bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of the effect of surfactants on the properties of polystyrene‐montmorillonite nanocomposites
Authors: Xie Wei , Hwu Jyh Ming , Jiang George J. , Buthelezi Thandi M. , Pan Wei‐Ping
Published: April 2004

Polystyrene‐Organo Montmorillonite (PS‐MMT) nanocomposites were prepared by suspension free radical polymerization of styrene in the dispersed organophilic montmorillonite. The results of X‐ray diffraction (XRD) and Transmission Electron Microscopy (TEM) indicated that exfoliated nanocomposites were achieved. The effect of organic modifiers (surfactants) on the properties of the synthesized nanocomposites was studied. It is found that polystyrene‐MMT nanocomposite with 5.0 wt% of organo‐MMT gave the greatest improvement in thermal stability, and polystyrene‐MMT nanocomposites with 7.5 wt% of organo‐MMT showed the greatest improvement in mechanical properties, compared with that of pure polystyrene (PS) in our experimental conditions. The alkyl chain length of surfactant used in fabricating organo‐MMT affects the synthesized PS nanocomposites: the longer the alkyl chain length that the surfactant possesses, the higher the glass transition temperature of the PS nanocomposite, However, the organoclay in the nanocomposites seems to play a dual role: (a) as nanofiller leading to the increase of storage modulus and (b) as plasticizer leading to the decrease of storage modulus. This results in a lower storage modulus of PS‐TMOMMT and PS‐TMTMMT nanocomposites than that of PS‐TMDMMT and PS‐TMCMMT nanocomposites. Further study is needed to confirm the above hypothesis.
Essential work of fracture of polypropylene and polypropylene blends over a wide range of test speeds
Authors: Grein C. , Plummer C. J. G. , Germain Y. , Kausch H.‐H. , Béguelin P.
Published: April 2004

The mechanical properties of extruded films of isotactic polypropylene (iPP) and ethylene‐propylene rubber toughened iPP (iPP/EPR) have been analyzed in terms of the specific essential and non‐essential work of fracture using high speed tensile test apparatus modified for quasi‐static testing in the range 0.0001 to 3 ms−1. Three iPP/EPR grades with modifier contents of 15, 21 and 30 vol% were investigated. As the deformation rate increased, relatively uniform necking of the whole ligament and extensive plastic deformation were progressively replaced by more localized plastic deformation in the blends, and by fully brittle fracture in the unmodified iPP. The non‐essential work of fracture and the total fracture energy were highly sensitive to these changes in deformation mechanism. However, the essential work of fracture, although dependent on the test speed, was less correlated with the extent of global plasticity.
Selectivity of peroxide‐initiated graft modification of ethylene copolymers
Authors: Parent J. Scott , Tripp Michael , Dupont John
Published: April 2004

Experimental data on the kinetics and selectivity of peroxide‐initiated graft modification of ethylene copolymers with vinyltriethoxysilane (VTEOS) and maleic anhydride (MAn) are presented. Rate data for the VTEOS modification and crosslinking of poly(ethylene‐co‐vinyl acetate) demonstrate the controlling influence of peroxide decomposition rates. Analysis of the selectivity for grafting versus crosslinking showed considerable scope for optimization of VTEOS modifications through variation of monomer and peroxide loadings. However, the MAn system was found to be less amenable to optimization, most likely because of differences in the graft propagation cycle and radical termination preferences.
Investigation of the rheological and mechanical properties of a polystyrene‐polyisobutylene‐polystyrene triblock copolymer and its blends with polystyrene
Authors: Antony Prince , Puskas Judit E. , Kontopoulou Marianna
Published: April 2004

The rheological and mechanical properties of a polystyrene‐polyisobutylene‐polystyrene (SIBS) block copolymer containing 30 wt% polystyrene (PS) and its blends with PS (SIBS/PS) were investigated. Atomic Force Microscopy (AFM) was used to visualize the nanostructured phase morphology of the SIBS, which is responsible for the mechanical strength of this thermoplastic rubber. The order‐disorder transition (ODT) for the SIBS block copolymer was found to be above 250°C. SIBS/PS blends with 10–30 wt% PS showed improved moduli and tensile strengths. Blends containing up to 40 wt% PS behaved as thermoplastic elastomers. In the region of linear viscoelasticity the blends revealed pronounced non‐Newtonian behavior and enhanced elasticity. This paper also reports the role of this styrenic block copolymer in the impact modification of PS.
Influence of chemical composition on the rheological behavior of condensation reaction resins
Authors: Doyle M. , Hagstrand P.‐O. , Månson J.‐Å. E. , Svensson L. , Lundmark S.
Published: April 2004

