bluuebunny/crossref_metadata_2025_split huggingface dataset:
Blends and interpenetrating polymer networks of polypropylene and polystyrene‐block‐poly(ethylene‐stat‐butylene)‐block‐polystyrene. 2: Melt flow and injection molding properties
Authors: Ohlsson Bertil , Törnell Bertil 
Published: April 2004

AbstractInjection molding and melt flow properties of a set of blends prepared by mixing the triblock thermoplastic elastomer polystyrene‐block‐poly(ethylene‐stat‐buty‐lene)‐block‐polystyrene with polypropylene and a processing oil are reported. Despite the high viscosity of the thermoplastic elastomer, the melt viscosity of the blends was similar to or lower than that of the pure polypropylene. The rheological behavior of the molten blends seems to be dominated by a low‐viscosity melt phase containing mainly polypropylene and oil. The surface of solidified extrudates from the capillary rheometer was rich in polypropylene and free from large domains of the thermoplastic elastomer. Injection molded plates had a similar surface morphology, although in this case, larger domains of the elastomeric phase were found in narrow, band‐shaped surface regions. These local surface heterogeneities were probably caused by flow‐induced phase segregation during mold filling. Weld lines in injection molded test pieces prepared from blends within the composition range giving interpenetrating network structures had no noticeable effect on either stress‐strain behavior or falling dart impact strength.
Cushioning performance of flexible polyurethane foams
Authors: Sims G. L. A. , Bennett J. A. 
Published: April 2004

AbstractImpact cushioning and deformation of flexible open‐cell polyester polyurethane (PU) foams were studied as a function of specimen geometry, including the incorporation of controlled voids. It was shown that cushioning behavior is dependent on sample geometry, which was in trun due to a complex balance of air compression and air flow, which changes with surface area‐to‐volume ratio of the impact specimen. Deformation studies show that impact compression proceeded initially by crushing the surface layers with little or no deformation of the center layers. As bulk compression was increased, deformation progressively propagated for the collapsed layers tending to a more uniform strain distribution at high bulk compression strains. Local asymmetric strain patterns were exaggerated using square cushions, because of cornr effects which complicated air flow paths. It was concluded that cushion curve determination of open‐cell foams would be more accurately performed using circular samples and deflecting air pressure form the top surface of the cushion to more closely simulate practical conditions. When designing at or near the margin, the number of cushions should be kept to a minimum and open surface area to volume ratios minimized by adopting square rather than strip cushions.
Optimized data collection for determination of the MWD from the viscosity data of polymer melts
Authors: Liu Yongming , Shaw Montgomery T. , Tuminello William H. 
Published: April 2004

AbstractNumerical differentiation is one source of loss of resolution in the differential transformation of viscosity to MWD. Resolution can be improved by increasing the amount of viscosity data, keeping in mind that optimizing this process is necessary for practical reasons. This problem was approached by finding the minimum point for practical reasons. This problem was approached by finding the minimum point density and coverage required to resolve bimodality. For given point density and range, the higher the superposition between the viscosity data and the “knee” in the viscosity function produced by each mode, the better the resolution. Testing time can be reduced and resolution can still be preserved by placing more points in the “knee” region in the viscosity function and by skipping the unnecessary points at low shear rates.
Properties and kinetics of thermally crystallized oriented poly(ethylene terephthalate) (PET). II: Physical and optical properties
Authors: Varma Pankaj , Lofgren E. A. , Jabarin S. A. 
Published: April 2004

