bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effectiveness of functionalized polyolefins as compatibilizers for polyethylene/wood flour composites
Authors: Wang Yeh , Yeh Feng‐C. , Lai Sun‐M. , Chan Hsun‐C. , Shen Hsiao‐F. 
Published: April 2004

AbstractThe effects of various types of compatibilizers on the mechanical properties of high‐density polyethylene/wood flour (HDPE/WF) composite were investigated. Functionalized polyolefins such as maleated and acrylic acid grafted polyethylenes, maleated polypropylene (PPgMA) and styrene‐ethylene/butylene‐styrene triblock copolymer (SEBSgMA) were incorporated to reduce the interfacial tension between the polyethylene matrix and the wood filler. Among them, it was found that maleated linear low‐density polyethylene (LLDPEgMA) gave maximum tensile and impact strength of the composites, presumably because of better compatibility with the HDPE matrix. Similar but less enhanced improvements in the mechanical properties, depending on the compatibilizer loading, were seen for the SEBSgMA system. Whereas acrylic acid grafted high‐density polyethylene (HDPEgAA) and maleated polypropylene (PPgMA) only slightly improved tensile modulus and tensile strength; and they both increased with increasing loadings of compatibilizers. A scanning electron microscopic study was employed to reveal the interfacial region and confirm these findings. In addition, dynamical mechanical thermal measurements also revealed the interaction between filler and matrix, and FTIR spectroscopy was used to assign the chemical fixation and the various chemical species involved at the surface of the wood fillers before and after surface treatment.
The effect of annealing on the nonlinear viscoelastic response of isotactic polypropylene
Authors: Drozdov Aleksey D. , Christiansen Jesper Declaville 
Published: April 2004

AbstractThree series of tensile relaxation tests are performed on isotactic polypropylene at room temperature in the vicinity of the yield point. In the first series of experiments, injection‐molded samples are used without thermal pre‐treatment. In the second and third series, the specimens are annealed at 130°C for 4 and 24 hours, respectively. Constitutive equations are derived for the time‐dependent response of semicrystalline polymers at isothermal loading with small strains. A polymer is treated as an equivalent temporary network of macromolecules bridged by junctions (physical cross‐links, entanglements and crystalline lamellae). Under loading, junctions slide with respect to their positions in the bulk material (which reflects the viscoplastic behavior), whereas active strands separate from their junctions and dangling strands merge with the network at random times (which reflects the viscoelastic response). The network is thought of as an ensemble of meso‐regions (MRs) with various activation energies for detachment of chains from temporary nodes. Adjustable parameters in the stress‐strain relations are found by fitting the observations. The experimental data demonstrate that the relaxation spectrum (characterized by the distribution of MRs with various potential energies) is independent of mechanical factors, but is altered at annealing. For specimens not subjected to thermal treatment, the growth of longitudinal strain does not affect the volume fraction of active MRs and the attempt rate for detachment of chains from their junctions. For annealed samples, the concentration of active MRs increases and the attempt rate decreases with strain. These changes in the time‐dependent response are attributed to broadening of the distribution of strengths of lamellae at annealing.
Composites from PMMA modified thermosets and chemically treated woodflour
Authors: Acha Betiana A. , Aranguren Mirta I. , Marcovich Norma E. , Reboredo Maria M. 
Published: April 2004

AbstractThe mechanical behavior of composites made from woodflour and a modified thermoset unsaturated polyester resin has been examined. Polymethylmethacrylate (PMMA), a common low profile additive (LPA), was used as the matrix modifier. Woodflour, the reinforcing filler, was used ‘as received’ and was also modified with a commercial alkenyl succinic anhydride (ASA), in order to enhance the compatibility with the resin. The composites exhibited higher flexural and compressive modulus and compressive yield stress than the neat resin, while flexural strength and ultimate strain were reduced. The addition of PMMA to the unfilled thermoset led to a LPA morphology and decreased the flexural modulus, but produced an increment in flexural strain at break, impact energy and toughness of the UP resin. No enhancement in the mechanical behavior of the composites was found when treated woodflour instead of unmodified woodflour was used.
Ethylene polymerization over MgO‐supported zirconocene catalysts
Authors: Kim Soo Jin , Lee Wha Young , Park Yeungho , Huh Wansoo , Ko Young Gwan 
Published: April 2004

