the final properties of short‐fiber reinforced polypropylene and constitutes the first part of a more ambitious project that also includes the development of a modeling strategy of the processing behavior for short‐fiber composites.
Biodegradable drag reducing agents and flocculants based on polysaccharides: Materials and applications
Authors: Singh Ram Prakash , Karmakar G. P. , Rath S. K. , Karmakar N. C. , Pandey S. R. , Tripathy T. , Panda J. , Kanan K. , Jain S. K. , Lan N. T.
Published: April 2004

Organic and inorganic flocculants are used in treatment of water and industrial effluents. Polymeric flocculants, synthetic as well as natural, because of their natural inertness to PH changes, low dosage, and easy handling, have become very popular in industrial effluent treatment. It has been established in the authors' laboratory that by grafting polyacrylamide branches on rigid backbone of polysaccharides, the dangling grafted chains have easy approachability to contaminants in effluents. Thus grafted polysaccharides are very efficient, shear stable and biodegradable flocculants. They also exhibit turbulent drag reducing characteristics. Among grafted guar gum, xanthan gum, carboxymethyl cellulose, and starch, grafted starch performs the best. Starch consists of amylose (a low molecular weight linear polymer) and amylopectin (a high molecular weight, branched polymer). The grafted amylopectin is found to be the best flocculant for various kinds of industrial effluents, providing credibility to the above‐cited model. In the present paper, the details about grafted polysaccharides as turbulent drag reducers and flocculants are given, along with their applications.
Enhanced shielding effectiveness of polymer matrix composite enclosures utilizing constraint‐based optimization
Authors: Mottahed Behzad D.
Published: April 2004

Many interrelated factors must be considered in the design of an electronic system. Finding the optimum design condition having been subjected to various design constraints is often not a trivial matter. Utilizing an approach to optimize the design of electronic systems would have many advantages. A design optimization approach allows designers to study and optimize the various design alternatives. To illustrate this approach, in this study the optimum design of electronic enclosures from the viewpoint of electromagnetic shielding effectiveness is considered. An optimization problem has been formulated and the influence of several design variables in the definition of the objective function and constraints set is examined. To solve the problem, a non‐linear optimization solution technique is utilized that allows users to optimize an objective function bound by equality and inequality constraints. A case study is presented to illustrate the utility of this technique in selection of the best composite materials for maximum absorption against radiated energy, a case with application in radar.
Rate‐effect on fracture behavior of core‐shell‐rubber (CSR)‐modified epoxies
Authors: Xiao Keqin , Ye Lin
Published: April 2004

A bisphenol A diglycidylether (DGEBA) epoxy was modified with up to 20 wt% of a core‐shell rubber (CSR), and mechanical properties were investigated at different crosshead rates (from 0.5 mm/min to 500 mm/min). The yield strength and Young's modulus decreased almost linearly with increasing rubber content or decreasing crosshead rate. Fracture toughness, KIC, was significantly improved by the addition of CSR to the pure epoxy. The optimum rubber content was between 15% and 20% at the lowest crosshead rate (i.e. 0.5 mm/min) and shifted to higher rubber content at higher crosshead rates. KIC decreased slightly as the crosshead rate was increased from 0.5 mm/min and dropped significantly when the crosshead rate approached 500 mm/min. Rubber cavitation‐induced local plastic deformation was identified as the principal energy absorption mechanism, and it was independent of rubber content and crosshead rate. The variation of KIC with rubber content and crosshead rate correlated well with the length of the stress‐whitened zone.
Ultrasonic in‐line monitoring of polymer extrusion
Authors: Françla D. R. , Jen C.‐K. , Nguyen K. T. , Gendron R.
Published: April 2004

In‐line ultrasonic monitoring of polymer co‐extrusion and twin‐screw extrusion are presented. Co‐extrusion of high density polyethylene (HDPE) and a thermoplastic elastomer based on polypropylene‐EPDM (ethylene‐propylene‐diene monomer) has been investigated by ultrasonic sensors consisting of piezoelectric transducers and clad buffer rods. One extremity of the rod (probing end) was installed flush with the die surface so as not to disturb the material flow. The other end was air cooled in order to protect the transducer from excessive heating. This approach has been demonstrated to be quite convenient for monitoring and controlling industrial material processes: first, it can work at temperatures up to 1000°C; second, the clad buffer rod probing end can be machined to the same shape as those of commercial temperature and pressure sensors commonly used in the extrusion process. Therefore, no modifications are required for the installation in the original equipment. The information obtained includes the position of the interface between polymers and the stability of the process. The same ultrasonic probe has also been installed on a barrel of a twin‐screw extruder. This study was performed using polyethylene and polystyrene. It has been verified that the ultrasonic sensor can be successfully operated along the extruder screw and that the ultrasound can give access to the material properties while the polymer is being processed. This means that the technique can be exploited to monitor and control in situ the characteristics of the polymer being transformed in operations typically performed on twinscrew extruders, such as compounding, visbreaking or reactive extrusion.
Injection molding of poly(ethylene terephthalate): Differential scanning calorimetry and confocal micro‐raman spectroscopy investigations of the skin‐core morphology
Authors: Fernández M. R. , Merino J. C. , Pastor J. M.
Published: April 2004

