bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of dispersed phase in incompatible polymer blends: Interfacial and rheological effects
Authors: Wu Souheng
Published: December 2004

The formation of dispersed phase in blends of incompatible polymers during melt extrusion with a co‐rotating twin screw extruder was studied, using nylon and polyester as the matrix and ethylene‐propylene rubbers as the dispersed phase. A master curve is obtained, i.e., Gηmα/γ = 4p±0.84, where G is the shear rate, γ the particle diameter, η the interfacial tension, ηm the matrix viscosity, ηd the dispersed‐drop viscosity, and p = ηd/ηm. The plus (+) sign applies for p > 1, and the minus (−) sign for p < 1. Thus, the dispersed‐drop size is directly proportional to the interfacial tension and the ±0.84 power of viscosity ratio. The dispersed drops are the smaller, when the interfacial tension is the lower and the viscosity ratio is the closer to unity. The interfacial tension is largely controlled by the polarities of the two phases, and can be varied over several orders of magnitude by using appropriate dispersants.
Phase transitions during shear flow of two‐phase polymer blends. I. Theory. Transition to “Homogeneous” melt state
Authors: Lyngaae‐Jørgenson J. , Søndergaard K.
Published: December 2004

A hypothesis for critical conditions for a transition from a two‐phase system to a homogeneous state during simple shear flow is advanced. It is predicted that at sufficiently high shear stress a homogeneous state is the stable steady state structure.
Phase transitions during shear flow of two phase polymer blends. II. Styrene‐acrylonitrile/poly(methylmethacrylate) transition to “Homogeneous” melt state
Authors: Lyngaae‐Jørgensen J. , Søndergaard K.
Published: December 2004

An advanced hypothesis derived in Part I (this issue) is tested with selected model blends. Blends of copolymers of styrene and acrylonitrile (SAN) and poly(methylmethacrylate), (PMMA) were studied because they are both amorphous, thermally stable, have large density differences, are easy to cut (in an ultramicrotome) and because comprehensive studies have been reported In the literature on this system. The melt viscosity of the blends were studied using a Rheometrics Mechanical Spectrometer and an Instron capillary rheometer. Light scattering measurements were performed during flow in order to measure the critical transition stress. The phase structure of quenched samples was studied by transmission electron microscopy on ultramicrotome cuts. It was shown that an Interpenetrating co‐continuous structure develops when flow is stopped, if a homogeneous phase Is formed during flow. Melt fracture limits the applicability of this approach to nearly compatible blends.
Linear low density polyethylenes and their blends: Part 2. Shear flow of LLDPE's
Authors: Utracki L. A. , Schlund B.
Published: December 2004

The steady state and dynamic shear behavior of eleven commercial linear low density polyethylenes (LLDPE) and one low density polyethylene (LDPE) resin were measured in capillary and parallel plate geometries at T = 150 to 230°C. The extrudate swell and the Bagley correction were determined. A large pressure effect on capillary flow of narrow molecular weight distribution LLDPE was observed and a new corrective procedure was proposed. After the correction the steady state viscosity was found to be equal to the dynamic (not complex) viscosity: η(\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}) = η'(ω = \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document}). A newly proposed four parameter relation between η and the deformation rate was found to provide a simple means for computation of the zero shear viscosity, ηo, and the primary relaxation time. Both these parameters showed a high degree of correlation. The expected relation: ηo ∝︁ Mw3.4 was observed for low molecular weight samples with low polydispersity. The LLDPE activation energy of flow, Eσ=29.9 ± 1.8 kJ/mole, was determined.
A study on poly(vinyl chloride) blends with chlorinated polyethylene and acrylic resin
Authors: Xi Xu , Liwu Zhang , Huilin Li
Published: December 2004

The compatibility, morphology, fusion behavior, and mechanical properties of blends of poly(vinyl chloride) (PVC), acrylic resin (ACR), and chlorinated polyethylene (CPE) (100/0–30/0–20) were studied. The experimental results show that the compatibility of the polyblend increases with the amount of ACR added. The blends composed of PVC/ACR/CPE (100/3–25/10–15) are fairly compatible. So far as impact strength is concerned, partially compatible blends are preferred.
Interrelationship between the crystallization behavior, injection molding conditions, and morphology of poly(ethylene terephthalate)/poly(methyl methacrylate) alloys
Authors: Nadkarni V. M. , Jog J. P.
Published: December 2004

