bluuebunny/crossref_metadata_2025 huggingface dataset:
The importance of timely polymer sintering while processing polypropylene foams in rotational molding
Authors: Pop‐Iliev Remon , Rizvi Ghaus M. , Park Chul B.
Published: April 2004

Producing polypropylene (PP) foams with satisfactory cell morphologies in rotational foam molding is feasible. However, the narrow interval between the melting temperature of PP and the onset decomposition temperature of the applicable chemical blowing agent (CBA), and the relatively low melt strength of PP at elevated temperatures are considered the greatest obstacles in processing PP foams. The experimental results revealed that the morphology of the foams obtained by processing PP pellets that have been pre‐compounded with a CBA could be governed by either pellet sintering or cell coalescence. The viscosity of the basic PP resin and the processing temperature determine which of these two key factors will assume a predominating influence towards the foaming process. The desired volume expansion ratio (VER) of the foam also plays an important role since it determines the formulation of the foamable resin and the shot size. Desirable PP foam structures in compounding based rotational foam molding can be obtained only if pellet sintering takes place prior to the decomposition of the CBA and if the processing temperature during the foaming process is kept lower than the temperature of cell coalescence.
A study of the stick‐slip phenomenon in single‐screw extrusion of linear polyethylene
Authors: Kay D. , Carreau P. J. , Lafleur P. G. , Robert L. , Vergnes B.
Published: April 2004

We present results of a study on the stick‐slip phenomenon observed for two linear polyethylenes (HDPE and LLDPE). Experiments were carried out in a single screw extruder using dies of different diameters and L/D ratios. The pressure and the mass flow rate have been measured simultaneously and the instant mass flow rate was determined using laser Doppler velocimetry. Our results clearly confirm the hypothesis that the flow jumps from one stable branch to the other during oscillations as suggested in the literature. The role of the melt compressibility in the reservoir is also established. The effect of the average mass flow rate imposed by the extruder QIN on the respective compression and decompression phases is in good agreement with effect predicted by the mass balance in the reservoir. We also used different reservoir volumes to confirm that the period of oscillations increases with the compressed melt volume upstream of the die.
Primary structure and physical properties of poly(ethylene terephthalate)/poly(ethylene naphthalate) resin blends
Authors: Maruhashi Yoshitsugu
Published: April 2004

The morphology and properties of blends of poly(ethylene naphthalate) (PEN) and poly(ethylene terephthalate) (PET) that were injection molded under various conditions were studied. Under injection molding conditions that make it possible to secure transparency, blends did not show clear crystallinity at blending ratios of more than 20 mol% in spite of the fact that crystallinity can be observed in the range of PEN content up to 30 mol%. Because both transparency and crystallinity could be secured with a PEN 12 mol% blend, this material was used in injection molding experiments with various injection molding cycles. Whitening occurred with a cycle of 20 sec, and transparency was obtained at 30 sec or more. This was attributed to the fact that transesterification between PET and PEN exceeded 5 mol% and phase solubility (compatibility) between the PET and PEN increased when the injection molding time was 30 sec or longer. However, when the transesterification content exceeded 8 mol%, molecularly oriented crystallization did not occur, even under stretching, and consequently, it was not possible to increase the strength of the material by stretching. PET/PEN blend resins are more easily crystallized by stretch heat‐setting than are PET/PEN copolymer resins. It was understood that this is because residual PET, which has not undergone transesterification, contributes to crystallization. However, because transesterification reduces crystallinity, the heat‐set density of blends did not increase as significantly as that of pure PET, even in high temperature heat‐setting. Gas permeability showed the same tendency as density. Namely, pure PET showed a substantial decrease in oxygen transmission after high temperature heat‐setting, but the decrease in gas permeability in the blend material was small at heat‐set temperatures of 140°C and higher.
Industrial solidification processes in polybutene‐1. Part II—influence of shear flow
Authors: Braun J. , Wippel H. , Eder G. , Janeschitz‐Kriegl H.
Published: April 2004

