bluuebunny/crossref_metadata_2025 huggingface dataset:
Molar mass of poly (ethylene terephthalate) (PET) during ultimate uniaxial drawing
Authors: Göschel Ulrich , Cools Paul J. C. H.
Published: April 2004

The changes of the average molar mass Mw, Mn, Mz, and molar mass distributions during multistep uniaxial drawing of poly(ethylene terephthalate) (PET) to achieve ultimate mechanical properties have been studied in detail by means of size exclusion chromatography (SEC) with triple detection: concentration, viscosimetry, and light scattering, using HFIP as solvent. An increase in molar mass of PET due to post‐polycondensation and/or transesterfication during drawing at a high temperature of 160 to 230°C was found. Moreover, drawing leads to crystallization and large orientation in the amorphous phase, which results in lower molecular mobility and prevents a further growth in chain length. Crazing under extreme drawing conditions occurs and affects a decrease in molar mass.
The effects of dual‐orifice air‐ring design on blown film cooling
Authors: Sidiropoulos V. , Vlachopoulos J.
Published: April 2004

Numerical simulations of turbulent air flows tangentially impinging on blown film bubbles have been carried out. The cooling air is assumed to originate from a dualorifice adjustable air‐ring. The streamline patterns and heat fluxes are determined through a finite volume numerical technique for modeling of turbulent air flow. It is shown that cooling efficiency is critically sensitive to the air‐ring design as minor modifications cause large variations in cooling performance. Additionally, for a given design, the operational setup of the air ring is equally critical to the cooling performance. It is explained that the large influence observed on heat transfer rates is primarily due to the Coanda effect, which forces air jets to attach themselves to surfaces.
Surface tension of polyethylene used in thermal coating
Authors: Demarquette Nicole Raymonde , Da Silva Fabio Teodoro , Brandi Sergio Duarte , Gouvêa Douglas
Published: April 2004

In this work the surface tension of a polyethylene used in thermal coating, identified as a mixture of low density polyethylene (LDPE) and stearic acid, was measured as a function of temperature for temperatures ranging from 120°C to 150°C using a pendant drop apparatus. The values were compared to the surface tension of the pure components (low density polyethylene and stearic acid). It was shown that the surface tension of the mixture is higher than the surface tension of the pure components (more than 25%). Surface analysis by Electron Spectroscopy for Chemical Analysis (E.S.C.A.) of the polyethylene used in thermal coating before and after surface tension measurement was conducted; the experimental results showed that the oxygen and the carbon present at the surface of both the powder and the drop were involved in COH and COOH bonds (for oxygen) and in CC and CO bonds (for carbon). It was shown that there is an increase of COOH and a decrease of COH bonds at the surface when the polymer is heated. It was also shown that there is an increase of C bounded to O at the surface of the drop and consequently a decrease of CC bonds. The decrease of COH was attributed to the drying of the polymer during heating and the decrease of CC was attributed to the coalescence of the polymer particles during pendant drop fomation.
Binary blends of metallocene polyethylene with conventional polyolefins: Rheological and morphological properties
Authors: Kwag Hanjin , Rana Dipak , Cho Kyucheol , Rhee Jangweon , Woo Taewoo , Lee Byung H. , Choe Soonja
Published: April 2004

The rheology and morphology of four sets of binary blends of polyethylene synthesized with metallocene catalysis (metallocene polyethylene: MCPE) with polyolefins prepared using Ziegler‐Natta catalysts have been investigated. The blend systems are MCPE with high density polyethylene (MCPE‐HDPE), polypropylene (MCPE‐PP), poly(propylene‐co‐ethylene) (MCPE‐CoPP), and poly(propylene‐co‐ethylene‐co‐1‐butylene) (MCPE‐TerPP). Cole‐Cole plots [storage melt viscosity (η′) versus loss melt viscosity (η″)], plots of the dynamic storage modulus (G′) versus the dynamic loss modulus (G″), and plots of the log melt viscosity (η*, η′, and η″) versus blend compositions were constructed. The morphology of the blends after microtoming and etching was studied. The phase morphology of MCPE‐HDPE appeared homogeneous, whereas the other three blends were heterogeneous. Rheological and morphological investigations indicated that the MCPE‐HDPE blend was miscible, but the other three blends were immiscible in the melt as well as in the solid state. These observations can be rationalized in terms of the similarity of the chemical structures of the polyolefins.
The effect of kevlar fiber reinforcement on the curing, thermal, and dynamic‐mechanical properties of an epoxy/anhydride system
Authors: Antón J. J. Suay , Pradas M. Monleóan , Ribelles J. L. Gómez
Published: April 2004

Curing, thermal, and dynamic‐mechanical relaxational behavior of an epoxy/‐anhydride resin and a Kevlar‐fiber/epoxy composite were compared. Reinforcement by Kevlar fibers had a catalytic effect on the curing reaction. Reinforced formulations produced higher extents of reaction than neat formulations at the same curing time. Curing kinetics was also studied by means of DSC heating scans. When the Kevlar content increased, the heat flow curves and the exothermic peak temperature shifted significantly to lower temperatures. The glass transition temperature of the matrix also decreased as the Kevlar content increased. Postcuring reduced the differences between the neat and reinforced formulations. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal dynamic‐mechanical measurements. The effect of fiber addition on the main dynamic‐mechanical relaxation was analyzed with a simple mechanical model.
Rotational molding of plastics: Comparison of simulation and experimental results for an axisymmetric mold
Authors: Olson L. G. , Crawford R. , Kearns M. , Geiger N.
Published: April 2004

