bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheological changes during the polymerization of polyurethane based interpenetrating polymer network(IPN)
Authors: Lee Y. M. , Yang Y. S. , Lee L. J. 
Published: December 2004

AbstractExperimental results on reactions forming polyurethanes and polyurethane‐polyester Interpenetrating polymer network (IPN) are discussed with particular interest in rheological and kinetic changes before the gel point. In the IPN formation, viscosity rise is affected by the amount of styrene and polyester in the reaction system. Plots of reduced viscosity vs. conversion do not fall into a single curve. The results may be explained by the concept of having intra‐molecular reaction or ring formation. The existence of hydroxyl group at the end of polyester molecule causes the graft reaction between the polyurethane phase and the polyester phase, which may speed up the viscosity rise of the reactive system. A simple method which based on rheological measurements only is proposed. This method of plotting reduced viscosity vs. reduced reaction time provides similar results as in the plots of reduced viscosity vs. conversion.
Coupling between stresses and moisture diffusion in polymeric adhesives
Authors: Yaniv G. , Ishai O. 
Published: December 2004

AbstractAn experimental procedure is suggested for quantitative evaluation of the interdependence of stresses and moisture diffusion in polymer‐dominated materials with special emphasis on epoxy resin based polymeric adhesives. It has been found that when such material is stressed in tension, the moisture diffusion rate increases; and when in compression, it decreases. At low stress levels, a linear relation was obtained between the coefficient of moisture diffusion and the applied stress, while at elevated levels it is nonlinear. Throughout the loading range, the coefficient correlates well with the volumetric changes in the stressed material.
The relationship between the equilibrium melting temperature and the supermolecular structure of several polyoxetanes and polyethylene oxide
Authors: Murphy C. J. , Henderson G. V. S. , Murphy E. A. , Sperling L. H. 
Published: December 2004

AbstractThe relationships between equilibrium melting temperatures (Tm*) and crystalline morphology of poly[3,3bis(ethoxymethyl)oxetane], (polyBEMO), poly[3,3‐bis (azidomethyl)oxetane], (polyBAMO), and poly(ethylene oxide), (PEO), were characterized. The Hoffman‐Weeks extrapolation procedure led to Tm* values of 92, 102, and 69°C for these three polymers, respectively. The gross morphologies of polyBEMO, polyBAMO, and PEO were studied as a function of melt‐liquid temperature (Ti) and isothermal crystallization temperature (Tc) by visible light microscopy. Spherulitic morphologies were observed for polyBEMO, polyBAMO, and PEO when Ti was above Tm*, while nonspherulitic (hedritic) morphologies were observed at Tls below Tm*. Mixed morphologies were observed when Tl was approximately equal to Tm*.
A kinetic model for curing reactions of epoxides with amines
Authors: Chern C.‐S. , Poehlein G. W. 
Published: December 2004

AbstractCuring reactions of epoxy resins are accelerated by added hydrogen‐bond donor solvent and hydroxyl groups produced during the course of polymerization. A kinetic model comprising several different polycondensation and polyaddition reactions that occur simultaneously is developed. The concept of diffusion controlled reactions is employed to describe the change of reaction rate constants with conversion after the formation of an infinite crosslinking network. Good agreement is obtained between the model predictions and experimental data available in the literature.
Tensile yield in polypropylene
Authors: Hartmann Bruce , Lee Gilbert F. , Wong Wayne 
Published: December 2004

AbstractUntaxial tension tests to the yield point were performed on polypropylene as a function of temperature from 22 to 143°C at a strain rate of 2 min−1. At 22, 42, and 71°C, measurements were also made at strain rates from 0.02 to 8 min−1. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (164°C). The ratio of thermal to mechanical energy to produce yielding is about three times smaller than for glassy polymers. The ratio of yield stress to (initial) Young's modulus is about 0.024 at room temperature and increases to 0.043 at 143°C. Yield stress is a linear function of unstrained volume.
Characterization of molecular orientation in injection‐molded thermoplastics by transmission and reflection infrared spectroscopy
Authors: Houska M. , Brummell M. 
Published: December 2004