Following some early rudimentary results on shear‐induced crystallization of polybutene‐1 (1, 2), the present paper contains more detailed results. In the course of this work the origins of the highly oriented crystalline surface layers, as well known from injection molded samples, are more closely investigated. For the purpose, a special extrusion experiment is used, in which melts of various degrees of undercooling are moved through a duct of large aspect ratio. When, after the release of the pressure at the die entry, a quench of the duct to a temperature far below the melting point is delayed, a relaxation phenomenon is observed, in accordance with the experiences with i‐PP. From these experiments one learns that the leading parameter of the process is something like the mechanical work done per unit volume, and that the relaxation time increases with decreasing temperature much faster than the viscosity of the melt. The results are qualitatively in excellent agreement with our previously obtained results for polypropylene.
Nylon 10 10–montmorillonite nanocomposite made by intercalating polymerization
Authors: Zhang Guosheng , Li Yongjin , Yan Deyue , Xu Youyong
Published: April 2004

Nylon 10 10–montmorillonite nanocomposite has been prepared successfully using intercalating polymerization. The nanocomposite was investigated by X‐ray diffraction (XRD), Fourier transform infrared (FTIR), Atom force microscopy (AFM), Scanning electron microscopy (SEM), Thermogravimetric analysis (TGA), Differential scanning calorimeter (DSC), and Dynamic mechanical analysis (DMA). The results show that there are uniformly dispersed silicate layers in the nylon 10 10 matrix. The resulting nanocomposites have higher onset decomposition temperature and dynamic storage moduli than those of pure nylon 10 10. In addition, it was found that montmorillonite plays an important role in heterophase nucleation of the crystallization of nylon 10 10 in composites. Mechanical testing shows that the tensile modulus of nanocomposites is superior to that of nylon 10 10, and the ultimate strain values of the nanocomposites remain at a level similar to nylon 10 10 if the content of montmorillonite is not more than 6 wt%.
Numerical simulation of the flow in an extensional flow mixer. Effect of fluid elasticity on the flow
Authors: Tanoue Shuichi , Iemoto Yoshiyuki
Published: April 2004

We discuss the viscoelastic flow of the matrix fluid in an Extensional Flow Mixer (EFM) obtained by a numerical simulation. The effect of the fluid viscoelasticity on the flow state in an EFM was considered by the comparison of the flow states of the purely viscous fluid and the viscoelastic fluid. The mixing performance of the EFM is also considered. The Phan‐Thien Tanner model was used as the constitutive equation of the viscoelastic fluid and the Carreau model was used as that of the purely viscous fluid. Results obtained are as follows: (1) Stagnation flows occur in the converging‐diverging plates (c‐d plates) in the case of viscoelastic fluid. The size of stagnation flow region becomes large when the fluid has a strain‐thickening elongational viscosity. (2) The absolute value of the extensional strain and the pressure drop in the c‐d region increase with fluid elasticity. Meanwhile, the residence time in the c‐d region decreases with that. (3) There is no stagnation region in the c‐d plates for a purely viscous fluid. The stagnation flow has an effect on the estimation value of EFM's performance. The prediction by the purely viscous fluid is not useful for the flow in an EFM because of extremely low accuracy.
Effect of ground fluororubber vulcanizate powder on the properties of fluororubber compound
Authors: Ghosh Arun , Bhattacharya A. K. , Bhowmick A. K. , De S. K.
Published: April 2004

Fluororubber vulcanizate powder (FVP) obtained from fluororubber based on tetrafluoroethylene/propylene/vinylidene fluoride terpolymer by mechanical grinding exists in a highly aggregated chain‐like structure. X‐ray photoelectron spectros‐copy (XPS) and infrared (IR) spectroscopy studies show that there are no chemical change on the rubber surface following mechanical grinding of the fluororubber vulcanizate after heat aging at 200°C for 10 days. The incorporation of FVP as a filler in the fluororubber compound results in a marginal increase of Mooney viscosity, Mooney scorch time and shear viscosity. While tensile strength, modulus and hardness marginally increase on addition of FVP into the fluororubber compound, tear strength decreases. Rhemetric studies show that FVP alone is susceptible to further crosslinking in the presence of a curing agent. Dynamic mechanical spectra reveal that the glass to rubber transition temperature shifts higher by the addition of FVP into the fluororubber compounds. Atomic force microscopy (AFM) images show uniform dispersion of FVP particles into the rubber matrix.
Recycling of silicone rubber waste: Effect of ground silicone rubber vulcanizate powder on the properties of silicone rubber
Authors: Ghosh Arun , Rajeev R. S. , Bhattacharya A. K. , Bhowmick A. K. , De S. K.
Published: April 2004