We present a validation study comparing the mold wall temperature estimates from an axisymmetric thermal finite element simulation of the rotational molding process with temperature data obtained during experiments conducted on industrial‐grade rotational molding equipment. The finite element model simulates the heat transfer processes involved in rotational molding through the end of powder deposition, and uses an Arbitrary Lagrangian Eulerian technique to track the growing molten plastic layer. The experiments were conducted with nine different operating conditions on a single axisymmetric mold shape. The simulation results for mold wall temperature agreed well with the experimental data under all of the conditions tested.
An investigation of the friction and wear behaviors of polyphenylene sulfide filled with solid lubricants
Authors: Yu Laigui , Yang Shengrong , Liu Weimin , Xue Qunji
Published: April 2004

Composites of polyphenylene sulfide (PPS) filled with solid lubricant particles of graphite (C), molybdenum disulfide (MoS2), and polytetrafluoroethylene (PTFE) were prepared by compression molding. The size of the solid lubricant particles was 3‐;5 µm. The friction and wear behaviors of the composites were examined with a pinon‐disk test rig. The worn composite pin surfaces and the transfer films formed on the counterface were analyzed with scanning electron microscopy. An X‐ray photo‐electron spectroscope (XPS) was used to characterize the chemical states of the elements in the transfer film. It has been found that graphite and PTFE as the fillers increase the wear resistance of PPS considerably, while MoS2 as the filler decreases the wear resistance of PPS greatly. The fillers promote the decomposition of PPS and generate compounds, which accounts for the changes in the wear resistance of the composites.
On‐line NIR sensing of CO2 concentration for polymer extrusion foaming processes
Authors: Nagata Takefumi , Tanigaki Masataka , Ohshima Masahiro
Published: April 2004

An on‐line sensor using near infrared (NIR) spectroscopy is developed for monitoring CO2 concentration in polymeric extrusion foaming processes. NIR absorption spectra are acquired by a probe installed at the foaming extruder die. The calibration curve relating the absorbance spectrum at 2019 nm to the dissolved gas concentration is derived so as to infer dissolved CO2 gas concentration on‐line from measured NIR spectra. Experimental results show the developed on‐line NIR sensor can successfully estimate dissolved CO2 concentration in the molten polymer and illustrate that the developed NIR sensing technique is among the more promising methods for quality control of polymeric extrusion foaming processes.
Novel variations in the microstructure of the auxetic microporous ultra‐high molecular weight polyethylene. Part 1: Processing and microstructure
Authors: Webber R. S. , Alderson K. L. , Evans K. E.
Published: April 2004

Recent publications have detailed how auxetic (negative Poisson's ratio) polymers have been fabricated by a novel thermal processing route consisting of three welldefined stages—compaction, sintering and extrusion. In this paper, the compaction stage of the processing route is omitted and the effects of this on the structural integrity, microstructure and Poisson's ratios of the extrudates examined. The effects of varying the processing parameters of the sintering and extrusion stages are studied so that a set of conditions that produce a highly fibrillar auxetic material with sufficient structural integrity to allow mechanical properties to be evaluated can be defined. Poisson's ratios as low as −4 have been obtained.
Polymerization of anilinium/DBSA in the presence of clay particles: Catalysis and encapsulation
Authors: Segal E. , Aviel O. , Narkis M.
Published: April 2004

This paper describes polymerization of anilinium‐DBSA complex to PANI‐DBSA (DBSA doped polyaniline) in an aqueous dispersion in the presence of mica or talc clays. It is found that the clay presence significantly accelerates the polymerization kinetics by metal ions, such as Fe+2 ions, present in the clays. Polymerization occurs preferentially on the clay particles' surface, causing their encapsulation with PANI‐DBSA shells. Further coating with PANI‐DBSA takes place on the already coated particles with thin PANI‐DBSA shells by an autoacceleration effect of anilinium‐DBSA polymerization by PANI. It is suggested that the catalytic/autoacceleration effect dominating in the coating process of clay particles with PANI‐DBSA can be extended to other particle/coating systems, which are already under investigation.
Friction welding of similar and dissimilar materials: PMMA and PVC
Authors: Lin C. B. , Wu Li Cheng
Published: April 2004

The effects of spin friction pressure and time on the friction welding between parts of the same material and different materials are discussed. The heat‐affected zone is divided into three regions: the plasticized region (Zpl), the partly plasticized region (Zpd), and the undeformed region (Zud). The tensile fracture morphology has three sections: the non‐plasticized central section (Fud), the plasticized peripheral section (Fpl), and the partly plasticized section between Fud and Fpl (Fpd). Friction pressure (spinning timing): 0.784 Mpa (6 seconds), 0.981 MPa (8 seconds and 10 seconds) in PMMA‐PMMA welding, 0.588 Mpa (10 seconds) in PVC‐PVC welding, and 15.7 MPa (15 seconds) in PMMA‐PVC welding attains better bonding strength, because these parts have larger Fpd and Fpl regions, which have no Fud in the central part.
Polyethylene compounds containing mineral fillers modified by acid coatings. 1: Characterization and processing
Authors: Haworth B. , Raymond C. L. , Sutherland I.
Published: April 2004

