bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of the residual mechanical properties of crazed polycarbonate. II: Design of experiments analysis
Authors: Clay Stephen B. , Kander Ronald G.
Published: April 2004

The Design of Experiments (DOE) approach was used to build quantitative empirical models of the residual mechanical properties of crazed polycarbonate as functions of relative craze density, crazing stress, and strain rate. Crazing did not affect the yielding behavior of polycarbonate, but increasing the strain rate increased the yield stress according to the Eyring theory. The Eyring activation volume for yielding of crazed polycarbonate was measured to fall between reported values for conformational changes of a dilute solution of polycarbonate chains and yielding of uncrazed polycarbonate. Also, with as little as 1% relative craze density, the failure stress was approximately 10% lower and the ductility was, on the average, 50% lower than for uncrazed polycarbonate properties. It was also found that increasing the crazing stress from 40 to 45 MPa increased the failure stress and ductility for a given magnitude of relative craze density.
Modeling of a Buss‐Kneader as a polymerization reactor for acrylates. Part II: Methyl methacrylate based resins
Authors: Troelstra E. J. , Van Dierendonck L. L. , Janssen L. P. B. M. , Renken A.
Published: April 2004

The Buss‐Kneader has proven to be a suitable reactor for the polymerization of acrylates. In this second part, the polymerization of methyl methacrylate and the ter‐polymerization of methyl methacrylate (MMA), hydroxyethyl methacrylate and n‐butylmethacrylate is carried out in a pilot Buss‐Kneader. The reactor had to be pressurized up to about 10 bars to avoid evaporation of MMA. Instabilities in output rate and temperature profiles were observed as a result of fluctuating die pressures. Because of good mixing there may be no diffusion limitation for radicals. As a result, even at high conversions, no gel effect was observed.
Numerical analysis of surface‐tension‐driven coating flow
Authors: Blunk Richard H. J. , Wilkes James O.
Published: April 2004

Bondline readout (BLRO) is a coating defect frequently exhibited on adhesively bonded, polymeric automotive body panels painted with high‐glamour/flow clearcoats. BLRO or telegraphing results from Marangoni‐type, surface‐tension‐driven flows. The goal of this study is to use an efficient one‐dimensional numerical code (based on the lubrication approximation) to obtain further insight into the mechanism of temperature‐ and concentration‐induced BLRO flows in order to validate a proposed BRLO mechanism and ultimately to help eliminate the highly undesirable BLRO coating defect. Further insight is realized by investigating numerically the effects on BLRO of gravity and five parameters—initial film thickness, heating rate, viscosity, solvent volatility, and solvent‐to‐resin surface‐tension ratio. Possible solutions to the BLRO problem are discussed.
The effect of stoichiometry on the fracture toughness of a liquid crystalline epoxy
Authors: Robinson Elizabeth J. , Douglas Elliot P. , Mecholsky John J.
Published: April 2004

The fracture toughness of a liquid crystalline epoxy was compared with that of a standard bisphenol‐A based epoxy to understand how both the liquid crystalline structure and the crosslink density affect fracture toughness. For the liquid crystalline epoxy, the liquid crystalline domain size decreased with increasing temperature of cure and away from the stoichiometric formulation. Quantitative fractography showed that there is a competition between the liquid crystalline domain structure and the stoichiometry in determining the fracture toughness. At some cure conditions the effect of the domains is dominant. When the cure conditions are adjusted to reduce the domain size, the domains become too small to affect the fracture toughness, and thus the effect of the stoichiometry is dominant. The result is that the formation of liquid crystalline structure only increases the fracture toughness relative to that of a traditional epoxy at and near the stoichiometric formulation.
Tools for multiaxial validation of behavior laws chosen for modeling hyper‐elasticity of rubber‐like materials
Authors: Chevalier L. , Marco Y.
Published: April 2004

We present an experimental approach to discriminate hyper‐elastic models describing the mechanical behavior of rubber‐like materials. An evaluation of the displacement field obtained by digital image correlation allows us to evaluate the heterogeneous strain field observed during these tests. We focus on the particular case of hyper‐elastic models to simulate the behavior of some rubber‐like materials. Assuming incompressibility of the material, the hyper‐elastic potential is determined from tension and compression tests. A biaxial loading condition is obtained in a multiaxial testing machine and model predictions are compared with experimental results.
Polyimide and nylon 6 blend film: Preparation, characterization and thermal behavior
Authors: Niyogi Sobhan , Maiti Sukumar , Adhikari Basudam
Published: April 2004

A polyimide blend system has been prepared from a base polyimide of BTDAODA by adding ε‐caprolactam at the poly(amic acid) stage where ε‐caprolactam undergoes polymerization to form nylon 6 during the thermal cyclodehydration of poly(amic acid). The blend has been characterized by elemental analysis. IR, 13C CPMAS NMR, XRD and simple chemical methods. The thermal analysis study (TGA and DTA) shows that the stability of the blend systems is more in the lower temperature region (up to 300°C) in comparison to the control polyimide system. The isothermal study at 400°C in inert atmosphere shows that the blend system is equally stable but the isothermal study in air at 400°C shows that the thermooxidative stability of the blend films (except BB 4) is higher. Also, isothermal study in air at 500°C shows more than 90% weight loss for all the films within 3 h, but in an inert atmosphere, the blend films show lower weight loss compared to the control film. Although the XRD pattern of all the blend and control films shows an amorphous character, the films developed some crystallinity when treated with boiling NMP where the blend films developed higher crystallinity.
Moisture diffusion behavior in bismaleimide resin subjected to hygrothermal cycling
Authors: Li Yanmei , Miranda John , Sue Hung‐Jue
Published: April 2004

