bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal characterization of ethylene polymers prepared with metallocene catalysts
Authors: Starck P. , Lehmus P. , Seppälä J. V. 
Published: April 2004

AbstractA new fractionation technique, segregation fractionation by differential scanning calorimetry (DSC), was applied to both lab‐scale and commercial metallocene copolymers produced with a variety of comonomers. Comparisons were made to other fractionation methods, such as temperature rising elution fractionation (TREF) and crystalline analysis fractionation (CRYSTAF). The new method represents an alternative tool for the relative qualitative analysis of chemical composition distribution (CCD) and the technique was found useful for the characterization of comonomer unit distribution. Differences in the catalyst system and in the thermal treatment were reflected in the melting pattern of the copolymers, obtained after fractionation. The new method was used to study CCD broadening in lab scale slurry polymerizations, and it was found that the effect of polymerization time and comonomer feed system on the CCD can be followed by segregation fractionation measurements. Dynamic mechanical analysis (DMA) was also used to evaluate the heterogeneity of the polyethylene structure. Studies of β‐transitions showed differences in the tan δ‐density correlations, which were influenced by the comonomer type. In most cases the intensity of the β‐transition increased with branching (decreasing density), but for ethylene‐1‐octadecene copolymers the situation was opposite at lower densities. This may be attributed to the crystallization of C16H33 branches.
Structural, rheological, and mechanical properties of ternary blends of PEN, PET, and liquid crystalline polymer
Authors: Kyotani Mutsumasa , Saeed Akhtar 
Published: April 2004

AbstractStructural, rheological, and mechanical properties of ternary blends of a liquid crystalline copolyester (LCP) composed of p‐hydroxybenzoic acid and 2,6‐hydroxynaphthoic acid, poly(ehtylene naphthalate)(PEN), and poly(ethylene terephtalate) (PET) were investigated using capillary rheometry, tensile testing, scanning electron microscopy, and X‐ray diffraction. Viscosity‐shear rate behavior of the ternary blends is very similar to that of pure polymers and their binary blends. The activation energy of flows of the ternary blends was smaller than those of PEN and PET. Tensile modulus and strength of extruded strands of the blends increased with increasing LCP content. The extruded strands of the blends consist of a crystalline and oriented LCP phase and an amorphous and unoriented PEN/PET blended phase. Tensile mechanical properties and structures of the ternary blends were discussed.
Polyimides based on novel multifunctional maleimide derivative
Authors: Patel C. B. , Patel H. S. 
Published: April 2004

AbstractMaleimido derivative (MAF) of aniline‐formaldehyde (AF) resin was prepared by the reaction of AF with maleic anhydride. The MAF was characterized by elemental analysis, IR spectroscopy and thermogravimetry. A MAF having 3 to 4 maleimido groups was reacted with various grades of furan resin (FR) through Diels‐Alder reaction. The resultant polyimides were characterized by IR spectral studies and thermal properties. Both MAF and FR components were polymerized in situ on glass and carbon fiber. The physical, chemical and mechanical properties of the resultant composites have been determined.
Neutron reflectometry studies on the interfacial width between polystyrene and various poly(alkylmethacrylates)
Authors: Schubert D. W. , Stamm M. , Müller A. H. E. 
Published: April 2004

AbstractFrom neutron reflectometry we have obtained the interfacial width (typically 2–8 nm) between incompatible polymers above the glass transition temperatures. The investigated polymer bilayers consist of a deuterated polystyrene top layer and various poly(alkylmethacrylates) as a bottom layer. We obtained interesting effects of the length of the alkyl group on the interfacial width. Using mean‐field theory we calculate Flory‐Huggins‐Stavermann interaction parameters χ from the interfacial width aI data. These results are compared with investigations of the interfacial width between deuterated poly(methylmethacrylate) and respective polyalkylmethacrylates.
Preparation and characterization of composites of polypyrrole
Authors: Bhat Narendra , Geetha P. , Pawde Sunita 
Published: April 2004