Research has been carried out to determine the effect of filler coatings on the processing properties of medium density polyethylene (MDPE) modified by an ultrafine grade of flame‐retardant magnesium hydroxide (Mg(OH)2) filler. Selected filler coatings were acid‐group terminated and were of varying aliphatic chain length. The filler dry‐coating process has been optimized by characterizing the reaction between Mg(OH)2 filler surface and the acid group, using spectroscopic techniques including Fourier transform infrared (FTIR) and X‐ray photoelectron spectroscopy (XPS). Using immersion calorimetry, the interactions between the fillers and the polyolefin matrix were shown to decrease on the addition of a fatty‐acid coating. Compounding torque and specific energy data relate to filler dispersion; qualitative analysis has demonstrated how the coatings provide a reduction in both size and number of particle agglomerates. MDPE compound processability was assessed by capillary rheometry; wall slip was evident in compounds containing uncoated Mg(OH)2 filler. Consequently, the development of molecular orientation of the polymer during injection mold filling, quantified by a reversion analysis, is modified by the effects of filler coating chain length and addition level, an effect that has important implications to link the mechanical properties of MDPE‐Mg(OH)2 composites to processing history.
Barrier properties of blends based on liquid crystalline polymers and polyethylene
Authors: Flodberg G. , Hellman A. , Hedenqvist M. S. , Sadiku E. R. , Gedde U. W.
Published: April 2004

Blends of an extrusion‐grade polyethylene and two different liquid crystalline polymers of Vectra type were prepared by melt mixing using poly(ethylene‐comethacrylic acid) as compatibilizer. Oxygen and water vapor permeability, transparency and welding strength of compression molded and film blown specimens were studied. The compression molded blends showed gas permeabilities conforming to the Maxwell equation assuming low permeability liquid crystalline polymer spheres in a high permeability polyethylene matrix. One of the liquid crystalline polymers with suitable rheological properties formed a more continuous phase in the film blown blends and a substantial decrease in oxygen and water vapor permeability was observed in these blends. The compression molded blends with 50% liquid crystalline polymer and some of blow molded blends showed very high gas permeabilities. It is believed that voids forming continuous paths through the structure were present in these samples. The blends showed significantly higher opacity than pure polyethylene.
Theoretical analysis and experimental characterization of the TPO/adhesion promoter/paint interface of painted thermoplastic polyolefins (TPO)
Authors: Mirabella Francis M. , Dioh Ndiba , Zimba Carl G.
Published: April 2004

Exterior and interior automotive applications of TPO (thermoplastic polyolefin) resins, which are, often, composed of a paint coating over an injection‐molded TPO, have increased interest in the surface chemistry and physics of TPOs. Specifically, the interface system composed of base‐coat paint/adhesion promoter/TPO is of primary importance in controlling the paint adhesion to the TPO. The major, active component in the adhesion promoter is a chlorinated polypropylene (CPO). A theoretical model based on phase thermodynamics and diffusion kinetics resulted in a prediction that the TPO/CPO interface should have a lower bound thickness of about 11 nm and an upper bound of about 400 nm. A battery of experimental strategies to characterize this interface system was discussed. Techniques used were transmission electron microscopy (TEM), atomic force microscopy (AFM) and scanning transmission X‐ray microscopy (STXM). The near‐surface morphology of both unpainted and painted, injection molded TPO plaques exhibited ethylenepropylene rubber particles close to the surface, i.e. within the first 0.1–0.8 micrometer of the TPO surface, and no “overlayer” of transcrystalline polypropylene at the surface of the TPO. Each of these microscopic methods showed that the adhesion promoter/TPO interface was very sharp. The thickness of this interface was measured with respect to the interdiffusion of the CPO and TPO by STXM. The STXM measurements yielded an apparent interface thickness between the adhesion promoter and TPO of 340 ± 80 nm. This was in good agreement with the theoretical predictions.
Influence of morphology on photo‐degradation of low density polyethylene films
Authors: Tanaka Akira , Uno Hiromitsu , Miyagawa Eiichi , Kitamura Mitsunobu , Nitta Koh‐Hei
Published: April 2004

The effect of the morphology on photo‐degradation was investigated for low‐density polyethylene materials. For this purpose, films with different degrees of crystallinity and different degrees of orientation were prepared. For all the films, photodegradation was promoted at 336K for 12 days using a weather meter. The following results were obtained. There existed an induction period before degradation or chain scission. The induction period was longer for stretched films than for un‐stretched ones. Also, the rate of degradation became lower for stretched films. However, both the induction period and the rate of degradation hardly changed with heat‐treatment condition, that is, the degree of crystallinity. In the induction period, the density changed in a complicated manner. This complicated change must be due to the change in the molecular aggregation state of the amorphous phase. The rheological and GPC measurements indicated that photo‐degradation causes the lowering of molecular weight and the increase in higher molecular weight fraction, and consequently the broadening of molecular weight distribution. The lowering of molecular weight may be caused by chain scission and the increase in higher molecular weight fraction by the formation of crosslinks.
Modeling domain mixing in semi‐interpenetrating polymer networks composed of poly(vinyl chloride) and 5% to 15% of crosslinked thermosets
Authors: Xu Xiaoming , Toghiani Hossein , Pittman Charles U.
Published: April 2004

