Showing papers on "Polymer blend published in 1996"

White light emission from a polymer blend light emitting diode

Abstract: A new type of polymer light emitting diodes that emit white light is reported. In these diodes, several electroluminescent substituted polythiophenes have been combined to give the necessary components of the visible spectrum. These emitting polymers are then mixed with an insulating polymer to diminish the energy transfer from high‐band‐gap polymers to low‐band‐gap polymers. The resulting emission at 20 V is shown to be close to the equienergy white point as defined by the CIE (Commission Internationale de l’Eclairage).

Relationship between rheology and morphology of model blends in steady shear flow

Abstract: Immiscible polymer blends display a complex flow behavior caused by the coupling between morphology and rheology. The flow induced microstructure has been studied on model systems of nearly inelastic polymers. For these systems, the elastic properties of the blend are mainly governed by the interface. Measurements of the storage modulus and of the first normal stress difference, both reflecting this enhanced elasticity, have been used to probe the blend morphology. From oscillatory measurements after cessation of flow the mean diameter of the disperse phase, as generated by the previous flow, has been calculated using the model of Palierne [Rheol. Acta 29, 204 (1990)]. A procedure based on a direct fitting of the dynamic moduli with the model is compared with one that uses a weighted relaxation spectrum. The steady state normal stress data, on the other hand, have been related to the morphology of the blend by means of the model of Doi and Ohta [J. Chem. Phys. 95, 1242 (1991)]. Since this model predicts a direct proportionality between the contribution of the interface to the normal stress and the specific interfacial area, the size of the droplets can be calculated once the proportionality constant is known. The conditions for which the model is valid have been determined and the required constant is obtained by comparing the results with those from the dynamic moduli. The resulting droplet sizes have been used to develop a data reduction scheme: The specific interfacial area is found to be inversely proportional to the ratio of interfacial tension over shear stress for several blends with various concentrations and viscosity ratios.

Interphase and compatibilization of polymer blends

Abstract: Polymer blends are mixtures of at least two polymers and/or copolymers comprising more than 2 wt% of each macromolecular component. Most blends are immiscible, and need to be compatibilized. The compatibilization must not only ensure improvement in performance, but it must be reproducible, insensitive to forming stresses and repeated processing. This review on compatibilization of polymer blends is prepared in three parts : (i) description of the interface/interphase; (ii) compatibilization by addition of a copolymer (with a special emphasis on the use of block copolymers) ; and (iii) reactive compatibilization.

Rheology of a Lower Critical Solution Temperature Binary Polymer Blend in the Homogeneous, Phase-Separated, and Transitional Regimes

Abstract: Small amplitude oscillatory shear rheology is employed in order to investigate the linear viscoelastic behavior of the lower critical solution temperature blend polystyrene/poly(vinyl methyl ether), PS/PVME, as a function of temperature and composition. At low temperatures, where the mixture is homogeneous, the dependence of the zero shear viscosity (η0) on concentration is measured and is well-described by means of a new mixing rule, based on surface fractions instead of volume fractions. Shift factors from time-temperature superposition (TTS) exhibit a Williams−Landel−Ferry (WLF) behavior. As the macrophase separation temperature is approached (the phase diagram being established by turbidity measurements), the blend exhibits a thermorheologically complex behavior. A failure of TTS is observed at low frequencies, both in the homogeneous pretransitional and in the two-phase regimes. Its origin is attributed to the enhanced concentration fluctuations, which exhibit a critical slowing down near the phase b...

Dimensional crossover in the phase separation kinetics of thin polymer blend films.

Abstract: The kinetics of phase separation in thin polymer blend films of polystyrene and polybutadiene on a silicon substrate is examined by optical microscopy of the free film boundary. Our observations on 1000 and 200 \AA{} films are consistent with a crossover from three- to two-dimensional spinodal decomposition kinetics in the (off-critical) viscous hydrodynamic regime. In this stage of phase separation the exponent $n$, characterizing the scale $R(t)\ensuremath{\sim}{t}^{n}$ of the coarsening pattern, is predicted to change from 1 to a value near 0.46 upon lowering the dimensionality.

