bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphology and mechanical behavior of polypropylene hot plate welds
Authors: Oliveira M. J. , Bernardo C. A. , Hemsley D. A. 
Published: April 2004

AbstractPolypropylene tensile bars were hot plate welded and analyzed by microscopy and mechanical tests. The welding process caused significant modifications to the microstructure and shape of the bars at the weld zone. The weld morphology was affected by both the welding parameters and the thermal history of the components. Oriented textures, coarse spherulites, voids or sharp notches occurring at the beads are the key morphological factors that affect the weld quality. Weld performance is dependent upon the type of testing method used. A tensile impact test has been shown to be potentially useful for quality control, as the fracture behavior is affected by the overall morphoiogy.
Electrical and mechanical behavior of carbon black–filled poly(vinyl acetate) latex–based composites
Authors: Grunlan Jaime C. , Gerberich William W. , Francis Lorraine F. 
Published: April 2004

AbstractThe electrical and mechanical behaviors of carbon black‐filled. Poly(vinyl acetate) latex‐based polymer composites were examined. These composites were found to exhibit percolation thresholds in electrical conductivity near 2 vol% carbon black due to their segregated microstructures. Storage modulus and ultimate tensile strength (UTS) both exhibited discontinuities at 10 vol% carbon black, corresponding to a critical pigment volume concentration. Drying composites at 60°C rather than room temperature produced a higher percolation threshold and better mechanical properties at carbon black loadings above 10 vol% carbon black. A figure of merit was proposed to assess the balance of electrical conductivity, storage modulus and UTS. The figure of merit exhibited a peak value at 10 vol% for composites dried at room temperature and was shifted to higher carbon black concentrations when composites were dried at 60°C.
Effect of interlayer structure, matrix viscosity and composition of a functionaiized polymer on the phase structure of polypropylene‐montmorillonite nanocomposites
Authors: Kim Kyu‐Nam , Kimm Hyungsu , Lee Jae‐Wook 
Published: April 2004

AbstractPolypropylene (PP)‐clay composites were prepared by melt mixing in an intensive mixer. Three grades of PPs with different melt viscosities were employed to investigate mixing characteristics and phase structure of the composites with various clays that belong to organically modified montmorillonite (org‐MMT). Depending on the matrix viscosity and nature of the organic layer in MMT, significant variations In the phase structure of the composites were found. In addition to the simple combination of PP and clay, various functionalized PPs were also incorporated in an attempt to enhance thermodynamic interaction between the org‐MMT and PP matrix. Major interest was focused on the effect of varying thermodynamic affinity between the components, on the phase evolution and mechanical properties of the composites. Within the available range of maleic anhydride (MA) content in PP, it was found that optimum content of the functional group exists, which balances favorable interaction with org MMT and tolerable homogeneity with PP matrix. Along with keeping the optimum MA content, it was also important to use a low viscosity PP matrix to achieve a mere random array of layered silicates. The observed phase structure was interpreted by using a model based on self consistent field theory.
Melt grafting of maleic anhydride onto elastomeric ethylene‐octene copolymer by reactive extrusion
Authors: Premphet K. , Chalearmthtlpa S. 
Published: April 2004

AbstractMelt grafting of maleic anhydride onto elastomeric ethylene‐octene copolymer was carried out in a twin‐screw extruder, in the presence of dicumyl peroxide as an initiator. Dimethyl formamide was used as an inhibitor to reduce crosslinking and as a solvent for peroxide initiator. The aim of the work is to produce the copolymer with reactive functionality without the expense of elastomeric characteristics. Particular consideration was, therefore, given to the effects of initiator and monomer concentrations, and of screw speed on the degree of grafting, percentage of conversion, amount of crosslinked products, and on the stress‐strain behaviors of the grafted products. The degree of grafting was found to be dependent mainly on the initiator and monomer concentrations. Increasing the initiator concentration increased the degree of grafting, and at the same time, increased the amount of gel (crosslinking). An increase in gel content of the grafted products resulted in a change of tensile behaviors from uniform deformation followed by strain‐hardening at high strains to low extensibility and fracture at low strains.
Morphology profiles generated by temperature gradient in PMMA modified epoxy system
Authors: Stefani P. M. , Riccardi C. C. , Remiro P. M. , Mondragóan I. 
Published: April 2004

