bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of supercritical carbon dioxide on morphology development during polymer blending
Authors: Elkovitch Mark D. , Tomasko David L.
Published: April 2004

Supercritical carbon dioxide (scCO2) was added during compounding of polystyrene and poly(methyl methacrylate) (PMMA) and the resulting morphology development was observed. The compounding took place in a twin screw extruder and a high‐pressure batch mixer. Viscosity reduction of PMMA and polystyrene were measured using a slit die rheometer attached to the twin screw extruder. Carbon dioxide was added at 0.5, 1.0, 2.0 and 3.0 wt% based on polymer melt flow rates. A viscosity reduction of up to 80% was seen with PMMA and up to 70% with polystyrene. A sharp decrease in the size of the minor (dispersed) phase was observed near the injection point of CO2 in the twin screw extruder for blends with a viscosity ratio, ηPMMA/ηpolystyrene, of 7.3, at a shear rate of 100 s−1. However, further compounding led to coalescence of the dispersed phase. Adding scCO2 did not change the path of morphology development; however, the final domain size was smaller. In both batch and continuous blending, de‐mixing occurred upon CO2 venting. The reduction in size of the PMMA phase was lost after CO2 venting. The resulting morphology was similar to that without the addition of CO2. Adding small amounts of fillers (e.g. carbon black, calcium carbonate, or nano‐clay particles) tended to prevent the de‐mixing of the polymer blend system when the CO2 was released. For blends with a viscosity ratio of 1.3, at a shear rate of 100 s−1, the addition of scCO2 only slightly reduced the domain size of the minor phase.
Melt tearing and ovality in wire coating
Authors: Hade Aaron J. , Giacomin A. Jeffrey
Published: April 2004

We investigate how to avoid tearing, egg‐shaped cross sections or foldover of the polymer melt cone in tube coating of wire. We use an isothermal Newtonian model for the melt cone. We calculate the melt stress and the draw ratio balance, the parameter used in industry to avoid process problems. The stress calculations help us explain ovality and tearing. To help practitioners apply the results we provide examples.
Nonisothermal two‐dimensional film casting of a viscous polymer
Authors: Smith Spencer , Stolle Dieter
Published: April 2004

A model is presented for simulating two‐dimensional, nonisothermal film casting of a viscous polymer. The model accommodates the effects of inertia and gravity, and allows the thickness of the film to vary across the width, but it excludes film sag and die swell. Based on the simulation results, three factors are shown to contribute to reducing neck‐in and promoting a uniform thickness: the self‐weight of the material, for low viscosity polymers; nonuniform thickness and/or velocity profiles at the die; and cooling of the film, especially when localized cooling jets are employed.
Overall numerical simulation of extrusion blow molding process
Authors: Tanifuji Shin‐Ichiro , Kikuchi Tsuyoshi , Takimoto Jun‐Ichi , Koyama Kiyohito
Published: April 2004

This paper focuses on the overall numerical simulation of the parison formation and inflation process of extrusion blow molding. The competing effects due to swell and drawdown in the parison formation process were analyzed by a Lagrangian Eulerian (LE) finite element method (FEM) using an automatic remeshing technique. The parison extruded through an annular die was modeled as an axisymmetric unsteady nonisothermal flow with free surfaces and its viscoelastic properties were described by a K‐BKZ integral constitutive equation. An unsteady die‐swell simulation was performed to predict the time course of the extrudate parison shape under the influence of gravity and the parison controller. In addition, an unsteady large deformation analysis of the parison inflation process was also carried out using a three‐dimensional membrane FEM for viscoelastic material. The inflation sequence for the parison molded into a complex‐shaped mold cavity was analyzed. The numerical results were verified using experimental data from each of the sub‐processes. The greatest advantage of the overall simulation is that the variation in the parison dimension caused by the swell and drawdown effect can be incorporated into the inflation analysis, and consequently, the accuracy of the numerical prediction can be enhanced. The overall simulation technique provides a rational means to assist the mold design and the determination of the optimal process conditions.
Novel variations in the microstructure of auxetic ultra‐high molecular weight polyethylene. Part 2: Mechanical properties
Authors: Alderson K. L. , Webber R. S. , Evans K. E.
Published: April 2004

A highly fibrillar auxetic form of ultra‐high molecular weight polyethylene (UHMWPE) has been fabricated by using a powder processing route comprising two stages—sintering and extrusion. The resulting material has a low density (720 kg/m3) and low flexural strength and modulus (up to 6 MPa and 62 MPa, respectively) but much larger negative Poisson's ratio when compared with auxetic UHMWPE fabricated using an additional preliminary compaction stage followed by sintering and extrusion. The effects of die geometry on the mechanical properties of this material are examined. The indentation resistance and ultrasonic attenuation of the novel, highly fibrillar auxetic material were measured, and it was found that the indentation resistance was enhanced only at very low loads (i.e. 5 N and 10 N) when compared with conventionally processed UHMWPE. After this, the lack of structural integrity of the material outweighed the benefits of its being auxetic. However, the ultrasonic attenuation was found to be extremely good, and much enhanced over conventionally processed UHMWPE, with the attenuation coefficient being at least 47 dB/cm, compared with 8 dB/cm.
Dispersed phase morphology of impact PP copolymers. Effects of blend composition as determined by TREF
Authors: Zacur Ruth , Goizueta Graciela , Capiati Numa
Published: April 2004

