bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fracture behavior of glass bead‐filled poly(oxymethylene) injection moldings
Authors: Hashemi S. , Din K. J. , Low P. 
Published: April 2004

AbstractThe mechanical properties of glass bead filled poly(oxymethylene) were investigated as a function of glass bead content and glass bead diameter using injection molded test pieces. Fracture toughness measurements were made using single edge‐notched tension and single edge‐notched bend specimens. The effect of notch orientation with respect to the mold fill direction on fracture toughness was studied using single gate and double gate moldings. Tensile strength and flexural modulus were measured using standard test pieces.It was found that; (i) fracture toughness of the filled and unfilled polymer was relatively independent of notch orientation, (ii) the presence of weldlines in the molded test pieces did not affect the fracture toughness of unfilled polymer or its composites, (iii) fracture toughness of filled polymer was always considerably lower than that of the unfilled polymer; fracture toughness decreased sharply with increasing bead concentration, (iv) fracture toughness was not a sensitive function of glass bead diameter; it decreased slightly as bead diameter increased, (v) strain energy release rate as measured under impact decreased with increasing bead concentration, (vi) tensile strength decreased linearly with increasing glass bead concentration and was inversely proportional to the square root of the bead diameter, (vii) weldlines did not affect the tensile strength of the polymer or its composities, (viii) flexural modulus increased linearly with increasing glass bead concentration according to the Einstein equation.
Prediction of process‐induced warpage in injection molded thermoplastics
Authors: Akay M. , Ozden S. , Tansey Tony 
Published: April 2004

AbstractThe main cause of warpage in injection moldings is the imbalance of the thermal residual stresses that are caused by a non‐uniform temperature distribution through the thickness of the moldings resulting from variation in cross sections, part geometries, and temperature difference between the mold surfaces. As the hot plastic melt is injected into the relatively cooler mold, a temperature gradient develops between the core of the molding and its surfaces, determining the magnitude of the residual stresses and warpage deflection. The relationship between the temperature difference of the two halves of the mold and warpage for a flat plate was measured and predicted by use of a finite element software package. The development of warpage in a 3D component (L‐shaped bracket) was also measured, and the results were compared with computer predictions.
The effect of interfacial instabilities on the strength of the interface in two‐layer plastic structures
Authors: Ranjbaran Mohammad M. , Khomami Bamin 
Published: April 2004

AbstractWe have experimentally investigated the coupling between interfacial instabilities and mechanical interlocking in polymeric films consisting of the incompatible polymer pair of polypropylene/high‐density polyethylene and the compatible polymer pair of linear low‐density polyethylene/high‐density polyethylene. Our experimental results show that mechanical interlocking between the two phases can be achieved by controlling the extent of interfacial instabilities by properly selecting the initial disturbance frequency and amplitude as well as the layer depth ratio. Additionally, it has been shown that strength enhancement of the interface due to mechanical interlocking is directly proportional to the extent of wave bending in the processing apparatus. In fact, it has been demonstrated that in our test geometry maximum strength enhancement can be achieved at dimensionless wavenumbers near unity that correspond to disturbances with the largest growth rates. Overall, it has been shown that mechanical interlocking induced by a controlled amount of interfacial instabilities (i.e., based on knowledge of the stability of the interface and growth/decay rate of interfacial waves) can significantly increase the interfacial strength of two layer polymeric structures consisting of incompatible and compatible polymer pairs. Moreover, this effect is more pronounced in incompatible polymer pairs that possess negligible interfacial strength in absence of mechanical interlocking.
The characterization of the halatopolymers: A review
Authors: Ibidapo T. Adesanya 
Published: April 2004