AbstractOrientation in injection moldings of polypropylene (PP), polyethylene (PE), polyamide 6 (PA‐6), and polystyrene (PS) was investigated by transmission and reflection infrared spectroscopy. Orientation of the surface was measured by the reflection method, the depth profiles of orientation and of the fraction of the crystalline phase were measured by the transmission spectroscopy of microtome sections. The maximum of orientation of PP lies in the subsurface layer (ca. 250 μm); the crystalline phase is oriented more than the amorphous one. The maximum of the depth profile of orientation corresponds to the minimum of the fraction of the crystalline phase in PP. The profile of orientation of PE Is similar; at the beginning (to a depth of about 500 μm) the parallel orientation of the c axis of the crystalline phase is the most distinct one, towards the center the orientation of the a axis passes from the perpendicular to the parallel one. Under the described molding conditions PA‐6 is not significantly oriented, the fraction of the crystalline phase increases towards the center of the molding. Unoriented PA‐6, the surface layer of which was removed by milling, has a highly oriented surface due to its mechanical treatment. No pronounced orientation of PS was observed under the molding conditions used.
Modeling of polymerization of melamine and formaldehyde using a functional group approach
Authors: Kumar A. , Chandra R. 
Published: December 2004

AbstractA functional group approach that accounts for the formation of higher oligomers was used in modeling the batch polymerization of melamine and formaldehyde. Five rate constants are required instead of 24 as needed in earlier studies to fit experimental data in the entire range. The model presented allows the formation of higher oligomers even though their formation is small. The batch polymerization of melamine and formaldehyde was studied under a wide variation of reaction parameters to find conditions that would lead to formation of higher oligomers preferentially.
Thermo‐oxidative degradation of polyolefins observed by isothermal long‐term DTA
Authors: Kramer E. , Koppelmann J. 
Published: December 2004

AbstractIsothermal differential thermal analysis (DTA) is well known for measuring thermal stability of polyolefins by determining the oxidative induction time at elevated temperatures. Oxidative induction time, measured up to 7,000 hours and over a temperature range from 240°C to 120°C, has been used to study the stability of polybutene‐1 and crosslinked polyethylene in the melt state. The Arrhenius plots of DTA results show that straight line extrapolation from high to low temperatures is not possible. Thermoanalytically measured oxidation induction times and mechanical failure in oven aging experiments agree for polybutene and crosslinked polyethylene, Measurements of molecular weight and of mechanical properties of polybutene‐1 during the induction period of oven aging experiments at low temperatures revealed that molecular weight and tensile properties are not sensitive indicators for the beginning of aging. The state of deterioration can be estimated easier by measurement of residual lifetime in the isothermal DTA experiment. Diffusion processes of stabilizers in polyolefins, as well as the consumption of stabilizer at elevated temperatures, especially during the induction period also was observed by DTA. Finally the extraction of stabilizer by hot water was measured by isothermal DTA.
A chemorheological model for the cure of unsaturated polyester resin
Authors: Lee Dai‐Soo , Han Chang Dae 
Published: December 2004

AbstractA chemorheological model is developed, using the free volume concept, for the prediction of viscosity during the cure of unsaturated polyester resin. We have incorporated into the development of the chemorheological model a mechanistic kinetic model of curing kinetics that predicts the degree of cure as a function of cure time. The mechanistic kinetic model uses an approach of free‐radical polymerization that takes into account diffusion‐controlled curing reactions, In order to test the usefulness of the chemorheological model developed, we have conducted cure experiments and measured viscosities of partially cured resin samples, using a general‐purpose unsaturated polyester resin. Specifically, the following measurements were taken: (1) the quantity of ethylenic double bonds in the resin system before and after the cure reaction by infrared spectroscopy, (2) the glass transition temperature by differential scanning calorimetry (DSC) and (3) the viscosity as a function of shear rate, at several temperatures, using a cone‐and‐plate rheometer. It is concluded that the chemorheological model developed is very useful for predicting the variation of viscosity during the cure of unsaturated polyester resin.
Effective elastic moduli for thin‐walled structural foam beams
Authors: Stokes Vijay K. 
Published: December 2004