Polypropylene (PP) blends, commercially known as “impact polypropylene copolymers” (IPC), are produced by a sequential gas phase polymerization process. The final product is a complex mixture of polypropylene (PP) and a range of ethylenepropylene copolymers (EPC) with different ethylene contents. In the present work, the composition of three different IPC was estimated by performing a step elution mode Analytical Temperature Rising Elution Fractionation (TREF) separation. The recovered fractions were analyzed by Differential Scanning Calorimetry (DSC), Size Exclusion Chromatography (SEC) and Fourier Transform Infrared Spectroscopy (FTIR). The morphology was examined by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Amorphous EPC were isolated in an independent way in order to perform a more careful characterization. The distinct particle size and shape of the dispersed phase for different IPC was interpreted in terms of the molecular characteristics of the blend components and their compositions.
Recycling of poly(ethylene terephthalate) into closed‐cell foams
Authors: Japon Sonia , Leterrier Yves , Månson Jan‐Anders E.
Published: April 2004

The increase of the elongational viscosity of recycled poly(ethylene terephthalate) (PET) is investigated with the aim of producing closed‐cell foams by means of a cost‐effective reactive extrusion technique. A recycled PET grade containing controlled contamination levels of polyvinyl chloride (PVC) and poylethylene (PE) is selected, and compared with virgin bottle‐grade PET as a reference. Reactive processing with a tetrafunctional epoxy additive induces randomly branched molecules with a lower degree of branching in recycled PET than in virgin PET, as shown by a molecular structure analysis. The corresponding increase in elongational viscosity is related to foaming experiments performed using supercritical CO2 in a pressurized vessel. Observations of foam microstructures reveal that modified virgin PET forms closed‐cell structures under a large variety of foaming conditions, as opposed to unmodified virgin and recycled PET, which collapse as a result of insufficient elongational resistance. Closed‐cell foams are also obtained using modified recycled PET, providing that the temperature at which the pressure is released is lowered to 260°. Recycling of PET into closed‐cell foams is thus achieved, although the processing window is slightly reduced compared to virgin PET.
Fracture behavior of styrene‐ethylene‐propylene rubber‐toughened polypropylene
Authors: Wei G.‐X. , Sue H.‐J.
Published: April 2004

The morphology and fracture behavior of isotactic polypropylene toughened by styrene‐ethylene‐propylene (PP/SEP) were investigated. The SEP rubber, having an average particle size of 0.2 µm, is found to be well dispersed in the PP matrix. The fracture toughness of SEP‐modified PP is greatly improved. The toughening mechanism investigation shows that a widespread crazing zone is generated in the crack tip damage zone. An intense narrow damage band in the center of crazed zone is formed. Crazing and shear yielding are found to be the dominant toughening mechanisms in PP/SEP. The crazes are initiated only by large SEP particles in the blend. The small SEP particles (< 0.3 µm) can neither cavitate nor trigger crazing. As a result, large scale shear deformation is suppressed in this blend. These findings are consistent with the notion that the crack tip plane strain constraint has to be relieved in magnitude in order for the deviatoric stress to reach a critical value for widespread shear banding.
Isothermal and nonisothermal crystallization kinetics of nylon 10 12
Authors: Li Yongjin , Zhu Xinyuan , Yan Deyue
Published: April 2004

This article studied the crystallization behaviors of a newly industrialized polyamide, Nylon 10 12, under isothermal and nonisothermal conditions from the melt. A differential scanning calorimeter (DSC) was used to monitor the energetics of the crystallization process. During isothermal crystallization, relative crystallinity develops in accordance with the time dependence described by the Avrami equation with the exponent n=2.0. For nonisothermal studies, several different analysis methods were used to describe the crystallization process. The experimental results show that the Ozawa approach cannot adequately describe the nonisothermal crystallization kinetics. However, Avrami treatment for nonisothermal crystallization is able to describe the system very well. The calculated activation energy is 264.4 KJ/mol for isothermal crystallization by Arrhenius form and 235.5 KJ/mol for nonisothermal crystallization by Kissinger method.
Polymer‐polymer miscibility study for plastic gradient index optical fiber
Authors: Lee Bongsoo , Choi Won Y. , Walker James K.
Published: April 2004

Gradient index (GRIN) materials have many applications in optical fiber communication, imaging and optical instruments. Almost all GRIN optical fiber or lenses are made of glass, which has limitations due to poor flexibility, difficulty in processing and high price. Therefore, polymers are being investigated to produce a GRIN material that solves the problems of GRIN glass. In this study, the optical transmittance and refractive indices of three kinds of miscible copolymers of Methyl Methacrylate/Benzyl Methacrylate, Methyl Methacrylate/Trifluoro‐ethyl Methacrylate and Benzyl Methacrylate/Trifluoro‐ethyl Methacrylate were examined.
Melting mechanism of a starved‐fed single‐screw extruder for calcium carbonate filled polyethylene
Authors: Thompson M. R. , Donoian G. , Christiano J. P.
Published: April 2004