AbstractHalatopolymers belong to a group of ion‐containing materials that display both salt‐ and polymer‐like properties. Their mode of synthesis and other characteristics have been widely reported. This work considers the various reports as defined by both polymeric structure and by the metal ions involved in formation. Also provided are data on other characteristics by which this group of materials can be identified. Synthesis of simple nonpolymeric backbone structures can give highly crystalline salts, which become more amorphous after thermal treatment. While the polymeric backbone‐structured halatopolymers are soluble, the nonpolymeric backbone counterparts are generally insoluble. The halatopolymers exhibit relatively high thermal stabilities.
Influence of melt stability on the crystallization of bis(4‐aminophenoxy)benzene‐oxydiphthalic anhydride based polyimides
Authors: Srinivas Srivatsan , Graham Marvin , Brink M. Heather , Gardner Slade , Davis Richey M. , McGrath James E. , Wilkes Garth L. 
Published: April 2004

AbstractNovel high performance semicrystalline polyimides, based on controlled molecular weight phthalic anhydride (PA) endcapped 1,4‐bis(4‐aminophenoxy)benzene (TPEQ diamine) and oxydiphthalic dianhydride (ODPA), were synthesized. They exhibited excellent thermal stability in nitrogen and air atmospheres as determined by thermogravimetric analysis (TGA). The glass transition temperatures (Tg) for these polymers ranged from 225°C for the 10,000 Mn (10K) polymer, to 238°C for the 30,000 (30K) Mn material. The observed melting temperatures for all the polymers were ∼420°C. The crystallization behavior of these polymers showed a strong molecular weight dependence, as illustrated by the observation that the 10K and 12.5K polymers crystallized with relative ease, whereas the 15K, 20K, and 30K polymers showed little or no ability to undergo thermal recrystallization. The thermal stability of these polymers above Tm was investigated by studying the effect of time and temperature in the melt on the cold crystallization and melting of these polymers. Increased time and temperature in the melt resulted in lower crystallinity because of melt state degradation, such as crosslinking and branching, as evidenced by an increase in melt viscosity, which was more prominent for the higher molecular weight polymers.
Effect of constitutive models on the numerical simulation of viscoelastic flow at an entry region
Authors: Loh K. W. L. , Tay A. A. O. , Teoh S. H. 
Published: April 2004

AbstractThe poor solutions of numerical simulations at a contraction has often been attributed to the numerical scheme used. However, the solution of a numerical simulation is also highly dependent on the constitutive equation. A study of various constitutive equations on the simulation of the 4:1 contraction flow is made in this paper, and their effects on the results analyzed. The constitutive models considered include the Upper Convected Maxwell model, the Oldroyd‐B model, the White‐Metzner model, the Phan‐Thien‐Tanner model and the Giesekus‐Leonov model. It was found that although the Phan‐Thien‐Tanner model gave the best results, the solution at higher shear rates were still not satisfactory.
Study of shear modification of LDPE by an NMR relaxation technique
Authors: Van Prooyen M. , Peemoeller H. , Rudin A. 
Published: April 2004

AbstractA low‐density polyethylene was shear modified by repeated extrusions. These operations resulted in no detectable changes in the polymer molecular weight distribution. The apparent melt viscosity and elasticity decreased after extrusion, as is commonly observed in shear modification. These rheological effects were fully reversible by annealing the melt. Transverse proton relaxation measurements showed the existence of four identifiable different regions in the polymer melt. The range of relaxation times encompassed two orders of magnitude. These reflect the existence of regions with different degrees of conformational order. Shear modification results in the breakup of a minor proportion of the most constrained regions, which have the shortest relaxation times. The apparent “entanglements” that are inferred from rheological measurements probably reflect the coexistence of segments of more than one macromolecule in chain‐folded domains, as indicated by molecular dynamics calculations. These results are evidence that the equilibrium state of LDPE is not a chain‐entangled, highest entropic condition, but rather a lowest free energy state in which chain folding is favored. They are consistent with other longstanding observations, such as the failure of experiments to produce amorphous polyethylene and the apparent lack of mixing of HDPE and LDPE on a molecular level.
In‐mold shrinkage and stress prediction in injection molding
Authors: Titomanlio G. , Jansen K. M. B. 
Published: April 2004