The skin‐core structure of injection‐molded plates of poly(ethylene terephthalate) (PET) has been investigated using Confocal Micro‐Raman Spectroscopy (CMRS) and Differential Scanning Calorimetry (DSC). CMRS has proved to be a useful tool for finding out about quantitative conformational changes in polymeric materials. In order to obtain a complete picture of isomer distributions in the injection molded industrial PET samples, spectroscopic measurements were correlated with DSC measurements. The spectroscopic results reveal two different structural zones related to the fabrication process: a skin layer and the core. The correlation between the apparent degree of crystallinity obtained by DSC and the percentage of the trans isomer obtained by CMRS has allowed the latter parameter to be separated into crystalline and amorphous trans isomer and to follow its change along the injection molded plate.
Film casting of polyethylene terephthalate: Experiments and model comparisons
Authors: Acierno D. , Di Maio L. , Ammirati C. C.
Published: April 2004

Cast film extrusions were carried out on polyethylene terephthalate (PET), on a laboratory line. The thermal and the geometrical behavior of the film, in the region from die to chill roll, was studied in different working conditions. The experimental evaluations were performed with an Infrared Thermography (I.R.T.) apparatus. Simplified modeling, describing the non‐isothermal behavior of the web, was used to predict temperature, width and thickness of the film in machine direction (MD) as a function of the distance from the die. The above‐calculated profiles were compared to those obtained by experimental thermography maps. Measured temperatures resulted different between edge and center of film, i.e. transverse direction (TD) temperature profiles were highlighted. On the contrary, model temperatures are assumed varying only along the machine direction (MD) of web. Thus, from the comparison between experimental and theoretical results, an acceptable agreement was found only in some cases.
Model filled rubber. VI: Dynamic property dependence on filler particle size of rubber compounds during curing
Authors: Cai Jianfen J. , Salovey Ronald
Published: April 2004

The effect of particle size on curing kinetics and dynamic properties was examined with model filled rubber compounds containing monodisperse size crosslinked polystyrene (PS) particles synthesized from emulsifier‐free emulsion polymerization. In the process of curing, the magnitude of the dynamic moduli increased and the gelation time (GP) decreased as PS particle diameter decreased from 1.25 to 0.315 μm. GP was 5.5 hours for the pure matrix, 13 minutes for the composite containing 0.315 μ.m particles, 1.4 hours for 0.688 μm particles and more than 2 hours for 1.25 μm particles. We propose that in PS particle filled systems, the ability to form clusters was due to interparticle dispersive interactions which increase with decreasing particle size. The particle clusters function as physical crosslinks, so that the overall crosslink density was significantly enhanced. Rheologically, the dynamic moduli and gelation rate were increased with decreasing particle diameter.
Prediction of the gas permeability of heterogeneous polymer blends
Authors: Kolařík Jan , Fambri Luca , Pegoretti Alessandro , Penati Amabile
Published: April 2004

A recently introduced predictive scheme is used to calculate the permeability of various types of heterogeneous polymer blends, which are characterized by the ratio of the permeability of constituents in the range 10–10,000. The scheme combines a two‐parameter equivalent box model and the data on the continuity of constituting phases acquired by modifying equations proposed by the percolation theory; it takes into account the permeability of components and the interval of phase duality (co‐continuity) delimited by the critical volume fractions of components v1cr and v2cr. The scheme can be used in two ways: (i) permeability of blends predicted by using the “theoretical” value of parameters v1cr = v2cr = 0.16 should be regarded as a first approximation which may not well approximate experimental data due to the fact that real v1cr and v2cr are affected by relative viscosities of the components, interfacial energy, conditions of blend mixing, phase structure coarsening, etc.; (ii) conversely, by fitting experimental data, it is possible to determine v1cr and v2cr for the studied system; thus the scheme can be alternatively viewed as an efficient tool for phase structure analysis of polymer blends.
Deformation rate dependence of work of fracture parameters in polybutylene terephthalate (PBT)
Authors: Hashemi S.
Published: April 2004