The silicone rubber vulcanizate powder (SVP) obtained from silicone rubber by mechanical grinding exists in a highly aggregated state. The particle size distribution of SVP is broad, ranging from 2 µm to 110 µm with an average particle size of 33 µm. X‐ray Photoelectron Spectroscopy (XPS) and Infrared (IR) Spectroscopy studies show that there is no chemical change on the rubber surface following mechanical grinding of the heat‐aged (200°C/10 days) silicone rubber vulcanizate. Addition of SVP in silicone rubber increases the Mooney viscosity, Mooney scorch time, shear viscosity and activation energy for viscous flow. Measurement of curing characteristics reveals that incorporation of SVP into the virgin silicone rubber causes an increase in minimum torque, but marginal decrease in maximum torque and rate constant of curing. However, the activation energy of curing shows an increasing trend with increasing loading of SVP. Expectedly, incorporation of SVP does not alter the glass‐rubber transition and cold crystallization temperatures of silicone rubber, as observed in the dynamic mechanical spectra. It is further observed that on incorporation of even a high loading of SVP (i.e., 60 phr), the tensile and tear strength of the silicone rubber are decreased by only about 20%, and modulus dropped by 15%, while the hardness, tension set and hysteresis loss undergo marginal changes and compression stress‐relaxation is not significantly changed. Atomic Force Microscopy studies reveal that incorporation of SVP into silicone rubber does not cause significant changes in the surface morphology.
Study of the different flow patterns in the melting section of a co‐rotating twin‐screw extruder
Authors: Yichong Guo , Fuhua Zhu
Published: April 2004

Understanding the phenomena of twin‐screw extrusion (TSE) is the first step in investigating this process. Visualization technology incorporated in a co‐rotating twin‐screw extruder was developed for this purpose. This technology enabled the extrusion phenomena to be directly observed and analyzed. The present work focuses on the melting process. It is revealed and verified that there are different flow patterns in the melting section during extrusion, with different degrees of fill. A melting model for one type of flow pattern is established. The significance of the present work is to establish the variety conception for the flow patterns. According to this conception, corresponding models should be established for each flow pattern identified.
Study on composition and characteristics of maleated ethylene‐octene copolymer prepared by reactive extrusion on the morphology and properties of polyamide 6/ethylene‐octene copolymer blends
Authors: Premphet‐Sirisinha K. , Chalearmthitipa S.
Published: April 2004

Blends of polyamide 6 (PA6) and elastomeric ethylene‐octene copolymer (EOR), with and without maleated EOR (EOR‐MA) were studied. EOR‐MA with various amounts of grafted MA and gel content were prepared by reactive extrusion. The effects of EOR‐MA characteristics and composition on the morphology, thermal and mechanical properties of the blends were investigated. EOR‐MA was found to promote the toughness efficiency of PA6 remarkably. High impact resistance was achieved by the use of EOR‐MA containing less than 2% gel. The content of MA grafted on EOR‐MA in the range of 0.5%–1.0% gave a similar effect on the blend properties. The blend containing 20% of EOR grafted with 1% MA exhibited twenty times higher impact strength (1000 J/m) than pure PA6 (55 J/m). The presence of EOR‐MA in the blends led not only to a drastic reduction in the dispersed particle size, but also to some changes in fracture mechanisms, thus enhancing the impact resistance of the blends.
Rheological properties of hyperbranched polymer/poly(ethylene terephthalate) reactive blends
Authors: Kil Seung Bum , Augros Yannick , Leterrier Yves , Månson Jan‐Anders E. , Christel Andreas , Borer Camille
Published: April 2004

