bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between segment structures and elastic properties of segmented poly(urethane‐urea) elastic fibers
Authors: Yoshihara Nori , Ishihara Hideaki , Yamada Toshiro
Published: April 2004

Studies on segmented poly(urethane‐urea) (SPUU) elastic fibers having various segment structures were done in terms of elastic recovery and stress‐strain relationship (S‐S). Three kinds of segment structures were used: 1) the same composition having different sequences of segment units, 2) the same length of soft segments having different molecular weights of polyol, and 3) different segment structures having almost the same stress at 350% elongation. The SPUU elastic fibers having higher sequence numbers of both soft and hard segment units, that is, greater block structures, show better elastic recovery properties, especially delayed elastic recovery. The SPUU elastic fibers showing better elastic recovery take an optimum value for the number‐average molecular weight (Mn) of soft segments jointed with urethane bonds. Here the optimum Mn depends on the molecular weight of polytetramethyleneglycol (PTMG) as a starting material. The hysteresis loss in S‐S for the pre‐elongation decreases with an increase of Mn of PTMG. The SPUU elastic fibers having greater block structures show lower stress with lower 2C1 and 2C1 + 2C2 of Mooney‐Rivilin plot constants for elastic fibers having the same composition. This indicates a lower density of crosslinks for finite deformation. An increase of the urea bonds or the molar ratio of urea bond to urethane bond raises the stress. It is found that the polymerization process, as well as composition, is important for design structures of SPUU elastic fibers.
A rheological and morphological model for blends of flexible and rigid macromolecules
Authors: Edwards Brian J. , Williams Karen L.
Published: April 2004

A model is developed that describes the complicated rheology and morphology of thermoplastic polymers blended with relatively small amounts of liquid‐crystalline polymers (LCPs). Such blends typically display properties superior to, but more complicated than, those of ordinary thermoplastic polymers. Viscosity predictions are obtained with this model that exhibit the wide range of behavior that is observed experimentally in these blended materials for both shear and elongational flows. For example, the viscosity‐composition curve can display a minimum at low compositions of LCP, and the addition of an LCP to a thermoplastic polymer can result in a reduction in the shear viscosity but an increase in the elongational viscosity. Corresponding morphological descriptions are also obtained for the internal microstructure of the blends that provide information about the underlying causes of the complicated rheological behavior.
Melt strength and extensibility of talc‐filled polypropylene
Authors: McInerney L. F. , Kao N. , Bhattacharya S. N.
Published: April 2004

Polypropylene homopolymer melts containing up to 50 percent by weight of talc filler (24 vol%) were tested on a Gottfert Rheotens melt strength testing unit. Melt strength and drawability parameters were measured from these tests to evaluate changes in the extensional behavior of the melt induced by filler addition. It was found that the melt strength of the polypropylene was decreased for talc additions of less than 40 wt% (17.5 vol%) under all test conditions. Addition of 50 wt% talc improved the melt strength under all testing conditions. Drawability, defined as the stretch ratio at strand break, decreased with increased filler loading. The melt strength of all materials was found to decrease with increased temperature within the range 180°C to 210°C. The melt strength of all melts showed dependence on the test extrusion rate, and this dependence was well described by an exponential relationship. Highest dependencies were seen for the unfilled and 50 wt% talc‐filled polymer. While it was found that addition of 50 wt% talc provided improvement in melt strength, high melt strength alone was a poor indicator of the melt processability, as drawability was also regarded as an important consideration.
Methyl methacrylate modification of polyolefin in a batch mixer and a twin‐screw extruder experiment and kinetic model
Authors: Cha Jaehyug , White James L.
Published: April 2004

Free radical grafting with methyl methacrylate onto molten polypropylene was investigated in both an internal mixer and a modular co‐rotating twin‐screw extruder. There has been little open literature on melt free radical grafting copolymerization of methyl methacrylate. There is also little information on the evolution of grafting reaction with respect to reaction time in an internal mixer and along the screw axes with methyl methacrylate. The influence of residence time on the degree of grafting in an internal mixer and a twin‐screw extruder was studied through measuring reaction yields with respect to reaction time in a mixer and evolution of reaction yield along the screw axis. The degree of grafting increased with initial monomer and peroxide concentration. The grafting reactions with three different peroxides were also investigated. The grafting levels were similar to maleic anhydride and suggested that only an individual methyl methacrylate unit be grafted. The melt viscosity was dramatically reduced with addition of peroxide. A kinetic scheme of our reaction system for methyl methacrylate was proposed and compared with the experimental results.
Rheology and extrusion of medical‐grade thermoplastic polyurethane
Authors: Lu Guangyu , Kalyon Dilhan M. , Yilgör Iskender , Yilgör Emel
Published: April 2004