In this paper, the chemorheological and dynamic mechanical behavior of melamine‐formaldehyde (MF) resins of four different formaldehyde/melamine (F/M) molar ratios (1.25, 1.5 1.75 and 2.00) are investigated. MF resins polymerize via a polycondensation reaction involving formation of up to 10 wt% of H2O on cure. This typically results in rapid and extensive foaming of the resin when it is cured under atmospheric pressure. Experimental adaptation for the foaming behavior of MF resins is used to gather rheological information concerning the curing kinetics and the mechanical response of neat MF resins of different molar ratios. Likewise, the procedures developed allow curing of the resins under atmospheric pressure, hence allowing volatile evacuation as occurs during venting procedures (commonly used during compression molding of MF molding compounds) or as a result of absorption by hydrophilic fillers or substrates. The results show that increased moisture content in the B‐stage leads to faster reaction rates and greater foaming. Gelation and vitrification times are identified for each molar ratio, and are found to increase with decreasing molar ratio. The dynamic mechanical behavior of carefully molded neat MF samples of different molar ratios is studied using DMTA. Tg is found to be 200°C for the resin with the lowest formaldehyde content (F/M = 1.25), and around 230°C for the other resins. The storage shear modulus above Tg is studied, and the results show that the crosslink density increases with increasing molar ratio.
On the dynamic mechanical behavior of polyimides based on aromatic and alicyclic dianhydrides
Authors: Bas Corine , Tamagna Cécile , Pascal Thierry , Dominique Alberola N.
Published: April 2004

A series of polyimides has been synthesized based on different dianhydrides and diamines. The microstructure of polyimide films has been analyzed by performing density measurements, X‐ray diffraction and UV‐visible spectrophotometry. The dynamic mechanical behavior was investigated according to both chemical and microstructural aspects. Thus, it was pointed out that the broadness of the β subglass transition is dependent not only on dianhydride flexibility but also on para‐ or meta‐diamine links. Such behavior is discussed in terms of intra‐charge transfer complex. On the contrary, the temperature location of the γ‐transition appears to be controlled by interchain packing. Based on a statistical approach, a correlation between microstructural data and gamma relaxation temperature is established.
In‐line color monitoring of polymers during extrusion using a charge coupled device spectrometer: Color changeovers and residence time distributions
Authors: Gilmor C. , Balke S. T. , Calidonio F. , Rom‐Roginski A.
Published: April 2004

A fiber‐optic–assisted, charge‐coupled device spectrometer was used to monitor the color of molten polymer concentrates during extrusion. Color coordinates L*, a* and b* were calculated from each of the reflectance spectra as polyethylene color concentrate was replaced by a purge material and as the purge material was replaced by another color concentrate. A method of calculating replacing component residence time distributions and component washout residence time distributions from the spectra was developed and applied. Results with a red and a blue concentrate showed that dimensionless time (time/average residence time) superimposed both residence time distributions and color coordinate variations during changeover from two different extruder screw speeds.
Dynamic modeling of blown‐film extrusion
Authors: Carl Pirkle J. , Braatz Richard D.
Published: April 2004

Past dynamic studies of blown‐film extrusion have been confined to the stability analysis of the linearized equations. The full set of nonlinear equations comprises a system of partial differential and algebraic equations with boundary conditions that vary from author to author. In this paper, the Numerical‐Method‐of‐Lines, which combines finite‐difference methods with ordinary differential/algebraic equation integrators, is used to solve the full system. Appropriate boundary conditions are selected to give physical results that compare well with experiment. An important boundary condition is the “minimum order reduction” condition on the gradient of the bubble‐tube radius with respect to distance above the extrusion die (the axial position). Transient startups and operational disturbances are examined. Calculations show the influence of oscillations in operating conditions such as heat transfer or inflation pressure on the bubble‐tube radius and film thickness. Steady‐state results obtained by integrating the transient equations for a sufficiently long time are qualitatively in agreement with experiment, in contrast to past simulations of these equations.
Mechanical properties of low nano‐silica filled high density polyethylene composites
Authors: Zhang Ming Qiu , Rong Min Zhi , Zhang Hai Bo , Friedrich Klaus
Published: April 2004

Modification of nanoparticles through graft polymerization is able to change the chemical nature of the particles' surfaces and provides an effective means for the preparation of nano‐fillers specified for composites manufacturing. The present work focuses on the mechanical role of grafted nano‐SiO2 particles in high density polyethylene composites prepared by melt compounding. The experimental results show that at a content of 0.75 vol%, the modified nano‐silica results in a rise in tensile stiffness, tensile strength and impact strength of the composites. The grafted nanoparticles can improve the mechanical performance of the matrix polymer more effectively than the untreated version. In addition, a further enhancement of the composites stiffness and strength can be achieved by crosslinking the concentrated masterbatches, which has not yet been revealed in the authors' previous works on grafted nano‐SiO2 particles/polypropylene composites. It is thus revealed that the introduction of the grafting polymers onto the nanoparticles increases the tailorability of the composites.
Theoretical influence of polyester molecular weight distribution variation on melt viscosity during injection molding and extrusion as influenced by ester‐ester interchange
Authors: Sudduth Richard D.
Published: April 2004