AbstractSupported zirconcene catalysts on a new support, MgO, were prepared and tested in ethylene polymerization. Three types of impregnation methods were employed to find an optimum supporting method for MgO. The direct impregnation of Cp2ZrCl2 on MgO showed low metal loading and polymerization activity, while the catalyst had a higher metal loading and polymerization activity when MgO was treated with methylaluminoxane (MAO) before supporting. Treatment of MgO with MAO during the supporting step invoked two types of catalytic sites, which was evidenced by the bimodal molecular weight distribution of the polymer products. MgO is considered to have potential as a support for metallocenes.
Evaluation of impact fracture toughness of polymeric materials by means of the J‐integral approach
Authors: Fasce Laura A. , Pettarin Valeria , Seltzer Rocío , Frontini Patricia M. 
Published: April 2004

AbstractThe most commonly accepted method of determining impact fracture toughness of polymeric materials that exhibit small scale yielding and negligible influence of dynamic effects is given by the ISO/DIS 17281 Standard, which states that for brittle behavior, basically a linear relationship exists between the fracture energy,U, and the energy calibration factor, ϕ. This relationship allows calculation of the critical strain energy release rate,GICfrom the slope of theUvs.BWϕ plot. This paper describes a simpler alternative methodology capable of evaluating impact fracture toughness using theJcparameter. TheJ‐integral is evaluated at the instability load point, by calculating the fracture energy required to produce cleavage behavior of a pre‐cracked specimen. The methodology is limited to single edge notched three‐point‐bending specimens with a crack to depth ratio equal to 0.5. Tests were carried out on an instrumented falling weight impact testing machine on the following materials: PP (polypropylene), HDPE (high‐density polyethylene), MDPE (mid‐density polyethlene) and RT‐PMMA (rubber toughened polymethylmetacrylate). Results are in excellent agreement with the critical values determined by the ISO/DIS 17281 Standard.
Nano‐alumina modified epoxy based film adhesives
Authors: Gilbert Eric N. , Hayes Brian S. , Seferis James C. 
Published: April 2004

AbstractEpoxy based film adhesives were developed that contained nano‐sized alumina particles of different size and shape. These nano‐scale materials were incorporated at 5 and 10 weight percent into an adhesive formulation that was filmed on polyester random mat scrim. Films were applied to composite substrates for fracture testing and aluminum substrates for lap shear and peel testing. Scanning electron microscopy was used to characterize the surfaces of both the aluminum and composite specimens. Results from the bonded aluminum samples showed that in almost all cases the additives increased the peel and shear strength of the adhesives. Composite samples yielded results that were less clear, but still demonstrated that nano‐scale additives can increase the fracture toughness of a thermosetting adhesive.
Gross melt fracture mitigation in converging dies: A singular behavior due to polymer wall slip
Authors: Goutille Yannick , Guillet Jacques 
Published: April 2004

AbstractThis work focuses on mitigating the gross melt fracture defect of polymer flowing through axisymmetrical and two‐dimensional dies. The die entrance angle is considered as well as the influence of the converging wall roughness. Singular results are obtained with a random styrene butadiene rubber (SBR) copolymer, as the gross melt fracture defect cannot be eliminated or mitigated by reducing the die entrance angle. Other experiments carried out with rough converging dies do not give better results. Indeed, the polymer essentially slips along the walls, as shown from capillary rheometer and birefringence experiments. Thus, these results point out the importance of elongational stresses and interfacial conditions in the die entrance region on flow instabilities and the gross melt fracture defect.
Free‐radical solution polymerization of styrene in a tubular reactor—effects of recycling
Authors: Cabral P. A. , Melo P. A. , Biscaia E. C. , Lima E. L. , Pinto J. C. 
Published: April 2004

AbstractThe styrene free‐radical solution polymerization reaction in a tubular loop reactor is studied here both experimentally and through simulation. An attempt is made to compare the performances of tubular loop reactors when the recycle ratio is varied, based on steady‐state and dynamic responses and on the quality of the polymer produced at different conditions. It is shown here that steady‐state responses of loop reactors and traditional tubular reactors are very similar as far as the quality of the polymer obtained is concerned. Therefore, the recycle ratio cannot be used as a fundamental operation parameter for grade transitions at plant site. However, it is also shown that the recycling of polymer material is very important to accelerate the attainment of the final steady‐state in tubular reactor configurations, because recirculation of material homogenizes the distorted radial profiles of the axial flow velocities.
An experimental study of morphology and rheology of ternary Pglass‐PS‐LDPE hybrids
Authors: Guschl Peter C. , Otaigbe Joshua U. 
Published: April 2004

