bluuebunny/crossref_metadata_2025 huggingface dataset:
Blends of thermoplastic polyurethane and maleic‐anhydride grafted polyethylene. I: Morphology and mechanical properties
Authors: Pötschke Petra , Wallheinke Katrin , Stutz Herbert
Published: April 2004

Thermoplastic polyurethane elastomers (TPU) and polyethylene (PE) form immiscible blends with an extremely low compatibility. In order to improve the dispersion, stability, and properties of these blends, polyethylene was grafted with maleic anhydride (PE‐g‐MA). Subsequently, it was blended with a commercial polyester ‐ type TPU in a twin‐screw extruder. With PE‐g‐MA as blend component, the particle size was dramatically reduced in comparison with PE. Coalescence was significantly reduced and the increase in particle size with composition was less pronounced than in blends with PE. In addition, the phase adhesion and the mechanical properties were improved by using PE‐g‐MA as minor component. Grafting of the MA onto the PE leads to a decrease of the molecular weight, the melt viscosity, and the mechanical properties of the pure PE. Hence, the reactive blend system exhibits a lower viscosity ratio. Comparison of these results with those from uncompatibilized blends with different viscosity ratios revealed that the reduction in viscosity ratio has a big influence on the blend morphology and because of that on the mechanical properties. In addition, there is a further effect on morphology and properties caused by the reduction in interfacial tension, which results from the compatibilizer formed at the interface.
Mechanical behavior of injection‐molded polystyrene/polyethylene blends: Fracture toughness vs. fatigue crack propagation
Authors: Bureau M. N. , Di Francesco E. , Dickson J. I. , Denault J.
Published: April 2004

Blends of polystyrene and polyethylene (PS/PE), including belnds in which a styrene/ethylene‐butylene/styrene (SEBS) terpolymer was employed as a compatibilizer, were studied. Their rheology showed that the effect of the addition of SEBS to PS/PE blends was strongly affected by the blend composition and the shear rates involved in the blending and post‐forming processes. The addition of PE to PS led to a reduction of fracture toughness compared with that of PS. This effect was attributed to the fine minor phase morphology of the blends obtained after extrusion blending and injection molding. The fatigue crack propagation (FCP) results showed that the fatigue crack growth rates were significantly reduced at low and moderate range of stress intensity factor (ΔK) by the presence of PE. Performance was enhanced when SEBS was present. The results also showed that both the fracture toughness and the FCP behavior of the blends were strongly dependent on the loading direction, the minor phase morphology, the composition of the blend, and, to a lesser degree, the presence of a compatibilizer. This study demonstrates that the fracture toughness and the FCP performance of such polymer blends can vary inversely.
Mathematical modeling and experimental studies of twin‐screw extrusion of filled polymers
Authors: Kalyon Dilhan M. , Lawal Adeniyi , Yazici Rahmi , Yaras Piraye , Railkar Sudhir
Published: April 2004

Extrusion of filled polymer is commonly employed in diverse industries including compounding operations. The analysis of extrusion of filled polymers is complicated especially by the ubiquitous viscoplasticity and wall slip of the filled polymers. Furthermore, the role played by entrainment of air in the processor, the continuously evolving microstructure, and hence the rheological behavior of the filled polymer in the mixing volume of the extruder and the flow instabilities associated with the converging flows involving the filtration of the binder polymer present additional challenges to the analysis. Specialized techniques are also necessary to quantitatively describe the dispersive and the distributive degree of mixing of the compound. The principal tasks of this study included the collection of experimental data from twin‐screw extrusion using an instrumented and industrial‐scale co‐rotating extruder in conjunction with a well‐characterized filled polymer, which exhibits viscoplasticity and wall slip. The process allowed the adequate mixing of the ingredients and the removal of its air content. Next, the processing data were compared with the results of numerical simulation using the Finite Element Method. The predictions compared favorably with the experimental temperature and pressure distributions obtained under different sets of operating conditions. The distributive degree of mixing (spatial homogeneity) of the filled polymer upon exit from the die was also characterized employing a wide angle X‐ray diffraction technique in spite of the amorphous nature of both the filler and the binder polymer, i.e., hollow glass spheres and poly(dimethyl siloxane) polymer.
Effects of nucleating agent and processing conditions on the mechanical, thermal, and optical properties of biaxially oriented polypropylene films
Authors: Yuksekkalayci Celal , Yilmazer Ulku , Orbey Nese
Published: April 2004