In this study Flory's initial molecular weight derivation involving polyester polymerization and ester‐ester interchange was expanded to address two types of blends relative to both the number average molecular weight and the weight average molecular weight. First, an add blend was considered where the numbers of molecules of the same length were simply added together to calculate new number and weight average molecular weights. Second, the complete transesterification blend was calculated using Flory's most probable distribution with the same number average as the add blend but with a very different weight average molecular weight. The ratio of the weight averages of the add blend to the transesterification blend were found to be significantly larger if the initial blending molecular weights were significantly different from one another. This ratio was also found to go through a maximum that occurred at approximately 50% by weight if the two different molecular weights had the same monomer molecular weight. If the monomer molecular weights were different, the location of this maximum could be quite different from 50% by weight. Since melt viscosity is proportional to the weight average molecular weight to a power ranging from 1 to 3.4, a very large ratio between weight average molecular weight of the add blend and the ester‐ester interchange blend was found to have a significant influence on the melt viscosity. A polyester blend mixture of micro‐domains of both a nearly pure add blend and a nearly complete ester‐ester interchange blend was used to explain how a short shot could be followed a few shots later with a part that flashed the mold in an injection molding application.
Ternary miscibility in blends of three polymers with balanced binary interactions
Authors: Woo E. M. , Mao Yung‐Jen , Wu Pi‐Ling , Su Chean‐Cheng
Published: April 2004

This study demonstrates and discusses ternary miscibility in a three‐polymer blend system based on balanced binary interactions. A truly miscible ternary blend comprising poly(ε‐caprolactone) (PCL), poly(benzyl methacrylate) (PBzMA), and poly(vinyl methyl ether) (PVME), was discovered and reported. Miscibility with phase homogeneity (excluding the PCL crystalline domain) in a wide composition range has been demonstrated using criteria of thermal transition behavior, cloud point, and microscopy characterization. At ambient temperature, the three‐polymer ternary system is completely miscible within the entire composition range (i.e., no immiscibility loop). However, at slightly elevated temperatures above the ambient. phase separation readily occurred in this originally miscible ternary blend. A quite low “lower critical solution temperature” (LCST) near 75°C was found for the ternary blend, which is much lower than any of those for the binary pairs. Balanced interactions with no offsetting Δχ among the three binary pairs were a key factor leading to a ternary miscible system.
Essential work of fracture (EWF) analysis for short glass fiber reinforced and rubber toughened nylon‐6
Authors: Ching Emma C. Y. , Li Robert K. Y. , Tjong Sie Chin , Mai Yiu‐Wing
Published: April 2004

The effect of fiber content on the fracture toughness of short glass fiber reinforced and rubber toughened nylon‐6 has been investigated using the essential work of fracture (EWF) analysis under both quasi‐static and impact rates of loading. Under quasi‐static loading rate, matrix plastic deformation played a major role. Addition of 10 wt% of short glass fibers into a rubber toughened nylon‐6 matrix improved the fracture toughness substantially. This is due to the synergistic effect that comes from matrix yielding and fiber related energy absorption such as fiber debonding, fiber pull‐out and fiber fracture. With further increasing the glass fiber content, up to 20 and 30 wt%, even though plastic deformation could still take place on the fracture surfaces, the depth of the fracture process zones was much smaller when compared with the system with 10 wt% of glass fibers. The reduction in fracture process zone caused the reduction in fracture toughness. Under impact loading rate, the unreinforced blend still fractured in a ductile manner with gross yielding in the inner fracture process zone and the outer plastic zone. The unrein‐forced blend therefore possesseed higher fracture toughness. For the fiber reinforced blends, the matrix fractured in brittle manner and so fracture toughness of the reinforced blends decreased dramatically. The impact fracture toughness increased slightly after incorporation of a higher weight percentage of glass fibers.
A study on the use of phenoxy resins as compatibilizers of polyamide 6 (PA6) and polybutylene terephthalate (PBT)
Authors: Dharaiya Dhawal , Jana Sadhan C. , Shafi Asjad
Published: April 2004

In this study we investigated the potential of phenoxy resins as compatibilizers in the blending of two high‐volume engineering thermoplastics—polyamide 6 (PA6) and polybutylene terephthalate (PBT), in an effort to establish the usefulness of blending as a method of recycling of mixed plastic wastes. It was found that phenoxy resins formed miscible blends with PBT, formed grafted copolymers with PBT through ester exchange reactions, and—though formed immiscible blends with PA6—produced energetic interactions in the form of hydrogen bonding with PA6. The ternary blend systems of 70 parts PA6, 30 parts PBT, and respectively 5, 10, and 30 parts phenoxy resins, all by weight, revealed at two‐phase nature—PA6 as the continuous phase and miscible blends of PBT and phenoxy resins as the dispersed phase—and were found to be stable to phase coarsening by annealing with mechanical properties at least as good as those of the component polymers.
Simulation of injection‐compression molding for optical media
Authors: Fan Bingfeng , Kazmer David O. , Theriault Richard P. , Poslinski Andrew J.
Published: April 2004

A numerical simulation of a coining type of injection‐compression molding is developed. A hybrid finite element/finite difference method is employed to model the temperature and pressure fields of the process using a non‐isothermal compressible flow model. Simulation results for CD‐R molding with respect to injection pressure and mold displacement are compared with experimental observations using an optical grade of polycarbonate. The simulation shows similar trends as experimental observations on the dependence of various processing parameters such as melt temperature, mold temperature, and packing pressure. However, the mold displacement measurement does not show the effect of punch delay time as does the simulation, and needs further investigation.
Influence of intermolecular entanglements on crystallization behavior of ultra‐high molar mass polyethylene
Authors: Fan Zhongyong , Wang Yiren , Bu Haishan
Published: April 2004

