bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of amorphous nylon on the properties of poly(butylene terephthalate) and 70/30 poly(butylene terephthalate)/nylon 6 blends
Authors: Kang Tae‐Kyu , Kim Yang , Cho Won‐Jei , Ha Chang‐Sik
Published: April 2004

In this work, the effects of adding small amounts of amorphous nylon (a‐nylon) on the properties of poly(butylene terephthalate)(PBT) have been studied. Miscibility and properties of PBT/a‐nylon blends were compared with those of PBT/nylon 6 blends. Blends were prepared in a twin‐screw extruder. The compositions of a‐nylon or nylon 6 were varied from 0 to 20 phr. Rheological, thermal, mechanical, and dynamic mechanical properties of the blends were examined using a capillary rheometer, a differential scanning calorimeter (DSC), a universal testing machine (UTM), and a Rheometrics Mechanical Spectrometer(RMS), respectively. The PBT showed a single endotherm around 225.4°C on the DSC thermogram at the first heating scan but exhibited a second endotherm at a temperature below that of the original endotherm at the second heating scan. When a‐nylon was added, the original endotherm was remarkably affected, but the second endotherm was not appreciably changed; i.e., the heat of fusion at the original endotherm decreased linearly with increasing a‐nylon content, meaning that the addition of a‐nylon affects significantly only the higher‐melting crystals of PBT. The impact strength of PBT was decreased with nylon 6 content but was increased with increasing content of a‐nylon. With an increase in the a‐nylon content, the tensile modulus and the flexural modulus of PBT were decreased. Of interest is, however, that the tensile strength was significantly increased with a‐nylon up to 15 phr. The melt viscosity of PBT was decreased with increasing a‐nylon content, whereas it was not significantly changed with nylon 6 addition; i.e. the addition of a‐nylon acted as a lubricant or a processing aid for PBT. The dynamic mechanical and the morphological studies showed that PBT was more miscible with a‐nylon than with nylon 6. It was also found that a‐nylon exhibited a compatibilizing effect for the PBT/nylon 6 blend of 70/30 wt% composition.
Hexafluoropropylene plasmas: Polymerization rate–reaction parameter relationships
Authors: Silverstein M. S. , Chen R. , Kesler O.
Published: April 2004

Plasma polymerization generates thin, pinhole‐free, and highly adhering films and is often described by the ratio of power to mass flow rate (energy per mass). This research explores the relationships between plasma reactor parameters such as monomer flow rate, plasma power, and reactor pressure and the rates of polymerization, etching, and deposition. The chemical structure of the amorphous, crosslinked plasma polymerized hexafluoropropylene consists largely of similar amounts of C*‐CF, CF, CF2, and CF3 groups and some C‐C groups. A dimensionless plasma parameter (E) proportional to power and inversely proportional to flow rate cubed was derived. E, reflecting both plasma energy and residence time, was used to describe various aspects of the plasma reactions. A dimensionless exponential expression successfully described the dependence of pressure on E with a master curve. An expression for polymerization efficiency (polymer conversion) derived in part through a mass balance was also successfully related to E using an exponential master curve. The rate of deposition was described as the difference between the rates of polymerization and etching. The deposition efficiency maximum and plateau were successfully described by the difference between polymerization and etching efficiencies, each related exponentially to E. The technique used to derive parameters to describe the dependence of plasma reactions on plasma operating conditions can be applied to any monomer/reactor system.
Effect of isothermal aging on the imidization of PMR‐15
Authors: Jordan Kelvin , Iroh Jude O.
Published: April 2004

The imidization of polymerizable reactive mixtures, PMR‐15 has been performed in a vacuum oven at isothermal aging temperatures ranging from 65 to 200°C for aging periods of 0.5 to 2.5 h. The weight loss of the resin and chemical changes that occurred as a result of aging were monitored gravimetrically and by FT‐IR spectroscopy. Differential scanning calorimetry was used to determine the temperature at which imidization took place. Imidization was observed to commence at 65°C after long aging times, t ≥ 2.5 h and at ∼95°C at a shorter time, t ∼0.5 h. At higher aging temperatures of 135 to 165°C, extensive imidization occurred. This was shown by the dramatic increase in imide absorption bands at 1780 and 1380 cm−1. Beyond 165°C, there were no significant changes in the imide absorption bands, suggesting that imidization was nearly complete. The activation energy for isothermal aging was determined from the slope of the log of the rate of weight loss vs 1/T curve to be ∼4.5 kJ/mol and is lower than the average activation energy for imidization ∼43 kJ/mol obtained from the plot of the log of the rate of increase of the imide carbonyl peak absorption at 1780 cm−1 vs 1/T.
Use of a fluoroelastomer processing aid with non‐olefin polymers
Authors: Xing K. C. , Wang W. , Schreiber H. P.
Published: April 2004

A die coated with fluoroelastomer (FE) has been used in the extrusion of thermoplastics other than conventional polyolefins, and including chlorinated polyethylene, polystyrene, polycarbonate, and an ionomer. Inverse gas chromatography was the source of acid/base interactions between FE and each of these matrix polymers. FE was found to be effective in reducing the apparent melt viscosity when the host polymer was acidic, or non‐interactive. With strongly interactive, basic polymers the effectiveness of FE flow modifier was anulled. These polymers may be considered as effective purging agents for extrusion equipment containing FE residues.
Mechanism of degradation of poly(vinyl butyral) using thermogravimetry/fourier transform infrared spectrometry
Authors: Liau Leo C. K. , Yang Thomas C. K. , Viswanath Dabir S.
Published: April 2004

