bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of stress and vapor exposure before and during aging on enthalpy relaxation of poly(vinyl chloride)
Authors: Berens A. R. , Hodge I. M. 
Published: May 2005

AbstractEnthalpy relaxations in glassy poly(vinyl chloride) following varied pre‐aging treatments and under varied aging conditions have been compared through observations of sub‐Tg endothermal DSC (differential scanning calorimetry) aging peaks. The extent of enthalpy relaxation for a fixed time and temperature of aging is progressively enhanced by the imposition and release of increasing mechanical stress before aging. The same effect is produced by sorption and desorption of increasing amounts of CO2 or CH3Cl vapor before aging. In contrast, the continued application of mechanical stress, or the presence of vapor, during the aging period suppresses enthalpy relaxation. The extent of suppression increases with increasing vapor pressure and solubility or increasing stress. These effects are interpreted as consequences of an increase in the enthalpy of the polymer under mechanical or sorptive stress and an enthalpy relaxation following the release of this stress. In addition to these effects on the DSC endotherm, a pronounced exotherm between the aging peak and Tg is observed for samples which have undergone shear yielding or orientation either before or during aging. This exotherm may be the result of release of stored strain energy during the DSC scan.
Anisotropic aspects of the environmental stress cracking of acrylonitrile‐butadiene‐styrene and styrene acrylonitrile copolymers in methanol
Authors: Faulkner Douglas L. 
Published: May 2005

AbstractCritical strains causing environmental stress cracking of injection‐molded poly(acrylonitrile‐butadiene‐styrene) (ABS) and poly(styrene‐acrylonitrile) (SAN) plaques were determined upon exposure to methanol. Measurements were obtained for samples strained either parallel or perpendicular to the melt flow direction and for samples located at various distances from the mold gate. Critical strains were significantly higher in the direction parallel to the melt flow compared to the transverse direction. The degree of anisotropy increased with increasing rubber content. For ABS containing 46 percent rubber, the critical strain at one point was determined to be 2.99 percent in the direction of melt flow, but only 0.47 percent in the orthogonal direction. For this material, critical strains determined parallel to the melt flow decreased with distance from the gate; whereas, critical strains for SAN and ABS containing 30 percent rubber remained essentially constant. Orientation of the plaques was assessed using shrinkage determinations and a thermal conductivity technique. Though a straightforward correlation of orientation with critical strain is observed for ABS, a similar relationship is not observed for SAN. These results suggest that although stress cracking occurs in the glassy matrix of ABS, it is the dispersed rubbery phase which controls the magnitude of strain required to initiate cracking.
Fatigue life prediction of filled polypropylene based on creep rupture
Authors: Trantina Gerald G. 
Published: May 2005

AbstractTo predict the fatigue performance of talc‐filled polypropylene in engineering applications, a simple relationship using constant stress data to predict the cycles‐to‐failure (Nf) was developed:

where k and n are constants from creep rupture tests, v is the cyclic frequency (≤1 Hz to avoid self‐heating), f(n) is a function that accounts for the wave form, and a is the peak cyclic stress with a zero minimum stress. For stress concentrations produced by central holes, σ is taken as the average net section stress and the effect of the stress concentration is ignored. Extensive tests were used to verify this expression for cyclic frequencies of 1.0 and 0.1 Hz, sinusoidal and triangular waveforms, stress concentrations produced by small and large holes, and 20 and 40 percent talc filler content.
Optimization of the polycondensation step of polyethylene terephthalate formation with continuous removal of condensation products
Authors: Kumar Anil , Sharma Satya N. , Gupta Santosh K. 
Published: May 2005

AbstractThe polycondensation step of poly(ethylene terephthalate) (PET) formation is assumed to include various side reactions in addition to the usual polymerization reaction. Polymerization in the batch reactor at constant pressure has been modeled to flash volatile components at the end of small discrete time intervals with polymerization occurring during the interval. The Hamiltonian has been written for the time interval and optimum temperature history computed for batch reactors for various reactor pressures. For low pressures, computed optimum temperature history is found to be of similar nature as that used in industry.
Thermodynamics of polymer solutions, especially poly(dimethyl siloxane) solutions
Authors: Panayiotou Constantinos G. 
Published: May 2005