AbstractRecent processing advances, developed to improve barrier properties and thermal stability of oriented poly(ethylene terephthalate) (PET), present a need to further study and understand the resultant material changes. The mechanical, optical, and infrared characteristics of PET sheets, previously oriented and subsequently thermally crystallized (under unconstrained conditions) have been investigated. The effects on properties, with respect to the initial mode of extension and extension ratio, have been studied. Results indicate that mechanical properties of this form of PET are dependent on the initial extension ratio, in addition to the initial mode of extension. Among thermally crystallized samples, optical property variations were found to be strong functions of initial extension ratios as well as the levels of thermal crystallinity achieved. Unoriented samples became completely opaque at low levels of thermally induced crystallinity, while highly oriented samples remained optically clear even with high levels of additional crystallinity induced by thermal exposure. Moderate levels of initial orientation were also found to inhibit the development of haze, resulting from additional thermal crystallization, although not to the extent observed for highly oriented samples. Crystal growth resulting from unconstrained thermal exposure was monitored using internal reflectance infrared spectroscopy. This growth was found to selectively occur in the directions of polymer chain orientation (alignment) for samples prepared under conditions of both uniaxial and equibiaxial stretching.
As‐molded shrinkage measurements on polystyrene injection molded products
Authors: Jansen K. M. B. , Pantani R. , Titomanlio G. 
Published: April 2004

AbstractAn experimental study of shrinkage in injection molded products is presented in this paper and documented with all information needed for any further analysis. In particular, the effect of holding pressure, holding time and mold geometry on product shrinkage was investigated for amorphous polystyrene. It turned out with increasing holding pressure the in‐plane shrinkages varied from 0.6% to 0.1%, while the product thickness increased from about 1% to 10%. The holding time only affected product shrinkage for settings less than gate freeze‐off time. Shrinkage usually increases along the flow path unless back flow sets in at the end of the holding stage. It was also found that if a constraint prevents in‐mold shrinkage to take place, final shrinkage may decrease if holding pressure and time are small. The effects of all the variables analyzed were described by a thermomechanical model recently proposed.
Dog‐legging in the melt spinning process
Authors: Rwei Syang‐Peng , Tang Hsiang‐In , Hu Yeh‐Ron , Bai Chi‐Chung 
Published: April 2004

AbstractExperiments were performed in a continuous capillary rheometry to investigate the dog‐legging mechanism in a melt spinning process. The bending angle of the spinline was measured under various spinning conditions while spinning PP, PET, and PEN fibers. Experimental results indicate that obstacles inside the capillary of the spinnerette are the primary cause of bending of the spinline. The bending angle is greatly influenced by the obstacle's dimensions and position inside the capillary. An increase in the obstacle's radius or a decrease in the obstacle's length caused the bending angle to increase. The closer the obstacle was to the exit of the capillary implied the bending angle would be the wider except for the block immediately above the exit. Also at high shear rates, PEN was found to be relatively insensitive to spinline‐bending than PET polymers. In accounting for the dog‐legging behavior, our results suggest that the die swell model is more realistic than the conventional vortex model.
Durability of in‐plant recycled glass fiber reinforced polyamide 66
Authors: Eriksson P. A. , Albertsson A.‐C. , Boydell P. , Månson J.‐A. E. 
Published: April 2004

AbstractA study of the effect of in‐plant recycling on the durability of glass fiber reinforced polyamide 66 is reported. Injection‐molded test bars were exposed to thermal agin, coolant aging, and creep testing. It was shown that thermal aging and coolant aging induced similar effects. The onset of embrittlement was revealed by both a reduction in elongation at break and loss of impact resistance. Samples based on 100% in‐plant regrind exhibited a more intense embrittlement compared to virgin samples during both thermal and coolant aging. For samples based on 25% recycled material, the deterioration rate was similar to that of virgin samples during thermal aging but slightly faster during coolant aging. Creep experiments indicated that inplant recycled materials can display reduced dimensional stability, which may be explained by a reduced degree of reinforcement due to fiber breakage during the recycling operation. Knock‐down (KD) factors were defined and determined for the in‐plant recycled samples. For creep resistance, tensile strength and modulus, the KD factors were strongly affected by fiber length. The highest KD factor, as determined for samples based on 25% and 100% recycled material, was 8% and 16% respectively.
Infrared imaging of stress‐crazing in rubber modified polystyrene
Authors: Telenkov S. A. , Wang Yingxia , Lu Yuesheng , Favro L. D. , Kuo P. K. , Thomas R. L. 
Published: April 2004