A study of starved‐fed single screw extrusion was initiated to understand the relation between its distinctive melting mechanism and the improved mixing capabilities attained during compounding of a calcium carbonate filler into HDPE. Experiments were carried out in a 63.5 mm single screw extruder, examining the effect of degree of starvation on a conventional and barrier feed screw. Interest was focused on the mixing/melting mechanism of starved‐fed solids‐conveying as it affects the size and number of filler agglomerates observed in the extrudate. The melting performance of both feed screws was examined using pressure and temperature measurements down the screw length as well as direct inspection of the polymer in the screw channel via rapid screw cooling. Both screws showed improved mixing quality with increased starvation.
The weldability of polypropylene strapping tape
Authors: Oliveira M. J. , Hemsley D. A.
Published: April 2004

Polypropylene strapping tape, produced with different draw ratios and types of surface embossing, was welded with a standard semi‐automatic strapping machine. The effect of the welding temperature, surface profile of the sealing tool and the tape properties (draw ratio and embossing pattern) on the microstructure and the joint strength was studied. A near optimal temperature range was identified. The draw ratio of the tape was found to influence the weld efficiency.
Chemical and physical blowing agents in structural polyurethane foams: Simulation and characterization
Authors: Modesti M. , Adriani V. , Simioni F.
Published: April 2004

Physical blowing agents such as n‐pentane and methyl formate and, for comparison, chemical blowing agents such as water were used to prepare structural polyurethane rigid foams of different densities by reaction injection molding. Experimental runs were carried out with formulations based on oligomeric isocyanate and a mixture of polyether polyols. The constitutive equations for the vaporization rate of the two blowing agents and the polymerization kinetics data are reported. Experimental results were compared with the prediction of a simplified theoretical model, and they showed a satisfactory agreement in terms of temperatures and density profile. All the specimens were characterized by physical‐mechanical properties such as hardness, impact strength, flexural strength and elastic modulus and the results were reported in function of the densities. The best mechanical performance were obtained with the physical blowing agents, due to a better density distribution profile and a thicker skin layer.
The crystallization kinetics of polyamide 66 in non‐isothermal and isothermal conditions: Effect of nucleating agent and pressure
Authors: Won J. C. , Fulchiron R. , Douillard A. , Chabert B. , Varlet J. , Chomier D.
Published: April 2004

The crystallization kinetics of virgin and nucleated polyamide 66 was investigated in non‐isothermal and isothermal conditions, by use of DSC and high pressure dilatometry. In non‐isothermal conditions, at atmospheric pressure, the results were first analyzed using the Ozawa equation, leading to an Avrami exponent of 4 in the case of the virgin grade and 2.1 for the nucleated polyamide. However, experimental and calculated kinetics showed a difference in the ending part of the crystallization, likely due to a large secondary crystallization phenomenon. Thus, the relative crystallinities were normalized to extract the primary crystallization from the whole signal and analyzed using the Douillard/Kim equation. In isothermal conditions, at atmospheric pressure, the Avrami exponents were similar to the values obtained in non‐isothermal conditions for both virgin and nucleated grades. Furthermore, the crystallization under pressure was examined in terms of crystallization supercooling. In non‐isothermal conditions, the crystallization supercooling (ΔTc) increases when the cooling rate increases, but it is not affected by the pressure since the crystallization temperature increase is due to the equilibrium melting temperature rise. In isothermal conditions, the supercooling (ΔT) rises according to the increase of the pressure for the same crystallization temperature.
Thermoplastic apparent interpenetrating polymer networks of polyurethane and styrene/acrylic acid copolymer obtained by melt mixing. Structure‐property relationships
Authors: Vatalis A. S. , Delides C. G. , Grigoryeva O. P. , Sergeeva L. M. , Brovko A. A. , Zimich O. N. , Shtompel V. I. , Georgoussis G. , Pissis P.
Published: April 2004

Thermoplastic apparent interpenetrating polymer networks (thermoplastic‐AIPNs) were prepared at several compositions by melting and pressing of crystallizable polyurethane (CPU), based on butylene adipate glycol (BAG), and styrene/acrylic acid random copolymer (S/AA). Structure‐property relationships in the thermoplastic‐AIPNs were investigated by means of wide‐angle and small‐angle X‐ray scattering (WAXS, SAXS), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), thermally stimulated depolarization currents (TSDC) techniques, dielectric relaxation spectroscopy (DRS) and several physico‐mechanical characterization techniques. The results obtained by the various techniques were critically compared to each other. They suggest that the two components show weak affinity to each other and that the thermoplastic‐AIPNs can be classified into two groups with high and low contents of CPU, showing essentially the behavior of CPU and S/AA, respectively. However, deviations from additivity and significant changes for several properties on addition of small amounts of either of the components suggest partial miscibility. Most of the results are explained by physical interactions of COOH‐groups of AA in S/AA with the ester groups of the flexible CPU blocks, which promote microphase separation in both the CPU and the S/AA components.
The production of a new partially biodegradable starch plastic by reactive extrusion
Authors: De Graaf R. A. , Janssen L. P. B. M.
Published: April 2004