AbstractIn this paper, we report the preparation and characterization of composites of polypyrrole (PPy) with polyvinylidene fluoride (PVDF), and cellulose. We used the techniques of chemical and electrochemical polymerization. These materials were characterized using X‐ray diffraction (wide and small angle (SAXS)), electrical conductivity and electron microscopy. The studies showed that homogeneous composites could be formed. The percentage crystallinity of the host polymer decreased, whereas some crystallization of PPy was noticed. SAXS studies revealed that the diffusion of PPy is in amorphous regions. The electrical conductivity of the composites was found to vary in the range of 10−8 S/cm to 10−4 S/cm. These composites were found to be useful in gas sensors for detection of chlorine and ammonia.
Thermoelastic behavior of carbon fiber/polycarbonate model composites
Authors: Privalko Valery P. , Sukhorukov Dmitry I. , Karger‐Kocsis Jozsef 
Published: April 2004

AbstractModel composites of polycarbonate (PC) containing single, multiple and chopped carbon fibers (CF) with and without and epoxy sizing were prepared by hot pressing. The thermoelastic behavior of model CF/PC composites was characterized by stretching calorimetry at room temperature. For small strains ϵ (i.e., ϵ ≈ 0.01) the specific mechanical work, specific heat effects and specific internal energy changes ΔU were completely reversible in stretching/contraction cycles and quantitatively obeyed the standard relationships for elastic solids. Young's moduli E and ΔU were significantly higher, whereas the linear thermal expansivities αL were lower for model CF/PC composites compared to those for the neat PC. Smaller values of the above parameters for composites reinforced with sized CF suggested weaker CF/PC interfacial interactions. Current theoretical models of thermoelastic properties of composite materials suggest the existence of unusually stiff, highly oriented PC structures in fairly thick boundary layers around CF. The onset of inelastic deformation, as well as mechanical failure in CF/PC model composites at significantly smaller strains compared to the neat PC were tentatively explained by the yield and subsequent plastic flow of the matrix polymer initiated by heat effects of fiber fragmentation processes, and by higher concentration of microvoids generated in fiber fragmentation/debonding events, respectively.
Influence of the structure of soft and stiff chain fragments on properties of segmented polyurethanes. I. Phase morphology
Authors: Privalko Valery P. , Privalko Eleonora G. , Shtompel Vladimir I. , Pissis Polycarpos , Kanapitsas Athanassios , Pradas Manuel Monleon , Ribelles Jose‐Luis Gomez 
Published: April 2004

AbstractModel segmented polyurethanes (SPUs) prepared from either oxypropylene glycol oligomer or butylene adipate glycol oligomer, both of molar mass 2 kg/mol (soft fragments, SFT), and three different diisocyanates (all‐trans 4,4'‐dicyclohexylmethane diisocyanate, t, t‐HMDI‐1.0; HMDI with 20% of trans isomers, t, t‐HMDI‐0.2; and 4, 4'‐diphenylmethane diisocyanate, MDI) (stiff fragments, STF) were characterized by specific heat capacity measurements in the temperature interval 140‐540 K, and by wide‐angle and small‐angle X‐ray scattering at room temperature. Limited miscibility of SFT and STF chain components resulted in incomplete separation into a regular three‐dimensional macrolattice of STF‐rich microdomains and SFT‐rich microphases. The composition of STF‐rich microdomains was estimated by fitting the softening temperatures to the Couchman's equation, whereas the relative contents of SFT‐rich and STF‐rich microphases were assessed by comparing the specific heat capacity change at the glass transition temperatures to corresponding additive values. The overall degree of microphase separation, as well as the mean macrolattice spacings between STF microdomains decreased in the order, MDI > t, t‐HMDI‐1.0 ≫ t, t‐HMDI‐0.2. The conformation of STF fragments within the STF‐rich microdomains changed from nearly extended (for MDI) through slightly contracted (for t, t‐HMDI‐1.0) to strongly contracted (for t, t‐HMDI‐0.2).
Synthesis and prperties of peroxy derivatives of epoxy resins based on Bisphenol A. 1. Effects of the presence of inorganic bases
Authors: Bratychak Michael , Brostow Witold 
Published: April 2004