Biologically degradable polymer mixture

Abstract: A biologically degradable polymer mixture contains at least one starch biopolymer made from renewable raw materials, a plasticizer, and a polymer selected from the following materials: an aromatic polyester; a polyester-copolymer with both aliphatic and aromatic blocks; a polyesteramide; a polyglycol; a polyester urethane; and/or mixtures of these components.

Efficient continuum model for simulating polymer blends and copolymers

Abstract: An efficient continuum model for simulating polymer blends and copolymers is presented. In this model, the interactions are short‐range and purely repulsive, thus allowing for excellent computational performances. The driving force for phase separation is a difference in the repulsive interaction strength between like and unlike mers. The model consists essentially of a molecular‐dynamics algorithm, supplemented by an appropriate Monte Carlo exchange process. To demonstrate the effectiveness of the model we study two systems, a symmetric binary blend of polymers and a symmetric diblock copolymer system. For the binary blend, we determine the phase diagram and find, as predicted by theory, that the critical interaction parameter scales with the inverse of the chain length of the polymers. For the diblock copolymer system, we study both the one‐phase region and the microphase separated lamellar region. For the latter, we show that constant‐pressure algorithms are more appropriate since, contrary to recent lattice simulations, the lamellar spacing can self‐adjust in such an ensemble.

Scanning thermal microscopy: Subsurface imaging, thermal mapping of polymer blends, and localized calorimetry

Abstract: We have used a platinum/10% rhodium resistance thermal probe to image variations in thermal conductivity or diffusivity at micron resolution and to perform localized calorimetry. The probe is used as an active device that acts both as a highly localized heat source and detector; by generating and detecting evanescent temperature waves, we may control the maximum depth of sample that is imaged. Earlier work has shown that subsurface images of metal particles buried in a polymer matrix are consistent with computer simulations of heat flows and temperature profiles, predicting that a 1 μm radius probe in air will give a lateral resolution of ∼200 nm near the surface, with a depth detection of a few μm. We have a special interest in polymer blends, and we present zero‐frequency mode and temperature‐modulation mode thermal images of some immiscible blends in which the image contrast arises from differences in thermal conductivity/diffusivity between single polymer domains. The behavior of domains is observed in real time as the blends are subjected to a slow temperature rise. We have also achieved localized differential thermal analysis of a number of polymers, and recorded events such as glass transitions, meltings, recrystallizations, and thermal decomposition within volumes of material estimated at a few μm3. This opens the way forward towards calorimetric imaging, by which it should be possible to distinguish between different regions undergoing either reversible or irreversible changes as the temperature is varied.

Polymer blends for enhanced asphalt binders

Abstract: Straight asphalt binders have been modified by addition of both high-density polyethylene (HDPE) and a blend of HDPE and ethylene-propylene-diene-monomer (EPDM). The blend composition was fixed to 90/10 HDPE/EPDM to illustrate the possibility of adapting the polymer to be added to the asphalt binder for specific end-use applications. Linear viscoelastic properties of unmodified and polymer modified asphalts at concentrations ranging from 1 to 5 wt% were studied before and after Thin-Film Oven Test (TFOT) aging. Temperatures ranging from -15°C to 60°C were considered. Standard tests such as Ring-and-Ball softening point, Fraass breaking point and TFOT aging were also performed on the whole set of samples. It was found that addition of rubber-modified polyethylene (HDPE/EPDM) to the straight asphalt results in materials with enhanced overall properties, and most important, dispersed phase much more stable than the equivalent HDPE modified asphalt, mainly before TFOT aging. Good results were obtained for 1% HDPE/EPDM samples. Optimum design is, however, required for the desired properties to be obtained.