The selection of operating conditions and geometry for the processing of thermoplastic polyurethane, TPU, is a complicated task. This complication arises from the relatively high melting temperature of the crystalline hard blocks and the oxidative and thermal degradation and crosslinking that occur at temperatures that are relatively close to the melting temperature of the TPU. This article documents the rheology, extrusion, and structure development of a medical‐grade TPU. The medical application requires that the additives commonly utilized in the development of polymeric resins, i.e., stabilizers, antioxidants, and lubricant, should be minimized; the TPU of this study contains no additives. At temperatures 10–20°C lower than the melting temperature of the TPU, the morphology of the hard blocks continues to evolve to generate a reversible increase in elasticity and shear viscosity of the TPU with increasing time. At temperatures greater than the melting temperature, the TPU undergoes degradation and crosslinking reactions, which give rise to a permanent increase in the elasticity and the shear viscosity of the TPU. The ramifications of the degradation and crosslinking at temperatures greater than 200°C and morphology modification upon the continuing evolution of the hard blocks at temperatures less than 200°C on the rheology and processing were investigated.
Quantitative determination of short‐chain branching content and distribution in commercial polyethylenes by thermally fractionated differential scanning calorimetry
Authors: Zhang Mingqian , Wanke Sieghard E.
Published: April 2004

A method for rapid quantitative analysis of the content and distribution of short chain branching (SCB) for α‐olefin/ethylene copolymers based on thermally fractionated DSC is presented. Eight commercial polyethylenes, four made with conventional Ziegler‐Natta catalysts and four made with metallocene catalysts, were analyzed by differential scanning calorimetry (DSC), after having been thermally segregated by successive nucleation annealing (SNA). The polyethylenes were also analyzed by temperature rising elution fractionation (TREF) and carbon‐13 nuclear magnetic resonance (13C‐NMR). The SNA‐DSC procedure segregates polyethylenes according to methylene sequence lengths (MSL). The relationship between DSC melting temperature and SCB content was obtained by calibration with linear hydrocarbons; TREF results were not used in the SNA‐DSC calibration. Deconvolution of the SNA‐DSC endotherms yielded estimates of the average SCB contents and SCB distributions. The SCB contents obtained from the SNA‐DSC for linear low density polyethylenes agreed very well with the SCB contents obtained by 13C‐NMR and TREF, and the SCB distributions measured by SNA‐DSC were very similar to those obtained by TREF. The SCB contents obtained by SNA‐DSC for ultra‐low density polyethylenes, made with metallocene catalysts, were about 20% lower than the values obtained by 13C‐NMR; the values obtained by TREF were even lower.
Crystallization of poly(butylene terephthalate)
Authors: di Lorenzo M. L. , Righetti M. C.
Published: April 2004

This article provides a thorough analysis of the crystallization process of poly(butylene terephthalate) (PBT). Isothermal crystal growth rates have been experimentally measured between 459 and 491 K, and analyzed according to the Hoffman and Lauritzen theory. A II–III regime transition occurs at 484 K, accompanied by a change in crystal morphology. By means of a non‐linear fitting procedure, precise values of the nucleation constant Kg were obtained. The lateral surface free energy σ was calculated and, from this, the α parameter of the Thomas‐Staveley expression was obtained.
Preparation and characterization of polystyrene‐based magnetic nanocomposites. Thermal, mechanical and magnetic properties
Authors: López Daniel , Cendoya Ione , Torres Francesc , Tejada Javier , Mijangos Carmen
Published: April 2004

In this paper we report results on both material preparation and characterization of a polystyrene‐based magnetic nanocomposite material. CoFe204 mineralized sulfonated polystyrene was prepared by in‐situ precipitation and oxidation of Co+2 and Fe+2 within a sulfonated polystyrene resin. The magnetic oxide particles of nanometer size were characterized by wide angle X‐ray diffraction (WAXD). Polystyrene‐based composite films were obtained by dispersion of the finely milled mineralized resin in a polystyrene matrix from the melt state (compositions ranging from 0 to 50 wt% of mineralized resin). The thermal and mechanical properties of the nanocomposite films were determined by TGA, DSC, and stress‐strain testing. The magnetic characterization of the samples was also performed. No significant changes in thermal stability, glass transition temperature or mechanical properties of the polystyrene matrix occur as a consequence of the content in mineralized resin. These results show that the filler acts as aninert diluent for the polymer matrix. On the other hand, the magnetic characterization of the samples reveals the presence of nanoparticles with diameters ranging from 3 to 8 nm, showing, at room temperature, coercive field values of around 800 Oe and saturation magnetization between 120 and 420 emu/g. The combination of these properties suggests the use of these systems in the preparation of magnetic recording materials with high recording density.
Chemorheology of model filled rubber compounds during curing
Authors: Cai Jianfen J. , Salovey Ronald
Published: April 2004

The rheological behavior and crosslinking kinetics of model filled rubber compounds during curing were investigated. The effect of chemical composition of monodisperse size particles, prepared by emulsifier‐free emulsion polymerization, on dynamic moduli and gelation time of the filled compounds was studied. All filled systems showed much shorter gelation times than the pure matrix in the order PSVP < PS < PMMA ≪ Pure Matrix. The dynamic moduli during curing increased with increasing interactions between particles and matrix. Physical crosslinking, due to either particle clustering or a network of filler particles with an adsorbed polymer layer, made a significant contribution to the overall crosslink density and the gelation of rubber compounds. As a result, the dynamic mechanical properties and curing kinetics of the rubber compounds varied with the chemical nature of the filler particles.
Role of coupling microscopic and macroscopic phenomena during the crystallization of semicrystalline polymers
Authors: Prabiiu N. , Schultz J. , Advani S. G. , Jacob K. I.
Published: April 2004

