bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new method to quantify crazing in various environments
Authors: Clay Stephen B. , Kander Ronald G. 
Published: April 2004

AbstractA new technique to quantify the rate of change of craze density in stressed transparent polymeric plates of polycarbonate was developed. The samples are placed under a creep load in a controlled temperature and humidity environment, during which the craze density is measured with a reflective imaging system at a defined rate. It has been shown that this unique method for crazy detection and quantification has sufficient repeatability to generate statistically acceptable data, obeying currently used, the method described in the present work is an in‐situ, quantitative, non‐subjective, direct measurement of craze density.
Physical chemistry of a phosphite processing stabilizer in polypropylene. Part 1: Solubility
Authors: Billingham N. C. , Garcia‐Trabajo P. 
Published: April 2004

AbstractThe solubility of a commercial aryl phosphite processing stabilizer for ployolefins, {tris (2,4‐di‐t‐butylphenyl)} (irgafos 168, Ciba Speciality Chemicals), has been measured in polypropylene over a range of temperatures. Measurements are complicated by hydrolsis of the phosphite, releasing 2,4‐di‐t‐butylphenol, which is much more soluble in the polymer. We have measured the solubility of this phenol, and of the phosphate oxidation product of the stabilizer. The result are interpreted on the basis of a regular solution model. They show that the phosphite has a very low solubility but that it is not particularly anomalous in comparison with other stabilizers of similar molecular weight and polarity. The phosphate is significantly more soluble than the phosphite at 70°C, but their solubiliies are comparable at 25°C. This is mainly due to the lower heat of fusion and melting point of the phosphate, whose compatibility is actually lower than that of the phosphite. The phenol is much more soluble because of its low melting point.
Finite element analysis of blow molding and thermoforming using a dynamic explicit procedure
Authors: Marckmann G. , Verron E. , Peseux B. 
Published: April 2004

AbstractThis paper reports on the development of a dynamic finite element procedure for the simulation of blow molding and thermoforming of thermoplastic hollow parts. The Principle of Virtual Work written herein takes inertia effects into account. The heat‐softened parison is assumed to be a nonlinear hyperelastic Mooney‐Rivlin membrane and is meshed with classical linear triangular finite elements. We adopt the explicit central differences time integration scheme with the special lumping technique. The moid is divided into triangular elements and the contact between the parison and the mold is assumed to be sticky. Therefore, contacted degrees of freedom of the parison are fixed on the solid boundary until the end of the simultion. Performances are highly improved by the use of an adaptive mesh refinement procedure based on a geometric criterion for detection and on the simple addition of a node at the mid‐side of the longest edge for subdivision. The method is illustrated through some examples of thermoformed and blow‐molded parts. Our results are compared with both experimental and numerical results from literature to validate the present theory.
A 3‐D finite element model for gas‐assisted injection molding: Simulations and experiments
Authors: Haagh G. A. A. V. , Peters G. W. M. , Van De Vosse F. N. , Meijer H. E. H. 
Published: April 2004

AbstractTo gain a better understanding of the gas‐assisted injection molding process, we have developed a computational model for the gas assisted injection molding (GAIM) process. This model has been set up to deal with (non‐isothermal) three‐dimensional flow, in order to correctly predict the gas distribution in GAIM products. It employs a pseudo‐concentration method, in which the governing equations are solved on a fixed grid that covers the entire mold. Both the air downstream of the polymer front and the gas are represented by a fictitious fluid that does not contributeto the pressure drop in the mold. The model has been validated against both isothermal and non‐isothermal gas injected experiments. In contrast to other models that have been reported in the literature, our model yields the gas penetration from the actual process physics (not from a presupposed gas distribution). Consequently, it is able to deal with the 3‐D character of the process, as well as with primary (end of gas filling) and secondary (end of packing) gas penetration, including temperature effects and generalized Newtonian viscosity behavior.
A new hypothesis to describe the mechanisms acting in a welded joint of semicrystalline thermoplastics
Authors: Bonten Christan , Schmachtenberg Ernst 
Published: April 2004