AbstractOligomers containing peroxy groups have been synthesized from epoxies and aliphatic and aromatic hydroperoxides. The dependence of reaction rates upon ratios of starting materials, the presence of an inorganic base as a catalyst, nature of solvent, quantity of water, and temperature have been investigated. The hydroperoxide + epoxy reactions proceed very slowly in the presence of NaOH but at satisfactory rates in the presence of KOH. The reactions do not proceed in acetone, methylethylketone, dioxane, or toluene, but do proceed in secondary and tertiary alcohol media. We have studied in particular the reaction between tert‐butyl‐hydroperoxide (tBHPO), diglycidyl ether of diphenylpropane and an epoxy resin based on Bisphenol A and epichlorohydrin. Structures of the products were confirmed by IR and 1H‐NMR spectroscopy. Mechanisms of reactions have been defined and an empirical equation that describes kinetics of the reaction between tBHPO and the epoxy has been developed. The peroxy oligomers so obtained were used to create networks based on a polyesteric resin. Going from 10 wt% of the peroxy oligomer to 25% increases significantly the rate of gelation as well as the final gel weight fraction. However, a further increase of the peroxy oligomer concentration to 50% affects only slightly the gelation kinetics and the plateau gel fraction.
Performance of polyethylene/ethylene‐vinyl alcohol copolymer/polyethylene multilayer films using maleated polyethylene blends
Authors: Villalpando‐Olmos J. , Sánchez‐Valdes S. , Yáñez‐Flores I. G. 
Published: April 2004

AbstractBlends of linear low density polyethylene (LLDPE) and linear low density polyethylene grafted with maleic anhydride (LLDPE‐gMA) were used to promote adhesion between LLDPE and ethylene‐vinyl alcohol copolymer (EVOH) in a coextruded three layer flat film, trying to avoid the use of a tie layer. These particular films could be an option when the equipment for a five layer system is not available. The effect of the modified polymer on the surface of cast films was characterized through contact angle measurements. T‐peel strength, and oxygen and water vapor transmission rate of the multilayer films were measured as a function of LLDPE‐gMA content. Compressed films with 0%, 0.03%, and 0.08% of maleic anhydride (MA) were also analyzed by infrared spectroscopy (FTIR). The increased T‐peel strength observed when using MA contents higher than 0.08% suggests a good interfacial adhesion between layers. This increase could be associated with specific interactions between the LLDPE‐gMA and the EVOH, as the development of covalent bonds through the reaction of the anhydride with the EVOH hydroxyl groups across the interface. This was proved by the FTIR analysis that showed an increase in the ester band absorbance with an increase on the maleated polymer content and bonding time indicating that a chemical reaction occurred, at the interface. The observed changes on the oxygen and water vapor barrier properties of the films were not significant.
Measurement of the coefficient of dynamic friction at extrusion processing conditions
Authors: Gamache E. , Lafleur P. G. , Peiti C. , Vergnes B. 
Published: April 2004

AbstractThe dynamic friction coefficients of several polymers have been investigated using a specific rotating device similar to an extruder. The increase in temperature during the measurements made it necessary to develop a theoretical approach in order to interpret the experimental data correctly. The rotation speed and particle shapes were found to have little influence on the friction coefficient. For HDPE and PVC, the friction coefficient decreased slightly with interfacial temperature, whereas it remained constant for PP. The order of magnitude of the friction coefficients was similar to what has already been published in the literature.
In‐situ monitoring of product shrinkage during injection molding using an optical sensor
Authors: Thomas Charles L. , Bur Anthony J. 
Published: April 2004