Essential work of fracture (EWF) analysis was used to study the effect of loading rate (v = 2, 5, 25 and 50 mm/min) on fracture toughness of PBT film of thicknesses 0.175, 0.275, 0.375 and 0.5 mm. Using single edge notched tension (SENT) specimens, it was found that the specific essential work of fracture, we, increases slightly with increasing loading rate but Within the specified range of loading rate, it showed no significant variation with respect to thickness. The specific non‐essential work of fracture, βwp, decreased with increasing rate and increasing thickness.
Barrier and mechanical properties of pulp fiber/polymer laminates and blends
Authors: Krook M. , Hedenqvist M. S. , Albertsson A.‐C. , Hellman A. , Iversen T. , Gedde U. W.
Published: April 2004

Paperboard laminates coated with two grades of poly(ε‐caprolactone) (PCL), poly(hydroxy butyrate‐co‐valerate) (PHBV) or a liquid crystalline copolyester (LCP) were prepared by compression molding, and the influence of the processing conditions and polymer content of the laminate on the laminate properties was studied. Ligno‐cellulose fiber/polymer blends were prepared from wet pulps and PCL and PHBV. The morphology, water vapor transmission rates, creasability, curl and twist and mechanical properties of the laminates and blends were studied. LCP and slowly cooled high molar mass PCL laminated paperboards showed the best creasing properties and the paperboards that were penetrated by the polymer showed the smallest degree of curl and twist. Extensive penetration occurred during compression molding of the paperboard with the low molar mass PCL at all temperatures and with PHBV and LCP at the higher molding temperatures. The water vapor transmission rates ranged from 1 to 300 times that of polyethylene depending on the polymer used and on the thermal history. In the case of blends, competitive properties were obtained only in those with a high polymer content. The laminate stiffness decreased and the strength increased in two polymer concentration regions, at ∼20 wt% due to fiber‐fiber separation and at ∼60 wt% due to phase inversion.
Modification of PET in high‐speed melt spinning by blending with PEN
Authors: Rwei Syang‐Peng
Published: April 2004

Blends of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) were melt spun using a high‐speed winding process in a single‐screw extruder combined with a spinning setup. The filaments had a single Tm and Tg, which indicates excellent compatibility in both the amorphous and crystalline phases. Birefringence and wide angle X‐ray measurements indicated that compounding PEN into PET suppresses stress‐induced orientation and decreases the stressinduced crystallization in the filaments. Adding PEN to PET relaxes the formation of skin‐core structures for as‐spun fibers and reduces the occurrence of broken filaments. Although the addition of PEN reduced crystallinity, it did not affect the tenacity and the shrinkage of the compounded filaments. The elongation of the fibers could be reduced by 30% to 40%, eliminating the need for a further drawing. These results are attributed to PEN's rigid backbone. Adding PEN to PET improves PETs spinnability during high‐speed spinning.
Dielectric rheological measurements of molten polymers
Authors: McBrearty Michael , Perusich Stephen
Published: April 2004

Rheological characterization of polymers above their melting points is performed with dielectric spectroscopy. A new in‐line interdigitated dielectric sensor as well as a commercial off‐line sensor were used to make the measurements. The dielectric dissipation or loss factor of a molten polymer was found to be directly proportional to independently measured rheological properties of the polymer. Time‐temperature superposition was used to translate dielectric and rheological curves to master curves where the curves are comparable in form, but the activation energy of a dielectrically‐induced relaxation was found to be lower than a rheological translational motion. The more localized and homogeneous effects imparted to the polymer during the dielectric measurement may cause the polymer to undergo a viscoelastic transition at a lower energy than the flow‐induced transition in rheological measurements. The dielectric methods detailed herein provide a new noninvasive technique to measure the viscoelastic properties of molten polymers.
Dielectric spectroscopy for polymer melt composition measurements
Authors: Perusich Stephen , McBrearty Michael
Published: April 2004