AbstractAn improved non‐random free‐volume theory of polymer solutions is presented. It is based on Flory's Equation‐of‐State theory which is modified to account for differences in the size of core volumes of segments in pure liquids and in solution. In addition, it is corrected for non‐randomness through Guggenheim's Quasi‐Chemical approach. The theory is tested against experimental results on heats of mixing, volumes of mixing, and χ interaction parameters of poly (dimethyl siloxane), polyisobutylene and natural rubber solutions with gratifying results. Relations with existing similar theories are discussed.
Thermal energy storage in columns packed with crosslinked polyethylene tubes
Authors: Boneh Hanoch , Marmur Abraham , Narkis Moshe 
Published: May 2005

AbstractAn energy storage system based on solid‐solid phase transition of crosslinked polyethylene was constructed and tested. The energy storage unit consisted of a column packed with crosslinked polyethylene tubes. The solid‐solid phase transition enables heat transfer by direct contact between the form‐stable polymer and the hot (cold) fluid. A theoretical model for the simulation of this system was developed. The heating‐cooling characteristics of the energy storage system were simulated by the model, using measured thermodynamic properties of the crosslinked polyethylene. The potential of various crosslinked polyethylene materials for energy storage applications will depend on sufficient high‐temperature stability.
Manufacture of urea‐formaldehyde concentrates using a gas‐liquid technology
Authors: Frontini P. M. , Borrajo J. , Williams R. J. J. 
Published: May 2005

AbstractThe performance of a laboratory packed‐column for the manufacture of urea‐formaldehyde (UF) concentrates is analyzed. Gaseous formaldehyde was generated by the thermal decomposition of paraformaldehyde in a carrier nitrogen stream. The UF solution was continuously recirculated through a glass column filled with Raschig rings. No pH control was necessary when the operation was started using a solution with a F/U molar ratio higher than 3.5 to 4. Otherwise, insoluble resins appeared during the operation. The formaldehyde absorption rate was controlled by the gas phase resistance. The vapor composition in equilibrium with a typical UF concentrate is provided as a function of temperature.
Shear dependence of thermal conductivity in polyethylene melts
Authors: Wallace D. J. , Moreland C. , Picot J. J. C. 
Published: May 2005

AbstractThermal conductivity measurements with a modified Couette flow cell were obtained as a function of shear rate for two linear polyethylene melts of weight‐average molecular weights 27,300 and 56,700, respectively. The lower‐molecular‐weight polyethylene revealed a maximum decrease in thermal conductivity of 55 percent at 150 s−1. After shearing at 400 s−1, approximately 90 minutes was required to recover the value corresponding to the zero shear condition. This was considered consistent with molecular orientation into the flow direction during shear with a subsequent relaxation upon the removal of stress. The higher‐molecular‐weight polyethylene gave a similar decrease in thermal conductivity at 50 s−1. Unlike the lower‐molecular‐weight melt, an increase was observed at higher shear rates. Enhancement of energy transport via cluster flow mechanism was presented as a possible interpretation of these results. A theory of molecular orientation of liquid poly(dimethylsiloxane) (PDMS) under shear flow was previously developed from thermal conductivity and birefringence data of this material. An attempt to clarify the difference in behavior between the two melts examined in this work, and between the polyethylene melts and the PDMS previously studied is presented.
Bubble formation mechanism during heat treatment of polymer films cast from solutions
Authors: Tong Ho‐Ming , Ouano Augustus C. 
Published: May 2005

AbstractA semiquantitative bubble formation mechanism is presented for the baking of polymer films, utilizing poly(methyl methacrylate) (PMMA)‐ethyl acetate (EA) solutions as the model system. It is shown that bubble growth phenomena can he accounted for in terms of the competition between vapor pressure buildup and the rate of vapor dissolution. According to the proposed mechanism, the local pressure buildup of solvent in the polymer film is controlled by the solvent partial pressure above a solution having a planar interface at the corresponding temperature and solvent concentration. This pressure can he estimated by Raoult's law. The vapor dissolution rate, on the other hand, is dominated by the liquid‐phase diffusion of the solvent. A method of obtaining the diffusion coefficient as a function of temperature and solvent concentration from isothermal thermogravimetric analysis (TGA) is also given.
Mechanical relaxation of flame retardant polycarbonate using the cole‐cole method
Authors: Taylor C. R. , Aloisio C. J. , Matsuoka S. 
Published: May 2005