AbstractA diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin was modified with 15 wt% of poly(methylmethacrylate) (PMMA) and cured with a stoichiometric amount of 4,4′‐diamino diphenyl methane (DDM). The reactive mixture was cured in a heated mold with different gradients of temperature. Temperature profiles in the mold were imposed by generation of a heat flux from the base, supported on a hot plate, and the top, cooled with water; they were measured along the mold. Depending on the thermal history in each position of the mold, the competition between the phase‐separation process and reaction kinetics produces opaque or transparent zones. Phase separation can also occur in the postcure process while the gelation does not take place before. Therefore, a thermoset plate with gradient of morphology and properties was obtained. Mass fractions of PMMA dissolved in the matrix were calculated with the Fox equation from glass transition temperatures measured along the mold. They were related to morphologies developed during curing. The superposition of the phase diagrams with the conversion‐temperature trajectories during cure permitted an explanation of the morphology gradients generated.
Relevance of mold‐induced thermal boundary conditions and cavity deformation in the simulation of injection molding
Authors: Pantani R. , Speranza V. , Titomanlio G. 
Published: April 2004

AbstractIn this work an amorphous PS was injection molded into a simple line‐gated rectangular cavity. The effect on post‐filling pressure curves and temperatures (at the polymer‐mold interface) of different holding pressures and times, and of two gate thickness configurations, was analyzed. Molding tests were simulated leading to a good description of pressure evolution in different positions along the flow path for all molding conditions analyzed. Comparison between simulation results and experimental data shows that: considering a rigid mold can lead to predicted values of post‐filling pressure profiles much different from experimental ones; heat transfer coefficient description plays a minor role in the prediction of pressure evolution, but its effect is relevant on temperature evolution in layers dose to the mold surface.
An experimental investigation of normal and shear stress interaction of an epoxy resin and model predictions
Authors: Hu Yafei , Ellyin Ferknand , Xia Zihui 
Published: April 2004

AbstractThe axial‐torsional interaction of an epoxy resin was investigated by subjecting thin‐walled tubular specimens to combined normal and shear stress components. It is shown that a superimposed normal stress (tensile or compressive) or hydrostatic pressure will influence shear creep behavior. Similarly, a superposed shear stress affects the normal stress response of the resin. The axial‐torsional stress interaction is also observed in transient stress responses under different strain paths, and in the creep deformation with non‐proportional stress histories. Urear viscoelastic constitutive models are unable to predict the aforementioned behaviors. Two typical nonlinear viscoelastic constitutive models are examined with respect to their capabilities to predict the observed response. It Is shown that the predictions of these two models agree only qualitatively but not quantitatively with the experimental results.
Interactions of chlorinated polyolefins with ethylene‐propylene copolymers and their relevance to painted TPOs
Authors: Ellis Thomas S. 
Published: April 2004

AbstractAn experimental and theoretical investigation of the phase behavior of blends of aliphatic polyesters, possessing diferent methylene content and chlorinated polypropylenes (PP‐Cl), containing 26, 32 and 65 wt% chlorine, respectively, has been performed. A window of miscibility was found only for the PP‐C165; however, this was sufficient to apply a binary interaction model of phase behavior in polymers and allow for an estimation of the segmental interaction parameters that define the overall polymer pair interaction. Complete immiscibility was found in all blends of polyesters containing PP‐C126 and PP‐C132; a result consistent with model calculations. A number of simplifications have been made concerning the structures of polymers and assumptions have been made to apply the theoretical model. The segmental interaction parameters obtained have been extended to estimate the thermodynamic interaction in blends of polyolefins and chlorinated polyolefins and then used to calculate the relevant interfacial thicknesses. These results have been compared with information presented in the literature.
Fracture and yielding behaviors of polystyrene/ethylene‐propylene rubber blends: Effects of interfacial agents
Authors: Haanh T. , Vu‐Khanh T. 
Published: April 2004