A TG/FTIR system was used to identify the products of thermal oxidative degradation of PVB, and also to elucidate the mechanism of degradation. This technique is useful in the kinetic analysis of fast reactions such as polymer degradation, unlike the use of a TG/GC/FTIR system, in which long retention times are needed to separate the products. A computer resolution method based on a pattern recognition technique is proposed to resolve the dynamic mixture IR spectra of the degradation products. A four‐component synthetic mixture was used to evaluate the performance of the resolution algorithm and was found to be accurate within ±5%. The method was then applied to PVB degradation. The dynamic information of PVB thermal oxidative degradation obtained by resolving the mixture IR spectra was used to elucidate the reaction mechanism and to determine the kinetic parameters. Results showed that PVB degradation in air took place at a temperature 50K lower and the overall activation energy dropped from 338 kJ/mole (in nitrogen) to 200 kJ/mole (in air) compared with the degradation in a nitrogen atmosphere.
Study of the stability of the film casting process
Authors: Silagy D. , Demay Y. , Agassant J‐F.
Published: April 2004

A theoretical study of the film casting process has been carried out. In this industrial process, a molten polymer is extruded through a flat die, then stretched in air and cooled on a chill roll. This involves mainly an extensional flow. Between the die and the chill roll, thick edges are formed and a neck‐in phenomenon is observed. Above a critical take‐up speed, a drawing instability, known as draw resonance, may occur. In this paper, a one‐dimensional model adapted from the classical model of the fiber spinning is developed (for a Newtonian or a Maxwell fluid). The influence of the processing parameters (draw ratio, Deborah number, and aspect ratio) on geometry of the lateral free surface (the so‐called neck‐in phenomenon) is studied. An unattainable zone very similar to the one encountered in fiber spinning is predicted, which only slightly depends on the stretching geometry (initial film width and stretching distance). The onset of draw resonance is studied through the linear stability method. A stability zone, depending on the geometry of the process, the elasticity of the polymer, and the draw ratio, has been obtained. This instability is observed with simultaneous width and thickness film variations. It is proved that the aspect ratio (stretching distance divided by die width) has a strong influence on the onset of the draw resonance instability.
Fracture toughening behavior and mechanical properties of polyphenylene oxide/high‐impact polystyrene blends
Authors: Tjong S. C. , Ke Y. C.
Published: April 2004

Blends of a poly(phenylene oxide) (PPO) with high‐impact polystyrene (HIPS) were injection molded. The static mechanical properties and fracture toughness of the blends were determined by means of the uniaxial tension, Brinell hardness and three‐point‐bending measurements. From the static mechanical test results, it was shown that the yield strength, Young's modulus and hardness values of the PPO/HIPS blends were considerably higher than those of their PPO and HIPS component polymers. Dynamic mechanical measurements indicated that the PPO/HIPS blends appear to be miscible as shown by the existence of a single glass transition temperature. Furthermore, theJintegral method based on ASTM E813‐89 procedure was used to characterize the fracture toughness of PPO/HIPS blends. TheJintegral analysis indicated that the PPO specimen exhibited the lowest fracture toughness (Jc). The PPO containing 50 wt% HIPS blend had the highestJc. SEM observations revealed that the crack growth zone of the pure PPO is relatively smooth. However, cavitation of the elastomeric particles and shear band formation were observed in the deformed zones ahead of the crack tip of the PPO with 50 wt% HIPS blend. The cavitation and shear band formation would dissipate bulk strain energy and their formation was responsible for the highestJcvalue observed in this blend.
Finite element analysis of 2‐D thermoviscoelastic responses based on the free volume theory and a recursive formulation
Authors: Lee H. H. , Chen R. S. , Cheng T. R.
Published: April 2004

A two‐dimensional thermoviscoelastic problem is analyzed by the finite element method based on free volume theory and thermoviscoelasticity. The stresses are computed according to a shift factor; the shift factor is in turn calculated from the free volume ratio, defined as the free volume divided by the total volume. The free volume ratio depends on normal stress as well as hydrostatic pressure, in addition to temperature. The effect of hydrostatic pressure on the free volume ratio can be approached by an equivalent temperature effect. A finite element analysis is developed, in which the constitutive equations are formulated in recursive form. As a nonlinear analysis, the procedure finds the solution iteratively, using a shift factor as the convergence parameter. For poly(vinyl acetate) stress‐strain curves under several loading conditions are discussed with respect to temperature and pressure.
Effect of the crystallinity and morphology on the microcellular foam structure of semicrystalline polymers
Authors: Doroudiani Saeed , Park Chul B. , Kortschot Mark T.
Published: April 2004