Absorption‐desorption‐reabsorption hygrothermal cycling was performed in bismaleimide resin. Dynamic mechanical analysis and swelling experiments were conducted to investigate the effect of hygrothermal cycling on the moisture diffusion behavior in the resin. Non‐Fickian diffusion behavior was observed in both the absorption and the reabsorption processes, while the desorption process is found to be Fickian. The molecular network structure of BMI appears to have changed during the hygrothermal cycling. This, in turn, altered the subsequent reabsorption process.
Investigation of appropriate cooling times for electrofusion jointing of PE pipes for gas distribution
Authors: Higuchi Yuji , Nishimura Hiroyuki , Inoue Fumio , Ishikawa Tetsuo , Miyaki Seiji
Published: April 2004

This study evaluates three types of fusion zones between electrofusion (EF) joints and pipes that were laid underground after three different cooling times following fusion. The study establishes the relationship between the cooling time and the fusion performance. The object was to determine an appropriate cooling time for EF jointing. Only a slight difference was observed in the molecular structure, e.g., the degree of crystallinity, while distinct differences were observed in deformation, morphology, and tensile creep strength. Based on these results, the effect of a temperature profile during the cooling process on the fusion zone was simulated. The simulation showed that the state of the fusion zone (melting, semi‐solid, or solid) when the pipe was laid underground was the main factor affecting the tensile creep strength, i.e. long‐term performance. These analyses provided criteria for choosing an appropriate cooling time.
Analysis of multiaxial impact behavior of polymers
Authors: Duan Y. , Saigal A. , Greif R. , Zimmerman M. A.
Published: April 2004

Impact performance is a primary concern in many applications of polymers. In this paper, finite element analysis (FEA) and ABAQUS/Explicit are used to simulate the deformation and failure of polymers in the standard ASTM D3763 multiaxial impact test. The specimen geometry and loading mode in this multiaxial impact test provides a close correlation with practical impact conditions. A previously developed constitutive model (“DSGZ” model) for polymers under monotonic compressive loading is generalized and extended for any loading mode and takes into account the different behavior of polymers in uniaxial tensile and compression tests. The phenomenon of thermomechanical coupling during plastic deformation is also included in the analysis. This generalized DSGZ model, along with thermomechanical coupling and a failure criterion based on maximum plastic strain, is incorporated in the FEA model as a coupled‐field user material subroutine to produce a unique tool for the prediction of the impact behavior of polymeric materials. Load‐displacement curves from FEA simulations are compared with experimental data for two glassy polymers, ABS‐1 and ABS‐2. The simulations and experimental data are in excellent agreement up to the maximum impact load. It is shown that not accounting for the different behavior of the polymer in uniaxial tensile and compression tests and thermomechanical coupling effects leads to an overestimation of the load and impact energy, especially at large displacements and plastic deformations. Friction also plays an important role in the impact behavior. If one neglects the friction between the striker and polymer disk, the predicted impact loads are lower as compared with experimental data at large displacements.
Interlaminar contact development during thermoplastic fusion bonding
Authors: Yang F. , Pitchumani R.
Published: April 2004

Fabrication of layered thermoplastics and thermoplastic‐matrix composites using processes such as tow placement, tape laying, and resistance welding is fundamentally based on the principle of fusion bonding, which involves applying heat and pressure to contacting thermoplastic surfaces. One of the important processing steps—intimate contact development—is considered in this paper. Interlaminar intimate contact development has a strong dependency on the thermoplastic surface geometry. Profilometric measurements of common thermoplastic prepreg tows, such as AS4/PEEK and IM7/PIXA, show that surface roughness features appear at several length scales and that the surfaces have fractal asperity structures. In this paper, principles of fractal geometry are used to describe prepreg surfaces. Based on this description, a microscale fluid flow model is developed to relate a degree of intimate contact to the process parameters (pressure, temperature, and time) and the fractal parameters of the surface. The model development and comparisons with experimental data are presented and discussed.
Crystallization and melting behavior of zenite thermotropic liquid crystalline polymers
Authors: Pramoda K. P. , Chung T. S.
Published: April 2004