The thermal and isothermal crystallization behavior of PET/PMMA (poly(ethylene terephthalate)/poly(methyl methacrylate)) alloys was investigated. The crystallization of PET is accelerated significantly by alloying with PMMA. As a result, crystalline specimens could be injection molded with the alloy at low mold temperatures of 19°, 55° and 90°C., whereas a mold temperature of about 130°C is normally required for crystallinity to develop in the virgin PET grade. The impact strength of the alloy specimens increased significantly with decreasing mold temperature despite a comparable degree of crystallinity. The increase in impact strength is correlated to the reduction in the crystallite size and broadening of the crystal size distribution with decreasing mold temperature.
Melt rheology of polyarylate/polybutylene terephthalate blends
Authors: Ausín A. , Eguiazabal I. , Munñoz M. E. , Peña J. J. , Santamaría A.
Published: December 2004

The viscosity, the activation energy of flow, and the exchange reactions of bisphenol A 50/50 isophthalic/terephthalic acid and poly(butylene terephthalate) blends are studied by means of an extrusion capillary rheometer, covering a range of 10 s−1 to 300 s−1 shear rate and 280°C to 300°C temperature. The results are interpreted in terms of compatibility and free volume additivity. The decrease in viscosity with time is explained as a result of transesterification rather than degradation.
Spectroscopic study of poly(ethylene terephthalate)/poly(amide‐6,6) blends
Authors: Pillon L. Z. , Utracki L. A. , Pillon D. W.
Published: December 2004

Fourier transform infrared (FT‐IR) studies of poly(ethylene terephthalate) (PET)/poly/(amide‐6,6) (PA) blends are presented. The blends were prepared in the molten state and in solution with trifluoroacetic acid (TFA) as the solvent. The PET/PA blend is a complex system containing, two crystallizable polymers with the ability to interact chemically. Some of the blends were prepared in the molten state in the presence of a catalytic amount of p‐toluenesulfonic acid (TsOH) to undergo the ester‐amide interchange reaction. Nuclear magnetic resonance (NMR) and FT‐IR have proven to be excellent techniques with which to study these blends. 1HNMR was used to follow the ester‐amide interchange reaction and FT‐IR to detect the presence of hydrogen bonding. FT‐IR studies showed the lack of hydrogen bonding in all the blends prepared in the molten state and its presence in the blends prepared in solution.
Dynamic mechanical behavior of continuous multilayer composites
Authors: Gregory Bryan , Hiltner Anne , Baer Eric , Im J.
Published: December 2004

The dispersion processes in multilayer laminate composites of styrene acrylonitrile (SAN) and polycarbonate (PC) were studied utilizing the torsion pendulum. A third damping peak with a log decrement intensity of approximately one was observed at a temperature intermediate to the damping peaks corresponding to the Tg's of the two constituent phases. Variations of numerous material and experimental parameters such as composition ratio, orientation, thermal history, thermal cycling, number of layers, and layer thickness, as well as overall changes in the composition of the phases had no effect on the observance of a third peak. Only the disruption of the continuous layer structure effectively eliminated this novel transition. The origin of this transition was explained by assuming appropriate temperature dependencies for the controlling viscoelastic parameters in such a continuous layer composite.
Minimum end time policies for batchwise radical chain polymerization. Part VI: The initiator addition policies for copolymerization with constant copolymer composition control
Authors: Chen Show‐An , Lee Song‐Tai
Published: December 2004

For batchwise radical chain solution copolymerization, the minimum end time problem with constant copolymer composition control is studied by considering the initiator concentration (or feed rate) and temperature as two control variables. During copolymerization, the more rapidly depleting monomer is continuously fed to the reactor to maintain the comonomer ratio constant. The volume variation due to contraction during copolymerization, in addition to monomer and solvent feeding, is also considered. It is found that the optimal initiator addition policy is to make the rate of initiation (2fkdIV) constant. The volume factor V is for taking account of volume variation. For the isothermal case, the number of moles of initiator in the reactor should remain constant. Experimental verification for acrylonitrile and styrene isothermal copolymerization with the proposed stepwise feeding of the more rapidly depleting monomer to simulate the optimal continuous monomer feeding policy shows that the present method is applicable.
Material selection considerations for gas separation processes
Authors: Koros W. J. , Story B. J. , Jordan S. M. , O'Brien K. , Husk G. R.
Published: December 2004

