The objective of this article was to review the use of carbon black (CB) as a conductive filler in polymers and polymer blends. Important properties of CB related to its use in conducting polymers are discussed. The effects of polymer structure, molecular weight, surface tension, and processing conditions on electrical resistivity and physical properties of composites are discussed. Several percolation. models applicable to CB/polymer blends are reviewed. Emphasis is placed on recent trends using polymer blends as the matrix to obtain conducting composites at a lower CB loading. A criterion for the distribution of CB in polymer blends is discussed. (C) 2002 Wiley Periodicals, Inc.
Poly(ethylene terephthalate) (PET) taken from postconsumer soft-drink bottles was subjected to alkaline hydrolysis after cutting it into small pieces (flakes). The reaction took place in an autoclave at 120-200degreesC with aqueous NaOH solutions and at 110-120degreesC with a nonaqueous solution of KOH in methyl Cellosolve. The disodium or dipotassium terephthalate received was treated with sulfuric acid and terephthalic acid (TPA) of high purity was separated. The I H NMR spectrum of the TPA revealed an about 2% admixture of isophthalic acid together with the pure 98% TPA. The purity of the TPA obtained was tested by determining its acidity and by polymerizing it with ethylene glycol by using tetrabutyl titanate as catalyst. A simple theoretical model was developed to describe the hydrolysis rate. The activation energy calculated was 99 kJ/mol. This method is very useful in recycling of PET bottles and other containers because nowadays TPA is replacing dimethyl terephthalate (the traditional monomer) as the main monomer in the industrial production of PET. (C) 2002 Wiley Periodicals, Inc.
The gelatinization and extrusion processes of corn starch were studied. Differential scanning calorimetry was used to determine the gelatinization temperature as a function of the water content. Plasticized corn starch was processed in single- and twin-screw extruders to produce thermoplastic materials. The mechanical properties of the films obtained in the twin-screw extruder with the addition of different quantities of water were evaluated. Dynamic mechanical analysis applied to thermoplastic starch samples obtained with 33% (w/w) total plasticizers showed two transitions, attributed to the presence of two phases in the starch-glycerol-water system. (C) 2002 John Wiley Sons, Inc.
A novel water-diluted hybrid coating, consisting of fluorinated poly(urethane-acrylate) (PUA) and colloidal silica, was prepared by introducing a small amount of fluorinated methacrylate units into the PUA chains. The surface composition and surface morphology of the hybrid film were studied extensively Attenuated total reflectance spectra of infrared analyses showed an enrichment of fluorine-containing polymer and silica particles on the surface. Using X-ray photoelectron spectroscopy with Ar+ etching, it was confirmed that a higher concentration than the calculated value of fluorine element was found on the surface of the fluorinated hybrid film, and the amount of silica increased from the very surface to the near surface. The fluorinated alkyl side chains of the fluorinated polymethacrylate were found to orient toward the surface. It is inferred that the silica particles prevent the migration of fluorine-containing chains for some kind of effect. A comparison of surface topography between the fluorinated PUA film and the fluorinated PUA/SiO2 hybrid film was carried out using atomic force microscopy Finally, the surface property of the hybrid coating was also determined by contact angle measurement. (C) 2002 Wiley Periodicals, Inc.
Hybrids consisting of poly(ethylene oxide-b-amide-6), PEBAX(TM), and zirconium oxide were prepared from hydrolysis and condensation of zirconium tetraisopropoxide in solution containing the dissolved organic polymer. These hybrids were characterized by thermogravimetric analysis, differential scanning calorimetry, infrared spectroscopy, and electron microscopy. Results show that the incorporation of the inorganic phase seems to promote the degradation of the organic polymer. Composite membranes consisting of a porous support of poly(vinylidene fluoride), PVDF, and a filter layer of PEBAX/ZrO2 were prepared and characterized by electron microscopy. Permeation tests of water or aqueous solutions containing poly(ethylene glycol) of different molar masses were carried out to determine the permeation rate and the membrane cutoff respectively. To determine the phosphate retention, permeation tests using a KH2PO4 aqueous solution were carried out. Independent of composition of the filter layer, values of phosphate retention were nearly equivalent to 80%. (C) 2002 John Wiley Sons, Inc.
The screw profile of a twin-screw extruder can be designed to contain kneading and conveying elements inducing different levels of degradation in the polymer melt. In this work, the level of degradation in polypropylene has been measured after multiple extrusions-for various screw profiles-using size exclusion chromatography and IR spectroscopy. The average molecular weight and the polydispersity have been reduced and the carbonyl and unsaturation indexes increase as the number of extrusions and the aggressivity of the screw profile increase. The kneading element with 90degrees caused the greater level of degradation. On the other hand, the addition of left-hand conveying elements reduces the level of degradation because of the extra volume of molten polymer held in the screw, reducing the viability of oxygen inside the barrel. (C) 2002 Wiley Periodicals, Inc.