Microcellular foam processing of polymers requires a nucleated cell density greater than 109 cells/cm3 so that the fully grown cells are smaller than 10 μm. A microcellular foam can be developed by first saturating a polymer sample with a volatile blowing agent, followed by rapidly decreasing its solubility in the polymer. In general, the cellular structure of semicrystalline polymer foams is difficult to control, compared to that of amorphous polymer foams. Since the gas does not dissolve in the crystallites (1), the polymer/gas solution formed during the microcellular processing is nonuniform. Moreover, the bubble nucleation is nonhomogeneous because of the heterogeneous nature of the semicrystalline polymer. In this paper, the effects of the crystallinity and morphology of semicrystalline polymers on the microcellular foam processing and on the cellular structure of products are investigated. First, polymer specimens with various crystallinities and morphologies were prepared by varying the cooling rate of the polymer melt. Then, the solubility and diffusivity of the blowing agent in and through specimens were studied. The specimens with differing crystallinities and morphologies were foamed and their cellular structures were compared. The experimental results agree with theoretical predictions, indicating that the crystallinity and morphology of semicrystalline polymers exert a strong influence on the foam processing and the structure of the product.
Experimental observation on entrance flow inside extrusion dies
Authors: Chang Yun‐Han , Wen Shu‐Heng , Liu Ta‐Jo
Published: April 2004

A flow visualization technique was employed to observe the flow fields at the entrance region inside extrusion dies. Four types of solutions, i.e., Newtonian, shear‐thinning, Boger, and viscoelastic fluids, were used as test fluids. Entrance flows inside center‐fed and end‐fed dies of different configurations were examined. It was found that, even though the swirling motions appear in the entrance region of center‐fed dies, no vortex develops. Shear‐thinning behavior tends to enhance swirling, but fluid elasticity suppresses the swirling. On the other hand, vortices exist at certain end‐fed die geometries, and vortices will grow if the fluid exhibits shear‐thinning, yet fluid elasticity reduces the size of vortices. Several inlet designs effective for eliminating vortices were studied.
Viscoelasticity of rubber‐toughened poly(methyl methacrylate). Part I: Deformational behavior
Authors: Mariani P. , Frassine R. , Rink M. , Pavan A.
Published: April 2004

Viscoelasticity of a rubber toughened poly(methyl methacrylate) has been investigated both in the linear and the non‐linear range by means of tensile creep and tensile constant strain rate tests. An empirical time‐temperature‐strain reduction scheme is proposed to analyze the modulus data obtained at different temperatures and strain levels: a single master curve and relevant time‐temperature and time‐strain shift factors have been obtained. Two different thermal histories were considered for testing. It has been shown that, once aging effects can be considered under conditions where aging time elapsed before testing is the same, modulus master curves obtained from linear and from non‐linear data substantially coincide. This shows that both temperature and strain level determine the modulus master curve via their influence on a single variable: the free volume of the material.
Linear low‐density polyethylene addition to polypropylene/elastomer blends: Phase structure and impact properties
Authors: Holz N. , Goizueta G. S. , Capiati N. J.
Published: April 2004

Morphology features and effects of particle size and composition of the disperse phase on the impact properties have been studied for the blends of isotactic polypropylene (PP)/ethylene‐propylene‐diene terpolymer and (EPDM)/linear low‐density polyethylene (LLDPE). The blend components were mixed in a twin‐screw extruder, press molded, and analyzed by scanning electron microscopy, SEM (fractured and toluene etched samples), and by transmission electron microscopy, TEM (RuO4 stained samples). TEM was most effective for the identification of component distribution and particle size measurement. An increasing degree of LLDPE and EPDM interpenetration was observed with the PE content. Not one case of a neat component separation was detected. LLDPE addition improves the EPDM dispersability, affecting mainly the larger particles. The impact properties at room temperature were especially dependent on the rubber content, whereas at low temperature the particle diameter appears to be the controlling parameter. The affect of LLDPE on blend toughness is more evident in the latter case.
A compatibilizer for a blend of polysulfone with a liquid crystalline polyester
Authors: Yang Hongli , Wu Xuqin , Li Shijin
Published: April 2004

A ternary blend of polysulfone (PSF), a thermotropic liquid crystalline polymer (TLCP), and a compatibilizer was investigated. The TLCP was composed of terephthalic acid (TPA), m‐phthalic acid (MPA), p‐acetoxybenzoic acid (Ac‐HBA), and 4,4′‐diacetoxy bisphenyl (Ac‐BP). The compatibilizer was a block copolymer of low molecular weight polysulfone and a rigid‐rod chain. Morphological investigations showed that the TLCP in the ternary system exhibited improved adhesion and dispersion in a much finer scale than in binary blends of PSF/TLCP prepared under the same processing conditions. Differential scanning calorimetry confirmed this result. Significant improvements were seen in the values of tensile modulus and strength.
On‐Line determination of density and crystallinity during melt spinning
Authors: Bansal Vishal , Shambaugh Robert L.
Published: April 2004

The density and crystallinity of polypropylene fiber were measured on the moving threadline during the melt spinning process. Heretofore, threadline densities have never been measured on‐line. These density measurements were accomplished by taking parallel, on‐line measurements of fiber diameter, fiber velocity, polymer mass flow rate fiber temperature, and fiber birefringence. Under certain spinning conditions, a distinct rise in density occurs along the threadline. This rise in density corresponds well with the rise in crystallinity as measured by birefringence.
A study of rib geometry for gas‐assisted injection molding
Authors: Yang S. Y. , Huang F. Z. , Liau W. N.
Published: April 2004