AbstractSince it is known that crosslinked polythylene can be worked, it is clear that the mechanics acting in the interior of a welded joint are not adequately explained yet. There are several criteria, hypotheses and models that attempt to describe what happens in a welded joint. In this paper, two new promising hypotheses, the Mixed Crystal Hypothesis and the Nexus Hypothesis, are introduced. The Mixed Crystal Hypothesis can be proven by the help of several different examination methods. Other examinations support the Nexus Hypothesis.
Enthalpy relaxation in polymeric glasses
Authors: Dfrozdov Aleksey D. 
Published: April 2004

AbstractConstitutive equations are derived for enthalpy recovery in a glassy polymer after quench from above the glass transition temperature Tg to a temperature T in the sub‐Tg region. The model is based on the trapping concept, which treats a disodered medium as an ensemble of cooperatively rearranging regions (CRR) hopping in potential wells as they are thermally activated. Rearrangement occurs when a CRR reaches some liquid‐like energy level in a hop. The rate of hops is described by the theory of thermally activated processes, whereas the probability to change trap in a hop is determined by the difference between the current and equilibrium concentrations of cages. A nonlinear parabolic equation is developed for the distribution of traps. This equation ia used to describe entropy recivery in amorphous and semicrystalline polymers. Fair agreement is demonstrated between experimental data for poly(ether imide), poly(ethyl terephthalate) and polystyrene and results of numerical simulation. Some phenomenological relations are suggested to predict the effect of temperature, molar mass and degree of crystallinity on material parameters.
Studies on epoxy modified with recycled rubber
Authors: Sipahi‐Saglam E. , Akovali G. , Kaynak C. , Akkas N. , Yetmez M. 
Published: April 2004

AbstractThis work covers studies on systems with car tire regrind used as the toughening phase in epoxy resins. Different surface modification techniques were used to improve the compatibility at the between the rubber particles and the epoxy matrix. Silane coupling agents, plasma surface modification and acrylic acid/benzoylperoxide were used to enhance the surface properties of rubber particles. Rubber parts of ground used car tires, with or without surface treatment, were mixed with epoxy. This mixture was poured into molds to obtain mechanical test specimens according to ASTM standards. After curing, mechanical tests were performed and the fractured surfaces of the specimens were examined under Scanning Electron Microscopy, SEM. Throughout the studies, changes in mechanical properties were followed by an increase in the volume percentage of rubber particles and by the effect of different surface treatment processes applied on rubber. A decrease in tensile properties and impact resistance was observed in general as compared to unmodified epoxy. On the other hand, slight increases in fracture toughness values were observed in all surface treated cases.
Elastomer biaxial characterization using bubble inflation technique. II: Numerical investigation of some constitutive models
Authors: Rachik M. , Schmidtt F. , Reuge N. , Le Maoult Y. , Abbeé F. 
Published: April 2004

AbstractAn elastomeric material was investigated with a bubble inflation rheometer, and its mechanical behavior was modeled as a rubbeer‐like solid. Classical strain energy functions were considered and the hyper‐elastic were calculated by a direct identification procedure from simple uniaxial and equibiaxial extension test data, and the reults are compared against those obtained by an inverse method from matching the meaured response to a finite element to a finite element analysis solution, which dependent on the unknown material parameters. The optimised employed the Levenberg‐Marquardt algorithm and Abaqus software to compute the cost function and its gradients. The constants so obtained were further used in finite element analysis, and the numerical results were compared with experiments. This study showed that the inverse method, used to estimate the material parameters, is a good alternative to the direct identification, especially since the latter often requires homogeneous strain state, which is very difficult to obtain.
Properties and manufacturing of a new starch plastic
Authors: De Graaf R. A. , Janssen L. P. B. M. 
Published: April 2004