The crystallization and melting behavior of a DuPont ZeniteTM series, namely, Z 6000 and Z 8000B, thermotropic liquid crystalline polymer (TLCP) have been investigated by differential scanning calorimetry (DSC). Both, non‐isothermal and isothermal crystallizations were carried out. From the non‐isothermal experiments, the crystallization temperature was found to be 234°C for a cooling rate of 10°C/min whereas it was only 228°C for 40°C/min for Z 8000B, and was found to be 296°C and 290°C, respectively, for Z 6000. In the isothermal experiment both the thermal and crystallization behaviors were studied as a function of the annealing temperature and annealing time. Two types of transition processes were evidence in the low temperature region of the isothermal crystallization. One is fast transition, which may be regarded as liquid crystal transition, and is characterized by the enthalpy, which is independent of annealing time. The other is slow process, related to crystal perfection, and it shows increases in the transition temperature and enthalpy, which is dependent on annealing time.
Effect of thermotropic copolyesteramide on the properties of polyamide‐66/liquid crystalline copolyester composites
Authors: Xie X. L. , Li R. K. Y. , Mai Y. W. , Tjong S. C.
Published: April 2004

Liquid crystalline copolyester‐polyamide 66 (LCPES/PA66) composites compatibilized by liquid crystalline copolyesteramide (LCPEA) were prepared by injection molding. The LCPES employed was a commercial copolyester, Vectra A950, and the LCPES was a semiflexible thermotropic copolyesteramides based on 30 mol% of p‐amino benzoic acid (ABA) and 70 mol% of poly(ethylene terephthalate) (PET). Thermal analysis, mechanical characterization, and morphological investigations were conducted on the blends. The dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) tests showed that LCPEA is an effective compatibilizer for the LCPES/PA66 composites. The mechanical measurements showed that the stiffness, tensile strength and Izod impact strength of the in‐situ composites are improved by adding LCPEA because of the compatibilization and reinforcement to LCPES/PA66 composites. However, the properties improvement vanished when LCP content reached 10 wt%. The drop weight dart impact test was also applied to analyze the impact fracture characteristics of these composites. The results showed that the maximum impact force (Fmax), crack initiation and propagation energy all improved with the addition of a small percent of LCPEA. From these results, it appeared that LCPEA prolongs the time for crack initiation and propagation. It also increases the energies for crack initiation and propagation, thereby leading to toughening of the LCPES/PA66 in‐situ composites. Finally, the correlation between the mechanical properties and morphology of the composites is discussed.
Relating the generation of dynamic strain energy to crack propagation in polymers
Authors: Dear John P.
Published: April 2004

With many fracture research studies, there is a need to compare frequently experimental findings and modeling simulations. One example is when studying the relationships between crack velocity and dynamic strain energy generated in polymers. It helps in these cases if the same computer can perform the modeling simulations as used to capture and process experimental data. Personal computer (PC)–size machines are often used to capture experimental data, and a fracture simulation model has been devised that can be hosted on a personal computer. In this study, the model is used with the frozen tongue experimental technique to research steady state crack propagation in medium‐density polyethylene (MDPE). This is to study the generation of dynamic strain energy in the material and the factors affecting its availability to the crack tip. This includes the effects of changes in the material's properties immediately about the crack tip, the conditions that determine the threshold to just maintain crack propagation, and the conditions that determine the relationship between crack velocity and strain energy up to the limiting crack velocity.
Gross melt fracture of polyethylene. I: A criterion based on tensile stress
Authors: Kim Seungoh , Dealy John M.
Published: April 2004

We propose the use of a critical tensile stress as a criterion for the onset of gross melt fracture (OGMF). This stress is estimated from the entrance pressure drop using the method of Cogswell. Carbon black tracer was used to verify that what we deemed to be GMF, based on the inspection of extrudate, was indeed the result of a brittle rupture. An orifice die was used to eliminate the complications arising from the presence of a capillary. Polyethylenes having a variety of molecular structures were used to evaluate the usefulness of the critical tensile stress for characterizing polymers. The critical stress was found to be independent of temperature and contraction ratio. It is also independent of entrance angle, as long as this is equal to or greater than 90 degrees. The critical stress is thus a material property and can be used to rate the tendency of polymers to exhibit gross melt fracture.
Development of a curvilinear viscoelastic constitutive relationship for time dependent materials. Part A: Theoretical discussion
Authors: Stephenson M. J. , Dargush G. F.
Published: April 2004

A viscoelastic constitutive relationship derived from a solid mechanics viewpoint using the curvilinear form of Hooke's law as opposed to an Eulerian context was developed. This approach has the advantage of obtaining the deformation relative to the original configuration as opposed to the current one. A constitutive model was derived for viscoelastic fluids where the stress depends on the history of the first spatial gradient of the displacement. A material (convected) coordinate system and body tensor mathematics were invoked to formulate the viscoelastic relationship. Complicated integration of a Jaumann or convected rate derivative was not required. Development of the model and its theory are given here in part A.
Hot embossing in microfabrication. Part I: Experimental
Authors: Juang Yi‐Je , Lee L. James , Koelling Kurt W.
Published: April 2004