AbstractWe have used an optical fiber sensor for in‐situ monitoring of product shrinkage during injection molding. The sensor, consisting of a bundle of optical fibers with a sapphire window at its end, is positioned in the ejector pin channel of the mold so that the sapphire window sits flush with the inside wall of the mold cavity. The optical view with this sensor is through the thickness (3.175 mm) of the molded product. The fiber bundle is divided into light excitation fibers and light collection fibers. Light from a helium neon laser is transmitted to the resin via the excitation fibers and the detected response is light that reflects from any interface at which there is a difference of index of refraction. When the molded product shrinks, it separates from the wall and sapphire window, and establishes the geometry of a Fabry‐Perot interferometer. During the molding of polystyrene, polypropylene and polyethylene, we observed optical interference fringes that were generated by the movement of the molded product away from the mold wall and window. By counting fringes, a measurement of shrinkage was made. Sensor behavior is described by a model that takes into account the reflection coefficient at each surface, the change in index of refraction of the resin and the coherence of the excitation light. The model has been used to describe asymmetric product shrinkage.
In‐situ reactive blending of polyethylene and polypropylene in co‐rotating and counter‐rotating extruders
Authors: Hettema R. , Van Tol J. , Janssen L. P. B. M. 
Published: April 2004

AbstractBlends of high‐density polyethylene (HDPE) and polypropylene (PP) were prepared in different twin‐screw extruders. Two additives, a peroxide initiator and a polymerizable monomer, were added to the polymeric feed components. A large influence on the physical properties, such as toughness and impact strength, and on the morphology was observed. Reactive extrusion substantially improves mechanical properties: a three‐fold increase of elongation at break and doubling of the impact strength. Variation of extruder settings also had a large influence on the product; the final properties were improved when the shear rate was raised, but sufficient residence time is necessary in reactive compatibilization. Scanning electron micrographs of the fracture surfaces of blends indicate a refinement of the surface structure.
Structural modifications induced by recycling of polypropylene
Authors: Incarnato Loredana , Scarfato Paola , Gorrasi Giuliana , Vittoria Vittoria , Acierno Domenico 
Published: April 2004

AbstractThe effect of numerous reprocessing cycles on transport properties of isotactic polypropylene (iPP) films was studied and related to the change of molecular weight and molecular weight distribution occurring during the recycling. Sorption curves of dichloromethane vapor in different samples of iPP were analyzed at 25°C to investigate the effect of structure modifications on the sorption mode. Moreover, gas permeability measurements were performed to evaluate the influence of reprocessing on the gas transport properties. The results obtained were attributed to modifications in the molecular structure of the polymer, evidenced from gel permeation chromatography (GPC), and to a different morphology of the films, as results from X‐ray diffractograms and dynamic‐mechanical thermal analysis (DMTA).
Thermal diffusivity of polyurethane foams measured by the modified ångström method
Authors: Prociak Aleksander , Pielichowski Jan , Sterzyñski Tomasz 
Published: April 2004

AbstractThe insulation efficiency of rigid polyurethane foams can be improved by increasing the cell isotropy of the polymer matrix and decreasing the heat radiation effect. The influence of the foam growth direction of the thermal properties of foams may be considerable, as shown by measurement of the thermal diffusivity. The modified Ångström method was used for the measurement of the thermal diffusivity D of rigid polyurethane foams. The influence of sample preparation and the measurement conditions on the D‐values were studied. It was found that to compare the insulation properties of polyurethane foams, the measurement conditions, must be carefully chosen. The ability to use small‐dimension samples makes this method very useful for the local measurement of the anisotropy of thermal properties of insulation foams.
Model filled rubber. I: Effect of particle morphology on suspension rheology
Authors: Cai Jianfen J. , Salovey Ronald 
Published: April 2004

AbstractMonodispersed polystyrene (PS) particels, crosslinked with divinylbenzene (DVB), were prepared by emulsifier‐free emulsion polymerization. The colloidal‐suspension rheology of a low‐molecular‐weight liquid polysulfide, which is used in commercial sealants, filled with these PS particles varying in size and particle‐crosslink density, was studied. At low frequencies or shear rates, the dynamic moduli and viscosity increased as particle diameter decreased from 1.25 to 0.315 μm or particle crosslink density increased from 0 to 5 mole% DVB. We suggest that particle‐particle interactions are dominant and lead to the formation of clusters in the concentrated suspension. Rheological properties associated with network buildup in suspensions were most sensitively monitored by a kinetic‐recovery experiment. The strength of, as well as the tendency for, cluster network formation in the colloidal suspensions increases with decreasing particle size, and increasing particle‐crosslink density, or decreasing surface roughness.
Effect of polymer properties on the structure of injection‐molded parts
Authors: Ben Daly H. , Sanschagrin B. , Nguyen K. T. , Cole K. C. 
Published: April 2004