Ultra high molar mass polyethylene (UHPE) was melted at 160°C for various times or at various temperatures for 5 min and then the crystallization of the UHPE was carried out on cooling. It was found that the crystallization temperature decreased as the heating time or heating temperature increased. During the melting process, thermal motion of the chains leads to a change of chain conformation from parallel‐extended chains to interpenetrated random coils, accompanied by the occurrence of entanglements. As a result, the crystallization temperature shifts to lower temperature. On the other hand, samples of UHPE with less entanglement were prepared from a dilute solution by a freeze‐drying procedure. It was observed that the crystallization temperature of the freeze‐dried samples from the melt depressed with dereasing solution concentration. UHPE would produce small crystals in the freezing process, thus leading to a reduction in melting point, and a sifting of crystallization temperature to lower temperature. Based on the melting point, the average volume of small crystals was estimated; it is even smaller than that of one single chain of the UHPE.
In‐situ microfiber reinforced composite based on PET and PE via slit die extrusion and hot stretching: Influences of hot stretching ratio on morphology and tensile properties at a fixed composition
Authors: Li Zhong‐Ming , Yang Ming‐Bo , Xie Bang‐Hu , Feng Jian‐Min , Huang Rui
Published: April 2004

An in‐situ microfiber‐reinforced composite (MRC) based on polyethylene (terephthalate) (PET) and polyethylene (PE) was prepared by slit die extrusion followed by hot stretching. Test specimens were prepared by injection molding at the processing temperature of the PE matrix. At this temperature, far below the melting temperature of PET, the PET phase is solid and able to keep its shape during processing. The morphological characteristics of the dispersed PET phase in the blend, at a fixed weight composition (15:85) of PET and HDPE, were dependent upon the hot stretching ratio. When the hot stretching ratio was increased from 1 (no stretching) to 47.62, the PET particles changed from spheres and ellipsoids to rodlike particles and finally to microfibers. The maximum and average diameters of the PET particles decreased steadily, while the minimum fiber diameter remained constant. The tensile modulus and strength of PET/PE blends were significantly enhanced with increasing hot stretching ratio, indicating that the microfibers have good reinforcement. Ultimate elongation decreased with increasing hot stretching ratio and there was a critical hot stretching ratio above which a ductile‐brittle transition occurred.
Multiple melting behavior of syndiotactic 1,2‐polybutadiene
Authors: Sasaki Takashi , Sunago Hayato , Hoshikawa Takuya
Published: April 2004

A differential scanning calorimetry study on a typical thermoplastic elastomer, syndiotactic 1,2‐polybutadiene, crystallized from the melt is presented. Endotherms observed upon heating for samples isothermally crystallized from the melt exhibited a double melting profile. The peak temperature of the endotherm that appeared at a lower temperature (low endotherm) showed stronger dependence on the heating rate than that appearing at a higher temperature (high endotherm). The results of partial melting experiments demonstrated that the high endotherm is not affected at all by melting of only the crystals responsible for the low endotherm, indicating that the double melting behavior is due to the existence of two crystalline species with different stabilities. Structures and melting mechanisms of these two different crystalline species are discussed on the basis of the observed difference in superheating behaviors upon melting. The results on overall rate of isothermal crystallization are also presented.
Prediction of water solubility in nylon melts based on flory‐huggins theory
Authors: Schaffer M. A. , Mcauley K. B. , Cunningham M. F. , Marchildon E. K.
Published: April 2004

The solubility of water in molten aliphatic polyamides (nylons) of high degrees of polymerization at conditions of subatmospheric water partial pressure and high temperature (225 to 300°C) has been modeled. A simple, semi‐empirical model based on Flory‐Huggins theory was fit to the available literature data for nylons 6, 66, 610 and 11 and to new experimental data for nylon 612. The model contains only two fitted parameters, and is able to adequately describe the available data for the effects of temperature and nylon type on the water concentration in the melt at various water partial pressures.
Comparison between five experimental methods to evaluate interfacial tension between molten polymers
Authors: Demarquette Nicole R. , De Souza Adriana Martinelli Catelli , Palmer Guillermo , Macaubas Paulo Henrique Pierin
Published: April 2004

In this work, an experimental comparison between five different techniques to measure interfacial tension between molten polymers is presented. The five techniques include two equilibrium methods: the pendant drop (PD) and the sessile drop (SD); two dynamic methods: the breaking thread (BT) and imbedded fiber retraction (IF); and a rheological method based on linear viscoelastic measurements of the blend (RM). The polymer pairs studied were polystyrene/polypropylene (PS/PP); and PP/high density polyethylene (PP/HDPE). It was possible to determine the interfacial tension between PP/PS with all the methods tested and the results corroborated within 20%. However, the interfacial tension between PP and HDPE could be evaluated only using rheological methods because of a too‐small difference of index of refraction between both polymers. The experimental precision increased in the following order: RM < SD < BT < IF < PD. The rheological method had the advantage of being simpler and faster than dynamic and equilibrium methods. However, when using the rheological method, care should be taken because the results obtained may depend upon the concentration of the blend used for the measurements. It was observed that the pendant drop and breaking thread methods cannot be used for polymers with high viscosity (above 5 × 105 Pa.s).
Microstructure analysis of high performance fibers in compression
Authors: Huh Wansoo , Kumar Satish , Wade Adams W.
Published: April 2004