The relationship among processing conditions, material properties, and part quality in hot embossing was investigated for three optical polymers: polycarbonate (PC), polymethyl methacrylate (PMMA), and polyvinyl butyral (PVB). A series of systematic embossing experiments was conducted using mold inserts having either single or multiple feature depths. The feature dimensions varied from 90 to 3000 μm. The processing conditions studied include embossing pressure, thermal cycles, and heating methods. The displacement profile, replication accuracy and molded‐in stresses were measured experimentally. It was found that for isothermal embossing, both replication accuracy and birefringence pattern depend strongly on the processing conditions. For non‐isothermal embossing, the molded parts showed excellent replication as long as the feature transfer was completed. The flow pattern under isothermal embossing resembles a biaxial extensional flow. Under non‐isothermal embossing, the polymer deformation involves an upward flow along the wall of mold features, followed by downward compression and outward squeezing. Rheological characterization and hot embossing analysis are presented in Part II.
Experimental investigation of the cure‐dependent response of vinyl ester resin
Authors: Flores F. , Gillespie J. W. , Bogetti T. A.
Published: April 2004

The objective of this research is to understand the influence of the thermochemical and thermomechanical material response of low temperature cured vinyl ester resin (Dow Derakane 411‐C‐50) on the development of residual stress and warpage during processing. The primary experimental technique is the bimaterial specimen experiment, in which the warpage of a bimaterial beam is used as a measure of residual stress. The bimaterial specimen experiment was developed to isolate the chemical and thermal contributions to curvature. Existing material models for shrinkage, modulus, and glass transition temperature as a function of cure were evaluated. These material models were used as input into the bimaterial equation for curvature prediction. The predicted curvatures were used along with the experimental curvatures to evaluate the material models and their ability to accurately describe the material response of the vinyl ester resin. Results showed that the model captured the overall experimental trend in curvature buildup during processing but overestimated the curvature from chemical effects during isothermal cure. Improved correlation was achieved by incorporating a time shift in the model to account for viscoelastic stress relaxation of the resin.
The payne effect for particle‐reinforced elastomers
Authors: Drozdov Aleksey D. , Dorfmann Al
Published: April 2004

The study deals with the Payne effect (a substantial decrease in the storage modulus of a particle‐reinforced elastomer with an increase in the amplitude of mechanical oscillations). The influence of temperature, concentration of filler and amplitude and frequency of strains is analyzed on the mechanical response of filled rubbery polymers. Constitutive equations are derived using the concept of two interpenetrating networks: one comprises semiflexible polymeric chains connected to temporary junctions, whereas the other is formed by filler clusters. Adjustable parameters are found by fitting experimental data for natural rubber, bromobutyl rubber and styrene‐butadiene rubber reinforced by carbon black and polymeric particles. The critical concentration of particles is determined that characterizes transition from an ensemble of disjoint clusters to the network of filler. The volume fraction of filler corresponding to this transition is found to be close to the theoretical predictions based on the percolation theory, as well as to experimental data for isolator—conductor transition.
Effect of graft ratio on the dynamic moduli of acrylonitrile‐butadiene‐styrene copolymer
Authors: Ahn Kyung Hyun , Ha Doo Han , Lee Byung Do , Doh Jae Goo , Choi Jin Hwan
Published: April 2004

The effect of graft ratio on the dynamic moduli of ABS (Acrylonitrile‐Butadiene‐Styrene Copolymer) has been investigated. Unlike previous papers, the storage modulus at low frequency shows both minimum and maximum as graft ratio increases, and the rubber particles do not agglomerate significantly at high graft ratios. The dependence of the rheological properties on the graft ratio is quite complicated. This arises from its morphological change that leads to different interactions between the rubbery phase and the matrix phase. The minimum has been reported previously, and is explained in terms of rubber dispersion. However, the maximum at high graft ratio has never been reported. The origin of maximum seems to come from the repulsive forces between the long graft chains of neighboring rubber particles. Analogy between our experimental results and simulation results has been discussed to deduce the mechanism of maximum storage modulus at high graft ratio.
Flow through a convergence. Part 2: Mixing of high viscosity ratio polymer blends
Authors: Meller Mika , Luciani André , Mårnson Jan‐Ander. E.
Published: April 2004

Dispersive mixing of high viscosity ratio blends was studied in a converging flow using a capillary rheometer equipped with dies having different entry profiles. Three inhomogeneous bimodal polyolefin blends, with stress‐dependent viscosity ratios ranging from 8 to 450, were used in this work. Such magnitudes of viscosity ratio indicate that the dispersed droplets can be mixed only in an elongational flow field. The mixing efficiency was found to be dependent on both the profile of the convergence and flow rate. At the lowest flow rates, the dispersive mixing efficiency was very low, but it increased with an increasing flow rate until a profile‐dependent maximum. This maximum mixing efficiency was observed prior to fracture of the matrix material, after which the efficiency decreased. Stress and deformation fields within different profiles were estimated by numerical simulation using the K‐BKZ equation, and the results were used to interpret experimental results. The dispersive mixing efficiency was found to be proportional to the maximum elongational stress within the converging section, and to the length of the region where the critical conditions for elastic fracture of droplet material were met. It is shown that the dispersive mixing mechanism in high viscosity ratio blends is mainly dictated by elastic fracture of the droplet, and hence is applicable over a wide range of polymer blending processes.
The flow of polymer melts through the clearance over a barrier flight in extruders
Authors: Hong Bo Ki , Kim Hyun Seog , Chung Chan I.
Published: April 2004