In this work a microscopic cell model of crystallization incorporating solute rejection is coupled with the macroscopic heat transfer using a finite element procedure to study the evolution of crystallinity. The role of coupling is analyzed using two contrasting polymers, polyethylene and polystyrene. Simulations of the solidification were carried out using both the coupled and the uncoupled formulations to elucidate the effect of coupling. Both polymeric systems considered were affected by this coupling on the evolution of the crystallinity; however, the initial solute content has more effect on the slower crystallizing system. An incremental stress model is also applied to predict the residual stresses generated during the crystallization of the two polymeric systems. It was found that the predicted residual stresses are significantly affected by coupling. Good agreement with experimental results was observed for crystallization half‐time results from the coupled solution by incorporating solute segregation effects for high undercooling, but the deviation was more significant at lower undercooling. For the slow‐crystallizing polymer, fair agreement was observed irrespective of the degree of undercooling. The results show that the solute segregation has only a secondary influence on these systems, especially compared to the effect of undercooling.
Morphology and mechanical behavior of polypropylene hot plate welds
Authors: Oliveira M. J. , Bernardo C. A. , Hemsley D. A.
Published: April 2004

Polypropylene tensile bars were hot plate welded and analyzed by microscopy and mechanical tests. The welding process caused significant modifications to the microstructure and shape of the bars at the weld zone. The weld morphology was affected by both the welding parameters and the thermal history of the components. Oriented textures, coarse spherulites, voids or sharp notches occurring at the beads are the key morphological factors that affect the weld quality. Weld performance is dependent upon the type of testing method used. A tensile impact test has been shown to be potentially useful for quality control, as the fracture behavior is affected by the overall morphoiogy.
Electrical and mechanical behavior of carbon black–filled poly(vinyl acetate) latex–based composites
Authors: Grunlan Jaime C. , Gerberich William W. , Francis Lorraine F.
Published: April 2004

The electrical and mechanical behaviors of carbon black‐filled. Poly(vinyl acetate) latex‐based polymer composites were examined. These composites were found to exhibit percolation thresholds in electrical conductivity near 2 vol% carbon black due to their segregated microstructures. Storage modulus and ultimate tensile strength (UTS) both exhibited discontinuities at 10 vol% carbon black, corresponding to a critical pigment volume concentration. Drying composites at 60°C rather than room temperature produced a higher percolation threshold and better mechanical properties at carbon black loadings above 10 vol% carbon black. A figure of merit was proposed to assess the balance of electrical conductivity, storage modulus and UTS. The figure of merit exhibited a peak value at 10 vol% for composites dried at room temperature and was shifted to higher carbon black concentrations when composites were dried at 60°C.
Effect of interlayer structure, matrix viscosity and composition of a functionaiized polymer on the phase structure of polypropylene‐montmorillonite nanocomposites
Authors: Kim Kyu‐Nam , Kimm Hyungsu , Lee Jae‐Wook
Published: April 2004

Polypropylene (PP)‐clay composites were prepared by melt mixing in an intensive mixer. Three grades of PPs with different melt viscosities were employed to investigate mixing characteristics and phase structure of the composites with various clays that belong to organically modified montmorillonite (org‐MMT). Depending on the matrix viscosity and nature of the organic layer in MMT, significant variations In the phase structure of the composites were found. In addition to the simple combination of PP and clay, various functionalized PPs were also incorporated in an attempt to enhance thermodynamic interaction between the org‐MMT and PP matrix. Major interest was focused on the effect of varying thermodynamic affinity between the components, on the phase evolution and mechanical properties of the composites. Within the available range of maleic anhydride (MA) content in PP, it was found that optimum content of the functional group exists, which balances favorable interaction with org MMT and tolerable homogeneity with PP matrix. Along with keeping the optimum MA content, it was also important to use a low viscosity PP matrix to achieve a mere random array of layered silicates. The observed phase structure was interpreted by using a model based on self consistent field theory.
Melt grafting of maleic anhydride onto elastomeric ethylene‐octene copolymer by reactive extrusion
Authors: Premphet K. , Chalearmthtlpa S.
Published: April 2004

Melt grafting of maleic anhydride onto elastomeric ethylene‐octene copolymer was carried out in a twin‐screw extruder, in the presence of dicumyl peroxide as an initiator. Dimethyl formamide was used as an inhibitor to reduce crosslinking and as a solvent for peroxide initiator. The aim of the work is to produce the copolymer with reactive functionality without the expense of elastomeric characteristics. Particular consideration was, therefore, given to the effects of initiator and monomer concentrations, and of screw speed on the degree of grafting, percentage of conversion, amount of crosslinked products, and on the stress‐strain behaviors of the grafted products. The degree of grafting was found to be dependent mainly on the initiator and monomer concentrations. Increasing the initiator concentration increased the degree of grafting, and at the same time, increased the amount of gel (crosslinking). An increase in gel content of the grafted products resulted in a change of tensile behaviors from uniform deformation followed by strain‐hardening at high strains to low extensibility and fracture at low strains.
Morphology profiles generated by temperature gradient in PMMA modified epoxy system
Authors: Stefani P. M. , Riccardi C. C. , Remiro P. M. , Mondragóan I.
Published: April 2004

A diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin was modified with 15 wt% of poly(methylmethacrylate) (PMMA) and cured with a stoichiometric amount of 4,4′‐diamino diphenyl methane (DDM). The reactive mixture was cured in a heated mold with different gradients of temperature. Temperature profiles in the mold were imposed by generation of a heat flux from the base, supported on a hot plate, and the top, cooled with water; they were measured along the mold. Depending on the thermal history in each position of the mold, the competition between the phase‐separation process and reaction kinetics produces opaque or transparent zones. Phase separation can also occur in the postcure process while the gelation does not take place before. Therefore, a thermoset plate with gradient of morphology and properties was obtained. Mass fractions of PMMA dissolved in the matrix were calculated with the Fox equation from glass transition temperatures measured along the mold. They were related to morphologies developed during curing. The superposition of the phase diagrams with the conversion‐temperature trajectories during cure permitted an explanation of the morphology gradients generated.
Relevance of mold‐induced thermal boundary conditions and cavity deformation in the simulation of injection molding
Authors: Pantani R. , Speranza V. , Titomanlio G.
Published: April 2004

In this work an amorphous PS was injection molded into a simple line‐gated rectangular cavity. The effect on post‐filling pressure curves and temperatures (at the polymer‐mold interface) of different holding pressures and times, and of two gate thickness configurations, was analyzed. Molding tests were simulated leading to a good description of pressure evolution in different positions along the flow path for all molding conditions analyzed. Comparison between simulation results and experimental data shows that: considering a rigid mold can lead to predicted values of post‐filling pressure profiles much different from experimental ones; heat transfer coefficient description plays a minor role in the prediction of pressure evolution, but its effect is relevant on temperature evolution in layers dose to the mold surface.
An experimental investigation of normal and shear stress interaction of an epoxy resin and model predictions
Authors: Hu Yafei , Ellyin Ferknand , Xia Zihui
Published: April 2004

The axial‐torsional interaction of an epoxy resin was investigated by subjecting thin‐walled tubular specimens to combined normal and shear stress components. It is shown that a superimposed normal stress (tensile or compressive) or hydrostatic pressure will influence shear creep behavior. Similarly, a superposed shear stress affects the normal stress response of the resin. The axial‐torsional stress interaction is also observed in transient stress responses under different strain paths, and in the creep deformation with non‐proportional stress histories. Urear viscoelastic constitutive models are unable to predict the aforementioned behaviors. Two typical nonlinear viscoelastic constitutive models are examined with respect to their capabilities to predict the observed response. It Is shown that the predictions of these two models agree only qualitatively but not quantitatively with the experimental results.
Interactions of chlorinated polyolefins with ethylene‐propylene copolymers and their relevance to painted TPOs
Authors: Ellis Thomas S.
Published: April 2004

An experimental and theoretical investigation of the phase behavior of blends of aliphatic polyesters, possessing diferent methylene content and chlorinated polypropylenes (PP‐Cl), containing 26, 32 and 65 wt% chlorine, respectively, has been performed. A window of miscibility was found only for the PP‐C165; however, this was sufficient to apply a binary interaction model of phase behavior in polymers and allow for an estimation of the segmental interaction parameters that define the overall polymer pair interaction. Complete immiscibility was found in all blends of polyesters containing PP‐C126 and PP‐C132; a result consistent with model calculations. A number of simplifications have been made concerning the structures of polymers and assumptions have been made to apply the theoretical model. The segmental interaction parameters obtained have been extended to estimate the thermodynamic interaction in blends of polyolefins and chlorinated polyolefins and then used to calculate the relevant interfacial thicknesses. These results have been compared with information presented in the literature.
Fracture and yielding behaviors of polystyrene/ethylene‐propylene rubber blends: Effects of interfacial agents
Authors: Haanh T. , Vu‐Khanh T.
Published: April 2004

The aim of this work is to investigate the effects of two triblock copolymers, used as coupling agents, on fracture and yielding behaviors of a blend of 80 volume % of polystyrene (PS) and 20 volume %of ethylene‐propylene rubber (EPR), over a large range of loading rates and temperatures. For this purpose, blends containing different concentrations of two triiblock copolymers were studied at various test conditions. The focus was put on the time‐temperature dependence of fracture performance of the blends. Addition of triblock copolymer makes the PS/EPR blend more ductile. The time‐temperature dependence of the brittle‐ductile transition in fracture performance of the blend is controlled by an energy activation process. The interfacial agent lowers the temperature at brittle‐ductile transition and reduces the energy barrier controlling the fracture process. This effect, however, is much more pronounced for the lower molecular weight interfacial agent. The correlation between temperature, loading rate and yield stress of the blends seems to be controlled by a molecular relaxation process according to the Ree‐Eyring theory. This model, based on the assumption of two relaxation processes (α and β) acting in parallel, allows prediction of yield stress at various loading rates and temperatures. Addition of the interfacial agents results in a reduction of the activation energy and an increase in the activation volume V* for both the α and β processes. Furthermore, the similarity of the value of the activation energy ΔHβ in the β yielding process and the energy barrier ΔH controlling the brittle‐ductile transition in fracture seems to suggest that a similar secondary relaxation mechanism controls the yielding and the fracture behavior of the blend.
Converging flow analysis, entrance pressure drops, and vortex sizes: Measurements and calculated values
Authors: Carrot Christian , Guillet Jacques , Fulchiron René
Published: April 2004