AbstractTernary blends of low‐density polyethylene (LDPE), polystyrene (PS), and a lowTgtin‐based phosphate glass (Pglass) were prepared at compositions ranging from 0–50 vol% Pglass in which either LDPE or PS was the continuous matrix phase. Differential scanning calorimetry was used to investigate the phase behavior of the pure components, PS‐LDPE blends and binary Pglass‐polymer hybrids. Interesting steady‐shear and transient rheology was observed for the hybrids. In particular, the steady shear viscosity curves for the hybrids of ϕPglass≤ 30% exhibited unusual, four‐region flow behavior, similar to that of liquid crystalline polymers. Two Newtonian plateaus at low (\documentclass{article}\pagestyle{empty}\begin{document}${\rm \dot \gamma }$\end{document}≤ 0.1 s−1) and moderate (0.4 ≤\documentclass{article}\pagestyle{empty}\begin{document}${\rm \dot \gamma }$\end{document}≤ s−1) shear rates connected by two distinct shear‐thinning regimes were apparent. This observed rheology is ascribed to a unique composite morphology of these multi‐component systems. Rheological data on the binary Pglass‐polymer systems suggest that the presence of the Pglass within both PS and LDSE contributes significantly to this unusual behavior, perhaps because of the interfacial behavior between the phases. Micrographs obtained via scanning electron microscopy reveal preferential placement of the Pglass phase dispersed within the PS‐phase and surrounding the LDPE phase. Optical shearing data confirmed the evolution of this microstructure under specific shear conditions.
Study on the phase behavior of EVA/PS blends during in situ polymerization
Authors: Cheng Shih‐Kai , Wang Cheng‐Chien , Chen Chuh‐Yung 
Published: April 2004

AbstractA triangular phase diagram of the polystyrene/styrene/ethylene vinyl‐acetate (PS/SM/EVA) system is established to account for the phase change during polymerization of SM. The phase behaviors for EVA and PS domains in the SM polymerization system are also studied by an optical microscope (OM) and a photometer. Both EVA and PS dissolve in SM quite easily, but PS and EVA are immiscible. Hence, the exclusion of PS from the EVA phase domain results during the polymerization. That is, the polymer solution will be phase‐separated at the initial stage of polymerization. Additionally, EVA phase inversion occurs as the conversion of SM increases to 15%, at which the volume ratio of EVA/PS is approximately unity. Monitoring the light transmittance level of EVA/PS/SM solution during polymerization, the EVA phase proves to have been completely inverted to the dispersed phase when the SM conversion reaches 20%.
Probe segregation and Tg determination of a supported ultra‐thin polystyrene film studied by X‐ray and neutron reflectivity, and SIMS
Authors: White Chris , Wu Wen‐Li , Pu Yuxie , Rafailovich M. , Sokolov J. 
Published: April 2004

AbstractSelective deuteration combined with X‐ray and neutron reflectivity has been used to determine the extent of probe segregation to an interface in ultra‐thin polymer films as a function of the number of thermal cycles. The extent of probe segregation to the interface was also investigated using Secondary Ion Mass Spectroscopy (SIMS). Significant probe segregation was not evident in these studies. X‐ray reflectivity has also been employed to measure the coefficient of thermal expansion of ultra‐thin polystyrene films supported on quartz. The glass transition temperature determined with this method is equivalent to that measured for bulk polystyrene films.
TOF‐SIMS study of injection‐molded polystyrene
Authors: Pisciotti Francesco , Lausmaa Jukka , Boldizar Antal , Rigdahl Mikael 
Published: April 2004