The grafting of polystyrene onto dissolved starch in a twin screw extruder has been studied. This copolymerization was initiated using the thermal initiators benzoyl peroxide and K2S2O8. As end product a mixture containing polystyrene‐grafted starch, homopolymer of polystyrene and starch was obtained. Parameters like screw rotation rate, fully filled length of the extruder, wall temperature and throughput have been varied in order to obtain information about their influence on conversion, graft percentages and molecular weight of the materials formed. To increase the amount of graft points, maleic acid anhydride (MAH) was added resulting in an increased grafting of polystyrene onto starch. Graft percentages of 60% could be achieved. The total conversion of styrene could be controlled by adjusting extruder parameters like barrel temperature, fully filled length and initiator type. Conversions of 95% were found. Molecular weights of the polystyrene formed could be controlled by adding a chain transfer agent (dodecylmercaptan) to the styrene phase. In this way the molecular weight (Mn) of the styrenic part could be varied from 20,000 to 140,000. The experiments with the chain transfer agent showed that the grafting of polystyrene onto starch is a process occurring at the interface between the dissolved starch and the styrene phase.
Percolation phenomena in carbon black–filled polymeric concrete
Authors: Rejón L. , Rosas‐Zavala A. , Porcayo‐Calderon J. , Castaño V. M.
Published: April 2004

Percolation in carbon black‐filled polymeric concrete, is discussed based on the measured changes in electrical conductivity and morphology of the composite at different concentrations of carbon black. The percolation threshold ranged between 6 and 7 wt% (based on resin weight) of carbon black. Above this concentration, the filler particles formed agglomerates in contact with each other, suggesting that the conduction process is nearly ohmic in nature. A power law predicted by percolation theory described the behavior of the conductivity as a function of carbon black content. Microscopic analysis showed the presence of a continuous structure formed by the polyester resin and carbon black, in which silica particles were embedded.
Comparative study of continuous‐power and pulsed‐power microwave curing of epoxy resins
Authors: Fu Bao , Hawley Martin C.
Published: April 2004

Three epoxy reaction systems, diglycidyl ether of bisphenol A (DGEBA) with curing agents meta phenylene diamine (mPDA), diaminodiphenyl methane (DDM), and diaminodiphenyl sulfone (DDS), were cured with both pulsed‐power and continuous‐power microwave curing systems. Isothermal curing was conducted at three different temperatures for each reaction system with both pulsed‐power and continuous‐power microwave curing systems. Extent of cure was measured with Fourier Transform Infrared Spectroscopy (FTIR). The temperature characteristics, incident and reflected power patterns, and the reaction rates were compared between the two curing approaches. The incident power and reflected power of both curing processes were observed to reveal reaction status. Continuous‐power microwave curing produced noticeably higher reaction rates than pulsed‐power microwave curing.
The vibration welding of polycarbonate/acrylonitrile‐butadiene‐styrene blends to themselves and to other resins and blends
Authors: Stokes Vijay K.
Published: April 2004

The weldabilities of two commercial blends of polycarbonate (PC) and acrylonitrile‐butadiene‐styrene (ABS) to themselves and to several other resins and blends are assessed through 120 Hz vibration welds of 6.35‐ and 3.2‐mm‐thick specimens. While the thicker specimens of both blends have relative weld strengths of 83%, the thinner specimens in one of the grades have a lower relative weld strength of 73%. Welds of thicker specimens of both grades to PC have relative strengths of 85%. Again, welds of thinner specimens of one of the grades to PC have a lower relative strengths of 68%. Welds of the thinner specimens of this grade with ABS have relative strengths of 85%. Welds of this material with poly(butylene terephthalate) (PBT), a PC/PBT blend, modified poly(phenylene oxide), and a poly(phenylene oxide)/polyamide blend, have relative weld strengths of 45%, 26%, 76%, and 20%, respectively.
Physical properties of isobutylene based block copolymers
Authors: Tse M. F. , Wang H.‐C. , Shaffer T. D. , McElrath K. O. , Modi M. A. , Krishnamoorti R.
Published: April 2004

Physical, mechanical and thermal properties of a new class of isobutylene based model block copolymers are studied and contrasted with those of traditional thermoplastic elastomers based on polydienes and saturated polydienes (polyolefins) such as Kraton (or Vector) and Kraton G block copolymers. Melt state rheological and dynamic mechanical measurements confirm that thermodynamic interactions between polystyrene (S) and polyisobutylene (iB) or poly‐p‐tert‐butylstyrene (tbS) and iB are comparable to, if not larger than, those between S and polybutadiene (B) or S and ethylene/butene‐1 copolymer (EB). Physical properties for the S‐iB‐S and tbS‐iB‐tbS block copolymers, particularly the injection‐moldability and cut‐growth characteristics, are found to be considerably different from those found for the S‐B‐S and S‐EB‐S systems. We attribute this behavior to the longer entanglement chain length of iB compared with those for B and EB.
Elastomeric joint performance of PVC, VC, and FRC Pipes
Authors: Lu J. P. , Burn L. S. , Whittle A. J.
Published: April 2004