Laboratory and in‐line dielectric spectroscopy studies of molten polymers revealed the ability to make composition measurements of the comonomer concentration along the polymer chains. The dielectric permittivity or capacitance was found to be proportional to the polymer sidechain composition. The length of the polar sidegroup dictated the optimum measurement frequency; i.e., a short sidechain, such as the C‐Cl bond in chlorosulfonated polyethylene, required a high measurement frequency (short relaxation time) due to the rapid mobility of the sidechain, whereas a longer sidechain, such as the vinyl ether sidegroup in Nafion®, required a much lower frequency (longer relaxation time) to orient the sidechain to a measurable extent. For in‐line process studies, a new cylindrical, interdigitated dielectric sensor and associated electronics were developed to make measurements on molten polymers at the exit of an extruder up to 400°C and 3000 lbs/in2. In‐line studies of molten polymers revealed a direct relationship between the dielectric signal and the polymer comonomer composition. The sensor represents a non‐invasive, real‐time process composition measurement and can be integrated to provide closed‐loop process control.
Mean residence time analysis for twin screw extruders
Authors: Gao Jun , Walsh Gregory C. , Bigio David , Briber Robert M. , Wetzel Mark D.
Published: April 2004

This paper presents and experimentally validates a physically motivated model for predicting the mean residence time in twin screw extruders. Accurate estimation of the mean residence time and the propagation delay through a plasticating extruder is critical for implementing feedback control schemes employing sensors mounted along the extruder. Experiments were carried out on a 30 mm Krupp Werner and Pfleiderer co‐rotating twin screw extruder equipped with reflectance optical probes over the melting section and mixing section and at the die. The residence time distributions for twelve operating conditions and two screw geometries are compared. The mean residence times predicted by our model are in good agreement with the experimentally measured mean residence times.
Structural changes of gel drawn, ultra‐high molecular weight polyethylene fibers with kerosene as a solvent
Authors: Xiao C. F. , Zhang Y. F. , An S. L. , Jia G. X.
Published: April 2004

Fibers of ultra‐high molecular weight polyethylene (UHMW‐PE) were prepared with the gel fiber drawing method. The solvent and extraction solvent used were a general kerosene and gasoline, respectively. The structural changes in the fibers during the drawing process were examined by wide‐angle X‐ray diffraction (WAXD), polarizing optical microscopy (POM), and a density gradient column. During the drawing process, a folded chain structure transformed into an extended‐chain in the fiber, the density of the fibers increased, and the dimensions of the orthorhombic crystallite size tended towards a narrow distribution simultaneously with the increasing draw ratio. The orthorhombic unit cell dimensions for the fiber with a draw ratio of 40 were a = 0.732 nm, b = 0.491 nm, and c = 0.254 nm. In the fiber with a draw ratio of about 40, kink bands were observed. It is suggested they correspond with the local crystalline slip due to the effect of winding tension. Also, the smaller the winding roller diameter, the more clearly they can be observed. In this work, the effect of the existence of kink bands on the structures of orientation and crystallinity of fiber bulk was not observed.
Effect of incorporating ethylene‐ethylacrylate copolymer on the positive temperature coefficient characteristics of carbon black filled HDPE systems
Authors: Lee Gun Joo , Suh Kyung Do , Im Seung Soon
Published: April 2004

In order to study the effect of introducing ethylene‐ethylacrylate copolymer (EEA) in carbon black‐HDPE composite systems, two HDPE‐EEA composites prepared by pre‐blending and masterbatch‐blending processes were compared with HDPE and EEA composites in terms of positive temperature coefficient (PTC) characteristics and percolation threshold. The percolation threshold of masterbatch‐blended composites occurred at the lowest carbon black concentration among four kinds of composites. The conduction path in the masterbatch‐blended composite is effectively formed as a result of the localization of carbon black distribution predominantly in the EEA phase, resulting in an increase of conductivity. Ipeak values, the resistivity ratio of the peak to 25°C, of two blend composites were lower than those of HDPE composites. The I85 values, the resistivity ratio of 85°C to 25°C, of masterbatch‐blended composites were higher than those of pre‐blended as well as HDPE composites. It is evident that since most carbon black is dispersed in the EEA phase of the masterbatch‐blended composites, the conduction networks are mainly broken by the crystal melting of EEA before the temperature reaches the crystal melting temperature of HDPE.
Experimental investigation of the energy balance for the metering zone of a twin screw extruder
Authors: Tenge Stephan , Mewes Dieter
Published: April 2004

The object of this study is to investigate experimentally the mechanical power transported from the screws to the polymer melt, the heat dissipated in the polymer melt, and the heat transferred to the barrel of the metering zone of a co‐rotating twin screw extruder. For the experimental investigations, different screw elements, mixing elements, and kneading discs are used. The experimental results for the dissipation show good agreement with known calculation models. For the calculation of the heat transfer, a new equation is used to calculate the mean temperature difference under consideration of the dissipation. The Nusselt‐number can be calculated in good agreement with the experimental results as a function of the Brinkmann‐number.
Effects of gauge length and strain rate on fracture toughness of polyethylene terephthalate glycol (PETG) film using the essential work of fracture analysis
Authors: Ching Emma C. Y. , Li Robert K. Y. , Mai Yiu‐Wing
Published: April 2004