AbstractThe purpose of this study was to provide experimental evidence of the separation of the polymer components at different scales during conventional processing. This was achieved by characterizing the surface and the bulk (cross section) of moldings manufactured with a high‐flow grade and a low‐flow grade of commercial polystyrene by the time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) analytical technique. Owing to the geometric constraints of the mold used, a weld was also obtained. Different surface spectra were observed for the two molded polystyrenes. The surface of the high‐flow grade moldings showed the spectral features of low‐molar polyolefin (paraffin) contaminants, whereas the bulk was dominated by polystyrene. Spectra from both the surface and the bulk of the low‐flow grade moldings were characteristic of polystyrene. Mold‐filling effects on the surface composition were observed in the flow front region of molded short‐shots of the low‐flow grade. The spectral changes indicated the abundance, in the surface, of the high end of the molar‐mass distribution of the material during the mold filling process. Two‐dimensional maps of the secondary ions from the low‐flow grade also showed an occasional alkali contamination, preferentially along the notch of the weld.
Preparation and properties of polyethylene‐clay hybrids
Authors: Kato M. , Okamoto H. , Hasegawa N. , Tsukigase A. , Usuki A. 
Published: April 2004

AbstractPolyethylene‐clay hybrids have been prepared successfully by melt compounding with maleic anhydride grafted polyethylene (MA‐g‐PE), organophilic clay and polyethylene. In these polyethylene‐clay hybrids, the silicate layers of the clay were exfoliated and dispersed to the monolayers. The hybrids exhibit higher tensile yield strengths and tensile moduli than those of polyethylene matrices and those of polyethylene‐inorganic clay composites. When the 5‐wt% clays were loaded, the tensile yield strength and the tensile modulus of the hybrid were, respectively, 1.4 and 1.8 times higher than those of the polyethylene/MA‐g‐PE mixture. The gas permeability of that clay hybrid decreased 30% compared with polyethylene/MA‐g‐PE mixture.
Continuous extrusion of microcellular polycarbonate
Authors: Gendron Richard , Daigneault Louis E. 
Published: April 2004

AbstractExtruded microcellular foams have been obtained from mixtures of polycarbonate (PC) and n‐pentane. Cell diameters were in the range of 2 to 5 μm and the foam densities varied between 400 and 700 kg/m3. Although two types of PC have been investigated, one linear and one branched, the presence of side branchings did not modify the extruded foam characteristics. Use of carbon dioxide as the blowing agent was also attempted, and cell sizes below 10 μm have been successfully obtained. One prerequisite for microcellular foaming was believed to consist in a concentration of the blowing agent close to its limit of solubility as that defined under the actual processing conditions of pressure and temperature. This hypothesis was validated from the observation of extrusion of regular PC foams (intermediate to low densities and cell sizes ranging between 100 μm and 1 mm) using moderate concentrations of blowing agents, and from solubility and viscosity measurements on similar polymer/blowing agent systems.
Effects of die geometry on cell nucleation of PS foams blown with CO2
Authors: Xu Xiang , Park Chul B. , Xu Donglai , Pop‐Iliev Remon 
Published: April 2004

AbstractThis paper investigates the effect of varying the geometry of the die on the cell nucleation behavior of extruded PS foams blown with CO2. Three interchangeable groups of carefully calibrated filamentary dies have been used in the experimental study. The dies were deliberately designed to have either different pressure drop rates while having identical die pressures and flow rates, or different die pressures while having identical pressure drop rates and flow rates. The experimental results revealed that the geometry of the die governs the cell density of extruded PS foams, especially because of its significant effect on the pressure drop rate across the die. However, the effect of the die back pressure on the cell density was found to be marginal, whereas its effect on the cell morphology was found to be predominant. In addition, regardless of die geometry, the CO2content proved to be a very sensitive parameter with respect to the cell nucleation behavior of extruded PS foams. On the other hand, the cell density was slightly improved by an increase of the tale content, especially at reduced concentrations of CO2.
Rheological effects of polyethylenes in film blowing
Authors: Fang Yunli , Carreau Pierre J. , Lafleur Pierre G. 
Published: April 2004

AbstractThe aim of this work is to correlate the rheological properties and processability of various polyethylenes during the film‐blowing process. The effect of rheology on the kinematics and dynamics of film blowing for five different polyethylene resins has been extensively studied using a fully instrumented laboratory unit. The complex viscosity, shear viscosity, uniaxial elongational viscosity, and non‐uniform biaxial elongational viscosity, as well as the strain rates and stresses during film blowing, have been determined and correlated to the bubble stability.G′ versusG″ plots were found to be virtually independent of temperature for all polymers investigated. The more elastic polymers (largerG′ values) were found to be more stable in film blowing. Also, the more stable polymer melts were found to be those possessing larger elongational properties.
Hyperbranched polymers in cationic photopolymerization of epoxy systems
Authors: Sangermano M. , Malucelli G. , Bongiovanni R. , Priola A. , Harden A. , Rehnberg N. 
Published: April 2004

