Papers by Costas Tzoganakis
International Polymer Processing, Sep 1, 1988
A fully-predictive mathematical model has been developed for the peroxide promoted degradation of... more A fully-predictive mathematical model has been developed for the peroxide promoted degradation of polypropylene in a plasticating single-screw extruder. The model is based on a free radical kinetic mechanism for the degradation reaction and on conventional plasticating extrusion theory. Solids conveying, melting, melt pumping and reaction phenomena have been combined and the interactions between flow pattern, mass and heat transfer fields via residence time distribution and the chemorheology of the reactive melt have been considered. Given the geometrical configuration of the screw, the operating conditions and the physical properties of the starting polymer, the model can predict: flow rate, pressure, temperature and molecular weight profiles in the extruder channel and in the die, and the residence time distribution in the system. Finally, model predictions are compared with experimental data from runs on a 38mm, 24:1 L/D single-screw extruder using various peroxide concentrations and rotational screw speeds.
Advances in Polymer Technology, 1989
An experimental study of the free-radical-induced crosslinking of linear-lowdensity polyethylene ... more An experimental study of the free-radical-induced crosslinking of linear-lowdensity polyethylene (LLDPE) in the melt phase has been carried out. Experiments have been p e~o r m e d both in a single-screw plusticating extruder and in an extrusion plastometer using a peroxide as the free-radical source. Concentration of the
Journal of Applied Polymer Science, Jan 15, 1989
Measurements of the residence time distribution (RTD) in a single-screw plasticating extruder wer... more Measurements of the residence time distribution (RTD) in a single-screw plasticating extruder were carried out during experimental studies of the peroxide-initiated controlled chemical degradation of polypropylene (PP). A radioactive tracer method was employed, and the effect of screw speed, temperature, and reaction on the RTD was examined. An increase of the peroxide concentration resulted in a broader distribution whereas an increase of the extrusion temperature was found to result in a narrower distribution. Use of low screw speeds simply increased the time delay through the extruder without affecting considerably the breadth of distribution. Results obtained from the present experiments were compared with several theoretical models.
Journal of Elastomers & Plastics, 1988
The shear viscosity and extrudate swell of the isotactic and atactic fractions of propylene-ethyl... more The shear viscosity and extrudate swell of the isotactic and atactic fractions of propylene-ethylene copolymers produced with different ethylene content were measured at various temperatures and shear rates, using a capillary rheometer. In the isotactic fractions of these copolymers, the theoretical ethyl ene content was in the range of 4 to 10 wt%. The results indicate that the shear viscosity is not sensitive to composition for the isotactic copolymers. The tem perature dependence of the viscosity seems to be about the same for both the isotactic and atactic fractions of these copolymers. The extensional viscosity of these copolymers was calculated using Cogswell's analysis of converging flows and it seems that the isotactic copolymers with higher ethylene content exhibit slightly higher extensional viscosity. Finally, results from extrudate swell measurements show that the isotactic copolymers exhibit higher swelling than the atactic fractions tested. Extrudate swell measurem...
Journal of Cleaner Production
Chemical Engineering Progress, 1988
Reaction permettant de modifier facilement et economiquement la distribution de la masse molecula... more Reaction permettant de modifier facilement et economiquement la distribution de la masse moleculaire suivant l'utilisation souhaitee
Journal of Applied Polymer Science, 2018
Environmental stress cracking (ESC) is one of the main failure mechanisms involved in polymer fra... more Environmental stress cracking (ESC) is one of the main failure mechanisms involved in polymer fractures. This paper focusses on the environmental stress cracking resistance (ESCR) of polyethylene (PE) in which ESC occurs through a slow crack growth mechanism. In order to predict the ESCR of PE, it is necessary to fully understand the molecular structure of the resin. This paper demonstrates the relationships between molecular structure characteristics and material responses based on experimental characterization and published literature trends. Relationships between ESCR, molecular weight (MW), percentage This is the peer reviewed version of the following article:
International Polymer Processing, 2017
A continuous extrusion devulcanization process has been developed by using supercritical CO2. Exp... more A continuous extrusion devulcanization process has been developed by using supercritical CO2. Experiments have been carried out on an industrial scale twin screw extruder to study the effects of processing conditions on the properties of devulcanized rubber. Using a fractional factorial design in three levels, the effects of process temperature, screw speed, and feed rate on the sol fraction, degree of devulcanization, Mooney viscosity, and tensile properties of devulcanized rubber have been investigated. The significance of the effects of the processing conditions decreases in the following order: flow rate, screw speed, and process temperature. Similar trends are noted for different responses with the exception of tensile properties. The observed relationship between the sol fraction and the degree of crosslinking in the rubber samples before and after devulcanization points to a highly selective disruption of the sulfur crosslinks in the rubber network during devulcanization rath...