Large, thin, plate‐shaped parts usually are strengthened with structural ribs. Ribs also serve as gas channels with gas‐assisted technology. The layout and geometry of these gas‐channel ribs are critical to the gas‐assisted injection molding (GAIM) process. In this study, the effects of rib geometry, including aspect ratio and fillet geometry, on the GAIM process are investigated. Experimental results indicate that increasing the rib width widens the allowable operation range and thus improves the moldability. Adding fillets to the rib corner significantly enhances the moldability. Adding fillets also reduces the loss of rigidity due to void formation in the rib. A curved fillet improves moldability and rigidity more than one that is straight.
Ceramic‐reinforced polymers and polymer‐modified ceramics
Authors: Mark J. E.
Published: April 2004

The composites discussed in this review are prepared using techniques similar to those used in the new sol‐gel approach to ceramics. Organometallis such as silicates, titanates, and aluminates are hydrolyzed in the presence of polymer chains (for example polysiloxanes and polyimides) that typically contain hydroxyl or amino groups. The functional groups are used to bond the polymer chains onto the silica, titania, or alumina being formed in the hydrolysis, thus forming organic‐inorganic composites. When the polymer chains are present in excess, they constitute the continuous phase, with the ceramic‐type material appearing as reinforcing particles. When present in smaller amounts, the polymer is dispersed in the continuous ceramic phase, to give a polymer‐modified ceramic. Under some conditions, bicontinuous systems are obtained. The composites thus prepared are characterized by electron microscopy, X ray, and neutron scattering intensities, density determinations, and stress‐strain and impact‐strength measurements.
Properties of side chain liquid crystal polyesters containing chiral groups in the main chain
Authors: Mehl G. H. , Valvo F. , Lacey D. , Goodby J. W. , Das‐Gupta D. K.
Published: April 2004

The synthesis and investigation are reported for the phase behavior of a set of three liquid‐crystalline side chain polyesters (SCLCPs), consisting of aromatic diacids and diols bearing cyano biphenyl moieties in the side chain. The materials contain a chiral center in the main chain and show a cholesteric phase indicative of a helical order with a preferred twist. In addition, they exhibit Tg's below room temperature and smectic bilayer phases. Depending on the substitution pattern of the aromatic core, Sc* or SA* phases are observed. These polymers were synthesized in a four‐step synthesis, starting from available materials. The dielectric relaxation behavior and the pyroelectric responses of the three SCLCPs tend to conform to their respective structure.
Dielectric and pyroelectric characterization of anionic and native collagen
Authors: Guzzi Plepis Ana Maria De , Goissis Gilberto , Das‐Gupta Dilip K.
Published: April 2004

Reconstituted collagen membranes (thickness 20–40 microns), used in periodontal guided tissue regeneration, were prepared by solubilization of bovine serosa and bovine tendon using an alkaline treatment and by solubilization of bovine serosa in acetic acid. Dielectric properties of these materials were determined in the frequency range of 10−5−106 Hz (poling temperature = 313 K, poling time = 3 h, E = 107 V/m), using a General Radio Bridge system (high frequencies) and a discharge current technique (low frequencies). The true pyroelectric coefficient p(T) was determined for these materials by a direct method over an appropriate temperature range. Their magnitude appear to be in the range of 10−4 to 10−5 C/m2 K−1, which is considerably higher than that of the ferroelectric poly(vinylidene fluoride) (PVDF) and its copolymer vinylidene fluoride‐trifluorethylene (VDF‐TrFE).
Nonlinear stress‐strain behavior of glassy polymers
Authors: Chow T. S.
Published: April 2004

We have attempted to provide a unified account of the structural relaxation and mechanical properties of glassy polymers by reviewing recent results of a predictive model. One would like to understand how the effects of structural relaxation influence the performance of amorphous solids. The physics of glassy polymers is still evolving and the functional relationships between relaxation and deformation have not been firmly established. However, significant progress has already been made that can be utilized in solving problems in the large deformation of polymers. Equations have been derived that can be applied to provide quantitative prediction of the nonlinear stress‐strain relationships as a function of physical aging, strain rate, temperature, external stress field, and the filler concentration in composites.
Acoustic emission signal detection by ceramic/polymer composite piezoelectrets embedded in glass‐epoxy laminates
Authors: Wenger M. P. , Blanas P. , Shuford R. J. , Das‐Gupta D. K.
Published: April 2004

Piezoelectric composites, consisting of a ferroelectric ceramic powder of calcium‐modified lead titanate dispersed in two different polymer matrices, viz. from vinylidene fluoride trifluoroethylene and an epoxy, have been fabricated. The composites show a mixed connectivity structure, and the results of electromechanical characterization are given. Thin films of these materials have been incorporated into surface mounted acoustic emission sensors and their frequency response and ability to detect plate waves, generated by a simulated acoustic emission source, has been examined. In situ transducers embedded into glass‐reinforced laminate plates have also been examined and have been shown suitable for acoustic emission sensors.
Physical aging time scales and rates for poly(vinyl acetate) stimulated mechanically in the Tg‐region
Authors: Delin M. , Rychwalski R. W. , Kubát J. , Klason C. , Hutchinson J. M.
Published: April 2004