AbstractThe plastic yield and fracture of rubber‐modified polystyrene specimens under tensile load have been investigated at room temperature. The experimental procedure consisted of rapidly alternating measurements of transmitted and emitted infrared (IR) radiation from samples under tensile stress. The load‐displacement data were simultaneously recorded. Both single‐edge‐notched and dog bone‐shaped test coupons were studied. In each tensile test run, we observed a significant decrease of material transparency in the IR which occurred near the low yield point. A further increase in material deformation was accompanied by a substantial temperature increase. After material failure, the surface morphology of the test specimens in the vicinity of the crack was examined using atomic force microscopy (AFM). Our results are explained in the context of existing models of material crazing.
Degradation behavior of poly (caprolactone)–poly(ethylene glycol) block copolymer/low–density polyethylene blends
Authors: Tjong S. C. , Bei J. Z. 
Published: April 2004

AbstractBlends of poly(carprolactone)‐poly(ethylene glycol) block polymer (PCE) with low‐density polyethylene (LDPE) were prepared by extrusion followed by compression molding into thin film specimens. The morphology, thermal properties, degradation, and mechanical behavior of the blends were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), water immersion, static tensile testing, and dynamic mechanical analysis (DMA). The LDPE/PCE blends were immiscible for all chemical compositions. A LDPE/PCE (75/25 wt%) blend exhibited small reductions in weight and tensile strength after immersion in a buffer solution (pH = 5.0) at 50°C for extended periods of time. However, grafting maleic anhydride onto the LDPE/PCE blends improved the compatibility between the LDPE and PCE phases. Consequently, a 75/25 wt% blend of maleated LDPE/PCE exhibited significant losses in weight and tensile strength after immersion in the buffer solution. For comparison, blends of poly(caprolactone) (PCL) with LDPE were fabricated by similar techniques. The effect of compatibilizer on the degradation of LDPE/PCE and LDPE/PCL is discussed.
Plane strain fracture toughness of polyphenylene sulfide
Authors: Nishihata N. , Koizumi T. , Ichikawa Y. , Katto T. 
Published: April 2004

AbstractThe plane strain fracture toughness of polyphenylene sulfide (PPS), tested with different molecular structures such as linear PPS, heat‐treated PPS, and branched PPS, was investigated over a wide range of melt viscosity and crystallinity and compared with other mechanical properties. The fracture toughness of linear PPS increased with increasing melt viscosity, and it reached the highest fracture toughness calculated from linear elastic fracture mechanics (LEFM) observed in this study. In this high melt viscosity region, the linear PPS specimen showed slow crack growth instead of brittle fracture. Although the tensile properties of heat‐treated PPS and branched PPS are the same as those of linear PPS, the fracture toughness of linear PPS is superior. The fracture toughness is affected by the crystallinity of the specimen, and the effect of crystallinity on fracture toughness is smaller than that of melt viscosity and molecular structure.
A study on the ternary blends of nylon 6, a thermotropic liquid crystalline polymer, and a thermoplastic elastomer
Authors: Seo Yongsok , Kim Kwang Ung 
Published: April 2004

AbstractReactive extrusions were performed with blends of nylon 6 and a liquid crystalline copolyesteramide (LCP) including a functionalized elastomer (maleic anhydride grafted ethylene‐propylene‐diene terpolymer). The functionalized elastomer acts as a compatibilizer at the interface. The thermal behavior of the blends suggests partial compatibility of the components endowed by the produced graftcopolymer. A finer dispersion was observed for the compatibilized blends. Fine fibrils were also observed even when no extensional force was applied, indicating the importance of interfacial adhesion for the dispersed phase deformation. The shear viscosity of the ternary blend was lower than those of the neat polymers. The mechanical properties of the compatibilized blends, however, were not significantly improved except when an optimum amount of compatibilizer was added. Explanations for the compatibilizing action of the elastomer and mechanical performance of the ternary blends are presented.
Shear viscosity of carbon black filled polypropylene at very low shear stresses
Authors: Araki Takumi , White James L. 
Published: April 2004