Surface Modification via Chain End Segregation in Polymer Blends

Abstract: We have explored the use of chain end segregation as a means of controlling the properties of a polymer surface. Thin film blends of homopolystyrene (PS) and PS synthesized with low-energy oligotetrafluoroethylene chain ends (PS-TFE) were studied using neutron reflectivity. The fraction of PS-TFE that localizes near the surface was found to increase as a function of its concentration in the blend. Contact angle measurements indicate corresponding reductions in the surface tension due to the surface localization of the TFE chain ends. For a 10% blend of 6000 mol wt PS-TFE in 3 × 105 mol wt PS, the surface coverage of fluorocarbon ends was found to be >20%. A free energy model of the blends gives good qualitative agreement with the experimental results.

Diblock copolymers as emulsifying agents in polymer blends: Influence of molecular weight, architecture, and chemical composition

Abstract: Interfacial agents used in the compatibilization of immiscible polymer blends often consist of block copolymers containing at least one segment compatible with each of the two phases of the blend. This work examines the influence of the molecular weight, architecture, and chemical composition of the interfacial agent on its ability to emulsify a polymer blend. The system chosen is a blend containing 80% polystyrene and 20% ethylene-propylene rubber, compatibilized by diblock copolymers of poly(styrene-hydrogenated butadiene). The emulsification curve, which relates the dispersed phase particle size to the concentration of interfacial agent added to the system, was used as a tool to characterize the efficacy of the different interfacial agents. The observed behavior is similar to that of classical emulsions: a rapid drop in phase size at low concentrations of interfacial modifier, followed by a levelling off to an equilibrium diameter value once a “critical” concentration has been reached. For systems compatibilized by symmetrical diblocks (i.e., containing approximately 50% styrene by weight), the volume average particle diameter decreased from 2.7 μm for the unmodified system to about 0.4 μm once interfacial saturation is reached. The critical concentration for emulsification decreased with increasing interfacial agent molecular weight, due to the higher interfacial area occupied by longer molecules; however, this parameter did not affect the equilibrium particle diameter. The asymmetrical diblock copolymer (30% styrene) was found to be less effective than the symmetrical ones over the entire range of concentrations studied (5 to 35% modifier, based on the volume of the minor phase). Asymmetrical diblock copolymers would tend to form micelles, whereas symmetrical copolymers are less constrained at the interface. No significant difference was observed between the emulsifying capability of tapered and pure diblocks of similar composition and molecular weight. © 1996 John Wiley & Sons, Inc.

Functional Group Accessibility in Hydrogen Bonded Polymer Blends

Abstract: Accessibility of functional groups is an important concept in the mixing of polymers and involves factors such as chain connectivity, steric shielding, etc., all of which tend to limit the number of interchain contacts formed. Infrared spectroscopy is well suited to study functional group accessibility in carefully selected miscible hydrogen bonded polymer blend systems, because the fraction of interchain hydrogen bonded groups can be measured quantitatively. Such measurements have been made on blends consisting of a wide range of carbonyl containing (co)polymers with a 2,3-dimethylbutadiene-stat-4-vinylphenol containing 24 wt % 4-vinylphenol. Evidence has been obtained for decreasing accessibility of the carbonyl groups of the poly(n-alkyl methacrylate)s due to steric shielding from bulky side groups. Conversely, when these groups are spaced further apart in an ethylene-stat-vinyl acetate or ethylene-stat-methyl methacrylate copolymer chain, they become much more accessible. The effect of functional grou...

Process for making a foamed polymer

Abstract: The invention relates to a process for making a foamed polymer. The process involves (a) dispersing thermally degradable solid particles in polymer precursor; (b) crosslinking the polymer precursor to form a rigid, crosslinked polymer without degrading the particles; and (c) heating the polymer to degrade the particles and form the polymer foam.