AbstractIn this study, the distributions of both molecular orientation and crystallinity along the flow direction as well as across the thickness direction of injection‐molded specimens of poly(ethylene terephthalate) (PET) molded at different mold temperatures were investigated. The degree of molecular orientation at the surface of the specimens was compared with that of other injected materials (polystyrene, high density polyethylene, liquid crystal polymer) showing different thermal, rheological, and crystallization characteristics. It was found that the molecular orientation at the skin layer of the molding increases with the polymer relaxation time, the rigidity of the polymer molecules, and the crystallization rate of the polymer. Moreover, in the case of PET, it was found that the crystallinity at the skin layer and in the core of the molding depends on the mold temperature. For low mold temperatures, near the gate, the maximum of crystallinity was observed at the subskin layer because of the “shear‐induced crystallization” generated during the filling stage. On increasing the mold temperature, the maximum of crystallinity was found to shift to the skin layer as a result of the decrease of the thickness of this layer. For low mold temperatures, the variation of the molecular orientation in the thickness direction was found to be much the same as for the crystallinity of the polymer. This result indicates that the shear‐induced crystallization process improves the degree of molecular orientation in the flow direction since it inhibits the relaxation process of the polymer molecules.
A comparative study of fiber breakage in compounding glass fiber‐reinforced thermoplastics in a buss kneader, modular Co‐rotating and counter‐rotating twin screw extruders
Authors: Shon Keungjin , White James L. 
Published: April 2004

AbstractThe breakage of glass fibers was measured for several different types of continuous mixers including (i) Buss Kneader, (ii) modular intermeshing co‐rotating twin screw extruder, and (iii) modular intermeshing counter‐rotating twin screw extruder. Comparisons are made using different screw configurations, loadings, feeding ports, and mixing elements. Downstream feeding of glass fibers and milder screw configuration favor less breakage of glass fibers.
An experimental study of foamed polyethylene in rotational molding
Authors: Liu Shih‐Jung , Tsai Chia‐Hsun 
Published: April 2004

AbstractRotational molding of foamed polyethylene has increasingly become an important process in industry because of its thicker walls, low sound transfer, high stiffness and good thermal insulation. However, the foaming process of polyethylene during rotational molding has not been well studied. The focus of this article is to assess the rotomoldability of foamed polyethylene and to investigate how blowing agents can influence the process of rotational molding and the final product quality. Rotational molding experiments were carried out in a laboratory scale uniaxial machine capable of measuring internal mold temperature in the cycle. Mechanical property tests, as well as thickness distribution and density measurements, were performed on the rotationally molded parts. Differential scanning calorimetry and optical microscopy have also been employed to identify the material and structural parameters. It was found that the presence of blowing agent results in an improvement of the impact properties, which are counteracted by longer cycle times and uneven surfaces.
Melt temperature profile prediction for thermoplastic injection molding
Authors: Zhao Chunhua , Gao Furong 
Published: April 2004

AbstractA computer system is developed to quantitatively reveal how the melt temperature is affected by the operating conditions during the plastication, dwell and injection stages of the injection molding process. The variables considered in this study are rotation speed, back pressure, barrel heater temperatures, nozzle heater temperature, dwell time and injection velocity profile. A set of Artificial Neural Networks (ANN) has been developed to predict the effect of the operating conditions on the melt temperature during plastication. The dwell period is treated as a heat conduction problem. A free boundary model for the injection phase is developed to simulate the temperature development and melt flow due to the forward motivation of the screw. The overall prediction of nozzle melt temperature is in good agreement with the experimental measurement, validating the proposed procedure combining ANNs and mathematical modeling. This work enhances the understanding of the process and provides a basis for future work on the optimization and advanced control of the process.