AbstractBecause of the nonhomogeneous morphology of rigid structural foams, the elastic moduli determined from tension and bend tests are different, the latter being larger. These moduli also depend on the geometry of the specimen. In general, the elastic bending stiffness of foams is determined by the rigidity tensor, which combines geometry and material information. Although the bending problem for nonhomogeneous materials is more complex than the equivalent homogeneous problem, the analysis simplifies considerably for thin‐walled beams. The effective flexural modulus for a thin‐walled foam beam is shown to be the tension modulus that would be measured on a flat foam specimen of the same thickness. The flexural modulus measured by bend tests on flat bars is shown to have very little effect on the stiffness of most thin‐walled sections. This conclusion is independent of how the “true” material modulus varies across the thickness of the foam part.
Melt spinning of (multifilament) poly(ethylene terephthalate) fibers: A simulation approach
Authors: Dutta A. 
Published: December 2004

AbstractAn approach for modeling and simulation of multifilament melt spinning of poly(ethylene terephthalate) fibers is presented. It is shown that the quench conditions seen by the filaments within a bundle are not identical but differ for different rows of filaments. This, in turn, affects the spun fiber properties and introduces a degree of variability in the properties. The proposed approach allows determination of both the average properties and their variability for a given set of spinning conditions, spinneret geometry, and quench details.
The optical properties of bisphenol‐A polycarbonate
Authors: Philipp H. R. , Legrand D. G. , Cole H. S. , Liu Y. S. 
Published: December 2004

AbstractThe optical properties of bisphenol‐A polycarbonate resin as described by the complex index of refraction, N = n – ik, are derived by Kramers‐Kronig analysis of experimental absorption and reflectance data obtained in the range 40μm ≥ λ ≥ 105 nm. Electronic absorption processes in polycarbonate are characterized by two broad absorption peaks centered at ∼200 and ∼100 nm.
Adhesive tack and green strength of EPDM rubber
Authors: Bhowmick Anil K. , De Prajna P. , Bhattacharyya Ashis K. 
Published: December 2004

AbstractMeasurement of tack of EPDM (ethylene‐propylenediene terpolymer) rubber with natural rubber (NR) of four different molecular weights, styrene‐butadiene rubber (SBR), butadiene rubber (BR), bromobutyl rubber (BIIR), and polychloroprene rubber (CR) was done over a range of rates of testing, contact times, and temperatures of contact. The effect of different additives, namely carbon black, phenol‐formaldehyde resin, coumarone‐indene resin, and methyl methacrylate is also reported. Green strength of all the rubbers was measured. Tack strength increases with increase in contact time for all the rubbers. Adhesive tack between EPDM and low‐molecular‐weight NR is much higher than that between EPDM and NR of high molecular weight. Tack strength of EPDM with BIIR is the highest among the tack values obtained for synthetic rubbers. The adhesive tack between EPDM and natural/ synthetic rubber passes through a maximum when plotted against temperature of contact. It increases with testing rate. All these phenomena could be explained in terms of interdiffusion of rubber chains under different conditions and solubility parameter of two contacting rubbers. It was observed that tack strength varies with (contact time)1/2 and (rate)1/2 in accordance with the reptation theory. Phenol‐formaldehyde resin (PF) or coumarone‐indene (CI) resin in EPDM improves the tack strength quite significantly. The resin in the NR phase does not have a marked effect. The presence of carbon black decreases adhesive tack strength between EPDM and NR. The surface of EPDM, however, becomes smoother with the addition of the additives. Peel tests and commercial tack tests give similar results in the tack strength between EPDM/NR and EPDM/SBR.
Multiordering parameter models of volume and enthalpy recovery generalized to treat physical aging; a quantitative investigation
Authors: Chen Y. P. , Aklonis J. J. 
Published: December 2004