In order to understand the nature of kink band formation in high performance fibers, the compression behavior of pitch and PAN‐based carbon fibers (P75S, T‐50, T‐300, and GY‐70), and of polymeric fibers (DuPont Kevlar; PBZT; and PBO) was measured using a micro‐scale compression apparatus in an optical microscope. With increasing compressive strain, kink band formation was observed and the number of kink bands per unit length (referred to as kink band density) was determined. By extrapolating to zero kink band density, the critical compressive strain for rigid‐rod polymeric fibers was obtained and compared to that of the carbon fiber. Using the Euler buckling equation, a fundamental dimension of the buckling element for the compression of PBO and PBZT fibers was calculated to be a 0.42–0.57 µm diameter fibril, and not the smaller diameter microfibrils.
The influence of power‐law rheology on flow distribution in coathanger manifolds
Authors: Reid J. D. , Campanella O. H. , Corvalan C. M. , Okos M. R.
Published: April 2004

Coathanger dies are effective in delivering uniform flow if a polymer melt; however, when the fluid flow index varies from the design values, the flow is not uniform. Although mechanisms such as die lip adjustments have been effective tools for adjusting flow profiles, the issue of a variable flow index has not been fully addressed at the design stage. An analytical solution, based on the assumptions present in the 1‐D design equation, has been developed for the flow distribution in a coathanger manifold. This solution determines the flow distribution for a power‐law fluid with a flow index n* in a manifold designed for a separate flow index n*. From this solution, a uniformity index and a critical design angle are defined. The critical design angle is the angle at which the local derivative of the uniformity index with respect to n* approaches a maximum (for n* < n) or a minimum (for n* > n) as a function of the design angle. The critical design angle is independent of n and is presented as a function of the manifold aspect ratio.
All‐optical switching modulation in poly(vinyl carbazole)—based azobenzene blends
Authors: Wu Shuizhu , Yao Shenglan , She Weilong , Yan Kun , Zhao Jianqing
Published: April 2004

We report on the all‐optical switching polymer blends based on photoconductive poly(vinyl carbazole) (PVK) and azobenzene dyes. The optical switching effects of the blends were measured by using a 514 nm pump beam and a 632.8 nm probe beam. The blends' photoinduced reversible and repeatable change in the transmittance of the probe beam is attributed to the photoinduced anisotropy of the azobenzene dyes. The influencing factors of the optical switching effect, such as the modulation frequency and pump beam intensity, were studied experimentally.
Deformation behavior of an epoxy resin subject to multiaxial loadings. Part II: Constitutive modeling and predictions
Authors: Xia Zihui , Hu Yafei , Ellyin Fernand
Published: April 2004

Based on the experimental data presented in Part I, a nonlinear viscoelastic constitutive model, in differential form, is presented here. A distinctive feature of this model is the inclusion of a criterion to delineate loading and unloading in multiaxial stress states, and different moduli for loading and unloading behaviors. In addition, the model contains only five material constants and one modulus function, which can be calibrated in accordance with a well‐defined procedure. A comparison with the experimental data shows that the current differential model is capable of predicting the nonlinear viscoelastic behavior of the epoxy polymer qualitatively and quantitatively, including both the loading and unloading behavior. The predictions of an integral form of constitutive model are also included for comparative purposes.
Scratch visibility of polymers measured using optical imaging
Authors: Rangarajan P. , Sinha M. , Watkins V. , Harding K. , Sparks J.
Published: April 2004

As plastics replace metal in automotive and other applications, aesthetic concerns due to scratch or mar damage replace rust and corrosion issues. This paper presents a novel method to quantify the visibility of a scratch on a polymer surface. It is shown that the most important factor is the optical contrast between the damaged area and its surroundings. The critical optical parameters that affect a viewer's perception of scratch severity are identified as the size and roughness of the scratch, and the color and gloss of the surroundings. An optical imaging system and method for measuring the optical parameters that result in this contrast is described.
Functionalization of high density polyethylene with maleic anhydride in the melt state through ultrasonic initiation
Authors: Zhang Yuncan , Li Huilin
Published: April 2004