Advantages and disadvantages associated with common membrane types used in gas separation operations are reviewed. Comparisons between dense‐walled and several different types of asymmetric structures are made. In addition to overall membrane structure, the molecular natures of different membrane material types are treated. Tradeoffs between the use of rubbery and glassy polymers are considered first, followed by a treatment of the optimization of glassy membrane permeability and permselectivity properties. Material optimization principles are defined in terms of the basic thermodynamic solution and kinetic transport properties of polymers, and applications of these principles are illustrated for a modified poly(phenylene oxide) and a homologous series of polyimides derived from pyromellitic dianhydride.
The glass transition of compatible blends
Authors: Couchman P. R.
Published: December 2004

In a thermodynamic model of the glass transition, general but circular relations for the compositional variation of the glass‐transition temperature, Tg, can be derived from the entropy, the volume, and the enthalpy. The circumstances necessary for each of these to reduce to predictive relations are stated. Of these relations, that derived from the entropy should be the most general because of the expected rather wide applicability of the random mixing assumption, with which it is associated. The entropic theory is used to account for several aspects of the compositional variation of Tg, including problems not of solutions per se.
Properties and morphology of some injection‐molded polycarbonate‐styrene acrylonitrile copolymer blends
Authors: Skochdopole R. E. , Finch C. R. , Marshall J.
Published: December 2004

A series of blends was prepared with broad concentration ranges of polycarbonate (PC) and styrene‐acrylonitrile copolymers (SAN) containing 5.5 and 30 weight percent acrylonitrile (AN). These blends were then injection molded, and their properties were measured and correlated with the morphologies of the blends (as determined by transmission electron microscopy). The toughness properties were shown to be discontinuous and very sensitive to composition of the continuous phase in the blends. The dart impact toughness remained high up to 30–40 weight percent SAN and dropped rapidly above this SAN concentration. The notched Izod toughness fell off rapidly at 10 weight percent SAN and greater. The strength and modulus had a more linear dependence on composition. Results of studies of the Tg by differential scanning calorimetry (DSC) show the presence of two phases over the entire concentration and a small solubility of each phase in the other. The heat distortion temperature under load (DTUL) of the blends approximated a linear additivity curve for the components. As expected, the blends had much better clarity where the refractive indexes more nearly match (in the case of the 5.5 percent AN copolymer).
Polymer sorbents for phosphorus esters: I. Selection of polymers by analog calorimetry
Authors: Chang Y. , Noriyan J. , Lloyd D. R. , Barlow J. W.
Published: December 2004

Heats of mixing of a variety of solvents with dimethyl methyl phosphonate, DMMP, are presented. A qualitative correlation between the exothermicity of the heat of mixing of DMMP with a particular solvent and sorption of DMMP by polymers containing structural units analogous to the solvent is observed. By this approach, polymers containing acidic hydroxyl functionality, such as phenol‐formaldehyde condensation products and poly(styrene‐co‐vinyl benzyl hexafluorodimethyl carbinol), were identified as good sorbents for DMMP. Sorption isotherms, measured for these materials by the piezoelectric method, show enhanced sorption at low vapor activity and 135°C compared to polystyrene and poly(vinyl chloride) which lack these acidic sites and whose solvent analogs mix more endothermically with DMMP.
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

Experimental 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

An 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

The 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

Curing 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

Untaxial 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

Orientation 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

A 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

Isothermal 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

A 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

Because 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

An 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

The 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

Measurement 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

Multiordering 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

Compatible 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

A 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

It 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

Blending 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

In 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

The 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.
The phase behavior and mechanical properties of polyarylate and polycarbonate blends
Authors: Golovoy A. , Cheung M. F. , Van Oene H.
Published: December 2004

The phase behavior and mechanical properties of a series of polyarylate/polycarbonate blends were studied. The polymers are known to transesterify, the extent of which depends upon the thermal and shear history and affects phase behavior and properties. Single screw extrusion, twin screw extrusion, and solution casting were employed for blend preparation. Two transition temperatures, corresponding to a polycarbonate‐rich phase and to a polyarylate‐rich phase, were seen in blends that were solution cast or compounded in a single screw extruder at 285°C. But after injection molding a single Tg was observed, When annealed at 180°C for several hours the molded blend was found to phase separate. Blends that were compounded in a twin screw extruder exhibited a single Tg and could not be phase separated. The flexural and tensile properties of blends that were prepared in a twin screw extruder show a small positive synergism. But the impact properties were substantially below the rule of mixtures values, probably the result of advanced exchange reaction and thermal degradation.
Structure formation during polymer blend flows
Authors: Sakellarides S. L. , McHugh A. J.
Published: December 2004