AbstractThe aim of this work is to investigate the effects of two triblock copolymers, used as coupling agents, on fracture and yielding behaviors of a blend of 80 volume % of polystyrene (PS) and 20 volume %of ethylene‐propylene rubber (EPR), over a large range of loading rates and temperatures. For this purpose, blends containing different concentrations of two triiblock copolymers were studied at various test conditions. The focus was put on the time‐temperature dependence of fracture performance of the blends. Addition of triblock copolymer makes the PS/EPR blend more ductile. The time‐temperature dependence of the brittle‐ductile transition in fracture performance of the blend is controlled by an energy activation process. The interfacial agent lowers the temperature at brittle‐ductile transition and reduces the energy barrier controlling the fracture process. This effect, however, is much more pronounced for the lower molecular weight interfacial agent. The correlation between temperature, loading rate and yield stress of the blends seems to be controlled by a molecular relaxation process according to the Ree‐Eyring theory. This model, based on the assumption of two relaxation processes (α and β) acting in parallel, allows prediction of yield stress at various loading rates and temperatures. Addition of the interfacial agents results in a reduction of the activation energy and an increase in the activation volume V* for both the α and β processes. Furthermore, the similarity of the value of the activation energy ΔHβ in the β yielding process and the energy barrier ΔH controlling the brittle‐ductile transition in fracture seems to suggest that a similar secondary relaxation mechanism controls the yielding and the fracture behavior of the blend.
Converging flow analysis, entrance pressure drops, and vortex sizes: Measurements and calculated values
Authors: Carrot Christian , Guillet Jacques , Fulchiron René 
Published: April 2004

AbstractThe use of converging flows for the determination of the elongational behavior of polymer melts is interesting provided that the solving of the inverse problem is fast. For this purpose, this paper shows that the entrance pressure drops that occur during the axisymmetric flow of a polymer melt from the reservoir of a capillary rheometer into a cylindrical die with flat entry can be rapidly calcylated using a Wagner constitutive equation and Protean coordinates. This calculation technique performs particle tracking, which is absolutely necessary when using integral constitutive equations. In turn, the method also enables the determination of the particle path in the entrance zone and gives the boundary of the vertex. The appropriate solution is obtained through the minimization of the power consumption in the entrance zone. Calculation results are compared with experimental pressure drops and vortex pictures using two well‐characterized polyethylenes and show good agreement.
Effect of supercritical carbon dioxide on PMMA/rubber and polystyrene/rubber blending: Visosity ratio and phase inversion
Authors: Elkovitch Mark D. , Lee L. James , Tomasko David L. 
Published: April 2004

AbstractSupercritical carbon dioxide (scCO2) was added during blending of polystyrene or poly(methyl‐methacrylate) (PMMA) and a rubber impact modifier (SP 2207). The resulting blend morphologies were compared. The compounding took place in a Leistritz ZSE‐27 twin‐screw extruder at 100 RPM, at a temperature of 200°C, and with 2.0 wt% CO2 Injection. The viscosity reduction of PMMA, polystyrene, and SP 2207 was measured using a slit die rheometer attached to the twin‐screw extruder. A viscosity reduction of up to 84% was seen with PMMA, 70% with polystyrene and 30% with SP 2207. The solubility of CO2 in these polymers was measured in a high‐pressure vessel at 200°C and 13.78 MPa (2000 psi). A solubility of 5.79 wt% CO2 was seen with PMMA, 3.65 wt% with polystyrene, and 2.60 wt% with SP 2207. The injection of CO2 reduced the size of the dispersed rubber phase in both polystyrene and PMMA. For both blends (polystyrene/SP 2207 and PMMA/SP 2207) with and without the injection of CO2, the extruder length for phase inversion was shortened by about L/D = 4, or 10% of the total extruder length. The impact strength for a 70/30 polystyrene/SP 2207 blend was increased by 26% by the addition of CO2. The improvement in impact strength was not as large for blends of PMMA and SP 2207.
Polytetrafluoroethylene decomposition in air and nitrogen
Authors: Conesa J. A. , Font R. 
Published: April 2004