The nature of phase mixing in semi‐interpenetrating polymer networks (SIPNs) of poly(vinyl chloride) (PVC)/thermoset blends was studied by using both the glass transition temperature third power composition equation and DMTA modeling. From 5% to 15% by weight of an oligomeric MDI isocyanate or a low viscosity epoxy were blended separately with PVC to make two series of SIPNs. The DMTA‐derived Tg data were modeled by the Tg third power composition equation to characterize “energy interaction” features of PVC/thermoset phase mixing. Fitting experimental Tg values gave estimations of the characteristic parameters, K1 and K2 of the Tg power equation. K1 and K2 were each positive for the PVC/epoxy (K1 = 1.1, K2 = 7.2) and the PVC/isocyanate (K1 = 29.9, K2 = 38) blends, showing that binary hetero‐interactions (enthalpic effects) and conformational redistributions (entropic effects) during the binary hetero‐interactions both contributed favorably to phase mixing. Negative K1 ‐ K2 values for both groups of blends indicate entropic contributions predominate. The thermoset dilution produced a lightly crosslinked thermoset network, which was locked into the amorphous PVC, forming a mixed thermoset/PVC SIPN domain. Conformational redistributions of PVC and thermoset segments continue to occur within the developing SIPN domain before phase separation can occur. The combined series‐parallel Takayanagi coupling model, which assumed that a PVC phase and a mixed PVC/thermoset SIPN phase coexisted, was employed to describe the viscoelastic behavior of PVC/thermoset blends. Reasonable fits between the experimental DMTA plots and modeling predictions were found. The predictions were not sensitive to the degree of series‐parallel coupling. The modeled DMTA plots, like the experimental results, exhibited only a single E″ peak in the glass transition temperature range for both the PVC/PAPI and PVC/epoxy systems. Thus, very small PVC/thermoset SIPN domains (< 20 nm diameter) that are dispersed in separate domains of a PVC‐rich phase (despersive phase mixing characteristics) provide a reasonable explanation of the blends' phase structures.
A three‐dimensional analysis of coextrusion in a single manifold flat die
Authors: Gifford W. A.
Published: April 2004

The coextrusion of two polymers through a single manifold flat die is examined. The three components of velocity and the pressure are determined in each layer along with the interface between the layers. It is shown that even when the viscosity ratio is one (i.e., single layer), flat “layers” entering the die will not remain flat but will be distorted by the die. For coextrusion of two polymers, the distortion of the interface profile at the exit of the die and thus the uniformity of the layers depends upon the viscosity and flow rate ratios of the two polymers as well as the geometry of the die.
Impact fracture behavior of PP/EPDM/glass bead ternary composites
Authors: Liang J. Z. , Li R. K. Y. , Tjong S. C.
Published: April 2004

The effects of glass bead filler content and surface treatment of the glass with a silane coupling agent on the room temperature impact fracture behavior of polypropylene (PP)/ethylene‐propylene‐diene monomer copolymer (EPDM)/glass bead(GB) ternary composites were determined. The volume fraction of EPDM was kept constant at 10%. The impact fracture energy and impact strength of the composites increased with increasing volume fraction of glass beads (ϕg). Surface pretreatment of the glass beads had an insignificant effect on the impact behavior. For a fixed filler content, the best impact strength was achieved when untreated glass beads and a maleic anhydride modified EPDM were used. The impact strength exhibited a maximum value at ϕg=15%. Morphology/impact property relationships and an explanation of the toughening mechanisms were developed by comparing the impact properties with scanning electron micrographs of fracture surfaces.
Flaring dies to suppress die drool
Authors: Ding Fan , Zhao Lian , Giacomin A. Jeffrey , Gander Jesse D.
Published: April 2004

Die lip build‐up is the unwanted material accumulation on extrusion die lips. Here, flared dies are shown experimentally to suppress die lip build‐up. A semiempirical method for flared die design is also provided. Nonlinear viscoelastic constitutive equations are used to calculate the wall shear stress and first normal stress difference in flared dies. By incorporating melt memory, a promising design method for die flaring is presented. The stress history upstream of the die exit governs the die design. The upstream gap is selected to maximize undershoot of the first normal stress difference N1 at the die wall caused by flaring. The flare length, on the other hand, is selected to ensure a steady N1 at the die lips.
Foaming of PS/wood fiber composites using moisture as a blowing agent
Authors: Rizvi Ghaus , Matuana Laurent M. , Park Chul B.
Published: April 2004

This paper presents an experimental study on foam processing of polystyrene (PS) and high‐impact polystyrene HIPS/wood‐fiber composites in extrusion using moisture as a blowing agent. Wood‐fiber inherently contains moisture that can potentially be used as a blowing agent. Undried wood‐fiber was processed together with PS and HIPS materials in extrusion and wood‐fiber composite foams were produced. The cellular morphology and volume expansion ratios of the foamed composites were characterized. Because of the high stiffness of styrenic materials, moisture condensation during cooling after expansion at high temperature did not cause much contraction of the foamed composite and a high volume expansion ratio up to 20 was successfully obtained. The experimental results showed that the expansion ratio could be controlled by varying the processing temperature and the moisture content in the wood fiber. The effects of a small amount of a chemical blowing agent and mineral oil on the cell morphologies of plastic/wood‐fiber composite foams were also investigated.
Effects of SBS on phase morphology of iPP/aPS blends
Authors: Šmit I. , Radonjič G.
Published: April 2004