AbstractMultiordering parameter models have been quite successful in rationalizing volume and enthalpy behavior of glasses subjected to various thermal histories in the glass transition range and even at lower temperatures. In the past we suggested a generalization of such models to encompass what is now termed physical aging, i.e., recovery as monitored by mechanical experiments such as creep and stress relaxation. Our initial investigation indicated qualitative agreement between the generalized model and experimental behavior. We have now more completely investigated this area and found a convenient approximation through which behavior can be calculated in most situations without using a distribution of mechanical relaxation or retardation times. Using this technique, we find that essentially quantitative agreement between this model and experimental results is possible only when a very sharp distribution of volumetric recovery times, like that of a single ordering parameter model, is used, Broader distribution functions result in aging behavior which is much more sluggish than observed experimentally. This result is particularly disturbing since such sharp distribution functions have been shown to be incompatible with direct observations of volume recovery.
An investigation of the blend of partially brominated poly(2,6‐dimethyl 1,4‐phenylene oxide) and polystyrene in the primary (glass‐to‐rubber) transition region
Authors: Choe Soonja , Aklonis J. J. 
Published: December 2004

AbstractCompatible polymer blends can be used to test critically the viability of the damped Debye lattice (DDL) model of relaxation in the primary (glass‐to‐rubber) transition region. Since these blends form because of specific intermolecular interaction, the force constants that characterize intermolecular elastic interactions can be controlled to some extent by varying blend composition. The model predicts an unusual sharpening of the stress relaxation master curve of a marginally two‐dimensional DDL upon dilution with a plasticizer. We have prepared an appropriate two‐dimensional DDL by adding modest amounts of partially brominated poly(2,6‐dimethyl 1,4‐phenylene oxide) to polystyrene to form compatible blends. As predicted by the model, sharpening of the stress relaxation behavior upon dilution was observed for all blend compositions and for all diluents used. However, at higher brominated poly(phenylene oxide) concentrations, the anticipated diluent concentration dependence was not always observed and the sharpening of the stress relaxation behavior was less than expected. In similar experiments carried out on diluted homopolymers, the relative values of the solubility parameters of the polymers and the diluents strongly influenced the effectiveness of the diluent in changing the stress relaxation behavior. In this blend system, the particular chemical nature of the diluent was found to be much less important; in fact, the three diluents used all evoked approximately the same behavior despite their having solubility parameters that differed significantly.
Catalyst fragmentation during propylene polymerization: Part II. Microparticle diffusion and reaction effects
Authors: Ferrero Monica A. , Chiovetta Mario G. 
Published: December 2004

AbstractA mathematical model is used to predict the behavior of the support/catalyst/polymer macroparticle during the gas phase polymerization of propylene. The problem is focused on the micrograin level of the macroparticle, and the emphasis placed on the combined reaction and diffusion processes taking place in the micropartiele. Particular attention is given to the effect of the main geometry parameter, the size of the catalytic nucleus, on polymerization variables. Fragmentation rate, monomer concentration, and temperature are studied in terms of their dependence on the geometry‐related dimensionless numbers typical of the process. A strong influence of the micrograin size on the commanding process variables is predicted by the model. Fragmentation proves relevant to the overall process and critical to define the time scale of temperature excursions. Micrograin nucleus size are found to be important when computing both maximum temperatures and minimum yields. The model suggests criteria for predicting “a priori” the combination of reaction parameters that will produce a diffusion‐limited reaction regime in the microparticle.
A contribution to the understanding of polyethylene/ionomer/polyamide‐6 blends
Authors: Fairley Gary , Prud'Homme Robert E. 
Published: December 2004