AbstractThe shear viscosity of carbon black filled polypropylene with a range of different carbon blacks was investigated. This was accomplished using (a) a constant shear stress creep instrument, (b) a cone‐plate rotational rheometer, (c) a capillary extrusion rheometer. It was found that stresses exist for these compounds below which there are only finite deformations and no steady flow, Much attention was given to measurements of creep at low stresses, especially in the neighborhood of yield values. The magnitudes of yield stresses obtained from such creep measurements are significantly lower than those obtained using standard extrapolation to zero shear rate of higher stress data from rotational instruments. The shear viscosity behavior near the yield value differs significantly depending upon the carbon black used. A high viscosity was observed (∼109 to 1010 Pa.s) plateau in some compounds.
Polymer blends of PA6 and PPE compatibilized by poly[methylene (phenylene isocyanate)] (PMPI) coupler
Authors: Chiang Chih‐Rong , Ju Ming‐Yih , Chang Feng‐Chih 
Published: April 2004

AbstractAn oligomeric isocyanate, poly[methylene(phenylene isocyanate)] (PMPI), is demonstrated to be an efficient reactive compatibilizer for blends of polyamide‐6 (PA6) and poly(2,6dimethyl‐1, 4‐phenylene ether)(PPE). Use of this compatibilizer results in substantial improvements in mechanical properties. The multiple functional isocyanate acts as a coupling agent and reacts with PA6 and PPE endgroups during melt processing to produce a PA6‐co‐PMPI‐co‐PPE mixed copolymer at the interface. This in situ‐formed copolymer tends to reside at the interface to reduce the melt interfacial tension and enhance interface adhesion.
Burst pressure prediction of polyamide pipes
Authors: Germain Y. 
Published: April 2004

AbstractThe maximum pressure borne by a pressurized polymer pipe is a fundamental factor in the applications. This paper is aimed at showing that this factor can be calculated using a minimum knowledge of the mechanical behavior of the polymer. According to previous works developed for metal pipes, ductile rupture proceeds by a plastic instability. This theory is reviewed in the paper. A close form equation provides the burst pressure or critical hoop stress as a function of initial dimensions of the pipe and tensile test data. The model is checked against burst experiments performed on plasticized polyamide 12 pipes. The agreement is good at room and elevated temperature. Finally, generalization to other polymers is discussed. This approach can be used as a rapid method of assessing the performance of new polymer compounds.
A model for the thermoviscoelastic behavior of physically aged polymers
Authors: Drozdov Aleksey D. 
Published: April 2004

AbstractA constitutive model is derived for the viscoelastic behavior of physically aged amorphous polymers under non‐isothermal loading. The model is based on the concept of transient reversible networks, where a polymeric material is treated as a network of active chains (adaptive links) that break and reform because of micro‐Brownian motion. The breakage and reformation rates for active chains in an aged medium are assumed to depend on the current temperature and the time after cooling below the glass transition temperature. To validate the model, the long‐term viscoelastic response is predicted on the basis of data obtained in the standard short‐term creep tests and compared with data from long‐term experiments. Fair agreement is demonstrated between numerical results and observations. The model is used to calculate residual stresses in a polymeric spherical pressure vessel cooled down (after curing) to the room temperature. It is shown that physical aging of the polymer significantly affects stresses and displacements in the vessel.
Effects of processing conditions and copolymer molecular weight on the mechanical properties and morphology of compatibilized polymer blends
Authors: Hermes H. E. , Higgins J. S. 
Published: April 2004

AbstractThe mechanical properties and morphology of melt mixed polystyrene (PS)/polyethylene (PE) blends that were modified by the addition of up to 16% of a semicrystalline PS‐b‐hPB (hydrogenated polybutadiene) diblock copolymer with varying molecular weight are reported. As a result of the blocks of the copolymer penetrating the corresponding homopolymers, these diblock copolymers are capable of reinforcing the PS/PE interface significantly. This increase in interfacial strength between the immiscible blend components does not necessarily result in an improvement in the mechanical properties of the blends as measured by Izod or tensile tests. This may be because the effect of the copolymers on the rheological properties of the blends during processing outweighs their emulsifying/reinforcing effects. If found to be universally true for polymer blends, these results suggest that the relationship between the effects of copolymers on interfacial strength, their emulsifying effects, and the mechanical properties of copolymer modified blends are not as simple as suggested by many statements found in the literature.
The onset of nonlinear viscoelasticity in multiaxial creep of glassy polymers: A constitutive model and its application to PMMA
Authors: Dooling P. J. , Buckley C. P. , Hinduja S. 
Published: April 2004