Essential Work of Fracture (EWF) analysis was used to study the fracture toughness of a PETG film. In the study of the gauge length (Z) effect on the specific essential work (we) using Z = 50, 100, 150, 200 and 250 mm, it is observed thatweis Independent of gauge length, except that a slightly lowerwevalue was measured for Z = 50 mm. Interestingly, for specimens with long gauge lengths (Z ≥ 150 mm in this study), brittle fracture occurred. The minimum ligament length at which ductile/brittle transition took place was observed to decrease with increasing gauge length. There is a small strain rate effect onwewith loading rates less than 1 mm/min. But with higher loading rates,weshoweld no strain rate sensitivity.
Characterization of two precursor polyblends: Polyhydroxyamide and poly(amic acid)
Authors: Chang Jin‐Hae , Farris Richard J.
Published: April 2004

Blends of two precursor polymers, polyhydroxy amide (PHA) and poly(amic acid) (PAA), were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The presence of PHA enhanced thermal and mechanical properties of the polyblends. All of the polyblended films showed large endothermic peaks that decreased monotonically with increasing heat treatment temperature. The cyclization onset temperature (T1), initial decomposition temperature (T2), and weight residue at 900°C of the polyblends were shown to be in the ranges of 144–146°C, 532–540°C, and 44–45%, respectively. Also, the thermal stabilities were enhanced consistently with increasing annealing temperature from 25 to 250°C. The ultimate strength and initial modulus of the polyblends increased from 84 to 136 MPa and from 2.93 to 5.34 GPa, respectively, with increasing PHA content. Similar to the trend of thermal stability, increasing the annealing temperature of the polyblends increased the tensile properties of the films. The observed tensile properties are discussed in terms of the morphology of the fractured films as studied by scanning electron microscopy (SEM). The degree of crystallinity of the polyblends was characterized as a function of heat treatment temperatures by wide angle X‐ray diffractometry (WAXD).
Surface structure of isotactic polypropylene by X‐ray diffraction
Authors: Nishino Takashi , Matsumoto Takayuki , Nakamae Katsuhiko
Published: April 2004

With the glazing angle incidence of an X‐ray beam, the surface structure of compression molded isotactic polypropylene film was investigated by X‐ray diffraction. A comparison of the crystallinities between the surface and the bulk was made for films annealed in air at different temperatures and times. The crystallinity was lower for the surface compared with the bulk irrespective of annealing conditions. A drastic change in crystallinity occurred up to depths of several micrometers from the surface, and crystallinity decreased near the surface. The apparent crystallite sizes were smaller for the surface. This showed that crystal growth was restricted near the surface because of localized defects (including chain ends), and high chain mobility. Annealing at higher temperatures induced surface oxidation, which also decreased the surface crystallinity. The residual stress near the surface, attributable to quenching from the melt, was also detected by this method.
3‐D numerical simulations of nonisothermal flow in co‐rotating twin screw extruders
Authors: Ishikawa Takeshi , Kihara Shin‐Ichi , Funatsu Kazumori
Published: April 2004

Three‐dimensional nonisothermal flow simulations in the kneading disc regions of co‐rotating twin screw extruders were performed using a finite element method. The standard Galerkin method and penalty function scheme were applied to the flow field. The streamline‐upwind/Petrov‐Galerkin scheme was used in the temperature field to reduce numerical oscillation. The simulations were carried out under the operational conditions of The Japan Steel Works TEX30 machine for various rotational speeds. The configuration was ten 2‐lobe kneading discs with a 90° stagger angle. Experimental observations were also performed to validate the numerical simulations under the same operational conditions. The pressure in front of the tip in the rotation direction was higher than behind the tip, and the region behind the tip sometimes had a negative value. Since variation of the pressure gradient in the axial direction causes forward and backward flows in the disc gap regions, the disc gap regions play an important role for mixing. The temperature becomes higher with increasing rotation speed due to high viscous dissipation. A high temperature was observed on the disc surface, in the disc gap, and in the intermeshing regions. The numerical results of pressure profiles with the rotation and the temperature in the axial direction were in good agreement with the experimental observations.
Numerical simulation and experimental verification of nonisothermal flow in counter‐rotating nonintermeshing continuous mixers
Authors: Ishikawa Takeshi , Kihara Shin‐Ichi , Funatsu Kazumori , Amaiwa Teruo , Yano Kazunori
Published: April 2004