Grafting of maleic anhydride (MAH) onto high density polyethylene (HDPE) performed in the melt state through ultrasonic initiation by a laboratory‐scale ultrasonic extrusion reactor was studied in this paper. The effect of sonic intesity on the amount of grafted MAH, viscosity‐average molecular weight and melt flow index of the grafted product was investigated. The results show that the ultrasonic waves can obviously decrease the molecular weight of the grafted product and cause the increase of the amount of grated MAH, implying that the grafting reaction consists of the chain scission and the grafting reaction of the produced macroradicals with MAH. The percentage of grafting of the product amounts to 0.6%; its melt‐flow index is between 0.5 and 2.0 g/10 min, depending upon ultrasonic intensity, MAH content and grafting temperature. Compared with the method of peroxide initiation, in this method the crosslinking reaction can be prevented easily through the allocation of ultrasonic intensity. The mechanical properties of the improved HDPE/GF composite produced by ultrasonic initiatives are higher than in those produced by peroxide initiatives.
Chaotic volumetric transports in a single‐screw extrusion process
Authors: Hwang W. R. , Kwon T. H.
Published: April 2004

Volumetric material transports across distinct regions in the Chaos Screw (CS) system were described in terms of the volume‐preserving lobe dynamics. Kinematic properties of a spatially periodic Poincaré map were studied first with the volume‐ and orientation‐preserving two‐dimensional map, in order to provide mathematical frame works for analyses of manifold structures. The perturbed hyperbolic fixed point and the associated stable and unstable manifolds were obtained numerically. These manifolds form homoclinic tangles, and they divide the cross‐sectional area into three distinct regions: left, right, and outer. Six volumetric flow rates between the three regions were described in terms of the associated lobe dynamics. As the perturbation strength increases, representative flow rates between these regions were found to increase linearly as long as the fraction of no‐barrier zone is small.
Influence of the relative humidity on film formation by vapor induced phase separation
Authors: Caquineau H. , Menut P. , Deratani A. , Dupuy C.
Published: April 2004

The formation of polymer films produced by the phase separation process occurring when a cast poly(etherimide)/N‐Methyl‐2‐Pyrrolidone solution was exposed to humid air was studied. It was found that above a relative humidity value of 27%, the films presented a cell‐like structure. The size of the cells was shown to decrease when the relative humidity increased. This effect was more pronounced at the film/substrate interface than near the surface. A cell‐size gradient from one face of the film to the other was also clearly observed. A phenomenological model has been proposed to explain the morphology obtained by a phase separation induced by the water vapor in the studied system, takin into account thermodynamics and kinetics considerations. In this model, the cell‐like structure setting up is shown to result from a nucleation and growth process accompanied by a coalescence coarsening. It was illustrated by a composition path on the ternary phase diagram. It was shown how the relative humidity influenced the film composition leading to the preferential nucleation compared to the growth and coalescence of the cells. Finally, it was found that the cell‐size anisotropy resulted in the solvent and non‐solvent mass transfers in the film, bringing to the fore the determining role of kinetics.
Structure and properties of oriented polyethylene films
Authors: Srinivas Srivatsan , Brant Patrick , Huang Yu , Paul Donald R.
Published: April 2004

Cast films of a metallocene Linear Low Density Polyethylene (mLLDPE) have been cold‐drawn in the machine direction in two sequential steps to form ultra‐oriented films. The initial films were cast under low shear conditions to form essentially isotropic films, as shown by very low orientation birefringence. The first draw yields moderately oriented films, which display block‐shear type chevron morphology. Under controlled conditions, void formation occurs during the second draw and the ultradrawn films whiten (become opaque), and display a fine crystalline morphology. Surprisingly, the films do not become more permeable; rather, they become high barrier films. In their ultra‐oriented state, the water vapor transmission of the films is equivalent to that of poly(vinylidene chloride) (PVDC). The transport behavior of the films to various gases was studied using transient permeation methods. The decrease in permeability with orientation is attributed to an increase in the degree of crystallinity and increase in tortuosity due to the blocky crystalline morphology. A decrease in the permeability of the amorphous phase due to an increase in the amorphous phase density is also suggested by the data.
Cure kinetics, gelation, and glass transition of a bisphenol F epoxide
Authors: O'Brien Daniel J. , White Scott R.
Published: April 2004

Phenomenological cure kinetic relations for a commercially available amine‐cured epoxy were developed independently using differential scanning calorimetry (DSC) in isothermal and dynamic (constant heating rate) modes and using numerical optimization techniques. The resulting model was found to be independent of the method used to collect reaction rate data. The model was modified at high temperature to account for an observed deviation from Arrhenius behavior. The cure dependence of the glass transition of the material was also investigated with DSC. The gel point as measured by parallel plate rheometry was found to occur at a degree of cure of 0.71, a value significantly advanced from a simple Flory prediction based on the functionality of the cross‐linking agent.
Mixing dynamics in the SMX static mixer as a function of injection location and flow ratio
Authors: Zalc J. M. , Szalai E. S. , Muzzio F. J.
Published: April 2004

A detailed Lagrangian analysis of partially mixed structures in an SMX static mixer is presented, with emphasis on laminar flows with Reynolds numbers between 1 and 100. The distribution of a small amount of equal‐viscosity additive is examined based on computing the trajectories of passive tracer particles through the mixer. Three radial positions (one centerline and two off‐center) are chosen for injection and the mixing patterns are compared in order to investigate the effect of injection location on mixing. Mixing measures, such as the decrease in the variation coefficient with axial distance, and the increase in the average rate of stretching, are discussed in order to quantify mixing performance. It is found that mixing rates for the centerline injections are larger than for the off‐center injection positions investigated. The presence of self‐similarity in the stretching field and the mixing patterns, and the exponential decrease in variation coefficient with increasing axial distance provides evidence for chaotic mixing behavior in this device.
An investigation into the relationship between the impact performance of rotationally molded polyethylene products and their dynamic mechanical properties
Authors: Pick Louise Therese , Harkin‐Jones Eileen
Published: April 2004