The physical aging behavior of poly(vinyl acetate), PVAc, in the Tg‐region has been investigated using dynamic mechanical analysis (DMA). Tests in shear and flexure modes were performed for samples quenched from a stabilization temperature of 40°C to aging temperatures 35.0°C and 32.5°C (down‐jumps), and from equilibrium at a stabilization temperature of 32.5°C to aging temperature 36.2°C (up‐jump). Volume recovery was investigated for the same thermal histories using mercury‐in‐glass dilatometry. The time scales for the evolution of the storage and loss moduli during physical aging have been compared with the volumetric time scales. Aging rates, µ, have been calculated in the frequency and time domains. The evolution of dynamic mechanical properties during aging is found to be different from the volumetric behavior. In the case of the temperature down‐jump, the evolution of the volume ceases earlier than that for the storage and loss moduli. In the up‐jump experiment, the opposite is found. Aging rates for the storage and loss moduli are analyzed. A suggestion is offered that the evolution of dynamic mechanical properties during physical aging is retarded by the cyclic mechanical stimulus, and that this effect (rejuvenation) is more noticeable the higher is the damping; consequently rejuvenation in the Tg‐region can be caused by small strains in dynamic mechanical analysis.
Physical aging in polymers: Comparison of two ways of determining narayanaswamy's parameter
Authors: Godard Marie‐Elodie , Saiter Jean‐Marc , Burel Fabrice , Bunel Claude , Cortes Pilar , Montserrat Salvador , Hutchinson John M.
Published: April 2004

In this work, we have investigated by differential scanning calorimetry the enthalpy relaxation of two poly[methyl(α‐n‐alkyl)acrylates] in which it is possible to change the length of the two alkyl chains. In particular, we have evaluated the Narayanaswamy parameter, which controls relative contribution of temperature and of structure to the relaxation times, by two methods: Grenet's method (GM) and the peak‐shift method (PSM). The data obtained show that both methods lead to equivalent results. Nevertheless, PSM requires fewer experiments than GM, and PSM appears to be more practical. The results obtained on the two acrylates show that the parameter x increases with the lateral chain length, that is to say, that the temperature effects increase as the length of the alkyl chain is increased.
On the correlation between the viscosity of partially hydrolyzed polyacrylamide solution and the diffusion coefficient in the semidilute concentration regime
Authors: Kanatharana Jarujit , Sukpisan Jeerutha , Sirivat Anuvat , Wang S. Q.
Published: April 2004

The solution viscosity of neutral polyacrylamide (PAM), the partially hydrolyzed polyacrylamide (70% HPAM), and polyacrylic acid (PAA) were measured concurrently with the apparent diffusion coefficient in the dilute and semidilute concentration regimes. We identified the scaling relation η − ηs = A/D in the semidilute regime, where η is the solution viscosity, ηs is the solvent viscosity, D is the coefficient of the slow diffusion mode obtained from dynamic light scattering, and A is a prefactor found to have a unique value of ∼1.0 × 10−8 cP cm2/s. The scaling relation as well as the prefactor are independent of the the ionic strength, the solvent quality, the molecular weight, the charge density, the polyelectrolyte, and salt concentrations. For the neutral PAM, the product [η – ηs]D is proportional to the polyelectrolyte concentration Cp, consistent with Rouse theory and previous experimental findings.
Amine modified polyethylenes, prepared in near critical propane, as adhesion promoting agents in multilayered HDPE/PET films
Authors: De Gooijer J. M. , Scheltus M. , Koning C. E.
Published: April 2004

High density polyethylene [HDPE] grafted with 0.13, 0.04 and 1.04 wt% maleic anhydride (abbr.: PEMA) was modified with an excess of a variety of diamines in near critical propane. The resulting amic acid groups were quatitatively imidized to the corresponding imide (PEMI) in the melt. Increasing the percentage maleic anhydride grafted on the HDPE resulted, upon reaction with the diamines, in an increased gel content, due to crosslinking. Three‐layered films were prepared using HDPE film and polyethylene dterephathalate (PET) film as the outer layers and the PEMAs and PEMIs as the inner layer. Adhesion strengths were measured using a T‐peel test. Increasing the bonding temperature resulted in an improved adhesion. The most optimal system for adhesion proved to be HDPE grafted with 0.40 wt% MA and modified with a pendent secondary amine group. For this system the lowest number of reactive amine groups was lost owing to crosslinking reactions, so the highest concentration of amines is available for interactions with the PET film. The absence of extensive HDPE crosslinking in addition implies a better flow of the adhesive layer during lamination. From contact angle measurements, it was observed for all samples that after delamination of the three‐layered system, PET was present on the PE‐surface and PE was present on the PET‐surface.
Transport processes and feasible operating domain in a twin‐screw polymer extruder
Authors: Zhu Weimin , Jaluria Yogesh
Published: April 2004

