The strengthening of polar polymer blends with small carbon additives and the relaxation properties of the blends

It has been shown that the density, strength, and relaxation properties of a poly(vinyl chloride)butadiene-acrylonitrile synthetic rubber SKN-26 composite are influenced by the addition of DG-100 carbon nanoparticles as a filler.     

Influence of liquid crystalline polymer and recycled PET as minor blending components on rheological behavior,morphology, and thermal properties of thermoplastic blends

In this study, the potential of recycled poly(ethylene terepthalate) (rPET) as a well‐defined reinforcing material for the in situ microfibrillar‐reinforced composite (iMFC) was investigated in comparison with that of liquid crystalline polymer (LCP). Each dispersed phase (LCP or rPET) was melt blended with high density polyethylene (PE) by using extrusion process. The rheological behavior, morphology, and the thermal stability of LCP/PE and rPET/PE blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of LCP or rPET into PE significantly improved the processability. A potential of rPET as a processing lubricant by bringing down the melt viscosity of the blend system was as good as LCP. The elongated LCP domains were clearly observed in as‐extruded strand. Although the viscosity ratio of the rPET/PE system was lower than that of the LCP/PE blend system, most rPET domains appeared as small droplets. An addition of LCP and rPET into the PE matrix improved the thermal resistance significantly in air but not in nitrogen. The obtained results suggested the high potential of rPET as a processing aid and good thermally resistant material similar to LCP. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of conformational asymmetry on the surface enrichment of polymer blends II

We reexamine the influence of statistical segment length asymmetry on the surface segregation of homopolymer blends in a mean field thread model of polymer melts. By developing numerical self-consistent field solutions of the Edwards-Helfand equations, we demonstrate that the component with the smaller value of the parameter β² = a²/(6ν) (a is the statistical segment length and ν is the segment volume) is enriched at a neutral, impenetrable surface. Qualitatively, this finding is in agreement with our earlier analytical work and with experiment. However, in contrast to our earlier work, we find that the absolute magnitude of the segregation is a sensitive function of the chain lengths of the two species and of the compressibility of the system. © 1995 John Wiley & Sons, Inc.     

Structured polymer blends

Various morphologies can be realized via processing of incompatible polymer blends such as droplets or fibers in a matrix and stratified or cocontinuous structures as is shown for the model system polyethylene/polystyrene The structures induced are usually intrinsically unstable. Modelling of extrusion processes and continuous mixers yields expressions for the shear rate and shear stress but also for the limited residence time and the number of reorientations. These results could be combined with detailed knowledge of respectively distributive and dispersive mixing processes to predict the development of various morphologies as a function of time. Control of morphology is of utmost importance. In the case of droplets in a matrix, usually encountered in toughening of glassy polymers, the use of compatibilizers and/or reactions at the interphases is utilized. However, in designing specific morphologies i.e. structured polymer blends, fixation of intermediate morphologies before final processing is a prerequisite. Some preliminary results will be presented.     

Thermodynamics of polymer blends

The general principles of thermodynamic equilibrium in binary liquid systems are reviewed briefly, and extended to quasi-binary mixtures of polydisperse polymers. Molecular models allowing actual phase behaviour to be discussed in terms of molecular parameters are exposed to data on the system polystyrene/polyvinylmethylether. Disparity in size and share between the repeating units must be introduced to obtain reasonable agreement between theory and experiment. The neccessary introduction of the molar-mass distribution detracts from this agreement which makes clear that other aspects exist that must be taken into account. For example, cross association between repeating units has a marked effect on phase behaviour. Blends are subject to two kinds of thermodynamic aging which lead either to considerable mutual solubility in supposedly immiscible blends, or to metastable equilibria transforming into states of lower Gibbs energy. In both cases physical proerties of the blend will change with time.     

Pretreatment of recycled polymer raw material

The analysis of main methods and equipment for physical utilization (recycling) of polymer waste is performed. Main stages of the recycling as storage of waste, transportation, crushing and grinding, fractionation, sorting, washing, dehydration, agglomeration, and granulation are considered in detail.     