AbstractThe frequency dependence of the complex‐shear modulus of a nonbrominated flame‐retardant polycarbonate has been successfully represented from 1 hertz (hz) to 1 gigahertz (ghz) at 190°C using a mechanical analog of the Cole‐Cole dielectric analysis. Two sets of retardation times were required centered about 74 msec and 16 μsec. The β value for the short time response was 0.83 and for the longer time response was 0.58. The values of J determined from the common point at which the terminal‐zone arc and the transition‐zone arc touch the Jc″ = 0 axis yields an entanglement molecular weight, Me, of 1470 g/mole.
Recent studies of polymer reactions caused by stress
Authors: Porter Roger S. , Casale Antonio 
Published: May 2005

AbstractA singular class of polymer reactions can be caused by mechanical stress. Sufficient storage of mechanical energy to break chemical bonds in the main chain is generally possible only on deformation of polymers of high molecular weight. The corresponding appropriate conditions of high stress may occur in both polymer processing and use. This review summarizes reports of such polymer stress reactions published principally after 1980. The survey is organized by polymer type and by analysis technique.
Fatigue crack growth in polyethylene
Authors: Bucknall Clive B. , Dumpleton Paul 
Published: May 2005

AbstractFatigue crack propagation (FCP) rates are studied in 6 mm thick specimens of high density polyethylene (HDPE) containing razor notches, Centrally‐notched plates and single‐edg notched bars are subjected to sinusoidal tension‐compressio or tension‐zero cycling at 0.5 or 2.0 Hz under load control a room temperature; crack growth is monitored using a travelling microscope. After many thousands of cycles with no observable damage at the tip of the razor notch, a craze like zone begins to form. This zone grows slowly until it reaches the length characteristic of a mature crack at the same ΔK. Crack growth proper then begins. The number of cycles to initiate crack growth falls linearly with increasing ΔK at the razor notch Subsequent crack growth is determined both by the current value of ΔK and by loading history. When ΔK is increasing, FCP rates follow a standard Paris law curve. However, reduced, FCP rates are observed following an overload.
Multifunctional step growth polymerizations in cascades of isothermal, continuous flow, stirred tank reactors
Authors: Gupta Santosh K. , Bafna Sudhir S. , Kumar Anil 
Published: May 2005

AbstractThe step growth polymerization of RAf type multifunctional monomers (with A reacting with A) in cascades of isothermal, homogeneous, continuous flow stirred tank reactors (HCSTR's) is simulated. It is found that our equations reduce to those of Cozewith, et al. If either f or the molecular weights are large. However, under certain conditions, the low molecular weight correction is significant and the more exact equations of the present work must be used. Several possible start‐up strategies are discussed, of which one is amenable to analytical solution. This is the one in which all HCSTR's are filled initially with the steady state feed from the previous reactor and the outputs from any reactor, during its start‐up period, are discarded to an ‘off spec’ tank. It is found that for this case, in order to ensure nongelling operation, the mean residence time of any HCSTR must lie below a certain critical value, depending on the value of f and the feed conditions.
Response of polycarbonate, poly(methylmethacrylate), and epoxy resins to dynamic contact loading I. Experimental results
Authors: Hillig William B. 
Published: May 2005