The use of converging flows for the determination of the elongational behavior of polymer melts is interesting provided that the solving of the inverse problem is fast. For this purpose, this paper shows that the entrance pressure drops that occur during the axisymmetric flow of a polymer melt from the reservoir of a capillary rheometer into a cylindrical die with flat entry can be rapidly calcylated using a Wagner constitutive equation and Protean coordinates. This calculation technique performs particle tracking, which is absolutely necessary when using integral constitutive equations. In turn, the method also enables the determination of the particle path in the entrance zone and gives the boundary of the vertex. The appropriate solution is obtained through the minimization of the power consumption in the entrance zone. Calculation results are compared with experimental pressure drops and vortex pictures using two well‐characterized polyethylenes and show good agreement.
Effect of supercritical carbon dioxide on PMMA/rubber and polystyrene/rubber blending: Visosity ratio and phase inversion
Authors: Elkovitch Mark D. , Lee L. James , Tomasko David L.
Published: April 2004

Supercritical carbon dioxide (scCO2) was added during blending of polystyrene or poly(methyl‐methacrylate) (PMMA) and a rubber impact modifier (SP 2207). The resulting blend morphologies were compared. The compounding took place in a Leistritz ZSE‐27 twin‐screw extruder at 100 RPM, at a temperature of 200°C, and with 2.0 wt% CO2 Injection. The viscosity reduction of PMMA, polystyrene, and SP 2207 was measured using a slit die rheometer attached to the twin‐screw extruder. A viscosity reduction of up to 84% was seen with PMMA, 70% with polystyrene and 30% with SP 2207. The solubility of CO2 in these polymers was measured in a high‐pressure vessel at 200°C and 13.78 MPa (2000 psi). A solubility of 5.79 wt% CO2 was seen with PMMA, 3.65 wt% with polystyrene, and 2.60 wt% with SP 2207. The injection of CO2 reduced the size of the dispersed rubber phase in both polystyrene and PMMA. For both blends (polystyrene/SP 2207 and PMMA/SP 2207) with and without the injection of CO2, the extruder length for phase inversion was shortened by about L/D = 4, or 10% of the total extruder length. The impact strength for a 70/30 polystyrene/SP 2207 blend was increased by 26% by the addition of CO2. The improvement in impact strength was not as large for blends of PMMA and SP 2207.
Polytetrafluoroethylene decomposition in air and nitrogen
Authors: Conesa J. A. , Font R.
Published: April 2004

The kinetics of the thermal decomposition of polytetrafluoroethylene (PTFE) have been studied using dynamic TG‐DTG at heating rates between 1 and 25°C/min at atmospheric pressure. Two different atmospheres were used: on the one hand, an inert atmosphere (N2)in order to study the pyrolysis of the material, and on the other hand an oxidative atmosphere (synthetic air) to study the combustion of the polymer. The same kinetic model has been applied simultaneously to runs performed at different heating rates and different atmospheres allowing a good correlation of the weight loss data. The kinetic model considers that the overall decomposition of the PTFE is done via two different parallel processes. Dynamic measurements were performed by combined thermogravimetry mass spectrometry (TG‐MS) in order to determine the decomposition products. The evolution of 2F4, CF4, COF2, HF, hydrocarbons, benzene and some other compounds has been also analyzed.
Dispersion of graphite nanosheets in a polymer matrix and the conducting property of the nanocomposites
Authors: Chen Guo‐Hua , Wu Da‐Jun , Weng Wen‐Gui , Yan Wen‐Li
Published: April 2004

Poly(methyl methacrylate)(PMMA)/expanded graphite composite has been made via an in situ polymerization of methyl methacrylate(MMA) in the presence of expanded graphite obtained by rapid heating of the graphite intercalation compound (GIC). The composite was then blended with poly(vinyl chloride) (PVC) to form an electrically conducting composite. SEM, TEM and XRD showed that the graphite had been dispersed throughout the polymer matrix in the form of nanosheets with thicknesses of about 20 nm. The resulting composite showed excellent electrical conductivity despite a low concentration of graphite. The transition from an electrical insulator to an electrical semiconductor for the composite occurred when the graphite content was 3.5 wt%, much lower than that of conventional conducting polymer composites. Conductivity reached a maximum of 10−4 s/cm at a graphite concentration of 5.0 wt%. This improvement of conductivity could be attributed to the high aspect ration (width‐to‐thickness) of the graphite nanosheets dispersed in the polymer matrix.
Effect of maleic anhydride graft ratio on mechanical properties and morphology on nylon 11/ethylene‐octene copolymer blends
Authors: Li Qi Fang , Kim Dong Gil , Wu De Zhen , Lu Kun , Jin Ri Guang
Published: April 2004