The effects of nucleating agent, temperature of crystallization, and degree of machine direction (MD) orientation on the mechanical, optical, and thermal properties of biaxially oriented polypropylene (BOPP) films were investigated. Addition of nucleating agent improved only the initial tear resistance in the MD; however, the other mechanical and optical properties did not change appreciably. In the set of experiments in which the crystallization temperature was increased, the degree of crystallinity also increased. Thus, Young's modulus, yield stress, and tensile strength increased in both directions with higher degree of crystallinity. The yield strain did not change significantly, but the strain at break was higher. Although the initial tear resistance was smaller in both directions with increasing crystallization temperature, the tear propagation resistance did not change. In this case, haze and diffuse transmittance were slightly higher, but the total transmittance was constant. In the set of experiments in which the machine direction orientation was increased, the degree of crystallinity also became higher. Owing to the effects of higher crystallinity and higher MD orientation, the modulus, yield stress, and tensile strength increased, but the yield strain and tear propagation resistance did not significantly change in both directions.
Optical monitoring of polypropylene injection molding
Authors: Thomas Charles L. , Bur Anthony J.
Published: April 2004

We have constructed an optical fiber sensor for monitoring injection molding and we have developed a model to describe sensor behavior. The sensor consists of a sapphire window at the end of a sleeved ejector pin into which an optical fiber is inserted. The optical view with this sensor is through the thickness of the molded product. The measured optical signal was light that transmitted through the resin, reflected off the back wall of the mold, and retraced its path through the resin to the optical sensor, i.e., light transmitted through twice the thickness of the resin. While monitoring polypropylene during the packing and cooling phase of the molding cycle, we observed a decrease in light intensity due to scattering of light by the growing microcrystals. A characteristic minimum in the transmitted light intensity versus time curve is attributed to scattering by growing crystalling spherulites at the core of the molded product. Cavity pressure was also measured and was found to be an essential parameter in the process model. The model illustrates how temperature, pressure, and crystallinity affect the detected light intensity and clarifies the roles that temperature and pressure play in the crystallization process.
Thermomechanical properties of radiation‐modified blends of polyethylene with liquid crystalline copolyester
Authors: Kalkis Valdis , Maksimov Robert D. , Zicans Janis
Published: April 2004

The results of investigation of gamma irradiated blends of high‐density polyethylene (PE) with thermotropic polymer liquid crystal (PLC) are presented. The PLC used was a copolyester of 40% poly(ethylene terephthalate) with 60% p‐(hydroxy‐benzoic acid). The PLC content in the blends was 0, 5, and 10 wt%. The constituents were blended with the use of a single screw extruder. The specimens were prepared by compression molding. The irradiation of the samples was performed by a Co60 γ‐radiation source in inert atmosphere (argon) up to absorbed relatively low doses (up to 200 kGy; 1 Mrad = 10 kGy). The morphological, thermal, and mechanical properties were investigated for irradiated and unirradiated samples. The influence of gamma irradiation and addition of PLC on the temperature dependence of the elastic modulus as well as the effect of a “form memory” of the materials examined are discussed. It was found that an addition of the PLC affects substantially the stress‐strain relationship in tension at temperatures above the melting point of PE for the irradiated samples. The features of thermomechanical behavior of the PE + PLC blends, previously irradiated and oriented, at isometrical heating and cooling were also established. The results obtained testify that the addition of PLC to PE makes it possible to improve considerably the thermosetting properties of the heat‐shrinkable polymeric products.
Stress oscillation in amorphous copolyesters due to tensile impact
Authors: Karger‐Kocsis J. , Czigány T. , Moskala E. J.
Published: April 2004