Evidence for inversion of phase continuity during morphology development in polymer blending

Abstract: When polymer blends are prepared from a mixture of pellets, the melting order of the components is important in determining the mechanism of morphology development. Here, we show that an inversion of phase continuity occurs during processing when a minor phase component has a softening or melting transition temperature which is lower than the softening temperature of the major phase component. Three 80 :20 concentration systems were studied : polyarylate/rubber, polyamide 6,6/polystyrene, and polystyrene/ethylene propylene rubber. Initially, the minor phase was the continuous phase and coated the major phase in all three systems. As the major phase melted, a switching of phase continuity occurred, and in the final blend state, the major phase was the continuous phase. An increase in power input was required during the switching of the dispersed and matrix phases. The compounding process was studied through continuous video monitoring, torque-temperature analysis, and microscopy of quenched samples. A continuity inversion mechanism is proposed. It is found that the initial morphology of the blend consists of sheets of the major phase inside the minor phase. These sheets break up into irregularly shaped particles, which then coalesce around the minor phase. The effects of compatibilization (using reactive polymers or adding a premade diblock) on the rheology and morphology of the blend are also investigated. Interfacial reaction is seen to delay and intensify the inversion of phase continuity, whereas addition of premade diblock does not have any significant effect. The torque increases due to interaction of the major phase domains and due to reactive stabilization of the interface against coalescence, and the contributions of each to the torque can be decoupled.

Devolatilization: A critical sequential operation for in situ compatibilization of immiscible polymer blends by one‐step reactive extrusion

Abstract: The main objective of this study was to show that an efficient removal of residual monomers is very important for in situ compatibilization of immiscible polymer blends by one step reactive extrusion. One-step reactive extrusion means that when compatibilizing two immiscible polymers with one polymer containing potential functional groups and the other being chemically inert with respect to these functional groups, functionalization of the chemically inert polymer and its subsequent interfacial reaction with the functional polymer are accomplished in a single extrusion process. Two model blend systems were chosen : polypropylene/poly(butylene terephthalate) (PP/PBT) and high density polyethylene/polyamide 6 (HDPE/PA6). A co-rotating intermeshing twin screw extruder was used to process these blends. Glycidyl methacrylate (GMA) and maleic anhydride (MA) were used to functionalize PP and HDPE, respectively. Results showed that the mechanical properties of both blends in terms of elongation at break and impact strength were improved to a much greater extent with up-stream devolatilization compared with down-stream devolatilization.

Compatibilization of polymer blends by complexation. 1. Spectroscopic characterization of ion-amide interactions in ionomer/polyamide blends

Abstract: Electron paramagnetic resonance (EPR), Fourier transform infrared (FTIR), and solid-state 15N nuclear magnetic resonance (15N-NMR) spectroscopies were used to characterize the structure and relative strength of the interactions between metal sulfonate and amide groups in blends of lightly sulfonated polystyrene ionomers and an N-methylated polyamide, poly(N,N‘-dimethylethylene sebacamide), and low molecular weight model complexes. The metal sulfonate groups, which aggregate in the neat ionomer, were dispersed by the polyamide in the blend as a consequence of a complexation that involved the sulfonate cation and both the carbonyl oxygen and the amide nitrogen of the polyamide. The FTIR and 15N-NMR spectra were consistent with a 2pz electron redistribution model for the complex, in which electrons migrate from the nitrogen to the metal ion through the carbonyl group. The sulfonate anion did not appear to particpate in the complex, but it remained in the vicinity of the metal cation. The strength of the ion−...

Prediction of dispersed phase drop diameter in polymer blends: The effect of elasticity

Abstract: This paper discusses the prediction of the dispersed phase drop diameter in polymer blends considering the viscoelastic properties of polymers. The prediction is based on a simple force proportionality. Polymers are viscoelastic, and thus the elasticity of the matrix and the elasticity of the dispersed phase affect the drop size. The forces that deform a polymer droplet in a polymer matrix are the shear forces, η m γ and the matrix first normal stress, T 11,m . This deformation is resisted by the interfacial forces, 2 Γ/D and the drop's first normal stress, T 11,d . As a first approximation, the forces were balanced to predict the particle size in polymer blends. The diameter of the dispersed phase was predicted reasonably well for several systems at different operating conditions. It was observed for some systems (PS/PP, PS/EPMA, PS/PA330) that, as the shear rate increased, the diameter of the dispersed phase initially decreased. At a critical shear rate, the diameter reached a minimum value, and beyond it, the diameter increased with shear. This critical value was found to be between 100 to 162.5 s -1 for a PS/PP system. The force balance predicts this minimum drop diameter at a similar critical shear rate. The specific energy input (the amount of energy input into the blend) could not explain the phenomenon of a minimum drop diameter with increase in shear. This minimum is not observed for the high concentration systems, such as the 20% PP dispersed in PS, since the effects of coalescence become significant. In reactive blends, the predicted drop diameter was closer to the experimentally determined diameter, and there was less variation in diameter with changes in shear rate.