AbstractThe kinetics of the thermal decomposition of polytetrafluoroethylene (PTFE) have been studied using dynamic TG‐DTG at heating rates between 1 and 25°C/min at atmospheric pressure. Two different atmospheres were used: on the one hand, an inert atmosphere (N2)in order to study the pyrolysis of the material, and on the other hand an oxidative atmosphere (synthetic air) to study the combustion of the polymer. The same kinetic model has been applied simultaneously to runs performed at different heating rates and different atmospheres allowing a good correlation of the weight loss data. The kinetic model considers that the overall decomposition of the PTFE is done via two different parallel processes. Dynamic measurements were performed by combined thermogravimetry mass spectrometry (TG‐MS) in order to determine the decomposition products. The evolution of 2F4, CF4, COF2, HF, hydrocarbons, benzene and some other compounds has been also analyzed.
Dispersion of graphite nanosheets in a polymer matrix and the conducting property of the nanocomposites
Authors: Chen Guo‐Hua , Wu Da‐Jun , Weng Wen‐Gui , Yan Wen‐Li 
Published: April 2004

AbstractPoly(methyl methacrylate)(PMMA)/expanded graphite composite has been made via an in situ polymerization of methyl methacrylate(MMA) in the presence of expanded graphite obtained by rapid heating of the graphite intercalation compound (GIC). The composite was then blended with poly(vinyl chloride) (PVC) to form an electrically conducting composite. SEM, TEM and XRD showed that the graphite had been dispersed throughout the polymer matrix in the form of nanosheets with thicknesses of about 20 nm. The resulting composite showed excellent electrical conductivity despite a low concentration of graphite. The transition from an electrical insulator to an electrical semiconductor for the composite occurred when the graphite content was 3.5 wt%, much lower than that of conventional conducting polymer composites. Conductivity reached a maximum of 10−4 s/cm at a graphite concentration of 5.0 wt%. This improvement of conductivity could be attributed to the high aspect ration (width‐to‐thickness) of the graphite nanosheets dispersed in the polymer matrix.
Effect of maleic anhydride graft ratio on mechanical properties and morphology on nylon 11/ethylene‐octene copolymer blends
Authors: Li Qi Fang , Kim Dong Gil , Wu De Zhen , Lu Kun , Jin Ri Guang 
Published: April 2004

AbstractMechanical properties and morphologies of nylon 11/ethylene‐octene copolymer blends have been investigated. The ethylene‐octene copolymer (POE) employed in this study was grafted with maleic anhydride (MAH) and thus has the potential to react with the amine group of nylon 11. Nylon 11/POE‐g‐MAH and nylon 11/POE/POE‐g‐MAH blends with varying MAH graft ratios were prepared. In this paper, the effect of MAH graft ratio on ductile‐brittle transition temperature (DBTT), mechanical properties, and morphology of blends was studied. The results showed that incorporation of POE‐g‐MAH could remarkably improve the compatibility between the nylon and POE elastomers, thus increasing the toughness of the resultant blends. The compatibilizing effect on impact strength became more pronounced with increasing MAH graft ration. DBTTs of blends were initially lowered dramatically with the increasing maleic anhydride graft ratio, but over 0.56% MAH content, DBTTs of blends did not drop further, while tensile strength and tensile modulus dropped slightly because of the decreased glass transition temperature (Tg) of nylon 11/POE blends, resulting from the increased compatibility between the two phases. The role of MAH graft ratio on the POE particle size and dispersion of POE on nylon 11 matrix was also studied.
Relationship between local residence time and distributive mixing in sections of a twin‐screw extruder
Authors: Shearer Gifford , Tzoganakis Costas 
Published: April 2004

AbstractLocal residence time and distributive mixing were measured in conveying sections and kneading blocks of a twin screw‐extruder. The residence time measurements were completed using carbon black as the tracer and an infrared temperature probe to detect the temperature decrease caused by the changing surface emissivity. The validity of this experimental technique was extensively evaluated. A mixing limited interfacial reaction between polymer tracers was used to directly measure the distributive mixing in the twin‐screw extruder. Possible relationships between mixing and residence time in the sections of the twin‐screw extruder were investigated by combining these two measurements. Distributive mixing in conveying sections was related to the local average residence time and the fill. In contrast, distributive mixing in kneading blocks was related to the local average number of screw revolutions experienced by the polymer. Forward stagger kneading discs achieved the greatest amount of distributive mixing, which was attributed to a combination of local stagnant flow regions and more frequent interfacial reorientation.
Polyimide nanocomposites: Comparison of their properties with precursor polymer nanocomposites
Authors: Chang Jin‐Hae , Park Kwang Min 
Published: April 2004