The supermolecular structure of binary isotactic polypropylene/poly(styrene‐b‐butadiene‐h‐styrene) (iPP/SBS) and isotactic polypropylene/atactic polystyrene (iPP/aPS) compression molded blends and that of ternary iPP/aPS/SBS blends were studied by optical microscopy, scanning and transmission electron microscopy, wide‐angle X‐ray diffraction and differential scanning calorimetry. Nucleation, crystal growth, solidification and blend phase morphology are affected by the addition of amorphous components (SBS and aPS). As a compatiblizer in immiscible iPP/aPS blends, SBS formed interfacial layer between dispersed honeycomb‐like aPS/SBS particles and the iPP matrix, thus influencing the crystallization process in iPP. The amount of SBS and aPS, and compatibilizing efficiency of SBS, determine the size of dispersed aPS, SBS, and aPS/SBS particles and, consequently, the final blend phase morphologies: well‐developed spherulitic morphology, cross‐hatched structure with blocks of sandwich lamellae and co‐continuous morphology. The analysis of the relationship between the size of spherulites and dispersed particles gave the criterion relation, which showed that, in the case of a well‐developed spherulitization, the spherulites should be about fourteen times larger than the incorporated dispersed particles; i.e. to be large enough to engulf dispersed inclusions without considerable disturbing of the spherulitic structure.
Investigation of wavelike flow marks in injection molding: A new hypothesis for the generation mechanism
Authors: Tredoux Louis , Satoh Isao , Kurosaki Yasuo
Published: April 2004

The wavelike flow mark phenomenon is one of the surface defects that can occur during the injection stage of the injection molding process. The generating mechanism of this phenomenon is not yet well understood. In this paper, flow visualization data showing the way in which flow marks generate are reported for the first time. On the basis of these observations a new hypothesis for the mechanism causing flow marks is proposed. A mathematical expression is developed that expresses nondimensional flow mark curvature in terms of the processing conditions, the thermal properties of the polymer and the mold, and the interval of flow mark generation. This mathematical relationship is then tested over a wide range of operating conditions and for three different materials. Finally, the practical implications and significance of this new hypothesis are discussed.
Effects of reinforcing fibers on the crystallization of polypropylene
Authors: Manchado Miguel A. López , Blagiotti Jerrico , Torre Luigi , Kenny José M.
Published: April 2004

The effects of the incorporation of different types of fibers on the crystallization kinetics and thermodynamics of isotactic polypropylene (iPP) are investigated. The study is mainly performed by thermal analysis, both in isothermal and constant cooling rate conditions, utilizing differential scanning calorimetry (DSC). The crystallization kinetics of the studied composites is successfully described by the Avrami model. Moreover, the effects of different kind of fibers are studied comparing the values of kinetics parameters such as the Avrami exponent n, the kinetic constant of the crystallization rate, Kn and the half‐time of crystallization, T 1/2. The results of the investigation show that the fibers behave as effective nucleant agents for the crystallization of polypropylene. In fact, a dramatic decrease of the half‐time of crystallization, T1/2, as well as a sensible increase of the overall crystallization rate, Kn, are observed in the presence of all the fibers analyzed. These effects are more marked in the presence of aramid fibers. The Avrami model is successfully applied to describe the crystallization kinetics of the composites. The kinetic curves obtained under non‐isothermal conditions confirm the results obtained under isothermal conditions and demonstrate the nucleating action of the fibers on the PP crystallization. Furthermore, the spherulite growth and the transcrystallinity on the surface of the fibers are investigated by optical polarizing microscopy. It is observed that transcrystallinity takes place in all kind of fibers studied, but also in this case, aramid fibers are the most effective in promoting transcrystallinity.
Reaction injection molding process of glass fiber reinforced polyurethane composites
Authors: Kim Dae Su , Macosko Christopher W.
Published: April 2004

Structural reaction injection molding (SRIM) was used to produce polyurethane composites containing random continuous glass fiber mats. A long rectangular mold was used to carry out the SRIM experiments. 4,4′‐diphenylmethane diisocyanate and poly(propylene oxide) triol were used to formulate a thermoset polyurethane system. Dibutyltin dilaurate was used as a catalyst. A second order Arrhenius equation described the PU polymerization kinetic data obtained from the adiabatic temperature rise measurement. A viscosity as a function of temperature and conversion was developed using rheometer data. The pressure rise at the gate was measured during filling. The flow behavior within the mold was described by Darcy's law and the Kozeny's equation. The temperature profile within the mold measured by thermocouples during filling and curing coincided fairly well with the simulation results. The thermal transient problem at the wall was solved using the overall heat transfer coefficient, and it was analyzed as a function of Biot number. The dimensional stability of the fiber reinforced PU parts was excellent compared to the pure PU parts.
Nonlinear dynamic behavior of rubber compounds: Construction of dynamic moduli generalized master curves
Authors: Riccò Theonis , Pegoretti Alessandro
Published: April 2004