AbstractIn‐mold shrinkage may occur for product parts that solidify under low holding pressure and are not restricted by ribs or flanges. It not only affects the final product dimensions but in addition may have a large effect on the residual stress distribution. A simple elastic model is used to study the effect of in‐mold shrinkage on final product dimensions and residual stress distributions. Friction between polymer surface and mold wall as well as deformation of the mold cavity are taken into account. The model uses local values for temperature, pressure, and crystallization, which belong to the standard output of most simulation codes.
Computer simulation of weld lines in injection molded poly(methyl methacrylate)
Authors: Dairanieh I. S. , Haufe A. , Wolf H. J. , Mennig G. 
Published: April 2004

AbstractComputer simulation packages have had success in predicting filling behavior in extremely complicated geometries. However, few packages offer the possibility of predicting the location and strength of weld lines. This work examines the sensitivity of Moldflow's weld‐line prediction algorithm to variations in material properties and processing conditions. Qualitatively, the algorithm correctly predicted the effects of changes in viscosity, density, and PVT relationship on weld‐line strength of a poly(methyl methacrylate). The algorithm is also successful in predicting the influence of variations in the injection time on weld line strength. However, the algorithm predictions for changes in the mold and die temperatures were at odds with the experiment. An attempt was made to correlate Moldflow's computed viscosities with the experimentally measured reduction in the strength in the weld‐line area. It was shown that a one‐to‐one relationship existed between these two quantities. Whereas the potential of using the viscosity to predict weld‐line strength has been demonstrated, further refinement of this new concept is needed and its validity for other systems has to be established.
Morphology, thermal, and mechanical properties of polyacetal/ionomer blends
Authors: Horrion J. , Cartasegna S. , Agarwal P. K. 
Published: April 2004

AbstractThis study is directed towards the development of modifiers for and the understanding of their role in improving the impact properties of an engineering polymer, polyacetal (POM). It is demonstrated that modifiers that induce ion‐dipole interactions can lead to substantial enhancements in the room temperature impact performance of POM without sacrificing its unique balance of mechanical, thermal, and chemical resistance properties. The mechanical and physical properties of blends of a commercial copolymer type polyacetal (POM) with terpolymers of ethylene, methylacrylate and acrylic acid (EAAT) and its zinc ionomer form (EAAT‐Zn), are reported. Substantial differences both in the mechanical and impact performance were found in these two modified POM systems. DSC and optical microscopy studies of such blends demonstrates only minor differences in the microcrystalline structure of the two blend systems. A nearly three fold reduction in the spherulite size of POM was found from addition of as little 5% of either modifier, thus ruling out this mechanism for the observed increased toughness of the blends. Dynamic mechanical measurements and cryofractured surface microscopy observations indicate that enhancements in the physical properties of POM modified with zinc ionomers of EAAT are due to enhanced interfacial adhesion and to the (inherent) mechanical rigidity (due to ionic interactions), of the modifier. In these blends the tensile and impact strength are found to be a function of the degree of neutralization of the terpolymer acid content. In particular, an optimum balance of impact and tensile properties is obtained with partial neutralization (in the range of 25 to 50% of the terpolymer acid content) and at modifier addition levels in POM in the range of 5 to 10%. The EAAT modifier for POM was found to be ineffective even up to 20% addition as compared to EAAT‐Zn modifier. Ion‐dipole interactions are thus shown to be more influential than the hydrogen bonding that occurs in EAAT‐POM blends. The study suggests a new approach to modify polar engineering polymers via such interactions.
Structure and crack growth in gas pipes of medium‐density and high‐density polyethylene
Authors: Tränkner T. , Hedenqvist M. , Gedde U. W. 
Published: April 2004