We have developed non‐Newtonian and nonisothermal flow simulation codes in twin screw extruders using the finite element method. These codes can simulate the fully filled part of several kinds of screw elements, such as full flight screws, kneading discs, rotors, and their combinations. In this paper, we describe how we applied them to simulate a counter‐rotating nonintermeshing continuous mixer, LCM100G, by Kobe Steel, Ltd. The LCM100G is a Farrel‐type continuous mixer that has two mixing stages. We focused on the second mixing stage, since the flow domain of this stage is almost filled by polymer melts. Numerical simulations at various flow rates were performed. We also carried out experimental observations to verify the numerical simulations. Pressure and temperature profiles from the simulations were found to be in good agreement with the experimental results.
Mechanical properties of acrylic based latex blend coatings
Authors: Agarwal N. , Farris R. J.
Published: April 2004

A complete characterization of the mechanical properties of acrylic based latex blend coatings comprising hard (Tg = 45°C) and soft (Tg = −5°C) phases is presented. Although clear and transparent in appearance, these blends remain phase separated through the entire range of compositions based on their hard phase content. Blends with less than 50% hard phase (soft blends) show a typical rubber‐like behavior with large elongation to break and low stiffness, whereas those with more than 50% hard phase (hard blends) exhibit a progressively glassy behavior. The values of effective Young's moduli and Poisson's ratios lie within the bounds calculated from Hashin‐Shtrikman models and exhibit a sigmoidal shaped profile as a function of composition, in close agreement with the solutions of Hill‐Budiansky equations. These results, along with interpretations based on a percolation theory, indicate that a phase inversion to a continuous hard matrix from the soft one occurs around 30–40% hard phase content, a conclusion further supported by scanning electron micrographs of the fracture surfaces.
The Izod impact strength of modified methyl methacryate/styrene copolymer molding and the toughening mechanism
Authors: Takaki Akira , Yamazaki Kaoru , Narisawa Ikuo
Published: April 2004

To better understand the Izod impact strength of modified poly(methyl methacrylate‐co‐styrene), the fracture mode and whitened state of molded specimens were studied. The Izod impact strength was closely related to the amount of whitened area, and the degree of whiteness improved with increasing whitened area and degree. The whitened area was strongly related to the transition rate for shear yielding in tensile testing. The degree of whitening was strongly related to the elongation at break in low‐speed tensile testing. Transmission and scanning electron microscopy were also used to develop an understanding of the mechanisms of energy absorption and the fracture process.
Effects of coupling agents on the oxidation and darkening of cellulosic materials used as reinforcements for thermoplastic matrices in composites
Authors: Urreaga J. Martínez , Matías M. C. , De La Orden M. U. , Munguía M. A. Lechuga , Sánchez C. González
Published: April 2004

Oxidation and darkening occur during the processing of composites made from thermoplastic matrices and cellulosic reinforcements. We have studied the effects of several coupling agents on both the oxidation and darkening of cellulosic materials at temperatures close to those used in the processing of cellulose‐reinforced thermoplastics. A maleated polypropylene wax (Epolene E‐43TM) and two silanes (N‐2‐aminoethyl‐3‐aminopropyltrimethoxy silane and methyltrimethoxysilane) were used as coupling agents. Oxidation was measured by Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy. Standard colorimetry was used to measure darkening. Coupling agent effects depend on the nature and extent of cellulose modification achieved by treatments and the nature of the coupling agent. Epolene wax E‐43 produced scarce effects on both the oxidation and darkening of cellulosic materials at 200°C. Only for longer oxidation times was an increase in oxidation and darkening observed in E‐43‐treated samples. Silane coupling agents inhibited the formation of carbonyl and carboxyl groups for shorter oxidation times. The diaminosilane produced a stronger darkening, probably due to a chemical reaction that generated new chromophores containing CN bonds.
Chemorheological analysis of an epoxy‐novolac molding compound
Authors: Hsieh T. H. , Wang T. L. , Ho K. S. , Wang Y. Z.
Published: April 2004

The chemorheological behavior of an epoxy‐novolac molding compound was studied by a combination of differential scanning calorimetry and dynamic rheological measurements. Based on a modified version of Kamal and Sourour's kinetic expression, a procedure aiming at the phenomenological description of cure kinetics was developed. In combination with our kinetic study, an empirical Arrhenius‐type expression was adopted for the description of the dependence of complex viscosity on temperature, frequency, and conversion by allowing the pre‐exponential factor and the flow activation energy to be frequency‐ and conversion‐dependent. At low conversions (α < ∼0.05), the system behaves approximately as a thermoplastic material; at higher conversions, the rheological behavior of the system was dominated by the extent of cure reaction.
Morphology and mechanical properties of blends of polycarbonate and segmented copolyetherester
Authors: Gaztelumendi M. , Nazábal J.
Published: April 2004