AbstractMixtures of epoxy resins in the presence of epoxy hyperbranched polymers (HBP), in the range of 5–15 wt%, were investigated in the cationic photocuring process. No significant differences in rate of polymerization or final epoxy groups conversion were observed. At low concentration, HBP acts as plasticizer and causes a decrease of the glass transition temperature of the epoxy matrix and of the E′ value. At higher concentration (about 15 wt%), two Tg values are evident, indicating a biphasic structure of the system. The SEM analysis of the fracture surface of the samples confirms a particulate structure with separate HBP domains interconnected to the epoxy matrix. In all the samples investigated, a clear increase of the impact resistance was observed, resulting either from the plasticization effect or from the particulate structure induced by the presence of the HBP resin.
Tribological behavior of pure and graphite‐filled polyimides under atmospheric conditions
Authors: Samyn P. , De Baets P. , Schoukens G. , Hendrickx B. 
Published: April 2004

AbstractAs the use of common engineering plastics in tribological systems is limited to low sliding velocities and low loads because of creep and insufficient temperature resistance, there is increasing interest in application of high‐performance polymers such as polyimides, characterized by their ability to maintain favorable mechanical properties up to their melting point. However, for practical design, tribotesting remains necessary for determination of the material's performance under a given contact situation. In this article, two commercially available polyimides are tested at relatively high sliding velocities and contact pressures under atmospheric conditions of temperature and humidity. A consistent overview of tendencies in friction and wear for pure polyimides as a function of applied normal loads and sliding velocities is given. Addition of 15% by weight graphite powder as internal solid lubricant strongly influences friction and wear. Its behavior is compared with pure polyimide grades and differences are discussed in relation with experimental measured bulk‐temperatures. A linear temperature law is derived as a function of pv‐levels and a steady‐state condition is found at different temperature levels, in accordance with thermal conductivity of the polymer bulks. In case of graphite additives, a steady state in temperature coincides with the regime condition of wear rate.
Enhanced apparent payne effect in a gum vulcanizate at low temperature approaching glass transition
Authors: Pan Xiao‐Dong , Kelley Edward D. 
Published: April 2004

AbstractFor a vuleanized elastomer compound containing no filler, variation of dynamic moduli with strain was examined in the transition zone approaching glass transition at 0.1, 1, 10, and 15 Hz. In the complete absence of filler‐filler/filler‐polymer interactions, the nonlinearity in dynamic moduli becomes enhanced upon approaching glass transition regardless of testing frequency. Under the test protocol employed, the extraordinary nonlinearity at 10 Hz and 15 Hz is shown to be associated with a spectacular shear‐heating event. At 10 Hz and −19°C, a pronounced yielding‐like peak in the in‐phase stress component emerges at small strain (< 2%) during testing of increasing strain. However, the corresponding temperature rise here is only about 0.4°C. Interestingly, at or above 0°C, no such peak in the in‐phase stress component emerges for compounds filled with reinforcing filler above the percolation threshold. Discussion is also made relating the observations to the sliding friction of rubber materials.
Experiments on the induction welding of thermoplastics
Authors: Stokes Vijay K. 
Published: April 2004

AbstractIn induction welding of thermoplastics, induction heating of a gasket, made of a ferromagnetic‐powder‐filled bonding material and placed at the interface of thermoplastic parts to be joined, is used to melt the interface; subsequent solidification of the melt results in a weld. Tensile tests on induction butt‐welds of polycarbonate (PC), poly(butylene terephthalate) (PBT), and polypropylene (PP) are used to characterize achievable weld strengths, and microscopy is used to correlate weld strength with the morphology of failure surfaces. In PC, PBT, and PP relative weld strengths as high as 48%, 43%, and 55% of the respective strengths of PC, PBT, and PP have been demonstrated. Relative weld strengths on the order of 20% have been demonstrated in PC‐to‐PBT welds.