The structure formation processes that occur during the flow of dilute blends of high density polyethylene (HDPE) or polypropylene (PP) In a linear low density polyethylene (LLDPE) carrier phase have been studied. Due to low surface tensions, high deformations of the dispersed minor phase can be induced under slow flow conditions leading to the formation of slender filaments. Measurements on a slit die, having a large, converging flow entrance region, demonstrate that the mechanism for filament formation is droplet bursting, yielding growing tails during shear flow, or, unsteady drop elongation during extensional flow. Tail growth can be modeled as the flow of a slightly tapering cylinder in a fluid of different viscosity, For dispersed to carrier phase viscosity ratios greater than unity, extensional flow occurs in the tail phase, which can induce oriented crystallization. For ratios less than unity, the flow is compressive, which. Inhibits crystallization. Drop deformation and crystallization in the converging flow entrance region is greatly enhanced by the extensional flow, and droplet growth can be described by a model assuming a time‐dependent, planar, extensional flow field. Data for birefringence and melting points of as‐crystallized fibers are also presented and discussed.
Can the gel point of a cross‐linking polymer be detected by the G′ – G″ crossover?
Authors: Winter H. H.
Published: December 2004

Dynamic mechanical measurements allow direct determination of the instant at which a network polymer gels. In such an experiment, the evolution of G′(t,ω0) and G″ (t,ω0) is measured in small amplitude oscillatory shear as a function of cross‐linking time t. The frequency ω0 is kept constant throughout. At the beginning of the experiment, G″ is orders of magnitude larger than G′, and at completion of reaction, this order is reversed. It recently has been suggested by Tung and Dynes that the gel point (GP) might occur at the time at which G′ and G″ cross each other. However, there is much dispute whether GP occurs exactly at the crossover or just somewhere in its vicinity. This study resolves the dispute by modeling the rheological behavior at GP: There is only one class of network polymers for which GP coincides with the crossover. This class of polymers exhibits, when reaching GP, power law relaxation G(t) ∼ t−n with a specific exponent value n = 1/2. Examples are stoichiometrically balanced network polymers and networks with excess cross‐linker, however, only at temperatures much above the glass transition. Otherwise, the power law behavior would be masked by vitrification. Power law relaxation seems to be property of polymers at GP in general. However, some polymers have a different exponent value, n ≠ 1/2, in which case the crossover occurs before GP (for n < 1/2) or after GP (for n > 1/2); i.e. the crossover cannot be used for detecting GP. While there are no networks known to us with n < 1/2, recent experiments showed that network polymers that are lean on cross‐linker exhibit power law relaxation with n > 1/2. A new method is suggested for measuring GP of these imbalanced networks.
An investigation of instability of phase morphology of blends of nylons with polyethylenes and polystyrenes and effects of compatibilizing agents
Authors: Chen Cheng Chung , Fontan Eusebio , Min Kyonsuku , White James L.
Published: December 2004

Investigations of instability of phase morphology of blends of nylons with polyethylenes and polystyrenes and the effects of “compatibilizing” additives or “agents” are described. Annealing coarsens the phase morphology of blends of nylons with polyethylenes and polystyrenes. Phase growth is observed for various periods of annealing time. The addition of compatibilizing agents, specifically maleic anhydride grafted polyolefins to polyethylene‐nylon blends and syrene‐maleic anhydride copolymers to polystyrene‐nylon blends, stabilize the phase dimensions. Styene‐maleic anhydride copolymer is found more effective than styrene acrylonitrile copolymer as a compatibilizing agent. The mechanisms of this behavior are critically discussed.
Estimation and control in polymerization reactors. A review
Authors: Eliçabe G. E. , Meira G. R.
Published: December 2004