Rheological and structural modification of polyethylene (PE) has been an area of great interest. ... more Rheological and structural modification of polyethylene (PE) has been an area of great interest. Most of the research done in this area has been focused on modifying the rheology and consequently the structure of the PE either by creating selective crosslinking or chain scission. These modifications are achieved through numerous chemical reactions (mainly peroxides and silanes) and high energy irradiation techniques including electron beams and gamma (γ) rays. Although crosslinks are capable of enhancing many structural properties, they do not improve other industrially important aspects such as processability. Long chain branching (LCB), on the other hand, is highly desirable as it can improve both the melt strength and the processability of the polymer. Long chain branches in PE have been created by using constrained geometry catalyst (CGC) systems. These catalysts produce long chain branched polyethylene (LCBPE) with a relatively narrow molecular weight distribution (MWD). Irradi...
Polymer Engineering & Science, 2000
ABSTRACT
Polymer Engineering & Science, 1999
This paper presents a technology to determine the melt viscosity of a =/supercritio-d CO, solutio... more This paper presents a technology to determine the melt viscosity of a =/supercritio-d CO, solution using a linear capillary tube die mounted on a foaming extruder. CO, was injected into the extrusion barrel and the content of CO, was varied in the range of 0 to 4 wt% using a positive displacement pump. Single-phase PS/CO, solutions were formed using a microcellular extrusion system and phase separation was prevented by maintaining a high pressure in the capillary tube die. By measuring the pressure drop through the die, the viscosity of PS/CO, solutions was determined. The experimental results indicate that the PS/CO, solution viscosity is a sensitive function of shear rate, temperature, pressure, and CO, content. A theoretical model based on the generalized Cross-Carreau model was proposed to describe the shear-thinning behavior of PS/CO, solutions at various shear rates. The zeroshear viscosity was modeled using a generalized Arrhenius equation to accommodate the effects of temperature, pressure, and CO, content. Finally, the solubility of CO, has been estimated by monitoring the pressure drop and the absolute pressure in the capillary die.
Polymer Engineering and Science, 2004
ABSTRACT Polypropylene (PP) was modified through a peroxide-induced degradation and a catalytic h... more ABSTRACT Polypropylene (PP) was modified through a peroxide-induced degradation and a catalytic hydrosilylation reaction in the melt phase. The effects of temperature and co-catalysts on the reaction and the surface characteristics of the hydrosilylated polypropylene (SiPP) were studied. Axisymmetric Drop Shape Analysis-Profile (ADSA-P) was used to characterize the surface wettability. The morphology, roughness and heterogeneity of the surface were investigated by the lateral force mode of atomic force microscopy (LFM). Proton nuclear magnetic resonance (1H NMR) spectroscopy was employed to quantify the conversion of terminal double bonds. X-ray photoelectron spectroscopy (XPS) was used to quantify the surface chemical composition. LFM images showed that the surfaces of the PP and DPP samples were rough but heterogeneous and that the surfaces of the SiPP samples appeared rough but homogeneous. The surface wettability was well correlated to the surface microstructure and surface chemical composition. The surfaces investigated were modeled based on the microstructure observed, and a new scheme was developed to calculate surface free energy and adhesion work. Results showed that there is an optimum reaction temperature in terms of the conversion of double bonds, and that increasing the amount of co-catalyst promotes the conversion.