Mechanical properties and morphologies of nylon 11/ethylene‐octene copolymer blends have been investigated. The ethylene‐octene copolymer (POE) employed in this study was grafted with maleic anhydride (MAH) and thus has the potential to react with the amine group of nylon 11. Nylon 11/POE‐g‐MAH and nylon 11/POE/POE‐g‐MAH blends with varying MAH graft ratios were prepared. In this paper, the effect of MAH graft ratio on ductile‐brittle transition temperature (DBTT), mechanical properties, and morphology of blends was studied. The results showed that incorporation of POE‐g‐MAH could remarkably improve the compatibility between the nylon and POE elastomers, thus increasing the toughness of the resultant blends. The compatibilizing effect on impact strength became more pronounced with increasing MAH graft ration. DBTTs of blends were initially lowered dramatically with the increasing maleic anhydride graft ratio, but over 0.56% MAH content, DBTTs of blends did not drop further, while tensile strength and tensile modulus dropped slightly because of the decreased glass transition temperature (Tg) of nylon 11/POE blends, resulting from the increased compatibility between the two phases. The role of MAH graft ratio on the POE particle size and dispersion of POE on nylon 11 matrix was also studied.
Relationship between local residence time and distributive mixing in sections of a twin‐screw extruder
Authors: Shearer Gifford , Tzoganakis Costas
Published: April 2004

Local residence time and distributive mixing were measured in conveying sections and kneading blocks of a twin screw‐extruder. The residence time measurements were completed using carbon black as the tracer and an infrared temperature probe to detect the temperature decrease caused by the changing surface emissivity. The validity of this experimental technique was extensively evaluated. A mixing limited interfacial reaction between polymer tracers was used to directly measure the distributive mixing in the twin‐screw extruder. Possible relationships between mixing and residence time in the sections of the twin‐screw extruder were investigated by combining these two measurements. Distributive mixing in conveying sections was related to the local average residence time and the fill. In contrast, distributive mixing in kneading blocks was related to the local average number of screw revolutions experienced by the polymer. Forward stagger kneading discs achieved the greatest amount of distributive mixing, which was attributed to a combination of local stagnant flow regions and more frequent interfacial reorientation.
Polyimide nanocomposites: Comparison of their properties with precursor polymer nanocomposites
Authors: Chang Jin‐Hae , Park Kwang Min
Published: April 2004

A precursor poly(amic acid) was obtained by solution polymerization of pyromellitic dianhydride and benzidine in N, N‐dimethylacetamide. Poly(amic acid)/Organoclay hybrids were prepared by the solution intercalation method with dodecylamine‐montmorillonite. A polyimide hybrid was obtained from poly(amic acid) hybrid by heat treatment at various temperatures. The film type polyimide hybrids showed better thermal properties than poly(amic acid) hybrids. Also, the thermal stability of the two polymer hybrids were enhanced linearly with increasing clay content from 0 to 8 wt%. Tensile properties and gas barriers of the hybrids, however, were enhanced remarkably compared to pristine polymers. Intercalations of the polymer chains in clar were examined through wide angle X‐ray diffraction (XRD) and electron microscopy (SEM and TEM). Transmission electron microscopy revealed that a partially exfoliated structure had been obtained from polyimide/organo‐clay hybrids.
In‐line versus off‐line rheological measurements on S‐PVC formulations releant for flow in extrusion dies
Authors: Glomsaker Terje , Hinrichsen Einar L. , Thorsteinsen Pål
Published: April 2004

The supermolecular structures present in S‐PVC during processing are dependent on the thermomechanical history and affect the rheological behavior. Motivated by the need to have reliable rheological data relevant for numerical modeling of 3D flows in extrusion dies, we compared standard off‐line capillary measurements with‐inline measurements obtained from an instrumented die mounted on an extruder. Different PVC formulations showed different slip behavior in‐line, and also differences in comparison with the off‐line results. Cogswell analysis on entry pressure drops was used in order to obtain elongational information. For one formulation, with plug flow both in off‐line and in‐line measurements, an analysis based on the resistance to flow in contracting zones was the only way to get flow data that could be used in 3D profile simulations. The temperature sensitivity of measurements was used in order to discuss our results in terms of structural changes within the melt due to differences in thermomechanical history and formulation. Finally, an example of a 3D simulation of the flow of this formulation in an industrial extrusion die is given and compared with observations.
The effects of melt vibration blending on the subsequent crystallization and melting behavior of polypropylene/ultra high molecular weight polyethylene
Authors: Wang Kejian , Zhou Chixing
Published: April 2004