The flow of a polymer and the associated heat transfer in a fully intermeshing, co‐rotating twin screw extruder are investigated numerically. The control volume technique is used for numerical modeling and simulation, considering both Newtonian and non‐Newtonian fluids. The velocity distributions in the screw channel are compared with experimental resultlsf and good agreement is obtained. Owing to limitations arising from the physical aspects of the problem, the numerical results show that not all operating conditions are feasible. A feasible domain, in terms of screw speed and mass flow rate, in which the extruder operation is satisfactroy, is obtained for pure starch. To improve the applicable range of this model, an axial formulation is adopted for the translation region that characterizes the domain away from the intermeshing zone of the extruder. This model yields results consistent with the earlier down‐channel model while the feasibility region is extended towards lower mass flow rates. For the upper limit, a physicdal restriction arises in terms of the maximum flow rate for a pressure rise in the extruder. Thus, the model can be used for simulating a wide range of operating conditions while retaining the appropriate physical behavior of the process.
Feasible compositions for random copolymerizations
Authors: Smith Raymond L. , Malone Michael F.
Published: April 2004

Using the attainable region approach, feasible compositions and conversions for random copolymers are determined, along with altermatives for the related reactor configurations. This analysis attempts to find all of the possible compositions that can be produced by any system of reactros and mixing. The average copolymer compositions are bounded by the feed composition and the instantaneous copolymer composition produced at the initial conditions. Since the instantaneous copolymer composition can be found through the Mayo‐Lewis equation, that case and the feed composition mark the limiting feasible compositions. The results can also be used to determine the range of feed compositions for which a specific copolymer product composition is possible. If the addition of monomer at any point in the reactor system is possible, e.g., by side‐feeding, the analysis indicates that any desired copolymer composition can be obtained.
Crystallization kinetics of poly(butylene terephthalate) (PBT): Influence of additives and free carboxylic acid chain ends
Authors: Pillin Isabelle , Pimbert Sylvie , Feller Jean‐François , Levesque Guy
Published: April 2004

Degradation of poly(butylene terephthalate) (PBT) induced by blending time at 260°C leads to an increase of both carboxylic end groups and melt viscosity index and a decrease of the molecular weights. Crystallization kinetics of pure PBT and PBT blended with and epoxide, which was used to reduce the free carboxylic acid concentration, were compared. Lower carboxylic acid concentrations were obtained, but the molecular weights still decreased. The crystallization kinetics of PBT blended with pigments and/or mineral fillers were also studied. Dyes, some of which are known for their nucleation activity, were used for differentiating extruded PBT tubes in optical fiber loose cables. Post‐shrinkage appeared to depend on the type of pigment used. Pigments Concentration, particle size and chimical nature have been correlated to the PBT crystallization kinetics. An increase of the nonisothermal crystallization temperature was observed, more or less important according to the pigment used. Talc and mica were also tested in PBT blends, with and without pigments. Their mucleation activity parameters were measured and compared with those for the pigments. An average value of the crystallization temperature, nearly constant and independent of the Pigment, was obtain controlled shrinkage on industrial products with strict dimension requirements.
The morphology of hyperbranched polymer compatibilized polypropylene/polyamide 6 blends
Authors: Jannerfeldt G. , Boogh L. , Månson J.‐A. E.
Published: April 2004

The influence of hyperbranched polymer grafted polypropylene (PP‐HBP) on the morphology of polypropylene (PP)/polyamide 6 (PA6) blends has been investigated. The final morphology was strongly influenced by the PP‐HBP compatibilizer concentration. At low concentrations, PP‐HBP acts as an emulsifying agent, reducing the size of the dispersed phase and preventing coalescence. This is due to the high reactivity and diffusitivity of PP‐HBP rapidly forming a high density of copolymers at the interface. Compared to the use of maleic anhydride grafted PP (PP‐MAH) at identical concentrations, PP‐HBP yielded a smaller dispersed phase particle size. Therefore, PP‐HBP allows the use of less compatibilizer to obtain identical morphologies. At higher compatibilizer concentrations, it has been shown that the PP‐HBP efficiently stabilizes the interface and inhibits both coalescence and breakup of the PA6 droplets. The high concentration of reactive sites and the ability of PP‐HBP to react with both chain‐ends of PA6 suggest that interfacial stabilization occurs because of the formation of a partly crosslinked interface. The interfacial stabilization effects generated by PP‐HBP should allow one to control the morphology of polymer blends in order to create specific functional morphologies.
An analysis of photopolymerization kinetics and stress development in multifunctional acrylate coatings
Authors: Stolov Andrei A. , Xie Tao , Penelle Jacques , Hsu Shaw L. , Stidham Howard D.
Published: April 2004

Polymerization kinetics and stress buildup of multifunctional acrylic coatings have been studied simultaneously using a cantilever deflection method and real time one‐bounce infrared reflectance spectroscopy. Cantilever deflection due to stress buildup in the film is correlated with crosslink density in the polymerizing mass. Stress buildup was observed not to occur instantaneously after radiation was introduced but rather after a certain time interval. The time delay between onset of polymerization and initiation of stress indication is attributed to the introduction of crosslinks, leading to a gel state. The measured stress‐conversion relationship can be predicted using an approach incorporating monomer reaction probability. Stress buildup can vary considerably as a function of processing conditions such as film thickness, temperature at solidification point, and the type, concentration and absorptivity of photoinitiator, which govern the degree of crosslinking. Under certain processing conditions, an uneven distribution of the monomer conversion in the film may severely alter the stress‐film thickness relationship. In some cases the cantilever material anisotropy can be detected based on the cantilever deflection measured.
Compatibilizers for thermotropic liquid crystalline polymer/polyolefin blends prepared by reactive mixing: The effect of processing conditions
Authors: Son Younggon , Weiss R. A.
Published: April 2004