Specimens from amorphous copolyester (aCOP) sheets of different composition and molecular mass characteristics were subjected to instrumented tensile impact loading in the speed range of 2 – 3.7 m/s at ambient temperature. Stress oscillation was observed in the necking phase, especially for the aCOP with smaller entanglement density. It was found that the appearance of stress oscillation is limited to a given frequency or strain rate range (estimated by the ratio of the incident speed and clamped specimen length). Necking occurred by cold drawing which was evidenced by the shape recovery of the broken specimens when heated above the glass transition temperature (Tg ≈ 90°C). According to polarized light microscopy and differential scanning calorimetry (DSC), the stress oscillation was generated by diffuse shear banding without crystallization. This is the first report according to the authors' knowledge on the stress oscillation phenomenon in amorphous polymers in which crystallization was not involved.
Composites of poly(vinyl acetate) filled with calcium carbonate: Microscopy, diffractometry and thermophysical properties
Authors: Kovačević Vera , Lučić Sanja , Hace Draco , Packham David , Šmit Ivan
Published: April 2004

Calcium carbonate (CaCO3) is used as filler in poly(vinyl acetate)(PVAc) composites to enhance the mechanical properties. The filler is often commercially surface treated with stearic acid to optimize the interfacial bonding and wetting. The effects of the interface on properties were studied using scanning electron microscopy (SEM) of films with initial and deformed morphologies. Plasticizing additives cause a significant change in the appearance of the films and a reduction in the glass transition temperature of the matrix from 40°C to ≈ 18°C, which was not altered by further addition of the filler. A PVAc composite fracture surface shows the particles adhering well to the matrix, suggesting good adhesion and reinforcement. The SEM study is complemented by WAXD, SEM/X‐SEM, XPS, and thermal analysis.
Thermal characterization of ethylene polymers prepared with metallocene catalysts
Authors: Starck P. , Lehmus P. , Seppälä J. V.
Published: April 2004

A 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

Structural, 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

Maleimido 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

From 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

In 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

Model 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

Model 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

Oligomers 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

Blends 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

The 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

We 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

Blends 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

The 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

The 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

Monodispersed 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

In 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

The 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

Rotational 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

A 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.
Uniform purging of resins in contact bed purge vessels
Authors: Pittenger B. H. , Carson J. W. , Prescott J. K. , Purutyan H.
Published: April 2004

Resin storage vessels such as bins, silos, and tanks often double as purge vessels, in which products are purged of volatiles or polymerization reactions are controlled. Processing is achieved by gas flowing among resin particles or pellets. Problems associated with these purge vessels include typical bin flow problems such as flow stoppages due to arching or ratholing, erratic discharge, particle segregation, and flooding or flushing. In addition, purging may be non‐uniform or incomplete, and cross contamination between grades may occur. These problems are often the result of either a funnel flow pattern, where some of the material in the vessel moves while the rest remains stationary, or a non‐uniform velocity profile, where some parts of the vessel flow much faster than others. Also, the location and the manner in which gas is injected into the vessel contents affect the uniformity of exposure of polymer particles to the gas. This paper describes methods of designing purge vessels to eliminate stagnant regions. Also, velocity gradients of solids in mass flow vessels (where all of the material is in motion whenever any is withdrawn) are discussed. Considerations of the gas introduction schemes that do not disturb the resin flow patter are also described.
A comparison between experiments and predictions for the blow molding of an industrial part
Authors: Debbaut Benoît , Homerin Olivier , Jivraj Noor
Published: April 2004

We present a numerical simulation for the blow molding of an industrial high density polyethylene part. The rheology of the polymeric material is described by means of an integral viscoelastic fluid model with a multi‐mode relaxation spectrum. A membrane element is applied for performing the blow molding simulation of geometrically complex objects such as a bottle with a handle; the motion governing equations are described by means of a Lagrangian representation. The contact between the parison and the moving mold is handled by means of a robust algorithm. The numerical tool is applied for the production of a bottle with a handle. The predicted results are compared with their experimental counterparts. In particular, we focus on the thickness distribution of the blow product.
Effect of viscosity variation with temperature on the compounding behavior of immiscible blends
Authors: Ratnagiri Ram , Scott Chris E.
Published: April 2004