In this paper, a study of the relationship between the impact performance of rotationally molded polyethylenes and their dynamic mechanical properties is carried out. A wide range of conventional linear low density polyethylene powders and met‐allocene catalyzed linear low density polyethylene powders were rotationally molded and tested. Instrumented falling weight impact tests were carried out over a temperature range of −60°C to 20°C. Dynamic Mechanical Thermal Analysis (DMTA) tests were also carried out between −100°C and 90°C, at a frequency of 100 Hz. Comparisons between the impact performance of metallocene catalyzed LLDPEs and Ziegler‐Natta LLDPEs are made. The transitions evident in the DMTA results are related to changes in impact performance with temperature. The beta transition is found to fall in the transition region between high impact performance at low temperatures and lower impact performance at ambient temperatures.
Electrochemically synthesized polythiophene films with self‐organized microstructure
Authors: Wang Xi‐Shu , Feng Xi‐Qiao
Published: April 2004

The microstructure of electronically conducting polythiophene (Pth) films synthesized electrochemically was studied using a scanning electron microscope. A self‐organization phenomenon was observed in the films, which grew on a substrate with periodically arrayed holes of diameter less than 100 nm. Owing to the low bending stiffness and the high cohesive energy of nanowires, they combined in a self‐assembling manner into an interesting array of bundle shapes, each bundle having about 20–100 bonded nanowires. The physical mechanism of this phenomenon is elucidated using the theory of elastic buckling.
UV fluorescence monitoring of the mixing of molten polymers in a batch mixer
Authors: Cassagnau P. , Melis F. , Bounor‐Legare V.
Published: April 2004

A fluorescence monitoring device was developed to study the distributive mixing process inside the chamber of a batch mixer. A bifurcated UV‐fluorescence probe was implemented instead of the thermocouple measuring the temperature of the melt. Hydroxymethyl anthracene was used as fluorescence tracer and was preliminarily dispersed in the minor component. Furthermore, the main polymer of this study was a copolymer of ethylene and vinyl acetate (EVA). Structure development during mixing of miscible polymer blends, low viscosity ratio blends (plasticizer/polymer), and immiscible polymer blends was investigated by this method. It was shown that the mixing process of a miscible system depends on the shear rate, which governs the temperature of the melt and consequently the melting process of the solid masterbatch‐tracer at the early stages of mixing. On the other hand, the presence of a miscible component of very low viscosity, as, for example, mixing of DOP in EVA, delays the onset of mixing. This lubricant effect was shown to be due to the fact that DOP migrates to the wall of the chamber rather than inside the polymer, though it is well miscible with the EVA phase. The study of immiscible polymers, as, for example, polypropylene in EVA, did not show any fundamental difference with miscible polymer blends. This observation is actually inherent to the UV‐fluorescence tracer disperesed in a masterbatch system, which allows quantification of the distributive mixing process only.
Compatibilizers based on polypropylene grafted with itaconic acid derivatives. Effect on polypropylene/polyethylene terephthalate blends
Authors: Yazdani‐Pedram M. , Vega H. , Retuert J. , Quijada R.
Published: April 2004

New types of compatibilizers based on functionalized polypropylene (PP) were synthesized by radical melt grafting either with monomethyl itaconate or dimethyl itaconate. The effect of these new modified PP compounds were tested as compatibilizers in PP/polyethylene terephthalate (PET) blends. Blends with compositions 15/85 and 30/70 by weight of PP and PET were prepared in a single‐screw extruder. Morphology of the compatibilized blends revealed a very fine and uniform dispersion of the PP phase as compared with that of noncompatibilized blends of the same composition, leading to improved adhesion between the two phases. Whereas dimethyl itaconate derived agent showed less activity, the monomethyl itaconate parent compound showed an increase of the impact resistance of PET in PP/PET blend. This was attributed to the hydrophilic nature of the monomethyl itaconate part of this compatibilizer. The tensile strength of PET in noncompatibilized blends gradually decreases as the PP content increases, while blends containing functionalized PP exhibited higher values.
Tyrosine imprinted polymer beads with different functional monomers via seed swelling and suspension polymerization
Authors: Zhang Liyong , Cheng Guoxiang , Fu Cong , Liu Xiaohang
Published: April 2004