Intrinsically conducting polymer blends

Polyaniline (PANI) doped with different dopants (HCl, dodecyl benzene sulfonic acid, (+)‐Camphor‐10 sulfonic acid, dinonyl naphthalene disulfonic acid) was synthesized by chemical oxidation method. The FTIR studies indicated that the back bone structure of doped PANI was similar. Thermal stability was evaluated in nitrogen atmosphere by dynamic thermogravimetry and PANI‐HCl sample showed minimum weight loss below 400°C. The electrical conductivity of PANI was not affected by the structure of dopants. The microwave absorption studies of several polymers blends containing PANI‐HCl and/or carbon black were also carried out by using wave guide technique.     

Interfaces in polymer blends

We investigate the structure and thermodynamics of interfaces in dense polymer blends using Monte Carlo (MC) simulations and self‐consistent field (SCF) calculations. For structurally symmetric blends we find quantitative agreement between the MC simulations and the SCF calculations for excess quantities of the interface (e.g., interfacial tension or enrichment of copolymers at the interface). However, a quantitative comparison between profiles across the interface in the MC simulations and the SCF calculations has to take due account of capillary waves. While the profiles in the SCF calculations correspond to intrinsic profiles of a perfectly flat interface the local interfacial position fluctuates in the MC simulations. We test this concept by extensive Monte Carlo simulations and study the cross‐over between “intrinsic” fluctuations which build up the local profile and capillary waves on long (lateral) length scales. Properties of structurally asymmetric blends are exemplified by investigating polymers of different stiffness. At high incompatibilities the interfacial width is not much larger than the persistence length of the stiffer component. In this limit we find deviations from the predictions of the Gaussian chain model: while the Gaussian chain model yields an increase of the interfacial width upon increasing the persistence length, no such increase is found in the MC simulations. Using a partial enumeration technique, however, we can account for the details of the chain architecture on all length scales in the SCF calculations and achieve good agreement with the MC simulations. In blends containing diblock copolymers we investigate the enrichment of copolymers at the interface and the concomitant reduction of the interfacial tension. At weak segregation the addition of copolymers leads to compatibilization. At high incompatibilities, the homopolymer‐rich phase can accommodate only a small fraction of copolymer before the copolymer forms a lamellar phase. The analysis of interfacial fluctuations yields an estimate for the bending rigidity of the interface. The latter quantity is important for the formation of a polymeric microemulsion at intermediate segregation and the consequences for the phase diagram are discussed.     

Influence of blend miscibility on the proton conductivity and methanol permeability of polymer electrolyte blends

The influence of miscibility on the transport properties of polymer electrolyte blends composed of a proton conductor and an insulator was investigated. The proton‐conductive component in the blends was sulfonated poly(ether ketone ketone) (SPEKK), while the nonconductive component was either poly(ether imide) (PEI) or poly(ether sulfone) (PES). The phase behavior of PEI‐SPEKK blends was strongly influenced by the sulfonation level of the SPEKK. At low sulfonation levels (ion‐exchange capacity (IEC) = 0.8 meq/g), the blends were miscible, while at a slightly higher level (IEC = 1.1 meq/g), they were only partially miscible and for IEC ≥ 1.4 meq/g they were effectively immiscible over the entire composition range. The PES‐SPEKK blends were miscible over the entire range of SPEKK IEC considered in this study (0.8–2.2 meq/g). At high IEC (2.2 meq/g) and at low mass fractions of SPEKK (<0.5), the miscible blends (PES‐SPEKK) had higher proton conductivities and methanol permeabilities than the immiscible ones (PEI‐SPEKK). The opposite relationship was observed for high mass fractions of SPEKK (>0.5). This behavior was explained by the differences in morphology between these two blend systems. At low IEC of SPEKK (0.8 meq/g), where both PEI‐SPEKK and PES‐SPEKK blend systems exhibited miscibility, the transport properties were not significantly different. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2253–2266, 2006     