With the visualization corotating twin-screw extruder, the melting of HDPE pellets under different screw configurations and operational conditions was investigated on-line. It is shown that the melting progression of polymer pellets in corotating twin-screw extruders is different from that in single-screw extruders. Screw configuration, screw speed, and feed rate are three decisive factors in polymer melting. Based on the melting phenomena, a new melting mechanism, island-sea melting model, was defined. It was found that island-sea melting model is an important mechanism to realize high efficiency melting progression. The state of polymer, the degree of fill, and the structure of kneading blocks are factors in determining the energy consumption of kneading blocks in melting zone. The conveying of polymer pellets in kneading blocks, in which pellets were compressed and deformed, consumed much more energy than the conveying of polymer melt. This indicates that the control of the deformation of polymer pellets in corotating twin-screw extrusion is a useful concept in developing new screw elements for high efficiency polymer melting. (C) 2002 Wiley Periodicals, Inc.
A stress-induced crystallization model for semicrystalline plastics is proposed based on the theory that stress-induced orientation of molecules and chains increase the melting temperature of thermoplastics, and hence, the supercooling which is the driving force for crystallization. By assuming that the effect of stress on crystallization is only by increasing the melting temperature, the basic quiescent-state crystallization equation can be directly applied to model stress-induced crystallization kinetics. The model has a minimum of experimentally based constants. A simple experimental technique, such as a rotational rheometer, can be used to determine the melting temperature shift. The model predicts the most prominent features of stress-induced crystallization. The main advantage of the model is that the parameters in the quiescent-state crystallization model do not change. Consequently, the parameters in the melting temperature shift model are easy to determine, and unknown constants are kept to a minimum. (C) 2002 Wiley Periodicals, Inc.
Simulations of the injection-compression molding (ICM) process based on a Leonov viscoelastic fluid model has been employed to study the effects of processing conditions on the birefringence development and distribution in injection-compression molded parts. A numerical algorithm combined with a modified control-volume/finite-element method is developed to predict the melt front advancement and the distributions of pressure, temperature, and flow velocity dynamically during the injection melt-filling, compression melt-filling, and postfilling stages of the entire process. Part birefringence was then calculated from residual stresses following the thermal-mechanical history of the entire molding process. Simulations of a disk part under different process conditions including compression speed, switch time from injection to compression, compression stroke, packing pressure, and postfilling time were performed to understand their effects on birefringence variation. The simulated results were also compared with those required by conventional injection molding (CIM). It has been found that an ICM part shows a significant reduction of part birefringence near the gate area as compared with CIM parts. However, ICM parts exhibit higher birefringence values near the rim of the disk. The minimum birefringence occurs around the location where injection is switched over to compression. Although longer postfilling time and higher packing pressure result in higher birefringence values, their effects are not very significant. On the other hand, higher compression speed, larger compression stroke, and shorter switch time exhibit greater effects on the increase of part birefringence. Flow-induced residual stress is the major origin of birefringence formation in the present case. The simulated birefringence for both ICM and CIM parts show good coincidence with those obtained from measurements by using a digital photoelasticity technique. (C) 2002 Wiley Periodicals, Inc.
We have taken blends of a bitumen with three homopolymers that produce systems softer than the bitumen, and to each have added small quantities of different semicrystalline polyolefins. The intention is to discover whether these Will form an extensive network system within a blend with a low T-g in which crystallites create the cross-links, as may happen with the isotactic polypropylene present in some atactic polypropylene systems. Such thermoplastic cross-links might provide a useful feature for certain uses, such as in built-up roofing membranes. These were found only within one blend based upon the polybutadiene, in two blends based upon chlorinated polyethylene, but in none based on the Lycra(R) whose blends with LLDPEs and the HDPE flowed below the crystal melting temperature. The E" plots indicate the presence of many loss processes within the blends at low temperatures: the tan 6 plots show other processes active up to 200degreesC within the soft matter. The behavior we discovered suggests that the properties of binary polymer blends are not associated solely with the components, but that, when the material is stiff or after heating, certain polymer-bitumen interactions may also be significant, and are sensitive to slight differences of structure between LLDPEs, even when present at the 3.4% level. (C) 2002 Wiley Periodicals, Inc.
The toughening of glass fiber reinforced nylon-6,6 (PA-6,6) by using the functionalized triblock copolymer styrene-(ethylene-co-butylene)styrene, grafted with maleic anhydride (SEBS-g-MA) was examined. Blends containing 2.5, 5, 7.5, 10, and 12.5 wt% copolymer were prepared by melt blending in a single-screw extruder. Emphasis was given to the study of mechanical properties in comparison with morphology and thermal properties of the aforementioned samples. Although the amount of SEBS-g-MA that was added in PA-6,6 was not enough to produce a super-tough material, a significant increase in the resistance to crack propagation and impact strength was observed in all blends. This behavior was proportional to the amount of SEBS-g-MA that was added for samples having up to 10%, rubber, while additional. amounts seem to have no further effect. A small decrease in tensile strength was also observed. From FTIR spectroscopy and DSC analysis it was shown that the grafting extent of SEBS-g-MA to PA-6,6 was very low. (C) 2002 Wiley Periodicals, Inc.