AbstractMeasurements of the resistance force to a wide range of contact loadings have been performed on poly(methylmethacrylate), polycarbonate, and epoxy specimens. Rigid spherical indenters of 4.5, 9, and 18 mm diameter, as well as cones of various apex angles, were driven into thick specimens at constant velocity over the range 0.005 to 150000 mm/min. The objective of this study was to develop a data base useful for the understanding and analysis of the phenomena involved when polymeric solids are impacted by small hard bodies. Spheres and cones were used because these symmetrical shapes offer the best chance for analysis in terms of viscoelastic extensions of the classical Hertz elastic contact problem. Measurements covered penetration depths from first detection of contact, where the strains are smallest and the material response should most likely be interpretable in terms of linear viscoelastic analysis, to much greater depths where the strains far exceed the yield values. The observations are tabulated, as are the values of parameters that allow the data to be modeled to within experimental error. These parameters fit into a specially developed empirical law designed to facilitate subsequent treatment of the data using Laplace transform methods. An analysis is offered to try to sort out time‐dependent force relaxation from depth‐dependent force increase during the progress of the penetration. The results of the response at small penetration depths are in broad accord with published relaxation moduli. However, the dependence of force upon indenter geometry does not follow simple expectation.
Minimizing curl induced upon drying layered solvent coated films
Authors: Penwell R. C. , Chow T. S. 
Published: May 2005

AbstractThe problem of minimizing edge curl in a solvent dated layered polymeric composite web is discussed. Basic material relations are presented, with experimental data, which can be used to optimize coating and drying conditions to produce a flat surface. Viscoelastic equations, derived to understand the effects of material and geometrical parameters on curl, are discussed and applied to minimize curl in a dried condition. The results clearly indicate that coating, material, and geometrical parameters can be understood and used to minimize curl.
Diffusion of water in glassy epoxide prepolymers
Authors: Garcia‐Fierro J. L. , Aleman J. V. 
Published: May 2005

AbstractSorption isotherms show that epoxide prepolymers sorb water in increasing amounts as the temperature decreases and the water vapor concentration increases. Below Tg the behavior is typical of a Fickian transport combined with a relaxation process. Diffusion coefficients as function of sorption rates provide temperature shift factors from which the activation energy for diffusion is 35.3 KJ/mol. Combined effect of temperature and water concentration is described by a second order polynomial.
High modulus of isotactic polypropylene attained by coextrusion with atactic polystyrene
Authors: Verbraak C. L. J. A. , Van Dam J. , Van Der Vegt A. K. 
Published: May 2005

AbstractOrientation‐induced crystallization of crystallizable polymer melts can occur, under certain conditions, during flow through converging channels. Attempts have been made to achieve this phenomenon in a two‐phase system, i.e., during simultaneous extrusion of a continuous concentric core of polypropylene within a polystyrene matrix through a conical duct. On one occasion, using Carlona P SY6100 (MFI = 11.0) with Hostyren N2000‐V‐01 (MFI = 25.0), a highly oriented polypropylene thread with a modulus of 14.6 GPa and a melting point of 178°C was extruded at a die temperature of approximately 170°C and a pressure lower than 40 MPa. It is, in principle, possible to form highly oriented, fiber‐like structures as reinforcing elements in a polymer matrix.
Life expectation of polycarbonate
Authors: Ram A. , Zilber O. , Kenig S. 
Published: May 2005

AbstractPolycarbonate (PC), one of the leading engineering plastics, suffers from deterioration under harsh environmental conditions. It is sensitive to the effects of light (UV) radiation, to thermal degradation, and to the attack of hot water, due to hydrolysis. By exposure of various commercial PC grades—at various molecular weights and stabilization—to either natural or accelerated conditions, a maximum lifetime of three years was predicted for the best‐behaving grades. The criterion for failure was mainly based on loss of ductility in tensile tests, as well as loss of optical clarity and chain scission. Hot water has a significant effect on the performance of PC samples, and this is considered to be its greatest weakness. Degradation after exposure at various temperatures (without UV or humidity) leads to estimation of a temperature‐endurance index, that may serve as a practical limiting criterion for polymer life expectancy.
Residual stresses and toughness of polycarbonate exposed to environmental conditions
Authors: Ram A. , Zilber O. , Kenig S. 
Published: May 2005