The flow of polymer melts through the clearance over a barrier flight in extruders involves high, rapidly changing shear rates. Polymer melts, being viscoelastic, are expected to exhibit a high elasticity when they flow through the clearance, so the flow through the clearance may not be predictable or stable. The flow through the clearance over a barrier flight was investigated using a shear refining (SR) module connected to an extruder. Three polymers with different melt properties were tested: branched low density polyethylene (BLDPE), high‐density polyethylene (HDPE), and polystyrene (PS). The measured drag flow rate through the clearance was found to be equal to the prediction for a purely viscous fluid, which gives a linear velocity profile in the clearance. At the threshold rotor speed of the SR module whereupon the predicted drag flow rate through the clearance is the same as the extruder output rate, the melt pressures at the inlet and the outlet of the SR module were nearly equal and stable. Below the threshold rotor speed, the inlet pressure was higher than the outlet pressure. Above the threshold rotor speed, the inlet pressure was nearly zero and the outlet pressure fluctuated. The magnitude of the pressure fluctuation increased with increasing rotor speed and decreased with increasing melt temperature. HDPE, which had a higher melt elasticity, showed more pressure fluctuation than BLDPE and PS. The pressure fluctuation probably results from the flow instability through the clearance caused by the melt elasticity.
Reactive extrusion of recycled bottle waste material
Authors: Hettema R. , Pasman J. , Janssen L. P. B. M.
Published: April 2004

The objective of this study is to investigate the effect of reactive processing of commingled bottle waste polymer in an extruder. A variety of peroxides and monomers were tested to assess their influence on the final mechanical properties of the product. The reactive extruded polymer blends were prepared in two types of extruders: a co‐rotating twin‐screw extruder and a Buss co‐Kneader single‐screw extruder. Blends were analyzed for mechanical and thermal properties. The effectiveness of the different monomers and peroxides was evaluated in terms of improvement in impact properties. It has been found that the toughness of the polymer blend is improved by reactive processing. Depending on the amount and type of reactants, the impact strength can be improved by 220%, with a slight reduction in the modulus compared to an unmodified physical blend. The most suitable monomers were n‐butylmethacrylate (BMA), t‐butylamino ethylmethacrylate (TBAEMA) and a combination of styrene/maleic anhydride (ST/MAH). The peroxide should have a short half‐lifetime compared to the average residence time in the extruder. The most effective monomers have a high initial reactivity and low rate of evaporation at the processing conditions used. Changes in processing conditions in the extruder influence the reaction conditions and therefore the final properties of the blend. Results were interpreted in terms of residence time, melting profile and peroxide concentration.
Ejection force modeling for stereolithography injection molding tools
Authors: Pham Giang T. , Colton Jonathan S.
Published: April 2004

Stereolithography (SL) molds have proven effective for short injection molding runs. However, they are susceptible to failure because of their poor mechanical properties, especially at elevated temperatures. A majority of these failures occur during the ejection stage, as a result of excessive ejection forces. An ejection force model was developed by combining the effects of thermal shrinkage and mechanical interlocking due to stair‐steps on the surface of SL tools. Finite element analyses were performed to validate and complement the ejection force equation. Measured forces and temperatures from injection molding experiments indicated that the ejection force model is valid for SL molds of both circular and non‐circular shape. The average differences between measured and predicted ejection forces were approximately 10%.
A comparison of induction time and crystallization rate for syndiotactic polystyrene
Authors: Sudduth Richard D. , Kyarala Pavan , Sheng Qin
Published: April 2004

One objective of this study was to measure the crystallization parameters for syndiotactic polystyrene (MW = 244,000) to support a computer simulation of this material in an injection molding application. A second objective was to introduce a new crystallization rate equation that adequately predicts crystallization rates over a broader temperature range than the Hoffman‐Lauritzen equation. A third objective was to establish a new clearly defined method for determining the true induction time of a semicrystalline polymer as a function of temperature. The new crystallization rate equation introduced in this study has been formulated to give appropriate crystallization rate constants for all the temperatures currently usable with the Hoffman‐Lauritzen equation. In addition, this new equation also predicts appropriate crystallization rate constants outside the range of the Hoffman‐Lauritzen equation from temperatures significantly below the glass transition temperature, Tg, to temperatures significantly above the melting point, Tm. Interestingly, the isolation of the true isothermal induction times from apparent induction times in this study nicely mirrored the isothermal crystallization rates at each specific temperature. Both the true induction time and the crystallization rate curves were found to be similarly unsymmetrical as a function of temperature. Also, the temperature at the minimum induction time and the temperature at the peak crystallization rate determined from nonisothermal crystallization rate measurements were found to be nearly identical. Consequently, the results from this study strongly suggest that there is a significant and potentially very useful relationship between induction time analysis and crystallization rate kinetics.
The mass transport of ethyl acetate in syndiotactic polystyrene
Authors: Chiang I. J. , Chau C. C. , Lee Sanboh
Published: April 2004