AbstractEnvironmental awareness has strongly stimulated the introduction of biodegradable materials based on renewable resources of natural origin. This paper describes the properties and manufacturing of such a bioplastic. In a counter‐rotating twin screw extruder, starch and polystyrene were mixed. To enhance material properties such as tensile strength and impact strength, two routes were followed. First, the starch was altered by grafting polystyrene onto the starch backbone using a counter rotating twin screw extruder. The newly formed material was blended with polystyrene in difierent ratios. Tensile strengths of 10 to 35 MPa were obtained while notched impact strengths varied from 0.5 J m−1to 1.5 J m−1. Soaking the material for a certain time in water end measuring the tensile strength of the wet material revealed that the tensile strength remained more the less the same for blends containing more than 30 wt% PS. Second, polystyrene grafted starch was used as a compatibilizer. A homogenous blend could bobtained (according to scanning electronic microscopy pictures) by adding the compatibilizer to a starch, polystyrene, and water mixture. Again, tensile and impact strengths were measured for different ratios of the polymers used. The tensile strength and the impact strength were of the same magnitude as they were with the blended material. X‐ray diffraction and DSC measurements revealed a highly ordered system. When the fraction of polystyrene was above 60 wt% of the blend, the amylose part of the starch crystallized.
Microstrcture development during the injection molding of PET/LCP blends
Authors: Turcott E. , Nguyen K. T. , Garcia‐Rejon A. 
Published: April 2004

AbstractA liquid crystal polymer (LCP) was blended polethylene terephthalate (PET) in different concetrations to improve the barrier properties of PET in injection stretch blow molded bottles. The improvement depends on the microstructure developed at various stages of the process.In this work, the emphasis is on the injection molding stage of the preform. The characteristics and number of morphological layers were directly related to the amount and type of LCP in the blend and the loction within the perform. It was found that at 10% LCP, three morphological layers were found across the thickness of the part, while at 30% LCP, five morphological layers could be identified. The LCP structure can be classified into four types: droplets, thick rods, thin fibrils and ribbons. Each morphological layer is made up of one or more types of structures. The evolution of on type structure to another depends on the particular flow regime ongoing at various locations in the mold. This microstructure development, during the flow, was examined in detail.
Structure and performance of impact modified and oriented sPS/SEBS blens
Authors: Yan R. J. , Shinozaki D. M. , Ajji A. 
Published: April 2004

AbstractBlends of syndiotactic styrene/p‐methyl styrene copolymer (SPMS) and poly (styrene)‐block ‐ploy(ethene‐co‐butylene)‐block‐polystyrene (SEBS) as well as theiruniaxial drwing behavior andd performance were investigated. Mixing was performed using a batch mixer at 280°C. Morphology was evaluted using scanning electron microscopy (SEM).Thermal properties, orientation and tensile properties were determined using differential scanning calorimetry (DSC), the spectrographic birefringence technique, and a tensile testing machine, respectively. The blends of SPMS/SEBS, 90/10 and 80/20 showed a two‐phase structure with an SEBS disperse phase in SPMS matrix. The average sizes of the SEBS paticles and tensile properties of the blends were affected by blending time and compositions. No significant effects on the modulus and strength were observed for the blends containing 10%SEBS or below. The quenched SPMS and SPMS/SEBS (90/10) blends were drawn at 110°C. and their crystallinity and orientation development compared. These were similar for both samples at low draw rations (<3.2), but were much faster for SPMS at higher draw ratios. The orientation process is shown to substantially invrease the strength and modulus in the drawing direction for SPMS and the blends. The toughness (energy under the stress‐strain curve) increased upon addition of SEBS and orientation, with a marked effect of the latter. SEM observation reveals that the dispersed SEBS has been extended to about the same draw ratio as the bulk blend in the drawn blends, indicating effcient stress transfer at the interface.
Reactive blending of poly (dimethylsiloxane) with nylon 6 and poly (styrene):Effect of reactivity on morphology
Authors: Marić M. , Ashurov N. , Macosko C. W. 
Published: April 2004