Microstructure of miscible polymer blends

The purpose of this work is to describe the application of new electron microscopy techniques to the study of polymer blends with very fine dispersion of phases (miscible blends). Blends of PVC with PMMA, PCL, POM and SAN were prepared by high temperature mixing on a two roll mill, or by solvent casting. Thin sections (or cast films) were investigated in the scanning transmission electron microscope and small phases were identified in most blends. The contrast was enhanced by electronic combination of bright and dark field signals, by an irradiation and staining technique and by differential mass loss. The specimens were further characterized by measurement of mass loss, resulting from electron beam damage. The non linear changes in the mass loss rate with concentration were interpreted as being influenced by partial solubility and molecular interactions.     

Surface studies of polymer blends

An outlook of the literature concerning surface studies of polymer blends is given. Attention is focused on both theoretical and experimental aspects, with emphasis on the importance of sample preparation procedures.     

Confined flow of polymer blends

The influence of confinement on the steady-state morphology of two different emulsions is investigated. The blends, made from polybutene (PB) in polydimethylsiloxane (PDMS) and polybutadiene (PBD) in PDMS, are sheared between two parallel plates, mostly with a standard gap spacing of 40 microm, in the range of shear rates at which the transition from "bulk" behavior toward "confined" behavior is observed. For both cases, the influence of the concentration was systematically investigated, as well as the shear rate effects on the final steady-state morphology. By decreasing the shear rate, for each blend, the increasing droplets, i.e., increasing confinement for a fixed gap spacing, arrange themselves first into two layers, and when the degree of confinement reaches an even higher value, a single layer of droplets is formed. The ratio between the drop diameters and the gap spacing at which this transition occurs is always lower than 0.5. While decreasing the shear rate, the degree of confinement increases due to drop coalescence. Droplets arrange themselves in superstructures like ordered pearl necklaces and, at the lower shear rates, strings. The aspect ratio and the width of the droplet obtained from optical micrographs are compared to predictions of the single droplet Maffettone-Minale model (MM model(1)). It is found that the theory, meant for unconfined shear flow, is not able to predict the drop deformation when the degree of confinement is above a critical value that depends on the blends considered and the shear rate applied. A recently developed extension of the MM model is reported by Minale (M model(2)) where the effect of the confinement is included by using the Shapira-Haber correction.3 Further extending this M model, by incorporating an effective viscosity as originally proposed by Choi and Showalter,4 we arrive at the mM model that accurately describes the experiments of blends in confined flow.     

Effects of polymer additives on pool boiling phenomena

The addition of small amount of soluble polymer makes the boiling behavior significantly different from that of pure water. The polymer additives reduce the tendency of coalescence between vapor bubbles. Consequently, they become smaller in size, larger in number, and tend to stay on the heating surface in a relatively orderly manner. No significant improvement in heat transfer rate caused by the polymer additives was observed in this work; the critical burn out heat flux was reduced slightly.     

Influence of solid surface on the compatibility in polymer blends produced in situ

Blends of linear polyurethane and poly(methyl methacrylate) were obtained in situ in the course of simultaneously proceeding reactions of polymerization and polyaddition. The effect of filler nanoparticles on the thermodynamic properties of the systems was investigated. Introduction of filler into the monomer mixture before curing increases the compatibility of final systems, as follows from diminishing thermodynamic interaction parameters. The reverse correlation has been established between the interaction parameter and the fraction of an interfacial region between two phases, its origin being the result of incomplete phase separation. Introducing filler into the reaction system determines simultaneously the increasing compatibility and increasing fraction of an interfacial region, i.e., prevents phase separation. Both effects are due to increasing of the interaction between two polymeric components at the interface with solid and changing conditions of incomplete phase separation in the course of reaction.     