Pure isotactic polypropylene (iPP) and 90/10 wt iPP/ultra high molecular weight polyethylene (UHMWPE) blends, prepared by a novel vibration internal mixer reformed from a coventional internal mixer via parallel superposition of an oscillatory shear on a steady shear, were investigated by differential scanning calorimetry (DSC) and wide angle X‐ray diffraction. After plasticating pure iPP in the vibration field, the number of β form crystals of iPP was increased. The β form exhibited a single DSC melting peak different from that of the bulk α form crystals of iPP. After mixing of UHMWPE with iPP, the melting point of the UHMWPE component shifted to a lower temperature. For blends mixed at the higher‐frequency and/or larger‐amplitude vibrations, the melting point of the UHMWPE component was further gently lowered while the bulk melting point of the iPP component was slightly increased. The crystallization peaks of the two components overlapped into one single peak, and the total crystallinity became higher, together with a larger amount of the β iPP. These results showed that the two components influenced each other in blending. Hence, the resultant morphology affected the subsequent crystallization and melting behaviors. Additionally, vibration in mixing possibly affected the conformation of some polypropylene chains to favor the subsequent packing in the β form.
Supercritical CO2 welding of laminated linear low density polyethylene films
Authors: Caskey Terrence , Lesser Alan J. , McCarthy Thomas J.
Published: April 2004

Supercritical carbon dioxide (SC CO2) is used as a reversible plasticizing agent to promote solvent welding in highly oriented LLDPE films. These films are laid up in a quasi‐Isotropic fashion to enhance material properties in all directions. It is shown tht, after processing, the oriented morphology and crystallinity are effectively unchanged. These laminated films are investigated both physically and mechanically. The mechanical strength of laminate interfaces is tested using a T‐Peel test. Tensile properties of the laminated film are evaluated and compared to the single oriented plies. Tear resistance is measured using a single specimen J1C.
Influence of fillers and oil on mill processability of brominated isobutylene‐co‐paramethylstyrene and its blends with EPDM
Authors: Kumar Bhuwneesh , De P. P. , De S. K. , Bhowmick A. K. , Majumdar S. , Peiffer D. G.
Published: April 2004

Milling behavior of brominated isobutylene‐co‐paramethylstyrene (BIMS), and its blends with ethylene propylene diene rubber (EPDM), with special reference to the effect of addition of different fillers, filler loadings and processing oil, was investigated over a range of temperatures in a drop mill operation. The critical nip gap (CNG, at which a front to back roll transition (F‐B transition) occurs, was also measured. Addition of different fillers reduced the value of the critical nip gap and the mill band formation indices for BIMS as compared to the gum polymer, indicating a decrease in the tendency to go to the back roll. The systems containing reinforcing fillers showed a lower value of the critical nip gap, as compared to systems containing low or non‐reinforcing fillers. For different filled blends of BIMS and EPDM, the CNG decreased on increasing the EPDM content, indicating a decrease in the tendency for a F‐B transition. The CNG decreased on increasing the N330 carbon black‐loading, while it increased with the addition of procesing oil. The results were explained in terms of rubber to metal adhension and viscosity of the polymers.
Oil resistant thermoplastic elastomers of nitrile rubber and high density polyethylene blends
Authors: Setua D. K. , Soman C. , Bhowmick A. K. , Mathur G. N.
Published: April 2004

Different grades of oil resistant thermoplastic elastomers (TPE) based on blends of nitrile rubber (NBR) and high density polyethylene (HDPE) have been developed. Chemical treatment of HDPE to evolve compatibility with NBR and dynamic vulcanization with different curatives have been studied. Determination of physico‐mechanical and thermal properties and relative crystallinity of these blends have been carried out. Oil resistance characteristics of the blends have been evaluated in different commercially used oils and fuels for applications as a substitute for NBR/polyvinyl chloride (PVC) blends.
A physical‐mathematical model for the dispersion process in continuous mixers
Authors: Potente H. , Kretschmer K. , Flecke J.
Published: April 2004

To modify the properties of polymers, mineral fillers are frequently added during the compounding process. Because of adhesive forces, these pulverized fillers tend to agglomerate. Therefore, in order to achieve good homogenization, it is essential not only to distribute them but also to break down the solid agglomerates. A number of relating models have been published, describing observations (agglomerate rupture, erosion, clustering) made during the dispersion process in a mostly isolated manner. New models for each observed effect have been developed and later superimposed in order to get a comprehensive model of the dispersion process. To verify the model, it was implemented into a program for the process simulation of co‐rotating twin‐screw extruders. It was then compared to experimental data. The results showed that the model is able to describe the experimentally determined data.
A full 3D finite element analysis of the powder injection molding filling process including slip phenomena
Authors: Hwang C. J. , Kwon T. H.
Published: April 2004

A full 3D finite element analysis system has been developed to simulate a Powder Injection Molding (PIM) filling process for general three‐dimensional parts. The most important features of the analysis system developed in this study are i) to incorporate the slip phenomena, the most notable rheological characteristics of PIM feedstock, into the finite element formulation based on a nonlinear penalty‐like parameter and ii) to simulate the transient flow during the filling process with a predetermined finite element mesh with the help of a volume fill factor and a melt front smoothing scheme. The treatment of the nonlinear slip boundary condition was successfully validated via a steady state pipe flow. For the purpose of comparisons, not only the numerical simulations but also experimental short‐shot experiments were performed with two 3D mold geometries using two typical materials of slip and no‐slip cases. The good agreements between the numerical and experimental results indicate that the melt front tracking scheme successfully simulates the transient filling process.
A new process for crosslinking thermoplastic polyurethanes using rubber industry techniques
Authors: Lambour Stéphanie , Mechin Françoise , Pascault Jean‐Pierre
Published: April 2004