AbstractReactive compatibilization was used to control and stabilize 20–30wt% poly(dimethylsioxane) (PDMS) dispersions in nylon 6 (PA) and poly(styrene) (PS), respectively. The effect of the type of reation (amine (NH2)/anhydride (An), NH2/ epoxy(E) and carboxylic acid (COOH)/E) on the morphology was studied with electron microscopy. PS and PDMS have mutual solvents thus it was possible to use gel permeation chromatography (GPC) to determine the concentration of block copolymer in PS/PDMS blends. Reactive blending of PA6 with difunctional PDMS‐(AN)2 did not decrease the PDMS particle size compared to the non‐reactive blend (∼10μm). Particle size decreaeased significantly to about 0.5 μm when PA6 was blended with a PDMS containing about 4 random An groups along the chain. For the PS/PDMS blends, GPC revealed that the NH2/An reaction formed about 3% block copolymer and produced stable PDMS particles ∼ 0.4 μm. No reaction was detected for the PS‐NH2/PDMS‐E blend and the morphology was coarse and unstable. Also, PS‐NH2/PDMS‐An reactivity was lower compared to other systems such as PS/ poly (isoprene) and PS/poly(methaacrylte) using the same reaction. This was attributed to the relatively thinner PS/PDMS interface dueto the high PS/PDMs immiscibility.
Reactive modification of polyethylene terephthalate with polyepoxides
Authors: Xanthos M. , Young M‐W. , Karayanndis G. P. , Bikiaris D. N. 
Published: April 2004

AbstractIn attempts to produce modified poldified polyethlene terephthalate (PET) ressins with improved rheology for applications requiring high viscosity and elasticity (e.g., lowdensity extrusion foaming, extrusion blow molding), a novel dimidodiepoxide of low molecular weight was evaluated aschain extender/branching ageent. Its reactivity was compared with that of an ethylene/glycidy1 methacrylate copolymer. The diepoxide showed higher reactivity than the copolymer and could be used at muchlower concentrations. The complex chain extension/degradation reactions occurring in the melt were followed in a batch mixer by torque changes, and by analyzing the prouducts for residual carboxy1 and hydroxy1 content, intrinsic viscosity, insoluble content and melt viscoelastic properties. The perliminary results of this work indicated an overall decrease in carboxy1 content, increase in hydroxy1 content, increase in intrinsic viscosity ans melt viscosity and storage modulus values depending on mixing time and the type and concentration of the additive. It is shown that under certain conditions. reaction of PET with less than 1 wt% diimidodiepoxide may produce materials with rheological characteristics similar to thouse of PET grades that are extrusion foamable by gas injection to low densities.
Transient elongational properties of an in situ generated polymer/polymer composite
Authors: Boyaud M. F. , Cassaugnau P. , Michel A. , Bousmina M. , Aït‐kadi A. 
Published: April 2004

AbstractThe elaboration of a n in‐situ composite consisting of ethylene vinyl acetate copolymer (EVA) and polybutylenetherephtalate (P m was investigated. An inter‐chain chemical reaction during processing operations was used to generate a grafted PBT‐g‐EVA copolymer at the interface of the two polymers. Composites with either nodular or fibrillar morphologies were obtained. Fibrillar morphology was achieved by stretching the extruded blend at the exit of the die. Elongational properties of such composites were investigated by using the fiber wind‐up technique. The influence of the aspect ratio of PBT solid inclusions on the elongational viscosity was discussed for a series of EVA/PBT composites. Clearly, the strain hardening softening properties were found to be strongly affected by the aspect ratio. Increasing the aspect ratio of PBT solid particles made the strain hardening weaker and even gave strain‐softening. This behavior is emphasized by the presence of the grafted PBT‐g‐EVA copolymer. The results suggest that strain‐hardening or softening of such composites is correlated to the homogeneity of the flow at EVA‐PBT interface: the elongational flow is disrupted in the interphase region so that the deformation around the particle is not homogeneous.
Rheological study of the miscibility of LLDPE/LDPE blends and the influence of Tmix
Authors: Hussein Ibnelwaleed A. , Williams Michael C. 
Published: April 2004