Polymer Engineering & Science, 2001
ABSTRACT
Macromolecular Symposia, 2008
The polymer electrolyte membrane fuel cell (PEMFC) holds tremendous promise for a variety of mobi... more The polymer electrolyte membrane fuel cell (PEMFC) holds tremendous promise for a variety of mobile and stationary power generation applications and is the cornerstone of the anticipated hydrogen economy. One of the major factors limiting fuel cell commercialization is the development of bipolar plates since bipolar plates account for approximately 70% of the PEMFC weight, and 60% of the stack manufacturing and materials cost. The objective of this research is to investigate a feasibility of a conductive composite family to be used as bipolar plates in a PEMFC, in order to get the highly conductive, light weight, and low cost bipolar plates. This work utilized a combination of a polypropylene and low cost conductive filler materials: graphite, conductive carbon black, and carbon fibers. The components were combined in a batch mixer and injection molded into samples for testing with loadings up to 65%wt of fillers. The novel blends were tested for electrical conductivity, hydrophobicity, rheology, and actual plates (16 cm 2) were tested in fuel cell testing trials. The impact of different types of fillers on the composite properties was evaluated, as well as the synergetic effect of mixtures of fill types within a polypropylene matrix. From the results, the highest conductivity, 1900 S/m (in-plane) and 156 S/m (through plane), was obtained with the 65% composite. Moreover, the effects of additives such as coupling agents, and intrinsically conductive polymer (polypyrrole) were observed in this work. The electrical conductivity was influenced by polypyrrole added to the polypropylene composite.
Macromolecular Reaction Engineering, 2013
A reactive extrusion process is developed for the modification of the rheological properties of a... more A reactive extrusion process is developed for the modification of the rheological properties of a high density polyethylene (HDPE) by inducing long chain branching (LCB) using a photoinitiator and ultraviolet (UV) light. A central composite response surface design is selected to design the experimental runs at different photoinitiator concentrations, polymer flow rates, and extruder screw speeds. The selected processing factors at the specified levels produce negligible amounts of gel as indicated by extraction experiments. Linear viscoelastic properties at low frequencies indicate the presence of long chain branches. Both zero shear viscosity and relaxation time of the modified samples are enhanced with the branching. According to further molecular characterization, the molecular weight averages are slightly increased, however, the polydispersity index (PDI) of the modified samples remains the same.
Journal of Applied Polymer Science, 2010
ABSTRACT Thermoplastic vulcanizates (TPVs) were prepared from polypropylene (PP) and reclaimed gr... more ABSTRACT Thermoplastic vulcanizates (TPVs) were prepared from polypropylene (PP) and reclaimed ground tire rubber crumbs. Three types of interfacial strengthening agents—degraded PP, hydrosilylated PP, and hydrosilylated PP grafted onto styrene–butadiene rubber—were prepared in melt via a stepwise series of reactions and employed to generate various degrees of interfacial adhesion in the aforementioned blends. The incorporation of the interfacial agents resulted in improvements in the mechanical properties of these TPVs, and the rubber particle size remained constant. The PP chain length and the functional groups present in the interfacial agents affected the magnitude of the improvement in the mechanical properties. The interfacial agents were primarily present on the surface of the rubber particles in the blends, as shown by energy-dispersive X-ray spectra. These interfacial agents in the PP/rubber crumb blends led to a unique preyield kink in their stress–strain curves, a plateau, or a sharp turning point in the region of approximately 3% elongation and approximately 4-MPa stress. These kinks were interpreted similarly to the cold flow of semicrystalline polymers in tension. The addition of the interfacial modifiers decreased the shear viscosity and increased the entrance pressure drop in flow through capillary dies, and this was attributed to changes in the elongational viscosity of the blends. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
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Papers by Costas Tzoganakis