Morphology development in the compounding of immiscible blends depends on a number of material properties and process conditions. In this work, different model blend systems are considered to outline the effects of the relative transition temperatures and viscosities of the blend components. We focus on the evolution of blend morphology, specifically phase continuity. A framework based on these factors is presented for analyzing the compounding behavior of immiscible blend systems. With the minor component at 10 wt%, it was found that phase inversion during compounding occurred in blends with a viscosity ratio of less than 0.2, independent of the relative transition temperatures. It was shown that in these constant mixer temperature runs, the torque trace was not a completely reliable indicator of phase inversion. When a temperature ramping program was used, the lower melting point component formed the continuous phase initially, independent of the viscosity ratio. Quantitative measures of the amount of minor component which was continuous at different mixing times were made using selective extraction in a Soxhlet apparatus. Results from compounding runs of polycarbonate/ polyethylene, an amorphous copolyester/polyethylene and polybutylene/polycaprolactone blends are presented.
Phase separation influence on the performance of CTBN‐toughened epoxy adhesives
Authors: Klug Jeremy H. , Seferis James C.
Published: April 2004

Epoxy adhesive systems were formulated and tested for their bonding behavior. Fumed silica and elastomer type and concentration were varied for the purpose of investigating their influences on intermediate and final adhesive performance properties. Of special interest was analyzing the role that flexibilized elastomer, that which does not phase separate during cure, played in these properties. Adhesive systems were tested with a commercial prepreg system using both bonded and cocured geometries. Dynamic mechanical analysis and optical microscopy showed the phase separation of the rubber was significantly influenced by the silica addition. Elastomer‐rich dispersed phase growth rates were depressed resulting in a lower percentage of toughening domains. Mode I and II fracture energies were a strong function of dispersed phase particle size, flexibilized elastomer type/content, and residual stress considerations at the resin‐resin interface. There were distinct differences between bonded and cocured fracture results with bonded samples generally outperforming cocured specimens due to changes in the surface roughness, resin flow properties, and interfacial stress build‐up. Collectively, this work illustrates the importance of phase separation behavior on the final part morphology and performance for liquid elastomer toughened epoxy adhesives.
Residual stress development in a bi‐layer coating
Authors: Yan Gu , White J. R.
Published: April 2004

Measurements have been made of the residual stress development in a solventdeposited thermoplastic coating and a two‐component thermoset by monitoring the bending of the steel substrate using strain gauges. The stresses in single layers were found to be significant when compared to the strength of the coatings. When the thermoset was applied on top of the thermoplastic (undercoat), the stress in the top coat was much less than that obtained when the thermoset was applied directly to the steel substrate. This was deduced using a new elastic analysis for tri‐layers (substrate plus bi‐layered coating).
Residual stresses in marine coatings under simulated service conditions
Authors: Yan Gu , White J. R.
Published: April 2004

Studies have been made of the effect of cyclic temperature changes and wet/dry cycling on the residual stresses in marine coatings applied to steel substrates. A thermoplastic and a thermoset have been use as single coatings and as bi‐layers consisting of the thermoset applied on top of the thermoplastic. Cyclic changes associated with differential thermal expansion/contraction between substrate and coating and with water absorption or desorption were observed, and it was found in addition that progressive changes in residual stress were sometimes superimposed on the cyclic changes. The effect was larger with the thermoplastic coating than with the thermoset. The stresses developed in the bi‐layers were generally smaller than those in single layer coatings and were generally less sensitive to the cyclic changes in conditions. The effects were partly controlled by the thicknesses of the two layers in the bi‐layer coatings. Stresses as high as 6 MPa were measured during the course of this work, a significant fraction of the failure strength of the coatings.
Processing of short fiber reinforced polypropylene. II: Statistical study of the effects of processing conditions on the impact strength
Authors: Barbosa Silvia E. , Kenny José M.
Published: April 2004