For rubber ring joints to resist plant root penetration in drier countries, it has been reported and promulgated into some national standards that a sufficiently high contact pressure between the rubber and the pipe must be maintained. The evaluation of the appropriate interfacial pressure to be used has been under discussion for some time and different values have been stated in different standards. This matter has been the subject of considerable controversy, and decisions on the interface pressure used will affect the performance and ease of insertion of a rubber ring joint. This paper reports and discusses previous and current research on root penetration past elastomeric joints, the existing test requirements of elastomeric pipe joints for resisting root penetration given in standards, and the inconsistencies in performance requirements across the different pipe material types. The initial interface sealing pressures for commonly used PVC. VC and FRC joints were assessed and these are discussed in light of the accelerated root intrusion tests performed in Black Hill Flora Centre in Adelaide, South Australia.
Three‐dimensional simulation of thermoforming process and its comparison with experiments
Authors: Nam Gi Joon , Lee Jae Wook , Ahn Kyung Hyun
Published: April 2004

Three‐dimensional solid element analysis and the membrane approximated analysis employing the hyperelastic material model have been developed for the simulation of the thermoforming process. For the free inflation test of a rectangular sheet, these two analyses showed the same behavior when the sheet thickness was thin, and they deviated more and more as the sheet thickness increased. In this research, we made a guideline for the accuracy range of sheet thickness for the membrane analysis to be applied. The simulations were performed for both vacuum forming and the plug‐assisted forming process. To compare the simulation results with experiments, laboratory scale thermoforming experiments were performed with acrylonitrile‐butadiene‐styrene (ABS). The material parameters of the hyperelastic model were obtained by uni‐directional hot tensile tests, and the thickness distributions obtained from experiments corresponded well with the numerical results. Non‐isothermal analysis that took into account the sheet, temperature distribution measured directly from the experiments was also performed. It was found that the non‐isothermal analysis greatly improved the predictability of the numerical simulation, and it is important to take into account the sheet temperature distribution for a more reliable simulation of the thermoforming process.
Morphological and mechanical properties of polypropylene [PP]/poly(ethylene vinyl acetate) [EVA] blends. I. Homopolymer PP/EVA systems
Authors: Ramírez‐Vargas E. , Navarro‐Rodríguez D. , Huerta‐Martínez B. M. , Medellín‐rodríguez F. J. , Lin J. S.
Published: April 2004

Morphological and mechanical properties of polypropylene [PP]/poly(ethylene vinyl acetate) [EVA] blends have been studied. Infrared results using thin films first indicated a transition toward compatibility between both components at concentrations above 40% EVA. The transition was verified with different experimental techniques and it was associated to morphological changes and mechanical properties. The PP/EVA blends were mechanically evaluated in terms of impact and tensile strength to determine the influence of blending on the performance properties of these materials. Agreement was found between the transition and the enhancement of both elongation at break and impact strength.
Novel strategies for novolak resin fractionation: Consequences for advanced photoresist applications
Authors: Narasimhan Balaji , Wanat Stanley F. , Rahman M. Dalil
Published: April 2004

The importance of well‐characterized novolak resins in the manufacture of high performance photoresists is paramount. Two novel fractionation methods for novolaks synthesized by solution condensation are reported in this paper. Solid resin solutions in methanol and ethyl lactate were fractionated by ultracentrifugation and liquid‐liquid centrifugation (using water and hexane as non‐solvents). The techniques resulted in high yield, low‐polydispersity (high Mw) resins that exhibited superior dissolution rates and lithographic performance when compared to resins obtained by conventional isolation techniques. The effects of solvent/non‐solvent ratio, temperature, and centrifuge rpm on resist performance were evaluated. It was found that at sufficiently high rpm and at 25°C, the Mw and the polydispersity of the fractionated resin increases and the dissolution rate decreases as the solvent/non‐solvent ratio decreases, Slow dissolution rates and improved lithographic performance characteristics in experimental i‐line formulations were obtained for resin solutions fractionated by liquid‐liquid centrifugation using a 1/2 ratio of ethyl lactate (and/or methanol) to hexane. Scaling laws between dissolution rate and polymer molecular weight were derived and the data seem to support reptation‐type diffusion. The use of appropriate process manipulation in order to precisely control resin properties and to design novel resins is discussed.
A laboratory spiral disk extruder for flow visualization
Authors: Maffettone Pier Luca , Grizzuti Nino
Published: April 2004

A laboratory spiral‐disk extruder for the study of gas entrainment phenomena is presented. The rotating plate is transparent, thus allowing for the direct observation of the steady liquid‐gas interface when operating under starve‐fed conditions. The extruder flow is modeled with the conventional single screw extruder approach. This leads to a simple working equation for the spiral screw, which is formally identical to the classical screw equation for standard extruders. The model is validated by comparing the predictions with experimental data taken in both closed and open die configurations.
Carbon black filled PET/PMMA blends: Electrical and morphological studies
Authors: Mallette J. G. , Márquez A. , Manero O. , Castro‐Rodríguez R.
Published: April 2004