The mass transport of ethyl acetate in syndiotactic polystyrene (sPS) has been studied. Two groups of specimens were prepared using press‐cooling and water‐quenching. The press‐cooled and water‐quenched specimens were identified as crystalline and amorphous structures, respectively, by X‐ray diffraction. The weight gain of ethyl acetate in sPS was monitored at temperatures from 50°C to 70°C. The crystallinity of a press‐cooled specimen prior to solvent sorption was greater than that after solvent sorption. However, solvent‐induced crystallization was observed in the water‐quenched specimen. The transport of ethyl acetate in both press‐cooled and water‐quenched specimens was anomalous and consisted of two stages. Each stage of the sorption curves was well fitted with Harmon's model. Both the diffusion coefficient and velocity component satisfy Arrhenius behavior. For the press‐cooled specimen, fluxes of Case I and Case II transport flow from the outer surface to the center, but for the water‐quenched specimen, the solvent is squeezed out. Pure Case II transport did not appear in the water‐quenched specimen.
Gross melt fracture elimination: The role of surface energy of boron nitride powders
Authors: Seth Manish , Hatzikiriakos Savvas G. , Clere Thomas M.
Published: April 2004

Boron nitride (BN) is an effective processing aid for the extrusion of polyethylenes. It postpones the onset of gross melt fracture to significantly high shear rates not previously attained with conventional fluoropolymers. However, BN particles containing relatively high amounts of boron oxide (B2O3) do not perform well as processing aids. A reliable procedure has been developed for measurement of surface energy of powders using the capillary rise technique through the use of Washburn's equation. It is based on finding the contact angle from liquid penetration experiments with polar and non‐polar liquids. Both the dispersive and non‐dispersive components of surface energy are determined. With this technique, the surface energy of a number of different powders has been assessed. These results of the surface energy of BN powders have been found to correlate well with the critical shear rate for the onset of melt fracture, indicating the important role that surface energy plays in gross melt fracture elimination.
Effects of flow on polymeric reaction
Authors: Yang I‐Kuan , Lin Jyh Dar
Published: April 2004

The esterification of the maleic anhydride residue (MA) in a hydrogenated styrene‐butadiene‐styrene block copolymer (SEBS‐g‐MA) with a polycaprolactone diol (PCL) was carried out in a melt. Experiments in static melts found that the reaction had an induction period followed by a rapid consumption of the reactants. The gel content accumulation was found synchronous to the consumption of the acidic groups during the reaction process, indicating that the crosslinking between the copolymer molecules prevailed over the esterification of the pendant acid group generated by the ring opening of the MA residue. The reaction rate was strongly affected by both the intensity and the pattern of flow. The reaction rate increased as the flow intensity increased. A back‐and‐forth shear was more effective in promoting the reaction rate than a one‐way shear. This reaction rate enhancement is due to the increase in the interfacial area and concentration gradient caused by the breakup of the dispersed droplets in the melt.
Modeling of a cokneader for the manufacturing of composite materials having absorbent properties at ultra‐high‐frequency waves. Part 1: Modeling of flow from residence time distribution investigations
Authors: Hoppe S. , Detrez C. , Pla F.
Published: April 2004

The purpose of this study is to gain better understanding of flow patterns and mixing conditions in a particular single‐screw extruder: the Buss Cokneader. To this end, the residence time distribution (RTD) of the polymer was investigated experimentally for different combinations of the operating variables (i.e. feed rate, screw rotation speed). The measurement of RTD used a standard stimulus‐response technique. Two kinds of tracer were used: free anthracene and anthracene grafted on the polymer. It was shown that only the second could characterize the actual flow of the polymer in the extruder. It does not perturb the flow and has the same rheological behavior as the studied fluid. Thanks to the RTD data, a model of the extruder based on the combination of ideal reactors, such as continuous stirred tank reactors or plug flow reactors, was finally set up. The establishment of relationships between model parameters and extrusion conditions allowed the prediction of RTD with good agreement.
Improved cathodic disbondment performance of polyethylene blends
Authors: Roy Debashis , Simon George P. , Forsyth Maria
Published: April 2004

Cathodic disbondment (CD) performance of a range of modified polyethylenes (PE) compression molded on to steel plates at 320°C is reported. Adhesion strength was measured by the 90° peel test and good dry adhesion strength was obtained for all modified polyethylene materials and blends, as well as for the neat polymer. It is shown that dry bond strength does not correlate with CD performance. Initial results of wet peel tests of samples in various concentrations of NaOH are presented where it is observed that for samples with improved wet adhesion strength, CD performance was also improved. Surface polarity was determined from contact angle measurements, and it is shown that increased surface polarity of the coating was not the only determinant for improved CD performance. Inorganic fillers such as talc were also found to improve CD performance by changing the bulk properties, with little measurable change in polarity. Some mechanistic aspects of CD performance are also discussed.
Oxygen plasma treatment of sisal fibers and polypropylene: Effects on mechanical properties of composites
Authors: Couto Elisete , Tan Ing Hwie , Demarquette Nicole , Caraschi Jose Claudio , Leão Alcides
Published: April 2004