AbstractIt has been reported that the addition of specific copolymers can improve the mechanical properties of blends of polyethylene with polyamide‐6. One of these, a poly(ethylene‐co‐methacrylic acid) (EMA) containing between 4 and 15 mol % of methacrylic acid units, has often been used. Binary polyethylene/EMA and EMA/polyamide‐6 blends were studied with the hope that the role of EMA as a compatibilizer in polyethylene/EMA/polyamide‐6 ternary blends might be better understood. Differential scanning calorimetry (DSC), laser small‐angle light scattering, and mechanical property results are discussed. DSC measurements show that one component of the binary blends does not modify the crystallinity of the other. However, laser small‐angle light scattering shows that the morphology of the mixtures changes under similar conditions. Tensile properties of polyethylene/EMA binary blends vary linearly as a function of composition, whereas those of EMA/polyamide‐6 blends deviate slightly from linearity. These results indicate no interaction between the crystalline components of the mixtures, and weak interactions in the amorphous phase.
Nuclear magnetic resonance studies of ionomers. 6. Polyurethane‐polyphosphonate blends
Authors: Natansohn Almeria , Rutkowska Maria , Eisenberg Adi 
Published: December 2004

AbstractBlending of a poly(ether urethane) with a polyphosphonate obtained by phase transfer catalyzed polycondensation of 4,4′‐biphenol and chloromethylphosphonic dichloride generates a phase‐separated material. One phase contains the soft segment of the polyurethane. This has been excluded from a high‐Tg phase that contains ionic species formed mainly by proton transfer and elimination reactions between the hard segment of the polyurethane and the polyphosphonate. Two glass transitions appear in the blend: one close to the Tg of the polyphosphonate and one belonging to the excluded soft segment of the polyurethane. The low temperature Tg decreases with the increasing content of the polyphosphonate, whereas the high temperature transition increases slightly, indicating an increasing purity of the soft segment and the presence of ionic interactions in the hard segment. The presence of ionic interactions is confirmed by NMR analysis of the blend. Comparison of the spectra of the blends with those of the pure components, along with two‐dimensional experiments, indicate a reaction involving the chloromethyl groups of the polyphosphonate and the nitrogens of the polyurethane.
Structure‐property‐processing relationships of polypropylene‐polybutylene blends
Authors: Hsu C. C. , Geil P. H. 
Published: December 2004

AbstractIn this paper we discuss PP‐PB blends in which both components are highly crystallizable. It was our intention to try to prepare homogeneous PP‐PB blends, assuming miscibility in the melt, by using the ultraquenching technique and to study the properties of the resulting blends following crystallization from the glass. Due to the possibility of preparing homogenous blends by ultraquenching, it should be interesting to compare the morphology, properties, and crystallization of the glass‐crystallized blends with the melt‐crystallized blends. We conclude that, in general, the above results suggest there is a considerable degree of compatibility, possibly even miscibility, of PP and PB in the melt, but that miscibility is difficult to obtain by ordinary melt mixing processes.
Characterizing polyethylene‐based blends with temperature rising elution fractionation (TREF) techniques
Authors: Kelusky Eric C. , Elston Clay T. , Murray Ron E. 
Published: December 2004

AbstractThe temperature rising elution fractionation (TREF) technique makes use of the differential crystallizabilities, introduced by short chain branches (SCB), to fractionate polyethylenes (PE) on the basis of the SCB level of any one chain. This allows one to probe the SCB distribution of a polymer. The TREF technique has been applied to blends of PE by recognizing that the two commercial types of low density polyethylene, high pressure (HP‐LDPE) and linear low density (LLDPE), have different short chain branching distributions. Other common copolymers of ethylene, like ethylene vinyl acetate (EVA) or terpolymers like ethylene/propylene/hexadiene (EPDM), also have different SCB types, levels, and distributions and therefore have different TREF behavior. We have constructed a TREF apparatus that can be used in a number of different types of blend studies. The first is an Analytical‐TREF, which gives a profile of the amount of polymer with a given SCB level and can be used to quantify HP‐LDPE/LLDPE blends. We have also modified the technique to construct a stop‐flow TREF apparatus, which enables one to separate fractions on the basis of the branching levels. The fractions can then be analyzed by size exclusion chromatography, IR, 13C NMR, or DSC. The use of these TREF techniques to characterize blends of HP‐LDPE/LLDPE, LLDPE/EVA, PE/EPDM, and PE/polyisobutylene is discussed.