AbstractA precursor poly(amic acid) was obtained by solution polymerization of pyromellitic dianhydride and benzidine in N, N‐dimethylacetamide. Poly(amic acid)/Organoclay hybrids were prepared by the solution intercalation method with dodecylamine‐montmorillonite. A polyimide hybrid was obtained from poly(amic acid) hybrid by heat treatment at various temperatures. The film type polyimide hybrids showed better thermal properties than poly(amic acid) hybrids. Also, the thermal stability of the two polymer hybrids were enhanced linearly with increasing clay content from 0 to 8 wt%. Tensile properties and gas barriers of the hybrids, however, were enhanced remarkably compared to pristine polymers. Intercalations of the polymer chains in clar were examined through wide angle X‐ray diffraction (XRD) and electron microscopy (SEM and TEM). Transmission electron microscopy revealed that a partially exfoliated structure had been obtained from polyimide/organo‐clay hybrids.
In‐line versus off‐line rheological measurements on S‐PVC formulations releant for flow in extrusion dies
Authors: Glomsaker Terje , Hinrichsen Einar L. , Thorsteinsen Pål 
Published: April 2004

AbstractThe supermolecular structures present in S‐PVC during processing are dependent on the thermomechanical history and affect the rheological behavior. Motivated by the need to have reliable rheological data relevant for numerical modeling of 3D flows in extrusion dies, we compared standard off‐line capillary measurements with‐inline measurements obtained from an instrumented die mounted on an extruder. Different PVC formulations showed different slip behavior in‐line, and also differences in comparison with the off‐line results. Cogswell analysis on entry pressure drops was used in order to obtain elongational information. For one formulation, with plug flow both in off‐line and in‐line measurements, an analysis based on the resistance to flow in contracting zones was the only way to get flow data that could be used in 3D profile simulations. The temperature sensitivity of measurements was used in order to discuss our results in terms of structural changes within the melt due to differences in thermomechanical history and formulation. Finally, an example of a 3D simulation of the flow of this formulation in an industrial extrusion die is given and compared with observations.
The effects of melt vibration blending on the subsequent crystallization and melting behavior of polypropylene/ultra high molecular weight polyethylene
Authors: Wang Kejian , Zhou Chixing 
Published: April 2004

AbstractPure isotactic polypropylene (iPP) and 90/10 wt iPP/ultra high molecular weight polyethylene (UHMWPE) blends, prepared by a novel vibration internal mixer reformed from a coventional internal mixer via parallel superposition of an oscillatory shear on a steady shear, were investigated by differential scanning calorimetry (DSC) and wide angle X‐ray diffraction. After plasticating pure iPP in the vibration field, the number of β form crystals of iPP was increased. The β form exhibited a single DSC melting peak different from that of the bulk α form crystals of iPP. After mixing of UHMWPE with iPP, the melting point of the UHMWPE component shifted to a lower temperature. For blends mixed at the higher‐frequency and/or larger‐amplitude vibrations, the melting point of the UHMWPE component was further gently lowered while the bulk melting point of the iPP component was slightly increased. The crystallization peaks of the two components overlapped into one single peak, and the total crystallinity became higher, together with a larger amount of the β iPP. These results showed that the two components influenced each other in blending. Hence, the resultant morphology affected the subsequent crystallization and melting behaviors. Additionally, vibration in mixing possibly affected the conformation of some polypropylene chains to favor the subsequent packing in the β form.
Supercritical CO2 welding of laminated linear low density polyethylene films
Authors: Caskey Terrence , Lesser Alan J. , McCarthy Thomas J. 
Published: April 2004

AbstractSupercritical carbon dioxide (SC CO2) is used as a reversible plasticizing agent to promote solvent welding in highly oriented LLDPE films. These films are laid up in a quasi‐Isotropic fashion to enhance material properties in all directions. It is shown tht, after processing, the oriented morphology and crystallinity are effectively unchanged. These laminated films are investigated both physically and mechanically. The mechanical strength of laminate interfaces is tested using a T‐Peel test. Tensile properties of the laminated film are evaluated and compared to the single oriented plies. Tear resistance is measured using a single specimen J1C.