The control of polymerization reactors is particularly arduous for several reasons; (a) difficulty in specification of the control objectives; (b) high exothermicities and viscosities involved: (c) complicated process dynamics: and (d) problems with measurement of the polymer structure. Computer control has now simplified many tasks such as sequential operations of batch reactors; but no less important, it has made feasible the implementation of elaborate state estimation and control algorithms. The tendency in the polymerization industry and in current research centers is centered on producing ‘tailor‐made’ polymers from the view of its microscopic and/or macroscopic structures. To this end, several solutions have been proposed. For example, in the ‘chemical approach’, open loop methods have been developed based on the detailed dynamic models of the processes. Any control technique requires a knowledge of the process to be controlled through mathematical models. These models may be developed either from detailed mass and energy balances, or through empirical input‐output or “black‐box” techniques. The most promising control techniques are probably optimal control, adaptive control, and their combinations. Optimal control is powerful because it utilizes directly the detailed non‐linear plant model. Adaptive control developed for linear plants has already proven satisfactory, in spite of the highly nonlinear nature of the polymerizations. Undoubtedly, improved solutions will be obtained when this technique is extended to non‐linear systems.
Effect of crosslink density on the molecular relaxations in diepoxide‐diamine network polymers. Part 1. The glassy region
Authors: Charlesworth John M.
Published: December 2004

The effects of systematically varying the crosslink density on the mechanical relaxations in the glassy region of typical highly crosslinked diepoxide‐diamine polymers are reported. Activation enthalpies and intensities for the β relaxation have been measured using a torsion pendulum at 1 Hz. The glyceryl groups, which are thought to be responsible for this process, are divided into a number of categories defined by the structure of the surrounding matrix. Concentrations of these units are calculated using probability theory, and a correlation is obtained with three measures of the relaxation Intensity, In the case of non‐stoichiometric networks, variations in the intensity of the β relaxation are interpreted in terms of the simultaneous motion of each class of glyceryl group. The manner in which these processes combine to produce a composite peak appears to be unimportant. For the γ relaxation (−140°C), it is shown that at least four methylene units are needed in the diamine component before the process is observable, whereas only two consecutive methylene units in the center of the diepoxide molecule produce the relaxation.
The modeling of batch and continuous emulsion polymerization reactors. Part II: Comparison with experimental data from continuous stirred tank reactors
Authors: Rawlings J. B. , Ray W. H.
Published: December 2004

A detailed model for emulsion polymerization is compared with extensive data from continuous stirred tank reactors. Model predictions are compared with both steady‐state and dynamic data, for polymerization of styrene, methyl methacrylate, and vinyl acetate. Good agreement between model and experiment is achieved with one set of parameters and without any data fitting. The results show that the model is capable of predicting all of the experimentally observed phenomena including steady‐state multiplicity, sustained oscillations, ignition and extinction dynamics, and overshoot during start‐up.
The modeling of continuous mixers. Part I: The corotating twin‐screw extruder
Authors: Meijer H. E. H. , Elemans P. H. M.
Published: December 2004

In many operations in polymer processing, such as polymer blending, devolatilization, or incorporation of fillers in a polymeric matrix, continuous mixers are used; e.g., corotating twin‐screw extruders (ZSK), Buss Cokneaders and Farrel Continuous Mixers. Theoretical analysis of these machines tends to emphasize the flow in complex geometries rather than generate results that can be directly used (1–5). In this paper, a simple model is developed for the hot melt closely intermeshing corotating twin‐screw extruder, analogous to the analysis of the single‐screw extruder carried out in 1922 and 1928 (6, 7). With this model, and more specifically with its extension to the complete nonisothermal, non‐Newtonian situation, it is possible to understand the extrusion process and to calculate the energy, specific energy, and temperature rise during the process with respect not only to the viscosity of the melt, but also to the screw geometry (location and number of transport elements, kneading sections and blisters, pitch, positive or negative, screw clearance, and flight width) and screw speed. To support the theoretical analysis, model experiments with a Plexiglas‐walled twin‐screw extruder were performed, in addition to practical experiments with melts on small‐ and large‐scale extruders, with very reasonable results, In Part 2, the Buss Cokneader will be analyzed analogously.
Calorimetric characterization of photosensitive materials
Authors: Appelt B. K. , Abadie M. J. M.
Published: December 2004

A negative‐acting dry‐film photoresist was examined via both photocalorimetry and conventional calorimetry. The photo reaction of the resist was investigated as a function of temperature, and two distinct regimes with different activation energies have been identified. Possible reaction mechanisms were discussed in terms of termination reactions of the polymerization as well as effects of vitrification. The thermal reactivity of this particular resist was studied as well. It was possible to use Kissinger's equations to predict thermal aging effects. Finally, the utility of photocalorimetry as a tool to examine quickly the reactivity of monomers and initiator systems was demonstrated.