Molecularly imprinted polymers (MIPs) in bead form were prepared by seed swelling and suspension polymerization with trimethylolpropane trimethacrylate (TRIM) as crosslinker and tyrosine as template. The appearance of the beads was found to be greatly influenced by the concentration of polyvinyl alcohol (PVA) used as dispersant and the ratio of water to TRIM (W/T) during polymerization. When W/T was 46:1 (V/V) and the concentration of PVA‐water solution was 4.6 (%m/m), the result was more desirable size distribution with fewer misshapen beads. A series of imprinted polymers with methacrylic acid (MAA), acrylamide (AM), 2‐vinylpyridine (VP) and 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) as functional monomers (FM), respectively, were prepared, where the molar ratio of tyrosine, FM and TRIM was chosen as 1:16:17. The molecule adsorbing and selecting analysis of the polymers showed that although all the imprinted polymers adsorbed the templates following the rule of Langmuir and exhibited an obvious molecule selecting capability compared with their control polymers (CP), the adsorbing constant and the separating factor were much different when the functional monomers varied. AMPS worked better than the other FM in the present work with a higher value of asymptotic maximum solid phase concentration (0.282 mol/kg), adsorbing constant (198.81/mol), and a larger separating factor (1.93) when phenylalanine was used as the competitive molecule.
Rheological and viscoelastic properties of multiphase acrylic rubber/fluoroelastomer/polyacrylate blends
Authors: Kader M. Abdul , Bhowmick Anil K.
Published: April 2004

Dynamic viscoelastic properties and dynamic mechanical properties of blends of acrylate rubber (ACM), fluoroelastomer and polyacrylate plastics have been investigated with a rheometer (ARES RDA III) at a frequency (ω) range of 0.1 to 100 rad.s−1. The analysis of thermorheological properties revealed that the dynamic moduli and dynamic viscosity of blends varied with the composition of the ACM/FKM blend and the level and type of polyfunctional acrylates. The blends showed negative deviation of the dynamic viscosity additive rule. Higher polyfunctional acrylates induced phase separations and showed temperature dependency. It was found that the data of the blends did not follow the Cole‐Cole plot of miscibility and the plot of log G′‐log G″ of the blend showed composition dependency. The dynamic mechanical analysis exhibited lower tan δ values for blends containing higher functional acrylates. Stress relaxation measurements showed longer periods of relaxation for all blends.
Effects of molecular weight and molecular structure of low profile additives on the properties of bulk molding compound (BMC)
Authors: Ma Chen‐chi M. , Hsieh Chung‐ting , Kuan Hsu‐chiang , Tsai Tsao‐yang , Yu Shih‐wen
Published: April 2004

The effects of molecular weight and molecular structure of styrene(St)‐based and vinyl acetate(VAc)‐based low‐profile additive (LPA) on the curing kinetics and compatibility of unsaturated polyester (UP)/LPA system and linear shrinkage, water absorption rate, surface gloss and pigmentability of bulk molding compound (BMC) were investigated. Results show that the curing reaction rate decreases with an increase of the molecular weight of LPA due to the chain entanglement effect. The plasticizing effect of LPA on the (UP) network was reduced with an increase of the molecular weight of LPA. Water absorption of BMC increases as the molecular weight of LPA increases, implying that more microvoids were formed inside the BMC, resulting a lower linear shrinkage rate, and worse pigmentability. However, good shrinkage control LPA does not necessarily lead to a smoother surface and better surface gloss. Furthermore, modified LPAs possess better compatibility with UP, the final curing conversion of UP is elevated, and both better shrinkage control and surface properties are also observed.
Ternary composites based on PP‐EPDM blends reinforced with flax fibers. Part I: Processing and thermal behavior
Authors: López‐manchado M. A. , Biagiotti J. , Arroyo M. , Kenny J. M.
Published: April 2004

The simultaneous effect of the incorporation of flax fibers and terpolymer ethylene‐propylene diene rubber (EPDM) on the properties of ternary composites with a PP matrix is investigated in this study. In order to evaluate the effects of the matrix composition and fiber percentage on the properties of the composite, an experimental design based on a Doehlert Uniform Net was employed. First, the processing conditions of these ternary composites were analyzed through a rheological study, where a noticeable increase of the viscosity upon the incorporation of the fiber and elastomer was observed. Then, the thermal behavior of the composites was studied with dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The results indicate a strong nucleation ability of the elastomer, showing a considerable increase of the rate of crystallization. These results concur with those obtained with an optical microscope, where it was observed that a higher number of active nuclei were formed in the presence of the elastomer. A previous characterization of the flax fibers used in this study has been also carried out by measuring the length and diameter distribution as well as the mechanical and thermal properties.
Ternary composites based on PP‐EPDM blends reinforced with flax fibers. Part II: Mechanical properties/morphology relationship
Authors: Biagiotti J. , López‐manchado M. A. , Arroyo M. , Kenny J. M.
Published: April 2004

The mechanical properties and morphology of ternary composites based on PP‐EPDM blends reinforced with natural flax fibers are analyzed. In order to evaluate the simultaneous effect of the incorporation of both and fibers, an experimental design based on a Doehlert Uniform Net has been employed. The tensile, flexural and impact behaviors of the composites are investigated, and the results show that flax fibers behave as an effective reinforcing agent in these systems. In fact, a considerable increase in the studied properties in the presence of the fibers was observed. It is interesting to note that the reinforcing effect is more noticeable as the EPDM content in the blend increases. Morphological studies by scanning electron microscopy (SEM) were also carried out.