The solid state features and the mechanical properties of melt mixed polycarbonate (PC)/segmented copolyetherester (CPEE) blends were investigated over the full composition range. The partially crystallized blends were composed of two amorphous phases but with only small composition differences in most blend compositions. The specific interactions, and the free volume decreases observed, gave rise to a decrease in the γ relaxation strength. The dependence on composition of both the decreases in the γ relaxation strength and in the free volume, as well as that of the modulus of elasticity and yield stress, were very similar to those of miscible blends. The nature of the amorphous phases of the blends at room temperature, changed from glassy to partially rubbery as the CPEE content was increased. As a consequence, to discuss the plots of the properties against composition at room temperature, the properties of the rubbery materials in the glassy state had to be determined. The synergistic modulus and yield stress behaviors appeared to be mainly determined by the γ relaxation strength and specific volume decrease, and that of ductility additionally by the Tg change.
The effect of strain rate, temperature, and molecular mass on the tensile deformation of polyethylene
Authors: Hillmansen S. , Hobeika S. , Haward R. N. , Leevers P. S.
Published: April 2004

Conventional tensile testing applied to high density polyethylene can lead to erroneous impressions of the tensile response of the material due to a local reduction in cross section of the sample. Several workers have developed novel tensile testing techniques to measure the response of a small element as it deforms. The true stress true strain curve that results describes tensile deformation of the material in a geometry‐independent manner. Here, results from previous workers, together with some of our own, are interpreted in terms of the Haward‐Thackray spring‐dashpot model, in which the spring defines a strain hardening process according to the theories of high elasticity and the dashpot describes a strain‐independent viscous process. The effects that temperature, strain rate, and molecular mass have on each process are investigated. For a pipe‐grade, modified high density ethylene copolymer, sufficient data have been measured to interpret the effects of strain rate and temperature in accordance with an Eyring flow process, where the parameters for the two mechanisms are found to be similar.
Thermal expansivity and thermal conductivity of amorphous thermoplastic polyimide and polymer liquid crystal blends
Authors: Brostow Witold , D'Souza Nandika Anne , Gopalanarayanan Bhaskar , Jacobs Elizabeth
Published: April 2004

Linear thermal expansivities αL and thermal conductivities of polyimide (TPI) and polymer liquid crystal (PLC) blends were studied. The glass transition temperatures Tg of our amorphous TPI and the PLC are, respectively, 240 and 220°C. The addition of the PLC induces orientation through the channeling process, as predicted by an extension of the Flory statistical‐mechanical theory of PLCs (27). Channeling was observed at PLC concentrations as low as 5 wt%. Thermal conductivity decreases with the addition of the PLC to the TPI. The anisotropic expansivity of the blends shows a strong dependence on PLC concentration and orientation direction. The pure PLC shows a maximum on the along‐the‐flow expansivity vs. temperature curves and also negative αL values. TPI addition moves the expansivities to positive values, but the maximum persists, even for 5% PLC only.
Preparation and properties of thermoplastic starch‐polyester laminate sheets by coextrusion
Authors: Wang L. , Shogren R. L. , Carriere C.
Published: April 2004

The effects of extrusion and formulation variables on the structure and properties of starch‐polyester laminates were examined. Three‐layer polyester/starch/polyester sheets were prepared using a twin‐screw extruder for the starch/water center layer, a single screw extruder for the outer polyester layers and a feedblock and coathanger type sheet die. Overall sheet and coating thicknesses were more uniform as coating polymer (poly(ε‐caprolactone), PCL) viscosity decreased (lower molecular weight), starch melt viscosity increased (lower moisture) and feedblock/die temperature increased. Peel strengths were 1 to 2 orders of magnitude larger for high than low molecular weight PCL. High peel strengths were associated with rough, wavy interfaces (interfacial instability). Addition of plasticizer such as glycerol and sorbitol to the starch decreased peel strengths. Peel strengths varied little with type of polyester coating, except, perhaps, for polylactic acid and polyesteramide, which were more difficult to peel. Some possible applications of laminated starch sheets include food packaging and controlled release of drugs, pesticides, insect diets, etc.
Numerical simulation of pressure and velocity profiles in kneading elements of a co‐rotating twin screw extruder
Authors: Bravo V. L. , Hrymak A. N. , Wright J. D.
Published: April 2004