AbstractThe microstructure and resistance to slow crack growth of two commercial polyethylene pipe materials were studied. Differential scanning calorimetry, small‐angle X‐ray scattering, and transmission electron microscopy were used to reveal the crystallite thickness and width distributions and the size of the lamellar stacks. The resistance to slow crack growth was assessed by uniaxial constant loading of notched specimens and by hydrostatic pressure testing of notched and unnotched pipes. The high‐density material contained roof‐lamellae, suggestive of a segregation of low molar mass species. Notched uniaxial testing revealed large differences in slow crack growth‐resistance between the two PEs despite the fact that the average tie‐chain concentration was similar. Hence, low‐molar mass segregation, which was found to be higher for the high‐density material, definitely decreases the resistance to slow crack growth. Notched uniaxial testing was a sensitive method for ranking these PEs according to their resistance to slow crack growth, and 15 times faster than that achieved in conventional unnotched pressure testing. Failure time extrapolations from higher temperatures to 20°C were made, using a multiple linear regression method (SEM‐Q1), the Arrhenius equation, and universal shift‐functions to investigate their applicability. The extrapolations resulted in longer life times compared with experimental data, regardless of the method used. The SEM‐Q1 method (lower‐confidence‐limit data) gave the best fit to the 20°C experimental data followed by the Arrhenius equation.
Sorption of low molar mass silicones in silicone elastomers
Authors: Gedde U. W. , Hellebuych A. , Hedenqvist M. 
Published: April 2004

AbstractElastomers based on polydimethylsiloxane (PDMS) are used as insulating material in outdoor electrical power applications. It is believed that migration of small molecule PDMS species plays an important role in the recovery of hydrophobicity of oxidized or polluted PDMS elastomer surfaces. This paper reports data on diffusivity and solubility of low molar mass PDMS liquids in PDMS rubbers (8000 < Mc < 16,000 g/mol) obtained by sorption measurements. It was found that the diffusivity (D) of linear PDMS liquids was approximately independent of the concentration of penetrant and that in the molar mass range 400 < Mc < 18,000 g/mol it decreased with molar mass (Mc) of the diffusing liquid according to D α Mc−0.8. Theory and previous data for other oligomers and elastomers predict that D is proportional to M−1. Linear PDMS liquids of lower molar mass exhibited a stronger molar mass dependence. The diffusivity of a given PDMS liquid increased with increasing elastomer crosslink density. The activation energy of the diffusivity was constant at 15.5 ± 2 kJ/mol for linear PDMS liquids of Mc larger than 1000 g/mol−1 with only a negligible influence of network density and filler content. The activation energy of the lowest molar mass penetrant was considerably lower, 6 to 7 kJ/mol. The solubility increased markedly with decreasing molar mass of the penetrant and with decreasing elastomer crosslink density.
Temperature profiles in batch methyl methacrylate polymerization in gelled suspension
Authors: Polacco Giovanni , Semino Daniele , Palla Maurizio 
Published: April 2004

AbstractA detailed analysis of a recently developed batch polymerization process is presented. The new technique, designed for the production of high purity polymers (e.g. for biomedical purposes), consists of a suspension polymerization in which the suspending phase is transformed into a gel before initiating polymerization. A detailed first principles model of the process is developed. Both experimental and theoretical results are for polymerization of methyl methacrylate in an aqueous phase, which has been gelled by the addition of agarose. The analysis is focused on the sensitivity of the system with respect to operating conditions, the kinetic parameters, and the heat transfer properties. The system thermal stability is a primary concern, because of the lack of agitation and the possible instability of the gelled phase at high temperature. Sensitivity to the maximum temperature is therefore examined. Parameters that can increase the polymerization rate, such as the initial initiator concentration, and many of the kinetic constants are found to affect mainly the time at which the maximum temperature appears, but not significantly its value. No problem of gel instability was found. An instability may appear only if the jacket temperature or the water to methyl methacrylate ratio is significantly varied. The model developed, and its use to compute system sensitivies, has proven to be valuable for reactor scale‐up and process understanding and optimization.
The relative influences of molecular structure on brittle fracture by fatigue and under constant load in polyethylenes
Authors: Zhou Y. , Lu X. , Zhou Z. , Brown N. 
Published: April 2004

AbstractThe resistance to failure under an oscillating load, fatigue, and to failure under constant load (CL), are presented for a large number of linear polyethylenes. The effects of fatigue and a CL on brittle fracture are compared with respect to the influence of the molecular structure such as branching and the molecular weight. Molecular weight has a relatively greater influence on fatigue, whereas branching is more important under CL.
Hydrolysis effects on the molecular weight degradation of condensation polymers as estimated from their prior drying condition
Authors: Sudduth Richard D. 
Published: April 2004