The nonlinear dynamic behavior of a vulcanized rubber compound employed in the production of tires was investigated. The values of the dynamic storage modulus, E', and the loss factor, tanδ, were measured at different frequencies, temperatures and strain amplitudes. Data were subsequently analyzed and treated by an empirical method of frequency‐temperature‐deformation reduction that provided for E' and tanδ, respectively, a single master curve and the frequency‐temperature and frequency‐deformation shift factors. The E' trend, extrapolated at higher strain amplitudes on the basis of the master curves, resulted in good agreement with E' values obtained from direct experimental measurements.
Effects of rubber‐rich domains and the rubber‐plasticized matrix on the fracture behavior of liquid rubber‐modified araldite‐F epoxies
Authors: Xiao Keqin , Ye Lin
Published: April 2004

The fracture behavior of a bisphenol A diglycidylether (DGEBA) epoxy, Araldite F, modified using carboxyl‐terminated copolymer of butadiene and acrylonitrile (CTBN) rubber up to 30 wt%, is studied at various crosshead rates. Fracture toughness, KIC, measured using compact tension (CT) specimens, is significantly improved by adding rubber to the pure epoxy. Dynamic mechanical analysis (DMA) was applied to analyze dissolution behavior of the epoxy resin and rubber, and their effects on the fracture toughness and toughening mechanisms of the modified epoxies were investigated. Scanning electron microscopy (SEM) observation and DMA results show that epoxy resides in rubber‐rich domains and the structure of the rubber‐rich domains changes with variation of the rubber content. Existence of an optimum rubber content for toughening the epoxy resin is ascribed to coherent contributions from the epoxy‐residing dispersed rubber phase and the rubber‐dissolved epoxy continuous phase. No rubber cavitation in the fracture process is found, the absence of which is explained as a result of dissolution of the epoxy resin into the rubber phase domains, which has a negative effect on the improvement of fracture toughness of the materials. Plastic deformation banding at the front of precrack tip, formed as a result of stable crack propagation, is identified as the major toughening process.
Plasma surface treatment of PCL/PC blend sheets
Authors: Hirotsu Toshihiro , Ketelaars A. A. J. , Nakayama Kazuo
Published: April 2004

Surface treatments using glow discharge plasmas from O2 and Ar were applied to blend sheets of poly(ϵ‐caprolactone)‐polycarbonate (PCL/PC), which had been produced by extrusion from melts of the mixture at various blend ratios. As to the reactivity of these two plasmas, O2‐plasma forms the oxidative species to be reactive in general, while Ar‐plasma is non‐oxidative. Weight loss by the oxidative O2‐plasma etching increased with the content of PCL in the polymer blends. The surface became hydrophilic by plasma treatment, and the changes were affected also by the blend ratio. PC and the PC‐rich blend sheets became more hydrophilic than the PCL‐rich blends after plasma treatments. The O2‐plasma treatments were more effective than non‐oxidative Ar‐plasma treatment in increasing the hydrophilicity. Hydrophilic change was related to the increase in the polar contribution of surface energy.
Numerical simulation of crystallization in high density polyethylene extrudates
Authors: Pillai K. M. , Advani S. G. , Benard A. , Jacob K. I.
Published: April 2004

Three‐dimensional numerical simulation of solidification of high density polyethylene (HDPE) in a parallelepiped shaped extrudate is accomplished using a cell model for spherulite growth on a microscopic level under quiescent conditions and coupled with an enthalpy based heat transfer equation on the macroscopic level. The parallelepiped is cooled from the melting point of HDPE by a stream of air blown across it. When the thickness of the extrudate is of the order of microns, the distribution of the degree of crystallinity and temperature is uniform, and the lumped system formulation to model crystallization and heat flow is applicable. But significant variations inside the extrudate are observed when the thicknesses are of the order of millimeters and centimeters. The non‐dimensional Deborah and Biot numbers are shown to be important in the applicability of the formulation. The effects of air speed and ambient temperature on the crystallization process are also studied. It is observed that both (1) an increase in the air speed and (2) a decrease in the ambient temperature increase the rate of crystallization in the parallelepiped. The former has much greater effect than the latter in changing the average convective heat transfer coefficient. As a result, increasing the air speed results in much larger spherulites compared to reducing the ambient temperature. Decrease of temperatures in the extrudate during the either cooling processes is observed to be non‐monotonic owing to the release of the latent heat during crystallization. Introducing a constant temperature (melting point of HDPE) at a cross section of the extrudate changes the distribution of relative crystallinity and temperature in the extrudate significantly: the temperature gradient becomes much higher along the extrudate axis, and the material near the cross section never solidifies. Also, the extrudate behaves more like a fin as the variations in the thickness direction become insignificant.
Tensile properties of linear low density polyethylene (LLDPE) blown films
Authors: Krishnaswamy Rajendra K. , Lamborn Mark J.
Published: April 2004

Various linear low‐density polyethylene (LLDPE; density ∼ (0.920 g/cm3)) resins that encompass those polymerized using Ziegler‐Natta, metallocene, and chromium oxide based catalysts were blown into film at similar process conditions, and the tensile properties of the resulting films were investigated in relation to their orientation characteristics. The tensile properties of the subject blown films were observed to be significantly different from those of isotropic/un‐oriented polyethylene specimens of similar density (crystallinity). Further, the tensile properties were different in the machine and transverse directions. These were explained in terms of the orientation and lamellar organization characteristics of the LLDPE blown films. Investigation of the temperature dependence (between −50°C and +50°C) of these tensile properties indicated an increase in modulus, yield stress and break stress with decreasing temperature pointing to the possible role played by the decreased mobility of the non‐crystalline phase at lower temperatures. Excellent correlation between the Elmendorf tear properties of the LLDPE blown films and their tensile yield characteristics was observed. This added substantial credibility to previous hypotheses that specimen stretching plays a significant role in Elmendorf tear tests and further supported the previously identified structural features and microstructural deformation mechanisms that are deemed responsible for the discernment of LLDPE blown film tear resistance.
Non‐newtonian rheological behavior of semi‐dilute ultra‐high molecular weight polyethylene solution in gel‐spinning process. 1: Concentration effect on the fundamental rheological properties
Authors: Ohta Yasuo , Murase Hiroki , Sugiyama Hiroshige , Yasuda Hiroshi
Published: April 2004