New polyurethane materials were obtained after chemical modification of a commercial thermoplastic polyurethane (TPU) using diisocyanates and diols or diamines. The reaction can be easily processed by the well‐known calendering technique often used by the rubber industry. It leads to a remarkable improvement of the thermomechanical properties of the material, due to the formation of chemical crosslinks between the TPU chains (“vulcanization”). As this new processing consists only of an intimate mixing of the starting TPU with solid reagents, followed by molding and curing stages, it allows the use of any and possibly highly reactive solid monomer (especially damines), which could not otherwise be considered except with constraining techniques like RIM; in the same way, the incorporation of organic or inorganic fillers also becomes possible.
Percolation phenomena in polymers containing dispersed iron
Authors: Mamunya Ye. P. , Muzychenko Yu. V. , Pissis P. , Lebedev E. V. , Shut M. I.
Published: April 2004

Metal‐polymer composites based on polyethylene (PE), polyoxymethylene (POM), polyamide (PA) and a PE/POM blend as matrix and dispersed iron (Fe) as filler have been prepared by extrusion of the appropriate mechanical mixtures, and their electrical conductivity, dielectric properties and thermal conductivity have been investigated. The filler spatial distribution is random in the PE‐Fe, POM‐Fe and PA‐Fe composites. In the PE/POM‐Fe composite the polymer matrix is two‐phase and the filler is contained only in the POM phase, resulting in an ordered distribution of dispersed Fe in the volume of polymer blend. The transition through the percolation threshold ϕc is accompanied by a sharp increase of the values of conductivity σ, dielectric constant ε′ and dielectric loss tangent tan δ. The critical indexes of the equations of the percolation theory are close to the theoretical ones in the PE‐Fe and POM‐Fe composites, whereas they take unusually high values in the PE/POMFe composite. Thus, t in the equation σ ∼ (φ – φc)t is 2.9–3.0 in the systems characterized by random distribution of dispersed filler and 8.0 in the PE/POM‐Fe system. The percolation threshold φc depends on the kind of polymer matrix, becoming 0.21, 0.24, 0.29 and 0.09 for the composites based on PE, POM, PA and PE/POM, respectively. Also the thermal parameters of the PE/POM‐Fe composite are different from those of all other composites. A model explaining the unusual electrical characteristics of the composite based on the polymer blend (PE/POM‐Fe) is proposed, in agreement with the results of optical microscopy.
Study on the residual wall thickness at dimensional transitions and curved sections in gas‐assisted molded circular tubes
Authors: Yang S. Y. , Chou H. L.
Published: April 2004

Plastic tubes and hollow rods can be fabricated using gas‐assisted injection molding technology with reduced cost. The residual wall thickness around dimensional transitions and curved sections is of great concern. This research investigated the uniformity of the residual wall thickness distribution in circular tubes with dimensional variations and curved sections. It was found that the wall thickness was not uniform near transitions. With the addition of fillets with proper angles around transitions, the uniformity of residual wall could be greatly improved. The residual wall thickness in curved sections was thick around the outer wall and thin around the inner wall. Low melt temperature and high gas pressure were found to reduce the deviation in the wall thickness around curved sections.
Investigation of structure development in polyamide 11 and polyamide 12 tubular film extrusion
Authors: Rhee Sangkeun , White James L.
Published: April 2004

The processability of single bubble polyamide 11 and polyamide 12 films was investigated. The development of crystalline structure and chain orientation of polyamide 11 and polyamide 12 films in single bubble film blowing was studied by differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXS), infrared (IR) spectroscopy, and birefringence. DSC measurements of both films revealed a spontaneous increase in glass transition temperature (Tg) and cold crystallization temperature (Tc) during aging at room conditions, with crystallinity and melting point remaining constant. Single bubble polyamide 11 and polyamide 12 films exhibited triclinic α and monoclinic γ crystals, respectively. The level of biaxial orientation was evaluated by calculating White‐Spruiell biaxial orientation factors with pole figure data. We were not able to produce biaxially oriented double bubble films with either polyamide 11 or polyamide 12.
A microscopy study of the transition from yielding to crazing in polypropylene
Authors: Dijkstra P. T. S. , Van Dijk D. J. , Huétink J.
Published: April 2004

The deformation mechanisms in polypropylene as a function of strain rate have been studied by scanning electron microscopy. Injection molded, dogbone specimens were tested in tension at a temperature of 50°C and strain rates from 10−4 to 90 s−1. With increasing strain rate a gradual transition from cold drawing and necking to nearly homogeneous deformation was observed. The transition is characterized by a strong elastic recoil after fracture. At \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \varepsilon } $\end{document} = 90 s−1, the elastic recovery has its maximum value of 70% of the strain at break (ε = 0.3). The morphology was studied post mortem at small strains outside the neck using permanganically etched samples. The transition in the macroscopic behavior was found to coincide with a change in the deformation mechanism. Whereas yielding is the dominant mechanism at low strain rates, homogeneous voiding is found at \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \varepsilon } $\end{document} = 90 s−1. A correlation is suggested between the failure of chain slip within the lamellae and the occurrence of voiding, leading to distinct voiding patterns in the spherulites.