The objective of this work is to validate, via comparison with available experimental data, the results obtained from the numerical simulation of polymer melt flow in the kneading disc section of an intermeshing co‐rotating twin screw extruder. A quasi‐steady state 3‐D solution of the conservation equations via the finite element method was obtained, and comparisons were made with experimental pressure profiles measured by McCullough and Hilton (1) on various kneading block elements. These measurements helped provide understanding of the flow patterns developed within the unit and provided a comprehensive approach of validating the numerical model. Results confirm the importance of a fully 3‐D model for this type of geometry, where the model predicts the development of flow patterns in the radial directions and within the intermeshing region. The influence of inlet and outlet boundary conditions was studied and it was determined that they play an important role in the physical significance of the model solution. Comparisons of the simulation results with experimental data by McCullough and Hilton (1) for two different configurations of kneading discs showed good agreement, with some differences in the peaks of pressure produced at the narrow clearances encountered in intermeshing co‐rotating twin screw extruders. Differences between simulation and experiments are attributed to a number of factors. It is difficult to measure the very steep pressure gradients generated over small lengths. The assumptions of isothermal flow and quasi‐steady state may cause an over‐prediction of the pressure peaks. Simulation results describe the general trends and produce good quantitative agreement in most of the kneading disc region.
Isothermal transient startup of a starved flow modular co‐rotating twin screw extruder
Authors: Kim Eung Kyu , White James L.
Published: April 2004

A model for flow start‐up of a Newtonian liquid in an initially empty modular selfwiping co‐rotating twin screw extruder is developed. The changes of length of fill in front of the die and kneading disc block elements and output flow rate with time were predicted for various modular screw configurations. Experiments were also carried out on a laboratory modular machine with windows to verify predictions. Generally, good agreement with the flow analysis was found.
Melt viscoelasticity of polyethylene terephthalate resins for low density extrusion foaming
Authors: Q̧uintans J. , Xanthos M. , Dey S. K. , Yilmazer U.
Published: April 2004

The rheological properties of conventional polyethylene terephthalate (PET) resins are not particularly suitable for low density extrusion foaming with physical blowing agents; as a result, chemically modified resins through chain extension/branching reactions are often used. Such resins have overall higher melt viscosity and higher melt strength/melt “elasticity” than unmodified materials. In this work, following a review of the prior art on PET chemical modification, an unmodified and a chemically modified resin were selected and characterized for their melt viscoelastic properties including shear and dynamic complex viscosity over a broad shear rate/frequency range, storage and loss modulus, and die swell. Certain rheological models were found to provide better fits of the entire viscosity curve for the unmodified vs. the modified resin. Foamed extrudates having variable densities (from about 1.2 to 0.2 g/cc), were prepared by carbon dioxide injection in monolayer flat sheet extrusion equipment. Foams with increasingly lower density, below 0.5 g/cc, were obtained by increasing gas pressure only in the case of the chemically modified resin. The effects of variables such as concentration of the physical blowing agent, resin rheology, resin thermal properties and choice of process conditions are related to product characteristics including density, cell size and crystallinity.
Morphology–mechanical property relations in syndiotactic polypropylene (sPP) fibers
Authors: Loos Joachim , Schimanski Tilo
Published: April 2004

Mechanical properties of melt‐spun syndiotactic polypropylene single filament fibers were studied in relation to their formation conditions. Depending on the processing parameters, fibers with rubber‐elastic properties can be prepared. Dynamic mechanical studies show almost unchanged rubber‐elastic properties after 1000 test cycles. A model of the fiber morphology is introduced to explain the rubberelastic behavior: small micel‐like crystals containing molecules in the planar alltrans conformation act as physical crosslinks in the amorphous matrix.
Engineering analysis of crosslinking polymerization of diallyl lsophthalate
Authors: Znoj Bogdan , Matjažkrajnc  , Barborič Franci , Golob Janvit
Published: April 2004

A kinetic model for crosslinking free radical polymerization of DAIM (monomer diallyl isophthalate) with initiator CHPC (dicyclohexyl peroxydicarbonate) is developed. An improved version of Batch and Macosko's model was used to describe the initiator efficiency (f) and the active radical fraction (Fact). The experimental data of allyl and carbonyl group consumption are used for the optimization of the model and calculating of f and Fact. From the developed kinetic model and experimental results, obtained by FT‐IR measurements of monomer conversion, the introduction of the Fact was proved. Application of this model may be of use in process modeling of DAIM and other crosslinking polymerizations with CHPC as initiator.