The rheological properties of a semi‐dilute ultra‐high molecular weight polyethylene (UHMw‐PE)/paraffin wax solution were investigated by mainly focusing on the influence of its concentration on the shear flow viscosity. It was found that the UHMw‐PE solution exhibits a shear‐thinning behavior at a very wide shear rate range from 10−4 to higher than 103 sec−1. Furthermore, this typical non‐Newtonian behavior was more obvious with a concentration increase. From the concentration dependence of the zero‐shear creep compliance or other rheological factor, it was found that the extremely large Me value of the system gives rise to various kinds of non‐Newtonian behaviors, especially those highly elastic in nature. Finally, the origin of the abnormal stress fluctuation during the steady shear measurement was found to be related to the shear‐induced structural development of the solution.
Laser‐induced plasma spectroscopy for plastic identification
Authors: Anzano J. M. , Gornushkin I. B. , Smith B. W. , Winefordner J. D.
Published: April 2004

The goal of this work was instant identification of post‐consumer plastics by laser induced plasma spectrometry (LIPS). LIP spectra from plastics in a 200–800 nm spectral window were compared with reference spectral libraries stored in a computer. The libraries consisted of representative spectra from different groups of recycled plastic samples. The plasma emission spectra of polyethylene terephthalate (PET), high density polyethylene (HDPE), polyvinyl chloride (PVC), low density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS) were studied. Simple statistical correlation methods including linear and rank correlations were used. The probabilities of correct identification ranged from 0.8 to 1 with values close to unity for most of the polymers studied.
Isotactic polypropylene solidification under pressure and high cooling rates. A master curve approach
Authors: La Carrubba V. , Brucato V. , Piccarolo S.
Published: April 2004

Solidification in industrial processes very often involves flow fields, high thermal gradients and high pressures: the development of a model able to describe the polymer behavior becomes complex. Recently a new equipment has been developed and improved to study the crystallization of polymers when quenched under pressure. An experimental apparatus based on a modified, special injection moulding machine has been employed. Polymer samples can be cooled at a known cooling rate up to 100°C/s and under a constant pressure up to 40 MPa. Density, Micro Hardness (MH), Wide angle X‐ray diffraction (WAXD), and annealing measurements were then used to characterize the obtained sample morphology. Results on one iPP sample display a lower density and a lower density dependence on cooling rate for increasing pressure. Micro hardness confirms the same trend. A deconvolution technique of WAXD patterns is used to evaluate the final phase content of samples and to assess a crystallization kinetics behavior. A master curve approach to explain iPP behavior under pressure and high cooling rates was successfully applied on density results. On the basis of this simple model it is possible to predict the final polymer density by superposition of the effect of cooling rate and the effect of pressure in a wide range of experimental conditions.
Micro‐mechanical deformation mechanisms in the fracture of hybrid‐particulate composites based on glass beads, rubber and epoxies
Authors: Lee Jonghwi , Yee Albert F.
Published: April 2004

Two tougheners, glass beads and carboxyl terminated butadiene acrylonitrile copolymer (CTBN), are used to toughen and stiffen an epoxy thermoset. Rubber‐encapsulated glass beads are used and the hybrid particulate composites containing them are compared with those containing non‐encapsulated glass beads. Within a certain range of composition, the rubber encapsulation is found to change the interactions between glass beads and CTBN particles, resulting in an increase in fracture toughness. The toughening effect is explained by the fact that the cavities of CTBN particles are larger in encapsulation systems than in non‐encapsulation systems. As more CTBN particles are incorporated into glass bead filled epoxies, the cavitation/shear yielding mechanism of CTBN particles replaces the micro‐shear banding mechanism of glass beads as the major micro‐mechanical deformation. Rubber encapsulation seems to enable this transition of major micro‐mechanical deformation to occur at a lower volume fraction of CTBN.
Numerical analysis of a reactive extrusion process. Part I: Kinetics study on grafting of vinylsilane to polyethylene
Authors: Fukuoka Takamasa
Published: April 2004

For controlling a reactive extrusion process in the subsequent study. the model equations of reaction kinetics and shear viscosity were studied. We focused on a free radical reaction between the molten polyethylene and vinylsilane. The kinetics model was expressed as a reaction rate equation with an apparent rate constant. The shear dependent of reacted polyethylene was formulated by employing the modified Cross model proposed in our early study. In addition, the average molecular weight was considered to correlate the shear viscosity with the reaction kinetics, leading to a series of rheo‐kinetics formulas. The experiments were carried out in a specific batch mixer suitably designed for sampling in arbitrary periods. Their reaction conversions, molecular weight distributions, and shear viscosity were measured, respectively, with an induced coupled plasma (ICP) emission spectrochemical analyzer, a high temperature gel permeation chromatography (GPC), and a capillary rheometer. Determining the parameters in each model, a simulator is set to investigate an engineering extrusion process.
Numerical analysis of a reactive extrusion process. Part II: Simulations and verifications for the twin screw extrusion
Authors: Fukuoka Takamasa
Published: April 2004