Polypropylene powder and sisal fibers were oxygen plasma treated, and the mechanical properties of their composites were tested. Two main effects were investigated: the incorporation of oxygen polar groups in the polypropylene surface and the surface degradation and chain scission of both polypropylene and sisal fibers. Prior to these treatments, three reactor configurations were tested to investigate the best condition for both effects to occur in PP films. Results showed that polypropylene‐cellulose adhesion forces are about an order of magnitude higher for PP film treatments at 13.56 MHz than at 40 kHz owing to much higher chain scission at lower frequencies, although it probably also occurs at high frequency and high power. Polypropylene powder treated with oxygen plasmas in optimum conditions for polar group incorporation did not result in improvement in any composite mechanical property, probably owing to the polymer melting. Sisal fibers and PP powder treated in conditions of surface degradation did not improve flexural or tensile properties but resulted in higher impact resistance, comparable to the improvement obtained with the addition of compatibilizer.
Recycling of poly(ethylene terephthalate) as polymer‐polymer composites
Authors: Evstatiev M. , Fakirov S. , Krasteva B. , Friedrich K. , Covas J. A. , Cunha A. M.
Published: April 2004

Microfibrillar reinforced composites (MFC) comprising an isotropic matrix from a lower melting polymer reinforced by microfibrils of a higher melting polymer were manufactured under industrially relevant conditions and processed via injection molding. Low density polyethylene (LDPE) (matrix) and recycled poly(ethylene terephthalate) (PET) (reinforcing material) from bottles were melt blended (in 30/70 and 50/50 PET/LDPE wt ratio) and extruded, followed by continuous drawing, pelletizing and injection molding of dogbone samples. Samples of each stage of MFC manufacturing and processing were characterized by means of scanning electron microscopy (SEM), wide‐angle X‐ray scattering (WAXS), dynamic mechanical thermal analysis (DMTA), and mechanical testing. SEM and WAXS showed that the extruded blend is isotropic but becomes highly oriented after drawing, being converted into a polymer‐polymer composite upon injection molding at temperatures below the melting temperature of PET. This MFC is characterized by an isotropic LDPE matrix reinforced by randomly distributed PET microfibrils, as concluded from the WAXS patterns and SEM observations. The MFC dogbone samples show impressive mechanical properties—the elastic modulus is about 10 times higher than that of LDPE and about three times higher than reinforced LDPE with glass spheres, approaching the modulus of LDPE reinforced with 30 wt% short‐glass fibers (GF). The tensile strength is at least two times higher than that of LDPE or of reinforced LDPE with glass spheres, approaching that of reinforced LDPE with 30 wt% GF. The impact strength of LDPE increases by 50% after reinforcement with PET. It is concluded that: (i) the MFC approach can be applied in industrially relevant conditions using various blend partners, and (ii) the MFC concept represents an attractive alternative for recycling of PET as well as other polymers.
Numerical analysis of polymer melt flow in the nipping region
Authors: Takase M. , Katsumoto R. , Kegasawa T. , Kihara S. , Funatsu K.
Published: April 2004

In the extrusion coating process, it has never been revealed how a polymer melt flows near the nipping region and how the cooling process occurs. We created a numerical simulation program for the polymer melt flow near the nipping region using the finite element method. Numerical results showed the effects of many individual factors (e.g. line speed, melt thickness, extrusion temperature, shear‐thinning property, etc.) on the cooling process and polymer melt flow near the nipping region. It was found that a polymer melt buildup that can be observed between two calender rolls in the sheet forming process also formed in the extrusion coating process, and that the amount of polymer melt buildup (bank) depended upon the coating condition. It was found that not only line speed and melt thickness contribute to the extrusion coating process significantly, but also the rheological property has an effect on the process.
Modeling of structural reaction injection molding. Part II: Comparison with experimental data
Authors: Polushkin Evgeny Yu. , Polushkina Olga M. , Malkin Alexander Ya. , Kulichikhin Valery G. , Michaeli Walter , Kleba Ingo , Blaurock Jochen
Published: April 2004

A flow channel for experimental modeling of the structural reaction injection molding (SRIM) process, for producing composites with a sandwich‐like structure, has been designed and constructed. It consists of a thin rectangular box, in which the reinforcing glass fabrics with different permeabilities are positioned parallel to each other. The core layer is a thick, porous mat. Location of the other denser and thinner reinforcing materials into the flow channel was symmetrical with respect to the spacer mat. The channel has transparent walls for observing propagation of the impregnation front in the spacer mat and in the reinforcing dense layers. Development of the impregnation front during filling the flow channel and the pressure profile in the gate were measured for non‐foaming reactive polyurethanes. Enough good correspondence between the calculated and experimentally observed flow front position and pressure profiles was obtained.
Chemical modification of polyurethane for two‐component injection molding
Authors: Bräuer M. , Hupfer B. , Nagel J. , Lehmann D.
Published: April 2004