In this work, the electrical and morphological properties of blends of poly(ethylene terephthalate) (PET), poly(methyl methacrylate) (PMMA), and carbon black (CB) were analyzed. Resistivity decreases similarly in both PET and PMMA with CB concentration. Similarly in the PET/PMMA blend, extensive modification to this behavior occurs, since resistivity becomes a function of morphology and specific location of CB in the polymers. A minimum in the resistivity of the blend with 5% CB (PET basis) is observed at 100% PET, whereas with an increase in the CB content to 20%, the minimum in the resistivity shifts to 60% PET. High conductivity is observed when PET is the continuous phase (having the larger viscosity). Large stresses lead to a large dispersion of CB and a high deformation and rupture of the dispersed PMMA phase. This situation itself promotes an increase of surface area of droplets and high CB concentrations at the interface. Consideration is given to models that predict a selective location of conductive particles in the PET matrix based on its lower interfacial tension with CB.
Long chain branching and polydispersity effects on the rheological properties of polyethylenes
Authors: Hatzikiriakos Savvas G.
Published: April 2004

The rheological behavior of linear, and branched polyethylenes is studied as a function of the weight average molecular weight (Mw) and its distribution (MWD) as well as the level of long chain branching in an attempt to identify correlations between long chain branching, polydispersity and rheological properties. It is found that a need for vertical shift of the viscoelastic moduli data to obtain the master curves using the time‐temperature superposition principle is associated with the existence of long chain branching in the structure of the polymer. The degree of vertical shift is found to correlate with the level of long chain branching. This correlation corroborates with the observation that long chain branching correlates with the horizontal flow energy of activation. Plots of atan(G″/G′) vs. G* (known as Van Gurp plots) also reveal some important features that can be used as signs of specific features in the structure of polymers. More specifically, the area included below the Van Gurp curves correlates with the level of long chain branching and polydispersity index. The correlations are presented in graphical form and they can be used to associate rheological properties with the presence of long chain branching and/or polydispersity.
Preparation and characterization of biaxially oriented films from polybutylene terephthalate based thermoplastic elastomer block copolymers
Authors: Li Hang , White James L.
Published: April 2004

Film casting and biaxial stretching of a series of polyester thermoplastic elastomers (TPEs) were studied. Biaxial orientation in the stretched films was characterized by wide‐angle X‐ray diffraction and birefringence measurements. Biaxial orientation factors were determined. The X‐ray diffraction and birefringence clearly indicated the development of planar biaxial orientation in the stretched films with biaxial stretching. The phenyl groups in the stretched PBT and TPE films gradually became more parallel to the film surfaces with increasing biaxial orientation. The lower the PBT content in the stretched TPE films, the lower the planar biaxial orientation achieved. The β form of crystalline PBT was found only in the stretched PBT films, but not in the TPE films.
Influence of residual stress on the relationship between pipe pressure and C‐ring tests
Authors: Whittle A. J. , Burford R. P. , Hoffman M. J.
Published: April 2004

The effects of residual stress in modified poly(vinyl chloride) pipes upon the relationship between pressure tests and C‐ring tests have been studied. A series of pressure tests were carried out at different hoop stresses using both fixed‐end and free‐end enclosures. The C‐ring test was used to determine the yield strength of the material as a function of time. The difference in behavior between the fixed end and free end configurations was less than predicted by the von Mises analysis assuming the only stresses in the pipe wall were generated by the applied internal pressure. Both configurations produced lower results than predicted on the basis of the C‐ring tests. The residual stresses in the hoop and longitudinal directions were measured. Taking into account the residual and applied stresses, the von Mises criterion for yield was used to calculate the uniaxial yield stress of the material for both end enclosure configurations. The results were similar to the yield stress measured in uniaxial tension. The von Mises criterion for yield has been shown to provide an acceptable method of analysis of pressure tests with fixed and free end enclosures and the C‐ring, when residual stress is taken into account.
Yield modeling of an aliphatic polyketone terpolymer in multiaxial stress states
Authors: Kartunen Nicole R. , Lesser Alan J.
Published: April 2004

A continuum yield model for pressure dependent anisotropic materials that accounts for the stress state has been combined with a thermally activated model to account for the temperature and rate dependence of yield stress. The resulting model has been applied to describe the yield behavior of a semicrystalline aliphatic polyketone terpolymer. Utilizing biaxial data from this thermoplastic, best‐fit values for loading along principal directions were determined. With these principal values, predictions for the yield strength under biaxial loading conditions were made. These predictions have been compared to experimental data obtained from the material at four different temperatures and three different strain rates. The experimental and theoretical results appear to compare quite well with each other.
Degradation of poly(methyl methacrylate) (PMMA) with aluminum nitride and alumina
Authors: Lee Yi‐Mu , Viswanath Dabir S.
Published: April 2004