Conjugated diene/monovinylarene block copolymers, methods for preparing same, and polymer blends

Abstract: A block copolymer comprising at least three consecutive conjugated diene/monovinylarene tapered blocks is provided. Other aspects of this invention include a polymerization process for preparing the block copolymer and polymer blends comprising the block copolymer. The block copolymer and polymer blends exhibit excellent optical and mechanical properties.

Influence of Short Chain Branching on the Miscibility of Binary Polymer Blends: Application to Polyolefin Mixtures

Abstract: The lattice cluster theory (LCT) is used to study the influence of monomer structure, i.e., short chain branching, on the miscibility of binary polymer blends. The systems are chosen as correspondi...

Blends of ultraviolet absorbers and polyesters

Abstract: This invention relates to a photo-stabilized polymer blend comprising: (a) at least one polyethylene terephthalate-based (PET) copolymer comprising 1,4-cyclohexanedimethanol, and (b) an ultraviolet absorber, at least one compound selected from the group consisting of cyclic imino esters.

Acrylate-containing polymer blends

Abstract: A polymer blend comprising (a) a modified block copolymer comprising (i) a polystyrene block and (ii) a polydiene block or a hydrogenated polydiene block, said polydiene block or hydrogenated polydiene block being modified to contain an average of one or more carboxyl groups; and (b) a polymer comprising a polymerization reaction product (i) at least one acrylic or methacrylic acid ester of a non-tertiary alcohol having 1 to 14 carbon atoms, inclusive, (ii) at least one monomer having carboxylic acid functionality which is present in an amount ranging from about 1 to about 15 parts by weight, based on 100 parts by weigth of polymer (b); and (iii) a titanate selected from the group consisting of (ethanol,2,2',2'-nitrilotris-titanium(4+) salt); titanium bis(ethyl-3-oxobutanolato-O1O3)bis2-propanolato; a reaction product of tetraalkyltitanate with a β-diketone and an alkanolamine; and tetrabutyltitanate (1-butanol,titanium(4+) salt).

Effect of Copolymer Architecture on the Interfacial Structure and Miscibility of a Ternary Polymer Blend Containing a Copolymer and Two Homopolymers

Abstract: The effect of copolymer architecture on the phase behavior of a ternary polymer blend containing two homopolymers and a copolymer as well as the interfacial characteristics of this blend in the phase-separated state are examined using Monte Carlo simulation. At low copolymer concentration (ca. 1%), the phase transition from miscible to immiscible does not change within the resolution of the simulation for any of the copolymer structures studied here, which include block, random, and alternating architectures. It is found, however, that the copolymer does migrate to the biphasic interface in the phase-separated regime and that the configuration of the copolymer at the interface is a function of sequence distribution within the copolymer. This effect is interpreted in terms of the efficiency of the copolymer to strengthen the biphasic interface. These results suggest that both block and alternating structures show promise as interfacial modifiers, while the purely random copolymer will have the weakest effe...

Miscibility of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) blends by transesterification

Abstract: The effects of transesterification on the miscibility of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) were studied. Blends were obtained by solution precipitation at room temperature to avoid transesterification during blend preparation. The physical blends and transesterified products were analyzed by wide-angle x-ray scattering, differential scanning calorimetry, and nuclear magnetic resonance spectroscopy. It was found that the physical blends are immiscible and when the extent of transesterification reaches 50% of the completely randomized state, independent of blend composition, the blends are not crystallizable and show a single glass transition temperature between those of starting polymers. The interchange reactions were significantly influenced by annealing temperature and time but negligibly by blend composition.