A newly designed extruder reactor for grafting vinyl monomers onto polyolefins was studied experimentally and theoretically. The process was made up of a self‐wiping co‐rotating twin screw extruder with a separated reaction zone and two vent zones. The reactive extrusion was performed using a linear low density polyethylene, vinyltrimethoxysilane and di‐t‐butylperoxide under different operation conditions. For the purpose of process analysis, we built a computer simulation based on the reaction kinetics and rheological models studied in the preceding paper. The flow field in the extruder was calculated by the flow analysis network (FAN) method with non‐isothermal non‐Newtonian flow conditions. The iterative procedure was organized to predict local pressure, filling factor, cumulative residence time and temperature along the extruder. Furthermore, we succeeded in representing the profiles of reaction conversion and shear viscosity. Calculated results showed good agreements with the experimental data.
Preparation and characterization of plasma‐polymerized benzonitrile films with ultrafast optical kerr effect
Authors: Zhao Xiongyan , Hu Xiao , He Yuankang , Chen Huiying
Published: April 2004

Plasma‐polymerized benzonitrile (PPBN) thin films were successfully prepared by radio frequency glow discharge techniques. The results of Fourier transform infrared (FTIR), UV‐Visible absorption spectra, X‐ray photoelectron spectroscopy (XPS) and on‐line MS revealed that extensive conjugation has been formed in the PPBN thin films and the polymerization of benzonitrile took place mainly through the opening of carbon‐nitrogen triple bonds. The morphology characterized by field emission microscopy (FEM) indicated that the fine, homogenous and brown transparent films could be obtained at comparatively low discharge power. Furthermore, the subpicosecond time‐resolved optical Kerr effect (OKE) was used to measure the third‐order optical nonlinearity. For the first time, an ultrafast response and nonresonant optical Kerr effect of PPBN films was observed.
Cure and reaction kinetics of an anhydride‐cured epoxy resin catalyzed by N‐benzylpyrazinium salts using near‐infrared spectroscopy
Authors: Park Soo‐Jin , Kwak Gun‐Ho , Sumita Masao , Lee Jae‐Rock
Published: April 2004

The cure behavior and the reaction kinetics of an anhydride‐cured epoxy resin catalyzed by cationic thermal latent initiator, N‐benzylpyrazinium salts, have been investigated by a near‐infrared (NIR) spectroscopy. The spectral changes are interpreted in terms of the mechanism of cure. NIR absorption bands are due to protons connected to carbon, nitrogen, and oxygen. In this work, the homogeneous model system involves a simple addition reaction mechanism leading to an exothermic reaction between epoxide and anhydride activated groups. A comprehensive account of the origin, location, and shifts during reaction of all major NIR absorption peaks in the spectral range from 4000 to 7100 cm−1 is provided. The extent of reaction is calculated from NIR absorption band at 4530 cm−1, which depends on epoxide concentration. The utility of NIR spectroscopy to study the kinetics of epoxy cure reaction has been established. Consequently, absorbencies in the NIR spectra suitable for quantitative studies of epoxy resin reaction kinetics have been identified.
A hybrid 3D/2D finite element technique for polymer processing operations
Authors: Yu Yun‐Wey , Liu Ta‐Jo , Hsu Chaug‐Liang , Yang Yeon‐Sheug
Published: April 2004

A hybrid 3D/2D finite element method is proposed to simulate polymeric fluid motions for various polymer processing operations that may involve complex flow geometries. The flow regime is divided into 2D and 3D regions, and the fluid flow is assumed to follow the Hele Shaw model in the 2D region. Mathematically the 2D and the 3D regions are linked by the conservation of mass and the continuation of pressure variations. Two example calculations have been used to illustrate the accuracy and efficiency of the new numerical technique, and it was found that a substantial amount of computing time can be saved to obtain numerical solutions that are as accurate as the complete 3D calculations.
Some thermodynamic and kinetic properties of the system PETG‐CO2, and morphological characteristics of the CO2‐blown PETG foams
Authors: Paul Handa Y. , Wong Betty , Zhang Zhiyi , Kumar Vipin , Eddy Sharon , Khemani Kishan
Published: April 2004

The solubility of CO2 in PETG, a glycol‐modified PET, was measured at different temperatures and over a broad pressure range, and diffusion coefficients were derived at the corresponding conditions. The solubility of CO2 is quits high. For example, almost 15 wt% CO2 can be dissolved in PETG at 35°C and 6.0 MPa. Consequently, CO2 is good blowing agent for PETG. Cellular foams in the density range of about 0.04 to 1.2 g/cm3 and diameters in the range of about 10 to 150 µm were produced. The foam density and the cell size were found to depend on the foaming temperature and time, with larger cells obtained at higher temperatures or when the sample was foamed for a longer time. The foam density decreased with an increase in the foaming temperature to about 90°C, beyond which the density tended to increase slightly due to the cell collapse or coalescence. The density reduction also depended on the pressure at which the polymer was saturated with CO2; the higher the saturating pressure at a given temperature, the greater the density reduction.