bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractBlends 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

AbstractExterior 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractDie 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

AbstractThis 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractStructural 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

AbstractThe 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

AbstractThe 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

AbstractSurface 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

AbstractThree‐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

AbstractVarious 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.