AbstractThe miscibility of LLDPE and LDPE blends and the influence of mixing temperature (Tmix) are discussed. Adequate amounts of antioxidants were added during melt blending. Dynamic and steady shear measurments were carried out at 190°C in a Rheometrics Mechanical Spectrometer 800.The dependence of rheological properties on blend composition indicated that blends of LLDEPE (butene) and LDPE mixed at 190°C and 220°C are only partially miscible; immiscibilty is likely to occur around the 50/50 composition and in the LDPE‐rich blends. Blends at 190°C are likely miscible in the LLDPE‐rich range. Tncreaasing Tmix did improve the miscibility of LLDPE/LDPE blends at 190°C or influence the dynamic sher properties (η′ or G′) of the “pure” resins of blends. Suggested that the molecular order [see Hussein and Williams, J. Non‐Newt. Fluid Mech., 86 105 (1999); Hussein and Williams, Macromol. Rapid Commun., 19, 323 (1998)] and mismatch of the molecular conformations of different polyethylene structures provide an explanation for the immiscibility of polyethylenes. Agreement was observed between themeasured dynamic properities and theortical predictions of Palierne and Bousmina‐Karner emulsion models.
Effective properties of cellular materials
Authors: Schjødt‐thomsen J. , Pyrz R. 
Published: April 2004

AbstractThis paper considers the effective properties of cellular materials. The present approach and some earlier proposed methods are compared and discussed. The main effort is placed upon the continuum mechanics approaches' ability to predict effective elastic properties. It is shown that two methods are distinctly better, namely a slight modification of the Mori‐Tanaka approach and a new approach by Dvorak and Srinivas, which is shown to predict the Young's modulus and shear modulus of the Divinycell H‐grade PVC foam almost exactly.
Recycled and restabilized hdpe bottle crates: Retention of critical properties after heat aging
Authors: Kartalis C. N. , Papaspyrides C. D. , Pfaendner R. , Hoffmann K. , Herbst H. 
Published: April 2004

AbstractOven aging was applied for about 8800 hours (more than one year) to evaluate the long‐term thermal stability of post‐used HDPE material recycled from bottle crates. For recycling, the remelting‐restabilization technique was applied. To study the effect of restabilization, crystallinity and melt flow rate were monitored during heat aging. Furthermore, tensile strength and tensile impact strength were followed together with the time until embrittlement. These data were enriched with microphotographs of the specimens' surfaces. Finally, repigmentation was used to evaluate the role of new pigments on the final performance of the recycled material. The results illustrate that restabilization is mandatory for improving the long‐term thermal stability of the post‐used crate material, enabling its reuse in the original application.
Visual analysis of cavity filling and packing process in injection molding of thermoset phenolic resin by the gate‐magnetization method
Authors: Ohta Takashi , Yokoi Hidetoshi 
Published: April 2004

AbstractThe Gate‐Magnetization method developed by Yokoi and coworkers for thermoplastics was used to investigate the flow behavior of glass‐fiber reinforced phenolic resin compound inside a mold cavity. Plug flow builds up in the cavity with a decrease of the local viscosity along the cavity wall due to the heat transfer from the wall and shear heating. Simultaneously, a high viscosity layer builds up from the crosslinking reaction along the cavity wall. The thickness of the high viscosity layer increased as the injection rate decreased. An unstable flow boundary formed between the reacted high viscosity layer along the wall and the low viscosity layer just under the layer.
An investigation of heat transfer effects in isothermal crystallization studies of low‐density polyethylene
Authors: Grady B. P. , Genetti W. B. , Lamirand R. J. , Shah M. 
Published: April 2004

AbstractIsothermal crystallization kinetics of low‐density polyethylene (LDPE) were measured from 96°C‐103°C using a power‐compensating differential scanning calorimetry (DSC). Crystallization kinetics were measured using different sample thicknesses and on samples compounded with nickel, a filler with high thermal conductivity. For the unfilled material, sample thickness and temperature had a significant effect on the rate of crystallization as measured by the Avrami rate constant K, but had no effect on the nucleation mechanism and dimensionality of growth, as measured by the Avrami constant n. The crystallization growth rate as expressed by K1/n scaled approximately with the thickness of the sample. For the filled material, K was much higher and independent of nickel content, suggesting a limiting growth rate for polyethylene at a given temperature in this equipment. The dependence of crystallization rale on sample thickness indicates that barriers to heat transfer can be important. This work shows that for most crystallization rates, thermal conductivity, rather than interfacial resistance between sample and pan, limits heat transfer. Even though thermal conductivity typically dominates heat‐transfer resistance, sample‐pan thermal contact is still important, and some guidelines are given to determine whether good contact is being made.