This paper deals with the thermal and thermal‐oxidative degradation of pure poly(methyl methacrylate) (PMMA), PMMA/A1N and PMMA/Al2O3 composites. Kinetic parameters were determined from the weight loss data using non‐isothermal Thermogravimetric Analysis (TGA). The amount and morphology of the carbon residue in the burnt samples under N2 and air atmospheres were also investigated using a Leco combustion analyzer. This study also showed that the normally accepted three‐stage polymer thermal degradation, and hence three regions of Arrhenius linearity, can be treated with one value of activation energy. This is a basic departure from the normally accepted three different regions and applying the same diffusion equation (such as Jander diffusion) separately to each region. In nitrogen atmosphere, the activation energy of pure PMMA was 129.4 kJ/mol; however, the activation energies of 14% PMMA/AlN and PMMA/Al2O3 were found to be 119.5 and 118.2 kJ/mol, respectively.
Polymer blend de‐mixing and morphology development of immiscible polymer blends during tube flow
Authors: Karami Askar , Balke Stephen T.
Published: April 2004

This work is an investigation of morphology and de‐mixing of polymer blends during melt flow through a tube. Morphology is the relative size, shape and location of each distinguishable phase present in a polymer blend. De‐mixing is the shear‐induced migration of different types of polymers away from each other during the flow. The ability to tailor de‐mixing during extrusion can potentially result in a new family of plastics waste recycling processes with mixed waste entering an extruder and separate streams of different polymer types leaving it. Also, control of morphology development can lead to the formation of layered structures without the need for two or more extruders and co‐extrusion. This work is directed at elucidating morphology development and de‐mixing of polymer blends in the most simple process design: melt flow through a tube. Shear‐induced migration was quantitatively shown in various polyethylene‐polypropylene, polypropylene‐nylon 6 and polyethylene‐nylon 6 blends. The migration observed was in accord with the hypothesis that the system tends to minimize its rate of energy dissipation for a fixed flow rate. The ratio of the viscosity of the dispersed phased to that of the continuous phase greatly influenced the morphology of polypropylene‐nylon 6 and polyethylenenylon 6 blends: a droplet‐dispersed phase structure occurred at a high viscosity ratio, whereas a multi‐layer structure resulted at viscosity ratios near unity. Shear‐induced deformation and coalescence contributed to formation of the multi‐layer structure.
The effects of PC‐PMMA block copolymer on the compatibility and interfacial properties of PC/SAN blends
Authors: Kang E. A. , Kim J. H. , Kim C. K. , Oh S. Y. , Rhee H. W.
Published: April 2004

Block copolymers of polycarbonate (PC) and polymethylmethacrylate (PMMA), PCb‐PMMA, were examined as compatibilizers for blends of PC with styrene‐co‐acrylonitrile (SAN) copolymer. PC‐b‐PMMA was added to blends of PC with SAN containing various amounts of AN. The average diameter of the dispersed particles was measured with an image analyzer, and the interfacial properties of the blends were analyzed with an imbedded fiber retraction (IFR) test and an asymmetric double cantilever beam fracture test. The average particle size and interfacial tension of the PC/SAN blends reached a minimum value when the SAN copolymer contained about 24 wt% AN. A maximum in the adhesion energy was also observed at the same AN content. Interfacial tension and particle size were further reduced by adding PC‐b‐PMMA to the PC/SAN blends. Fracture toughness of the blends was also improved by enhancing the interfacial adhesion by the addition of PC‐b‐PMMA. The addition of PC‐b‐PMMA copolymer was more effective at improving the interfacial properties of PC/SAN blends than was varying the AN content of the SAN copolymers. The interfacial properties of the PC/SAN blends were optimized by adding a block copolymer and using an SAN copolymer that had minimum interaction energy with PC.
Non‐isothermal crystallization and multiple melting behavior of syndiotactic polystyrene—pre‐melting temperature effects
Authors: Chiu Fang‐Chyou , Peng Chi‐Gong , Fu Qiang
Published: April 2004

This work investigated how pre‐melting temperature (Tmax) and cooling rate (C) affected the non‐isothermal melt crystallization, melting behavior and crystal structure of syndiotactic polystyrene (sPS) by using differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD) techniques. Experimental results indicated that raising Tmax or C decreased the crystallization peak temperature (Tp) and crystallization initiating temperature (Ti). The crystallization kinetics was analyzed through the Ozawa equation. Although the Ozawa exponent n and cooling function K(T) were determined for Tmax = 340°C and Tmax = 315°C specimens, for Tmax = 290°C specimens, the Ozawa equation was not applicable. Activation energies for the non‐isothermal crystallization processes of different Tmax specimens were estimated to be approximately 418 kJ/mol. As Tmax was raised the nucleation rate of sPS became slower. The multiple melting peaks were associated with different polymorphs as well as recrystallized crystals that formed during heating scans. The percentage content of α polymorph formed in the crystals under various crystallization conditions was estimated through WAXD experiments.
Creep modeling of ABS pipes at variable temperature
Authors: Lu J. P. , Burn L. S. , Tiganis B. E.
Published: April 2004