AbstractThe role of the size and type of residual stresses and their distribution in the interior of polycarbonate mold‐injected test bars was studied, in view of the interrelationship between toughness and thermal or environmental history. The large thermal gradient during solidification of the polymer in the mold builds up compressive stresses near the wall and tensile stresses in the core. Annealing followed by slow cooling may reverse the type of stresses near the surface, while quenching augments the compressive stress. The latter stress near the wall is responsible for the extraordinarily high impact strength of polycarbonate. Exposure to the atmosphere and immersion in hot water may affect the distribution of residual stresses and thus contribute to the embrittlement of the originally tough polymer. The importance of molecular weight and polymer stabilization is elucidated.
Rotary injection reaction injection molding (RI‐RIM). Part I: Basic design features
Authors: Briscoe B. J. , Khan M. B. , Richardson S. M. 
Published: May 2005

AbstractThis paper describes the basic design features of a new reaction injection molding (RIM) processing device, Rotary Injection RIM (RI‐RIM). The new design includes a novel mixing concept which furnishes high intermaterial contact area upon shear imposed rotary injection of the RIM components for effective in situ polymerization. This system operates in low pressure and laminar flow conditions, as opposed to the high pressure and turbulent flow, found in conventional RIM systems. The mixing process is described and quantified in terms of the various forces which govern the injection process. A progressive diminution in the average size of the dispersions generated is found with increasing rate of shear, continuous‐phase viscosity, and injection rate. These results are compared with those expected from traditional shear mixing (bulk convective shearing) under comparable conditions and the current system found to be more efficacious. Reaction molding experiments with RI‐RIM using a model polyurethane system are described and the influence of operating conditions on the mechanical properties of the finished moldings are elucidated. A detectable change in the morphology of the system is observed following increase in the total shear strain imparted to the initial mix of the multiphase reactants. It is suggested that the observed change is affected by a segregation between the components of the segmented polymer.
Study on the continuous loop tubular reactor for emulsion polymerization of styrene
Authors: Lee Der‐Yuan , Kuo Jen‐Feng , Wang Jenn‐Hwa , Chen Chuh‐Yung 
Published: May 2005

AbstractA continuous loop tubular reactor (CLTR) with a Bodenstein number of 100 and a recycle ratio of 0.992 (obtained under the conditions of a mean residence time of 25.0 to 59.95 min and a stirring rate of 418 rpm) was used for studying the emulsion polymerization of styrene (St). The recipe used in the study is 76.8 g St/l‐water, 3.73 g sodium lauryl sulfate (SLS)/l‐water, and 2.30 g potassium persulfate (KPS)/l‐water. The effects of the mean residence time on the performance of emulsion polymerization were studied. The overshoots in the monomer conversion and the particle number concentration were found to be higher as the mean residence time increased. The overshoots diminished at about 3 times the mean residence time. The steady state particle number concentration was independent of the mean residence time, while the steady state monomer conversion increased with increasing mean residence time.
Effect of early solvent evaporation on the mechanism of the spin‐coating of polymeric solutions
Authors: Skrobis Kenneth J. , Denton Denice D. , Skrobis Amy V. 
Published: May 2005

AbstractThe effect of solvent evaporation on spun‐on polymer thickness is investigated. Film thickness is shown to be proportional to spin speed raised to the negative of a constant, b. This constant is specifically considered. Of particular interest is the short initial period during spin coating signified by a rapid increase in solution viscosity, but where solvent diffusion in solution is not yet significant. Many previous theories have suggested the existence of a single value for b dependent only upon environment and spin coating system. Here, a single polymer dissolved in five pure solvents is examined. The polymer is Thermid IP‐600 (National Starch and Chemical Co.), an isoimide precursor. The solvents considered are n‐methyl‐2‐pyrrolidinone, dimethyl sulfoxide, dimethyl formamide, ethylene glycol dimethyl ether, and 2‐methoxyethyl ether. Spin Speed ranges from 0.6 to 7.0 kRPM and spin time is held at 15 s. It is shown that b varies from 0.97 for n‐methyl‐2‐pyrrolidinone to 0.57 for 2‐tncthoxycthyl ether. An empirical relation describing the behavior of b for this particular polymer and spin conditions used is b = [(MW)s(Pvap)s]/[(MW)n(Pvap)n]−0.1, where (MW)s and (MW)n are the molecular weights of the solvent and of n‐butyl acetate, respectively and where (PVaP)s and (Pvap)n are the vapor pressure of the pure solvent and the vapor pressure of n‐butyl acetate, respectively.