The rheological properties in solution, in shear and in uniaxial elongation of poly(ethylene terephthalate) (PET) reacted together with hyperbranched polymers (HBPs) were investigated. Two different PET grades, of low and high molecular weights, were compounded with sub‐ to over‐stoichiometric concentrations of HBPs of second and fourth pseudo‐generation, and subsequently subjected to a solid‐state polycondensation (SSP). The formation of microgels, which occurs at high HBP concentration, gave rise to a large increase in melt elasticity and a related decrease in melt strength. At low HBP concentrations, the complex viscosity of the unreacted HBP/PET was considerably reduced, thus demonstrating a lubrication effect of the HBP molecules. During SSP, the intrinsic and shear viscosities exhibited a gradual increase, which was similar for both PET and HBP/PET blends, and was correlated to an increase in molecular weight, through linear‐chain extension and branching reactions. The elongational viscosity of the reactive blends was also increased as a function of reaction time, and this increase was much larger in the case of the HBP/PET blends. A 400% increase in melt strength of the PET was obtained by combining SSP and trace amounts of an HBP of second generation, without any decrease in drawability.
Mechanical relaxations in heat‐aged polycarbonate. Part I: Comparison between two molecular weights
Authors: Lee‐Sullivan Pearl , Dykeman Donna , Shao Qing
Published: April 2004

As part of a wider research program related to polycarbonate embrittlement, the effects of heat‐aging on mechanical relaxation behavior have been studied by examining the relationship between secondary transitions and stress relaxation behavior. In this Part I, the differences in response between two molecular weight polycarbonates (PC) are compared for injection molded samples. Dynamic mechanical spectra showed that the presence of an intermediate β transition (∼ 80°C) is strongly dependent on molecular weight and heat‐aging. However, the β1 (35°C) and the γ (‐100°C) peaks are generally insensitive to either effect. The study also attempted to interpret the similarities and differences in relaxation response using free volume and conformational change arguments, which have been subject to much scrutiny. Using the KWW stretched exponential to characterize stress relaxation, it appeared that bulk free volume recovery concepts could explain differences in stress relaxation response but not the corresponding losses in toughness. Hence, it is proposed that changes in relaxation response are most likely due to an interplay of relatively large scale molecular volume and molecular conformation processes that affect intermolecular cooperativity. These high‐activation processes are related to the broad β region (β1 < T < Tg).
Mechanical relaxations in heat‐aged polycarbonate. Part II: Statistical analysis of low‐molecular weight data
Authors: Dykeman Donna , Lee‐Sullivan Pearl
Published: April 2004

The significance of heat‐aging effects on low‐molecular‐weight polycarbonate has been studied by performing a two‐factor Analysis of Variance (ANOVA). Although this work was primarily motivated by the large experimental scatter observed in stress relaxation results for LMW 2608 (part I), the effect of heat‐aging on the characteristics of secondary transitions (γ and β1) generated by dynamic testing was also investigated. Both types of tests were performed using a dynamic mechanical analyzer. The statistical analysis verified an earlier suggestion that both the secondary transitions were insensitive to heat‐aging. In the quasi‐static stress relaxation tests, the curve‐fitted KWW parameters (τ, Eo′ β′) were evaluated using ANOVA for increasing heat‐aging time and test temperature. Two other statistical techniques were also applied to test repeatability—the power of each aging time/test temperature combination and the number of observations needed to achieve 90% repeatability. In conclusion, both τ and β′ could describe the self‐retarding nature of volume recovery although the repeatability of β′ was substantially higher. However, the unrelaxed modulus, Eo, was found to be an unreliable indicator of whether heat‐treatment had caused changes in the intrinsic structure. Overall, the study showed that the repeatability of the stress relaxation test results is generally very poor for the confidence levels tested.
Environmental stress cracking (ESC) of plastics caused by non‐ionic surfactants
Authors: Kawaguchi Takafumi , Nishimura Hiroyuki , Kasahara Keiichi , Kuriyama Takashi , Narisawa Ikuo
Published: April 2004