One of the characteristic behaviors of plastic (or viscoelastic) materials is the creep phenomenon, which is defined as the continuing deformation under a constant load with time. Although research on creep of plastic pipes has been widely carried out in other plastics, little work has been reported for creep in ABS (acrylonitrile‐butadiene‐styrene) pipes at high temperatures. In this paper, the generalized Kelvin series of formulae, which consists of six Kelvin elements, a power model, as well as logarithmic regressions, are applied to the experimental data measured from creep tests under constant bending stresses at different temperatures for two ABS resins. The least‐squares method was used to adjust the Kelvin model parameters, and a Levenberg‐Marquardt non‐linear least‐squares regression procedure was used to determine the creep parameters in the power model. This led to empirical formulae for creep compliance defined as the reciprocal of the creep modulus. This creep modulus can provide a means to evaluate the long‐term structural properties for different resins used in pipe production.
Evaluation of three methods for the measurement of crystallinity of pet resins, preforms, and bottles
Authors: Bashir Z. , Al‐Aloush I. , Al‐Raqibah I. , Ibrahim M.
Published: April 2004

The control of crystallization is important at all processing stages of the PET bottle industry, from the manufacture of bottle resins to the fabrication of preforms and bottles. In this work, we sought to evaluate critically three methods of crystallinity measurement. We have used density, Differential Scanning Calorimetry (DSC), and Modulated Differential Scanning Calorimetry (MDSC) to study the crystallinity of PET chips, preforms, and bottles. The accuracy, precision, and general validity of each technique and the problems of interpretation are discussed.
A simulation of the non‐isothermal resin transfer molding process
Authors: Antonucci Vincenza , Giordano Michele , Nicolais Luigi , Di Vita Gandolfo
Published: April 2004

A simulation of the non‐isothermal resin transfer molding manufacturing process accounting for both the filling and the consolidation stage has been developed. The flow of an exothermally reactive resin through a porous medium has been analyzed with reference to the Darcy law, allowing for the chemorheological properties of the reacting resin. Thermal profile calculations have been extended to a three phase domain, namely the mold, the dry preform and the filled preform. The mold has been included in order to evaluate the thermal inertial effects. The energy balance equation includes the reaction term together with the conductive and convective terms, and particular attention has been devoted to setting the thermal boundary condition at the flow front surface. The moving boundary condition has been derived by a jump equation. The simulation performance has been tested by comparing the predicted temperature profiles with experimental data from literature. Further numerical analysis assessed the relevance of using the jump equation at the flow front position for both filling time and thermal profile determination.
Processing behavior of polycarbonate/functionalized‐ethylene copolymer blends
Authors: Dias Marcos L. , Fernandes Maria Josumitra A.
Published: April 2004

The melt blending of polycarbonate (PC) and ethylene‐methacrylic acid copolymers (EFC) either in the acid form (EFC‐H) or partially neutralized with sodium (EFC‐Na) or zinc (EFC‐Zn) was investigated. Torque monitoring of the blending showed that the polymers are capable of reacting generating new chemical species that increase the melt viscosity. As general behavior, the torque curves pass by a maximum that takes place before 30 min, the final torque being higher than that of the individual polymers. SEC analyses reveal that PC degradation also occurs and is stronger in the case of blends with EFC‐Na that acts to catalyze PC degradation, promoting CO2 formation. FTIR studies on chloroform insoluble fractions of the PC/EFC‐Zn blends showed that in addition to a very small number of carbonate groups, feature absorption bands of aromatic ester and hydroxyl groups appear in the new chemical species formed during the reactive processing.
Thermo‐chemical response of vinyl‐ester resin
Authors: Stone M. A. , Fink B. K. , Bogetti T. A. , Gillespie J. W.
Published: April 2004

This paper presents the thermo‐chemical characterization of Dow Derakane 411‐C50 commercial vinyl‐ester resin at low temperatures (20°C to 40°C). Differential Scanning Calorimetry (DSC) and Torsional Braid Analysis (TBA) are the experimental techniques used to characterize the material behavior. The cure kinetics are studied using DSC and are modeled using a modified autocatalytic equation with a maximum degree‐of‐cure term. Also, the effect of inhibitors in the resin system is accounted for by an inhibitor depletion model. The glass transition temperature (Tg) is also characterized using TBA and related to the degree of cure. It was found that the Tg and the degree of cure do not exhibit a linear relationship for this resin system. The findings presented in this work provide information for accurate cure modeling and process simulation of vinyl‐ester materials.
Analysis of the isothermal mechanical response of a shape memory polymer rheological model
Authors: Bhattacharyya A. , Tobushi H.
Published: April 2004

In this paper, we derive the isothermal mechanical response of a 4‐element rheological model for shape memory polymers (SMP) in the context of (i) constant stress, (ii) constant strain, (iii) constant stress rate, (iv) constant strain rate, (v) periodic strain. The effect of shape memory strain (modeled by a friction element) and the temperature dependence of the material properties on the SMP response are examined for a polyurethane shape memory polymer of the polyester polypole series. In particular, it is possible to identify a threshold frequency during periodic loading, near which the damping capacity of the SMP is strongly affected by an increasing shape memory strain. On the other hand, when the applied frequency is much greater than the threshold value, an increasing shape memory strain ceases to have any effect on the damping. It is also shown that at a given frequency (significantly greater than the threshold value), the damping capacity as a function of temperature attains a maximum. While this maximum value is frequency‐dependent (being inversely proportional), the temperature at which the maximum is attained is frequency‐independent, and is analytically shown to be the glass transition temperature.