The effect of processing conditions on the melt formation of a graft‐copolymer compatibilizer for blends of a thermotropic liquid crystalline polymer (TLCP) and polyolefins was investigated. The compatibilizer was formed by a melt acidolysis reaction of a 50/50 (w/w) blend of TLCP and the sodium salt of a poly(ethylene‐coacrylic acid) ionomer. The effects of various processing conditions in a batch mixer and a single‐screw extruder on the extent of reaction were assessed. The extent of graft‐copolymer formation and the efficacy of the product as a compatibilizer for TLCP/polyethylene blends were affected by the processing temperature and the screw (or rotor) speed.
Kinetics of structural evolution during crystallization of preoriented PET as followed by dual wavelength photometric birefringence technique
Authors: Venkatesvaran H. , Cakmak M.
Published: April 2004

A two‐color laser photometric measurement system was used to follow birefringence changes in annealing of prestretched PET films. This technique was shown to be capable of detecting large retardation (and thus birefringence) changes beyond one wavelength of the light. The use of green and red lasers in the photometric system allows the detection of the reversals in birefringence during the course of annealing. Unless critical orienialion/erystallinity levels are developed by stretching the films, heat setting the films at temperatures close to glass transition temper ature results in complete elimination of preferential orientation. At Intermediate stretch ratios, crystalline regions form and Ihe acl as anchor points establishing a network for the orienied amorphous chains. These Dims exhibit partial relaxation followed by rapid increase in birefringence due to the accelerating effect of orientation on crystallization. At high stretch ratios, where substantially oriented and strain crystallized structures are obtained, the initial relaxation stage disappears and birefringence continue to increase throughout the heat setting process even at temperatures very close to glass transition temperature. In these films, however, the total change of birefringence decreases as more of the chains are oriented and crystallized in the stretching stage, leaving a smaller fraction of polymer chains to rearrange during Ihe annealing stage. The kinetics of the structural change exhibit a complex behavior and the largest rates of structural changes were observed in films exhibiting intermidiate birefringence levels.
Light transmission and haze of polyethylene blown thin films
Authors: Wang Lei , Kamal M. R. , Rey A. D.
Published: April 2004

The surface and bulk morphologies of polyethylene blown films are obtained using non‐contact Atomic Force Microscopy (AFM). Based on these experimental observations, a model using the Mie Scattering theory is proposed to describe the forward transmission and scattering of a plane wave through the film. The light transmission properties are computed from the proposed model and the results are validated by experimental measurements.
The mechanical properties of insert‐molded bimaterial composites
Authors: Extrand C. W. , Bhatt S.
Published: April 2004

Bimaterial composite samples were constructed by injecting various polymers into a mold containing a fraction of a pre‐molded specimen. The resulting series composites were tested in tension. Breaking stresses were independent of fractional length. Conversely, both elongation to break and apparent stiffness varied with Although samples broke at or near the interface, adhesion was reasonably good, as indicated by transfer of material across interfaces.
Open‐celled microcellular thermoplastic foam
Authors: Rodeheaver B. A. , Colton J. S.
Published: April 2004

A theoritical model of the production of open‐cell microcellular foam is presented. This model allows the prediction of the conditions necessary to produce these materials. Experiments verify the model quite well. The results of the batch processing experiments indicate the processing parameters that promote the development of open‐celled microcellular polystryene foam. A saturation pressure of 17.2 MPa (2500 psig) provides the nucleation density necessary to form an impinged structure with microcellular bubble density. A foaming temperature of 200°C promotes the formation of both internal and surface porosity. A scaled time between 1 and 2.7 seconds develops a foam structure that intrudes a large volume. Samples foamed at 200°C for 1 and 2 seconds possess pores less than 1 μm in diameter. These samples represent scaled times of 1 and 2 seconds. Therefore, to produce open‐celled microcellular polystyrene foam with batch processing, samples should be saturated at approximately 17.2 MPa (2500 psig) and foamed for a scaled time between 1 and 2 seconds.
A new method to quantify crazing in various environments
Authors: Clay Stephen B. , Kander Ronald G.
Published: April 2004

A new technique to quantify the rate of change of craze density in stressed transparent polymeric plates of polycarbonate was developed. The samples are placed under a creep load in a controlled temperature and humidity environment, during which the craze density is measured with a reflective imaging system at a defined rate. It has been shown that this unique method for crazy detection and quantification has sufficient repeatability to generate statistically acceptable data, obeying currently used, the method described in the present work is an in‐situ, quantitative, non‐subjective, direct measurement of craze density.
Physical chemistry of a phosphite processing stabilizer in polypropylene. Part 1: Solubility
Authors: Billingham N. C. , Garcia‐Trabajo P.
Published: April 2004