The susceptibility of various plastics to environmental stress cracking (ESC) was studied using a variety of agents in common use. It was found that styrenic polymers are susceptible to ESC by many kinds of agents, including detergents, that have non‐ionic surfactants as their components. The ESC of acrylonitrile‐butadiene‐styrene (ABS) copolymer caused by non‐ionic surfactants was studied intensively, and the dependence of crack propagation behavior on temperature and on the kind of non‐ionic surfactants was investigated by edge crack tension (ECT) tests. The morphology at the crack tip of ECT specimens was investigated by a transmission electron microscope (TEM). It was found that crack propagation behavior was closely related to the morphology at the crack tip and the morphology was affected by temperature and type of surfactants. The change in morphology at different experimental conditions was attributable to the difference in the solubility and diffusivity of surfactants at the crack tips.
Binary and ternary blends of recycled high‐density polyethylene containing polypropylenes
Authors: Kukaleva N. , Simon G. P. , Kosior E.
Published: April 2004

Binary and ternary blends of the high viscosity recycled high‐density polyethylene (reHDPE) from milk bottles, containing either homopolymer polypropylene (PP) or copolymer polypropylene (coPP), were developed in an effort to reduce viscosity and encourage ease of processing by injection molding, without a significant loss in mechanical properties. A grade of PP and a grade of coPP that had crystallization temperatures close to and slightly lower than that of reHDPE were chosen for blending in order to obtain simultaneous crystallization of the reHDPE and (co)PP phases. The resulting reHDPE/(co)PP blends (reHDPE wt% = 77) generally showed very good mechanical properties and, in particular, sufficiently high impact strength while engendering considerably lower viscosity than reHDPE. The PP was more useful at very high and low shear rates whereas the coPP was the most efficient in the mid‐range of shear rates (102 – 103 sec−1). Good impact resistance shown by the reHDPE/(co)PP blends was attributed in part to the fine dispersion of (co)PP phase, possible involvement of a portion of the polymers in a co‐continuous structure and simultaneous crystallization of the components. Ternary blends of reHDPE (reHDPE wt% = 77), PP and low‐density polyethylene (LDPE) showed good mechanical performance, although they were more viscous than (co)PP blends. In the ternary blends, co‐crystallization of reHDPE and LDPE phases was preserved (1).
Lifetime prediction for ABS pipes subjected to combined pressure and deflection loading
Authors: Lu J. P. , Davis P. , Burn L. S.
Published: April 2004

As part of an investigation into the performance of acrylonitrile‐butadiene‐styrene (ABS) systems for water transportation, this paper presents a method for predicting the service lifetimes of buried pipes under in‐service loading conditions. A linear fracture mechanics approach was used to analyze brittle failure initiating from adventitious flaws located at the bore surface of pipe. Failure criteria were determined using the time‐dependent, quasistatic, plane strain fracture toughness of the ABS material, combined with empirical parameters that describe slow, steady crack growth. The expected operating conditions of a buried pipe were then separated into static loading contributions from internal pressure, diametrical deflection and residual stress. Idealized stress intensity factors associated with mode‐I crack opening under each of these components were determined using a finite element analysis and superposed to describe the general case in service. The computed nett stress intensity factor was then combined with the previously determined fracture toughness and slow crack growth data in an algorithm to simulate incremental radial crack growth from the pipe bore. Predicted failure times compared well with an experimental model of expected operating conditions, which combined hydrostatic pressure and parallel‐plate deflection loading of an internally notched pipe. The prediction method was also used to identify the factors that control the lifetime of a pipe in service. The influence of material visco‐elasticity was investigated by simulating variations in fracture toughness and slow crack growth resistance. It was proposed that, in practice, these variations are governed by opposing changes in visco‐elasticity. The effect of changing diametrical deflection and residual stress distribution were also simulated, allowing recommendations on pipe manufacture and installation conditions to be made.
Synthesis and crystallization behavior of nylon 12 14. II: Chain‐folded lamellar crystals and crystalline transformation behavior of nylon 12 14
Authors: Zhang Guosheng , Li Yongjin , Yan Deyue
Published: April 2004