AbstractA physically based, isostructural, constitutive model is described for simulating the onset of nonlinear viscoelasticity in multiaxial creep of glassy polymers, as needed in stress analyses of load‐bearing components. In the linear viscoelastic limit, shear response reduces to that of a generalized Maxwell model, while hydrostatic response is Hookean. Nonlinearity enters through Eyring‐type rate process kinetics. The equations of the model are solved numerically using a pseudo‐linear approximation through each time step, leading to an incremental equation for stress that would be convenient for use in finite element analyses. The model and its assumptions were tested using tension, shear and combined tension/shear creep experiments on well‐aged poly(methyl methacrylate) at 70°C. Reproducibility tests confirmed the assumption of constant glass structure for strains up to ∼ 1.5 × 10−2. Shear and pressure activation volumes were obtained by fitting the dependence of the shear compliance on stress invariants. The data showed unequivocally that shear activation volumes vary with log(relaxation time), and excellent agreement was obtained for a linear variation, consistent with the “compensation rule” of polymer thermo‐viscoelasticity. The activation volumes are large (many monome units), indicating the cooperative nature of the elementary flow process. Interestingly, they are of the same order as those applying to yield and plastic flow. Although the model finds success in simulating creep, it fails to describe so accurately the strain recovery on unloading. Possible explanations are suggested.
Distributive mixing in conveying elements of a ZSK‐53 co‐rotating twin screw extruder
Authors: Cheng Hongfei , Manas‐Zloczower Ica 
Published: April 2004

AbstractA fluid dynamics analysis package (FIDAP), using the finite element method, was implemented to simulate the 3‐D isothermal flow patterns in the conveying element of a ZSK‐53 co‐rotating twin screw extruder. The fluid was described by a power‐law model. The dynamics of distributive mixing was studied numerically by tracking the motion of particles in the mixer. The extent of distributive mixing was characterized in terms of length and area stretch as well as strain distributions. The length stretch reflects the overall capability of the mixing device to spread minor component particles away from their neighbors originally present in the same cluster. The area stretch reflects the evolution of intermaterial area when mixing two fluids with a passive interface. We observed an oscillatory behavior for the average intermaterial area stretch, which was explained in terms of a stretching and folding mechanism. Folding occurs during material takeover from one screw to the other. Operating at higher rotational speeds enhances distributive mixing efficiency.
Polymer weld strength predictions using a thermal and polymer chain diffusion analysis
Authors: Ezekoye O. A. , Lowman C. D. , Fahey M. T. , Hulme‐Lowe A. G. 
Published: April 2004

AbstractA new simplified model for strength prediction of welded polymer‐polymer interfaces is proposed. Two schools of thought exist for strength prediction of polymer‐polymer interfaces: microscopic analysis of polymer chain behavior, and macroscopic analysis of bulk polymer properties during welding. The microscopic analysis is based on De Gennes' reptation theory for macromolecules (1), and has been described extensively by both analytical and empirical techniques. Reptation models are based on constant temperature interfaces, which are not found in any actual welding process. Conventional macroscopic analyses of welding empirically relate strength to important thermal process parameters, such as power density and heating time, but do not address the behavior of the polymer chains. Little interaction exists between these two schools of thought. This study seeks to combine these two areas, using reptation theory to explain the polymer chain interactions on a macromolecular level, and relate the interface thermal signature to strength prediction. The result of the new model is a method for strength prediction that takes into account fundamental materials properties as well as the engineering conditions imposed in a realistic welding process to predict weld strength. The model is adapted to run for similar conditions as two separate empirical endeavors. The results show that the model is effective in predicting overall trends, which emphasizes the importance of examining heat transfer effects in any polymer welding process.