A thermoplastic polyurethane (TPU) was modified by reactive processing with 4,4′‐diphenylmethane diisocyanate (MDI). The use of this modified polyurethane was investigated for improved adhesion in composites with polyamide 6 (PA 6). Specimens were prepared by two‐component injection molding. With the modified polyurethane the tensile bond strength could be increased by about 50%. An insoluble and inseparable polyurethane residue on the PA 6 fracture surface found by ATR‐FTIR spectroscopy gave evidence of chemical bonding between PA 6 and TPU. Allophanate bonds were formed by the chemical modification. These groups functioned as an inert source of highly reactive isocyanate groups. Urea groups, the polyurethane chain were formed by the modification, too. These groups may improve the compatibility between the two components. A change in the morphology of the polyurethane was observed, which was caused by the change in molecular structure by the chemical modification. The high level of bond strength may be due to a combination of these phenomena.
Development of orientation and mechanical properties of extrusion cast polyamide 11 films in biaxial stretching process
Authors: Rhee Sangkeun , White James L.
Published: April 2004

The development of orientation of extrusion cast polyamide 11 films in the biaxial stretching process was studied with birefringence and wide angle X‐ray diffraction (WAXD) pole figures. White‐Spruiell biaxial orientation factors of the crystalline phase were calculated with the pole figure data. Both biaxially stretched films were developed. Planarity of hydrogen bonding planes with respect to the film surface was observed from WAXD pole figures. Mechanical properties of the films were studied. Tensile strength and elongation at break were successfully correlated with the out‐of‐plane birefringences.
Numerical investigation of continuous processes for catalytic hydrogenation of nitrile butadiene rubber
Authors: Pan Qinmin , Rempel Garry L. , Ng Flora T. T.
Published: April 2004

Dynamic behavior of continuous processes was numerically investigated for the catalytic hydrogenation of nitrile butadiene rubber, based on developed models, which took into account the coupling between kinetics and mass transfer. The evolution of hydrogenation reaction trajectories in both cases were analyzed. It is proposed that the coupling behavior between the catalytic hydrogenation and mass transfer was completely determined by the ability of the catalyst in activating hydrogen, carbon‐carbon double bond loading level and the relative capacity of reaction to mass transfer as well as the residence time in the reactor. Four dimensionless parameters were derived to characterize these aspects. The effects of operation conditions on the hydrogenation processes were investigated. The application of the ideal flow models to non‐ideal flows was in addition discussed. It is suggested that the optimal reactor for such a hydrogenation system would be a plug flow reactor with an instantaneous well‐mixing component in the inlet of it, and a reasonable approach to the proposed optimal reactor should be with the flow behavior of at least three continuous stirred tank reactors in series. Further research directions are suggested.
Modification of porous suspension‐PVC particles by stabilizer‐free aqueous dispersion polymerization of absorbed monomers
Authors: Shach‐Caplan M. , Narkis M. , Silverstein M. S.
Published: April 2004

The modification of porous PVC particles by an in‐situ stabilizer‐free polymerization/crosslinking of a monomer/crosslinker/peroxide solution absorbed within the PVC particles is presented. The modifying crosslinked polymers are polystyrene (PS) crosslinked with DVB (divinyl benzene), polymethyl methacrylate (PMMA) crosslinked with ethylene glycol dimethacrylate (EGDMA), and styrene‐MMA copolymer crosslinked with DVB. The modified PVC particles characterization includes polymerization yield, non‐extractables, 13C solid‐state CPMAS NMR, porosity measurements and also morphology and dynamic mechanical behavior (DMTA). The levels of nonextractable fractions found and 13C solid‐state CPMAS NMR results are indicative of low chemical interaction in the semi‐IPN PVC particles. Particle porosity levels and SEM observations indicate that styrene and MMA mainly polymerize within the PVC particles' bulk and just small amounts in the pores. MMA polymerization in the PVC pores is as crusts covering the PVC pore surfaces, whereas styrene polymerization in the PVC pores is by filling the pores. Dynamic mechanical studies show that tanδ and the storage modulus curves are influenced by the incorporation of PS and XPS but not by the incorporation of PMMA and XPMMA.
Flow patterns and mixing mechanisms in the screw mixing element of a co‐rotating twin‐screw extruder
Authors: Ishikawa Takeshi , Amano Tarou , Kihara Shin‐Ichi , Funatsu Kazumori
Published: April 2004

Non‐Newtonian and non‐isothermal flow simulations based on 3‐D FEM were applied to a special and conventional elements of a twin‐screw extruder. The screw mixing element (SME), a kind of special element, was a distributive mixing promoter consisting of a standard screw profile with slots cut across the flight tip to increase leakage flow. The full flight screw (FF) and the kneading block (KB) were examined as conventional elements in order to contrast the mixing behavior with the SME. The accuracy of numerical results was verified by experimentally measuring pressure and temperature. Additionally, marker particle tracking analysis was carried out to evaluate the distributive and dispersive mixing. Using the above analyses, the following results were obtained: The pumping capability of the SME was smaller than that of the FF and was the same as for the KB. The SME suppressed heat generation and showed the lowest temperature distribution of the three elements. For distributive mixing, the SME showed the best performance judging from the mixing coefficient G, residence time distribution, and area stretch distribution based on a laminar mixing mechanism. A higher rotational speed achieved better distributive mixing performance. For dispersive mixing defined by stress distribution, the SME showed the second best performance next to the KB. It also showed better dispersive mixing performance with increasing rotational speed. The SME had the advantages of low heat generation and good distributive mixing.