Chain‐folded lamellar crystals of nylon 12 14 have been grown from a dilute 1,4‐butanediol solution with the “self‐seeding” technique. The morphology and structure of nylon 12 14 lamellar crystals were studied by both transmission electron microscopy (TEM) and wide‐angle X‐ray diffraction (WAXD). Two kinds of electron diffraction patterns were detected when different areas were selected for diffraction, which indicates that the α crystal phase and the β crystal phase coexist for nylon 12 14 under the present crystallization conditions. The WAXD diffractograms of the crystal mats confirm the results obtained from electron diffraction (ED). In addition, the changes of the crystal structure as a function of temperature for melt‐crystallized and dilute solution‐crystallized nylon 12 14 were monitored by variable‐temperature WAXD and variable‐temperature infrared spectroscopy (IR). It was found that the melt‐crystallized sample undergoes a Brill transformation at 80°C–90°C, but no Brill temperature can be observed for the dilute solution‐crystallized nylon 12 14.
Effect of CO2 on crystallization kinetics of poly(ethylene terephthalate)
Authors: Takada Mitsuko , Ohshima Masahiro
Published: April 2004

The effect of CO2 on the isothermal crystallization kinetics of poly(ethylene terephthalate), PET, was investigated using a high‐pressure differential scanning calorimeter (DSC), which performed calorimetric measurements while keeping the polymer in contact with presurized CO2. It was found that the crystallization rate followed the Avrami equation with values of the crystallization kinetic constant dependent on the crystallization temperature and concentration of CO2 in PET. The presence of CO2 in the PET increased its overall crystallization rate. CO2 also decreased the glass transition temperature, Tg, and the melting temperature, Tm. As a result, the observed changes in crystallization rate caused by CO2 can be qualitatively predicted from the magnitude of Tg depression and that of the equilibrium melting temperature, Tm0.
Loss of surface and volume electrical conductivities in polymer compounds due to shear‐induced migration of conductive particles
Authors: Jana Sadhan C.
Published: April 2004

The loss of surface and volume electrical conductivities of conductive polymer compounds as a result of shear‐induced migration of conductive filler particles is elucidated with the help of model equations by considering flow of uniformly mixed conductive polymer compounds through two‐dimensional channels, as in injection molding or extrusion of sheets and films. Matrix polymers of shear‐thinning nature and non‐colloidal conductive particles of spherical shape are considered. The effect of particle migration is found to be most severe in the case of compositions around the percolation threshold—an otherwise uniformly mixed conductive compound turns into an insulator because of migration of conductive particles from the surface to the bulk. In addition, the extent of migration of particles and consequently the loss of conductivity are found to be the greatest for Newtonian polymer matrices, where the gradients of shear stress are the highest. The extent of migration gradually reduces as the polymer becomes more shear‐thinning.
Improvement of the mechanical properties of an HDPE/PS blend by compatibilization and incorporation of CaCO3
Authors: Sahnoune F. , Lopez Cuesta J. M. , Crespy A.
Published: April 2004

Generally, recycled polymer blends exhibit solid dispersion‐like morphology with poor mechanical properties. The aim of this work was to enhance the mechanical properties of a HDPE/PS (75/25) blend, in particular the stiffness and the impact strength. In order to improve the stiffness, CaCO3 filler was incorporated. It was shown that PS and CaCO3 were separately dispersed with poor adhesion to the HDPE matrix. The incorporation of CaCO3 significantly enhanced the stiffness but lowers the impact resistance. Elastomer copolymers were incorporated in order to compensate for the embrittlement caused by the CaCO3 filler. Depending on their chemical structure, either grafted with a reactive function or ungrafted, the elastomers acted differently at the interfaces of the HDPE/PS/CaCO3 system. SEBS acts exclusively at the HDPE‐PS interface whereas SEBSgMA acts at both the HDPE‐PS and the HDPE‐CaCO3 interface. The SEBSgMA elastomer lowered the stiffening effect caused by CaCO3 and provided an insufficient increase in impact properties. One the other hand, SEBS, which concentrates its action at the HDPE‐PS interface, retained much of the stiffening effect of CaCO3 and provided a greater improvement in impact properties than SEBSgMA. In the recycled HDPE/PS (75/25) blend, the incorporation of 20 vol% CaCO3 and 4 vol% SEBS led to an increase in both impact strength (from 39 to 70 kJ/m2) and in stiffness (from 1335 to 1560 MPa). So, encouraging results were obtained, enabling us to predict a promising future for this approach to the recycling of commingled plastics.
Synthesis and mechanical properties of unsaturated polyester based nanocomposites
Authors: Baran Inceoglu A. , Yilmazer Ulku
Published: April 2004