Plastic energy dissipation (PED) of individual polymer pellets as well as of densified polymer particulate assemblies may be the dominant heating/melting mechanisms in intermeshing corotating twin-screw extruders (Co-TSEs). In the present paper, the amount of PED is evaluated by conducting the uniaxial unconfined compression experiments on both molded cylindrical polymer samples and polymer particulate assemblies. The compression experiments were extended to a much higher deformation (strain) range. The results of this work clearly demonstrate the significant contribution to melting from even a single deformation of individual pellets. One severe deformation of PP pellets can provide almost one sixth of the energy required for their melting. For PS pellets, one severe deformation alone can provide sufficient energy to heat up the pellets to above their glass-transition temperature. On the other hand, the mechanical energy input during the compressive deformation of particulate assemblies is much lower than that of solid polymer samples, depending, to a great extent, on the degree of the particulate densification/void ratio of the particulate system. There are two types of PED in the melting section of Co-TSEs, localized PED of individual pellets in the partially filled kneading section and global PED of consolidated particulate assemblies in the fully filled section. The mandatory deformation of solid particulates, caused by the interaction of kneading paddle pairs, and the associated PED for both individual pellets and consolidated particulate assemblies, provides very efficient heating/melting of polymer feedstock in Co-TSEs. (C) 2002 Wiley Periodicals, Inc.
Polyethylene is one of the most widely used corrosion-protection thermoplastic coating materials that protects steel by providing a barrier to oxygen, water, and corrosive ions and performs very well. In order to further improve medium density polyethylene (MDPE) properties with regard to cathodic disbondment (CD), i.e., the loss of adhesion that takes place in the presence of cathodic protection (CP), various blends with functionalized polyethylenes containing polar functional groups such as maleic anhydride-grafted-polyethylene (MAH-g-PE) and other thermoplastic elastomers such as EPDM have been formulated to increase CD performance. Using compression molding and strew coating, the above modified polyethylenes have been applied on steel plate and pipe, respectively. The CD performance and 90 peel strength (dry and wet) of these formulations are investigated in this study. It is observed that dry bond strength does not correlate with CD performance. The improvement of CD performance for compression-molded materials and strew-coated samples is demonstrated. Also discussed, for comparison, is the performance of MDPE applied by a commercially relevant fluidized bed technique. Wet adhesion strength is shown to be an important parameter in assessing the CD performance of coatings. The disbondment mechanism of failed polymer surfaces has also been investigated using X-ray photoelectron spectroscopy, which allows us to monitor the mass transfer of the sodium cations along the crevice during CD. (C) 2002 John Wiley Sons, Inc.
The toughening of the epoxy resin diglycidyl ether of bisphenol A with hydroxy-terminated polybutadiene (HTPB) was investigated. A chemical link between the elastomer and the epoxy resin was promoted employing tolylene diisocyanate (TDI). In the first step, HTPB and TDI (in excess) reacted forming urethane links, and after increasing the temperature and adding a catalyst, TDI-HTPB reacted with epoxy resin forming oxazolidone links. The reactions were followed by FTIR and chemical analysis. The final cured materials contained up to 10 phr of elastomer. Impact resistance increased with elastomer concentration up to 5 phr of HTPB, which was present as rubber particles with average diameter ranging from 1 to 4 mum. Higher concentrations of HTPB resulted in larger particles and gave lower impact values. The overall results have shown that it is possible to obtain, with the process employed, an impact resistance increase of 100% with the use of HTPB as a toughening agent for the epoxy resin. (C) 2002 John Wiley Sons, Inc.
The poly(O-anisidine) (POA) coatings have been synthesized on low carbon steel (LCS) substrates by electrochemical polymerization (ECP) of O-anisidine. The synthesis of POA coatings was carried out under cyclic voltammetric and galvanostatic conditions from an aqueous solution of oxalic acid. It has been observed that the formation of POA coatings on LCS occurs after the passivation of its surface via the formation of polycrystalline iron oxalate (FeC2O4-2H(2)O) interphase. The formation of iron oxalate interphase is confirmed by fourier transform infrared spectroscopy, glancing angle x-ray diffraction (GAXRD) measurements and scanning electron microscopy (SEM). Uniform, granular, and strongly adherent dark green POA coatings were obtained on the LCS substrate by ECP of O-anisidine. These coatings were characterized by cyclic voltammetry (CV), potential-time (E-t) curves, UV-visible absorption spectroscopy and SEM. The potential-time curve is characterized by an induction time before the ECP of O-anisidine. The induction time is found to be dependent on the applied current density. The optical absorption spectroscopy study reveals the formation of conducting emeraldine salt phase of POA. Our results reveal that the oxalic acid is a suitable medium for the ECP of O-anisidine on the LCS substrate and it favors the formation of emeraldine salt (ES) phase of POA. (C) 2002 John Wiley Sons, Inc.