Within the general objective of analyzing and modeling the processability of polypropylene and of its short fiber composites, a statistical analysis of the relationship between processing conditions and final properties has been performed applying modern experimental design concepts. In order to gather the largest amount of information with a manageable quantity of experiments, Taguchi methods were used for the design of injection molding tests and for the analysis of experimental fiber orientation and impact strength results. Two levels of each variable of interest were selected, and the results of the analysis not only show which of the processing variables are predominant but also show that interactions between variables must be taken into account. The approach presented here offers a viable route to the scaling‐up of the injection molding process through the reduction of the number of variables in the prediction of the processing behavior of semicrystalline polymers and of their composites.
Kinetic study and simulation of the precopolytransesterification step in the copoly(ethylene‐polyoxyethylene terephthalate) production process
Authors: Cruz‐Guerra Cornelio De La , García‐De La Mora Gustavo A. , Cruz‐Gómez M. Javier
Published: April 2004

The kinetics of the precopolytransesterification step for the production process of the copoly(ethylene‐polyoxyethylene terephthalate), COPEPOET, has been analyzed. The prepolytransesterification step involves two competitive parallel reactions generating the same by‐product, ethylene glycol: 1. Prehomopolytransesterification reaction of bis (2‐hydroxyethylene terephthalate), BHET, with itself and 2. Precopolytransesterification reaction of BHET with poly(oxyethylene), POE. The kinetic constants of both reactions, BHET with BHET and BHET with POE, were calculated. The analysis was made as follows: 1. A kinetic model was developed in order to calculate the kinetic constants kH and kC of the prehomopolytransesterification and precopolytransesterification reactions; 2. The simulation of the precopolytransesterification step was carried out by integrating the differential equations, which describe the prepolytransesterification step. A fourth‐order Runge‐Kutta method was used for this integration. Several values that fall within the interval of 0.05 to 1.5 were assigned to the rate constant ratio kH/kC value, a set of kH/kC value, a set of kH and kC values were obtained. The parameters of the Arrhenius equation A and E were evaluated by means of a multiple regression analytical method; and 3. By comparison between theoretical and experimental data the best kH/kC value was obtained. The kH value was found to be several times smaller than that of kC.
Numerical modeling of injection/compression molding for center‐gated disk: Part I. Injection molding with viscoelastic compressible fluid model
Authors: Kim I. H. , Park S. J. , Chung S. T. , Kwon T. H.
Published: April 2004

The present study attempted to numerically simulate the process in detail by developing an appropriate physical modeling and the corresponding numerical analysis for injection molding and injection/compression molding processes of centergated disks. In Part I, a physical modeling and associated numerical analysis of injection molding with a compressible viscoelastic fluid model are presented. In the distribution of birefringence, the packing procedure results in the inner peaks in addition to the outer peaks near the mold surface, and values of the inner peaks increase with the packing time. Also, values of the density in the core region increase with the packing time. From the numerical results, we also found that birefringence becomes smaller as the melt temperature gets higher and that it is insignificantly affected by the flow rate and the mold temperature. As far as the density distribution is concerned, mold temperature affects the distribution of density especially near the wall. But it was not significantly affected by flow rate and melt temperature. Numerical results of birefringence coincided with experimental data qualitatively, but not quantitatively.
Numerical simulations of annular extrudate swell using various types of viscoelastic models
Authors: Otsuki Yasuhiko , Kajiwara Toshihisa , Funatsu Kazumori
Published: April 2004

In this study, numerical simulations of annular extrudate swell of high density polyethylene (HDPE) were carried out. Some important viscoelastic models, such as the Larson, the PTT and the K‐BKZ model, were employed for the swell calculation through various types of dies. These numerical results were compared with the experimental ones. The numerical results of the swell behaviors were very different in each viscoelastic model, while their simple shear flow characteristics were almost the same. As a result, the uniaxial elongational viscosity for large deformation as the steady state region is not important, but the property for relatively small deformation has remarkable effects on the numerical results for the die that have a uniaxial contraction region. Both reversible and irreversible types were tried for the Larson model. It was found that there was a difference between the irreversibility assumption of the K‐BKZ model and the Larson model. While there was a serious difference in the response for reversing strain among these viscoelastic models, the response was very important to predict annular extudate swell behavior.