The solubility of a commercial aryl phosphite processing stabilizer for ployolefins, {tris (2,4‐di‐t‐butylphenyl)} (irgafos 168, Ciba Speciality Chemicals), has been measured in polypropylene over a range of temperatures. Measurements are complicated by hydrolsis of the phosphite, releasing 2,4‐di‐t‐butylphenol, which is much more soluble in the polymer. We have measured the solubility of this phenol, and of the phosphate oxidation product of the stabilizer. The result are interpreted on the basis of a regular solution model. They show that the phosphite has a very low solubility but that it is not particularly anomalous in comparison with other stabilizers of similar molecular weight and polarity. The phosphate is significantly more soluble than the phosphite at 70°C, but their solubiliies are comparable at 25°C. This is mainly due to the lower heat of fusion and melting point of the phosphate, whose compatibility is actually lower than that of the phosphite. The phenol is much more soluble because of its low melting point.
Finite element analysis of blow molding and thermoforming using a dynamic explicit procedure
Authors: Marckmann G. , Verron E. , Peseux B.
Published: April 2004

This paper reports on the development of a dynamic finite element procedure for the simulation of blow molding and thermoforming of thermoplastic hollow parts. The Principle of Virtual Work written herein takes inertia effects into account. The heat‐softened parison is assumed to be a nonlinear hyperelastic Mooney‐Rivlin membrane and is meshed with classical linear triangular finite elements. We adopt the explicit central differences time integration scheme with the special lumping technique. The moid is divided into triangular elements and the contact between the parison and the mold is assumed to be sticky. Therefore, contacted degrees of freedom of the parison are fixed on the solid boundary until the end of the simultion. Performances are highly improved by the use of an adaptive mesh refinement procedure based on a geometric criterion for detection and on the simple addition of a node at the mid‐side of the longest edge for subdivision. The method is illustrated through some examples of thermoformed and blow‐molded parts. Our results are compared with both experimental and numerical results from literature to validate the present theory.
A 3‐D finite element model for gas‐assisted injection molding: Simulations and experiments
Authors: Haagh G. A. A. V. , Peters G. W. M. , Van De Vosse F. N. , Meijer H. E. H.
Published: April 2004

To gain a better understanding of the gas‐assisted injection molding process, we have developed a computational model for the gas assisted injection molding (GAIM) process. This model has been set up to deal with (non‐isothermal) three‐dimensional flow, in order to correctly predict the gas distribution in GAIM products. It employs a pseudo‐concentration method, in which the governing equations are solved on a fixed grid that covers the entire mold. Both the air downstream of the polymer front and the gas are represented by a fictitious fluid that does not contributeto the pressure drop in the mold. The model has been validated against both isothermal and non‐isothermal gas injected experiments. In contrast to other models that have been reported in the literature, our model yields the gas penetration from the actual process physics (not from a presupposed gas distribution). Consequently, it is able to deal with the 3‐D character of the process, as well as with primary (end of gas filling) and secondary (end of packing) gas penetration, including temperature effects and generalized Newtonian viscosity behavior.
A new hypothesis to describe the mechanisms acting in a welded joint of semicrystalline thermoplastics
Authors: Bonten Christan , Schmachtenberg Ernst
Published: April 2004

Since it is known that crosslinked polythylene can be worked, it is clear that the mechanics acting in the interior of a welded joint are not adequately explained yet. There are several criteria, hypotheses and models that attempt to describe what happens in a welded joint. In this paper, two new promising hypotheses, the Mixed Crystal Hypothesis and the Nexus Hypothesis, are introduced. The Mixed Crystal Hypothesis can be proven by the help of several different examination methods. Other examinations support the Nexus Hypothesis.
Enthalpy relaxation in polymeric glasses
Authors: Dfrozdov Aleksey D.
Published: April 2004

Constitutive equations are derived for enthalpy recovery in a glassy polymer after quench from above the glass transition temperature Tg to a temperature T in the sub‐Tg region. The model is based on the trapping concept, which treats a disodered medium as an ensemble of cooperatively rearranging regions (CRR) hopping in potential wells as they are thermally activated. Rearrangement occurs when a CRR reaches some liquid‐like energy level in a hop. The rate of hops is described by the theory of thermally activated processes, whereas the probability to change trap in a hop is determined by the difference between the current and equilibrium concentrations of cages. A nonlinear parabolic equation is developed for the distribution of traps. This equation ia used to describe entropy recivery in amorphous and semicrystalline polymers. Fair agreement is demonstrated between experimental data for poly(ether imide), poly(ethyl terephthalate) and polystyrene and results of numerical simulation. Some phenomenological relations are suggested to predict the effect of temperature, molar mass and degree of crystallinity on material parameters.
Studies on epoxy modified with recycled rubber
Authors: Sipahi‐Saglam E. , Akovali G. , Kaynak C. , Akkas N. , Yetmez M.
Published: April 2004

This work covers studies on systems with car tire regrind used as the toughening phase in epoxy resins. Different surface modification techniques were used to improve the compatibility at the between the rubber particles and the epoxy matrix. Silane coupling agents, plasma surface modification and acrylic acid/benzoylperoxide were used to enhance the surface properties of rubber particles. Rubber parts of ground used car tires, with or without surface treatment, were mixed with epoxy. This mixture was poured into molds to obtain mechanical test specimens according to ASTM standards. After curing, mechanical tests were performed and the fractured surfaces of the specimens were examined under Scanning Electron Microscopy, SEM. Throughout the studies, changes in mechanical properties were followed by an increase in the volume percentage of rubber particles and by the effect of different surface treatment processes applied on rubber. A decrease in tensile properties and impact resistance was observed in general as compared to unmodified epoxy. On the other hand, slight increases in fracture toughness values were observed in all surface treated cases.