Two classes of nanocomposites were synthesized using an unsaturated polyester resin as the matrix and sodium montmorillonite as well as an organically modified montmorillonite as the reinforcing agents. X‐ray diffraction pattern of the composites showed that the interlayer spacing of the modified montmorillonite expanded from 1.25 nm to 4.5 nm, indicating intercalation. Glass transition values of these composites increased from 72°C, in the unfilled unsaturated polyester, to 86°C in the composite with 10% organically modified montmorillonite. From Scanning Electron Microscopy, it is seen that the degree of intercalation/exfoliation of the modified montmorillonite is higher than in the unmodified one. The mechanical properties also supported these findings, since in general, the tensile modulus, tensile strength, flexural modulus, flexural strength and impact strength of the composites with modified montmorillonite were higher than the corresponding properties of the composites with unmodified montmorillonite. The tensile modulus, tensile strength, flexural modulus and flexural strength values showed a maximum, whereas the impact strength exhibited a minimum at approximately 3–5 wt% modified montmorillonite content. These results imply that the level of exfoliation may also exhibit a maximum with respect to the modified montmorillonite content. The level of improvement in the mechanical properties was substantial. Adding only 3 wt% organically modified clay improved the flexural modulus of unsaturated polyester by 35%. The tensile modulus of unsaturated polyester was also improved by 17% at 5 wt% of organically modified clay loading.
Transport of aromatic solvents through nitrile rubber/epoxidized natural rubber blend membranes
Authors: Mathai Asha Elizabeth , Singh R. P. , Thomas Sabu
Published: April 2004

The sorption and diffusion behavior of a series of aromatic solvents through blends of nitrile rubber (NBR) and epoxidized natural rubber (ENR) have been studied in the temperature range of 28–70°C. The effect of blend ratio, penetrant size and temperature on the transport properties was investigated. The relationship between the diffusion behavior and the morphology of the system was examined. Different transport parameters such as diffusion coefficient, permeability coefficient and swelling ratio have been calculated. Experimental permeability coefficients were compared with various theoretical models. The van't Hoff relation was used to compute the thermodynamic parameters.
Deformation behavior of an epoxy resin subject to multiaxial loadings. Part I: Experimental investigations
Authors: Hu Yafei , Xia Zihui , Ellyin Fernand
Published: April 2004

The mechanical behavior of an epoxy resin (Epon 826) was studied by performing a series of tests on thin‐walled tubular specimens. These tests deal with different aspects of the mechanical behavior of this epoxy resin. The deformation behavior, such as viscoelastic behavior, hydrostatic stress effect, multiaxial behavior and loading path effect, was investigated. It was found that the Epon 826 epoxy resin is a highly nonlinear viscoelastic material. The effect of hydrostatic pressure on the deformation behavior of this epoxy is not significant. However, it shows different tensile and compressive deformation behavior. The loading path was found to have an observable effect on the deformation response of this epoxy, especially in the high stress/strain range.
The effect of sample preparation on the mechanical properties of nylon 66
Authors: Bates P. J. , Wang C. Y.
Published: April 2004

Cutting test specimens from molded plaques is commonly used in mechanical testing. The mechanical properties of these cut specimens may be affected by cutting process as it could introduce extrinsic flaws and thermal effects on cut edge surfaces. The objective of this experimental research is to determine how band saw cutting affects the flexural and impact strengths of 33% short glass fiber (GF) reinforced polyamide 66 (PA66) and unreinforced PA66. The specimens for the flexural and impact tests were obtained by cutting molded plaques using different blade types, blade speeds, feed rates, and levels of polishing. Results were compared with those from uncut specimens. Surface morphologies of the specimens' cut edges (photographs and roughness) were assessed using Scanning Electron Microscopy and PRK Perthometer, respectively. The results indicated that higher flexural and impact strengths of cut specimens of 33% GF reinforced PA66 were achieved with high blade speed, low work piece feed rate and using a high number of teeth per unit length. For unreinforced PA66, higher impact strengths were achieved at low blade speeds and work piece feed rates.
Recycling of roofing membrane rubber by ultrasonic devulcanization
Authors: Yun Jushik , Isayev A. I.
Published: April 2004