AbstractA simple model has been developed to evaluate the potential random degradation of hydrolyzable polymers as a function of water remaining after drying but prior to processing. Molecular weight retention was found to be dependent on the initial molecular weight of the polymer as well as the hydrolysis efficiency, but independent of polymer crystallinity. At the same water content and hydrolysis efficiency, the model indicated that higher molecular weight polymers would be expected to yield a more significant molecular weight reduction. The potential degradation of hydrolyzable condensation polymers was also estimated from drying conditions recommended by producer companies. The results calculated from the hydrolysis model were in most instances consistent with producer company recommended drying conditions. A review of the literature also found that while the sensitivity of nylons to hydrolysis decreases with moisture content, nylon 6/6 specifically can sometimes increase in brittleness and viscosity to an unacceptable level after drying below a critical moisture content. Thus nylon 6/6 was found to have a preferred range of moisture content for optimum processing. The need for a test method to evaluate hydrolysis efficiency for hydrolyzable polymers was also discussed. Such a standard could be important in the practical evaluation of new materials developed to minimize hydrolysis susceptibility.
Numerical study of twin‐screw extruders by three‐dimensional flow analysis—development of analysis technique and evaluation of mixing performance for full flight screws
Authors: Kajiwara Toshihisa , Nagashima Yuki , Nakano Yoshio , Funatsu Kazumori 
Published: April 2004

AbstractWe have developed a method for predicting the three‐dimensional flow field in the melt conveying zone in counter‐rotating and co‐rotating twin‐screw extruders. We applied this technique to the full flight screws with thin flight width and open C‐shaped channels in both rotating type extruders having the same screw configurations. We compared the details of velocity and stress fields, the flow rates of transportation, and various kinds of leakage flows for both rotating type extruders. Also, we obtained the spatial distribution of tracer particles and residence time distribution using a numerical tracer experiment. The flow rate in the transport direction in the co‐rotating twin‐screw was larger than that in the counter‐rotating twin‐screw, and this suggested that the latter has higher transport performance when the screws have thin flight width and open C‐shaped channels as used in this study. As for the distributive mixing, it was found that the co‐rotating twin‐screw excels in the area of fluid rearrangement between the two screws and distribution in the rotational direction, while the counter‐rotating twin‐screw has the desirable characteristic of wide distribution in the axial direction. With regard to dispersive mixing, there was no considerable difference between calculated stress fields in both rotating type extruders.
Chemorheology of a highly filled epoxy compound
Authors: Spoelstra A. B. , Peters G. W. M. , Meijer H. E. H. 
Published: April 2004

AbstractBased on measurements of the dynamic viscosity, a strategy is proposed to find an expression that relates the viscosity of an epoxy compound during curing, to the temperature, shear rate, and degree of reaction. It appeared that the dynamic viscosity is a unique function of the effective shear rate (i.e. the product of frequency and strain) over a wide range of frequencies and strains after being corrected for the temperature. The effective shear rate dependence of the viscosity is described with a power law with an exponent that depends on the conversion. The effect of temperature is described with an Arrhenius‐type equation with conversion dependent parameters. Differential scanning calorimetry is applied to determine the kinetic equation that is used, in combination with the thermal history, to obtain the conversion during the rheological measurements. The description of the viscosity gives a good prediction of the measured viscosity in the region between melting and gelation of the compound. The theories proposed in the literature to detect the gel point from dynamic experiments are examined. It is found that neither the G′‐G″ crossover, investigated by e.g. Tung and Dynes (1), nor the frequency‐independence of tan(δ), described by Winter (2, 3), can be used to determine the gel point of the given material. In contrast, the curves of G′ against conversion for measurements performed at equal strain but with different thermal histories appear to converge at a conversion of ∼18%, which agrees with the gel point determined through extraction experiments.