The recycling of vulcanizates based on EPDM roofing membrane rubber using a new ultrasonic devulcanization reactor with a grooved barrel was carried out. This reactor provided continuous devulcanization at an output as high as 2.52 g/s. Die pressure and ultrasonic power consumption were measured as a function of processing conditions. The mechanical properties of virgin vulcanized and revulcanized roofing membranes were measured. Tensile strength of the revulcanized rubber was found to be similar to that of the virgin vulcanizate. Gel fraction, crosslink density, and dynamic properties of the virgin vulcanizate, the ultrasonically devulcanized rubber, and the revulcanized rubber were determined. Also, dynamic properties and the cure behavior of the virgin compound and of the devulcanized roofing membrane were investigated. All these properties were found to be dependent on processing conditions during devulcanization. The thermal stability of the virgin compound, virgin vulcanizate, and devulcanized and revulcanized rubbers were studied by means of TGA. It was found that the thermal stability of all the vulcanizates in air and nitrogen environments remained practically intact, while that of devulcanized rubber in air environment was a function of processing conditions.
Flexible polymer composite electromagnetic crystals
Authors: Marrett Courtney , Moulart Alexandre , Colton Jonathan , Tcharkhtchi Abbas
Published: April 2004

The dielectric properties of a ceramic powder (BaTiO3) filled thermoplastic elastomer (EPDM TPE) were investigated for use in a flexible electromagnetic crystal. Materials were produced that had a high dielectric constant (approximately 9) and low loss tangent (less than 0.01). Materials were extruded and injection molded so as to povide low‐cost processing. Mechanical and electromagnetic test results showed the effect of processing conditions on the final quality of the composite. The shear rate during processing and the number of mixing cycles were found to affect the final material characteristics significantly. An electromagnetic crystal woven from extruded rods showed good reflectivity in the 10–15 GHz region.
Layered silicate nanocomposites based on various high‐functionality epoxy resins: The influence of an organoclay on resin cure
Authors: Becker Ole , Simon George P. , Varley Russell J. , Halley Peter J.
Published: April 2004

The influence of an organically modified clay on the curing behavior of three epoxy systems widely used in the aerospace industry and of different structures and functionalities was studied. Diglycidyl ether of bisphenol A (DGEBA), triglycidyl p‐amino phenol (TGAP) and tetraglycidyl diamino diphenylmethane (TGDDM) were mixed with an octadecyl ammonium ion modified organoclay and cured with diethyltoluene diamine (DETDA). The techniques of dynamic mechanical thermal analysis (DMTA), chemorheology and differential scanning calorimetry (DSC) were applied to investigate gelation and vitrification behavior, as well as catalytic effects of the clay on resin cure. While the formation of layered silicate nanocomposite based on the bifunctional DGEBA resin has been previously investigated to some extent, this paper represents the first detailed study of the cure behavior of different high performance, epoxy nanocomposite systems.
Erosion and breakup of polymer drops under simple shear in high viscosity ratio systems
Authors: Lin Bin , Sundararaj Uttandaraman , Mighri Frej , Huneault Michel A.
Published: April 2004

The deformation and breakup of a single polycarbonate (PC) drop in a polyethylene (PE) matrix were studied at high temperatures under simple shear flow using a specially designed transparent Couette device. Two main breakup modes were observed: (a) erosion from the surface of the drop in the form of thin ribbons and streams of droplets and (b) drop elogation and drop breakup along the axis perpendicular to the velocity direction. This is the first time drop breakup mechanism (a), “erosion,” has been visualized in polymer systems. The breakup occurs even when the viscosity ratio (ηr) is greater than 3.5. although it has been reported that breakup is impossible at these high viscosity ratios in Newtonian systems. The breakup of a polymer drop in a polymer matrix cannot be described by Capillary number and viscosity ratio only; it is also controlled by shear rate, temperature, elasticity and other polymer blending parameters. A pseudo first order decay model was used to describe the erosion phenomenon and it fits the experimental data well.
Effectiveness of functionalized polyolefins as compatibilizers for polyethylene/wood flour composites
Authors: Wang Yeh , Yeh Feng‐C. , Lai Sun‐M. , Chan Hsun‐C. , Shen Hsiao‐F.
Published: April 2004

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

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

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

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

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

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

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

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