Enthalpy relaxations in polymer blends and block copolymers: Influence of domain size

It is now well known that enthalpy relaxation measurements can be used to establish polymer-polymer blend phase behavior when the glass transition temperatures of the two polymers are virtually coincident. In the most simple cases, the aging kinetics of an immiscible blend will be representative of the pure polymers superimposed upon each other. However, in many cases the situation is more complicated because of the presence of interface material. In this paper the relation between enthalpy recovery peak separation, domain size and interface thickness is considered. The discussion is based on relaxation experiments involving di-block copolymers of styrene and 2-vinyl pyridine, blends of polystyrene and poly(2-vinyl pyridine) and blends of poly(vinyl chloride) and poly(isopropyl methacrylate). If the amount of material in the interface is too large due to either a small average domain size or a thick interface no peak separation will occur. The first situation is found for the microphase separated block copolymer system whereas the second possibility occurs for blends of polymers which are on the verge of miscibility like poly(vinyl chloride) and poly(isopropyl methacrylate).Presented in part at the Sixth International Seminar on Polymer Physics Relaxation in Polymers, Gomadingen, October 3–8, 1988, F.R.G.     

Solvent effect on the miscibility of polymer blends

Starting from the Flory-Huggins theory applied to a polymer/polymer/solvent solution, an expression has been derived showing the overall effect of solvent on the composition of the polymer blend in the final solid state. This expression has been experimentally verified by investigating the miscibility of two polymer blends: polystyrene/poly(α-methylstyrene) cast from tetrahydrofuran and cyclohexane, and polystyrene/poly (methyl methacrylate) obtained from tetrahydrofuran and chloroform. Besides the usual differential scanning calorimetry technique, thermogravimetric analysis might be helpful for detecting the miscibility of polymer blends.     

Influence of chain end groups on the matrix-assisted laser desorption/ionization spectra of polymer blends

The positive ion matrix-assisted laser desorption/ionization (MALDI) spectrum of an equimolar blend of Nylon 6 (Ny6) and hydroxyl-terminated polybutyleneterephthalate (PBT) shows a surprisingly strong imbalance between the two components. Since the average molar masses and the polydispersions of the two polymers are comparable, it follows that the efficiency of MALDI is quite different for the two components of the blend. This finding prompted us to a more detailed study, and to synthesize Ny6 and PBT samples terminated with different end groups, in order to analyze their blends by MALDI. The negative ion MALDI spectra of the mixtures investigated show that PBT samples do not yield signals, so that only Ny6 peaks appear in these spectra. By comparing positive and negative ion MALDI spectra of mixtures of Ny6 terminated with various end groups, it was found that the peak intensity depends on the nature of the end groups. The results reported in the present study may help to clarify some fundamental aspects of the mechanisms of ion formation, when MALDI mass spectrometry is applied to macromolecules. End group ionization efficiency appears to be the most important parameter in determining the relative intensity of peaks in the MALDI spectra of the polymer blends investigated. End-group-dependent ionization is the key to the rationalization of the relative peak intensities in MALDI spectra of polymer mixtures.     

Automotive industry and polymer blends

A key to the success of plastics in the automotive industry is the use of alloying technology which, relatively quickly leads to tailor-made materials at interesting cost-performance ratios. In this paper an overview of the various criteria used in the laboratory in testing alloys for auto parts is given and an attempt is made to point out the most significant determinations. The results obtained comparing the materials indicate how inadequate the standard methods are in describing the real behaviour of the items under operating conditions. Nonetheless, just making some modifications in test geometry leads to a sufficiently realistic correspondance between laboratory test data and item performance.     

Novel biodegradable ester-based polymer blends

We have found, within the polyester family, interesting and potentially useful patterns of three-component compatibility. The bacterially produced biodegradable polyester, poly(hydroxybutyrate) (PHB) and its copolymers with hydroxyvalerate (HV) together with polymers such as cellulose acetate butyrate (CAB), polycaprolactone, poly(lactic acid), and a series of high-molecular-weight, non-crystallizable ester-based plasticisers have been identified as possible candidates in the production of blends in which aspects of performance can be varied with a degree of independence of cost. The compatibility ranges can be conveniently represented in the form of triangular graphs, with the relative weight fraction, or percentage, being represented along each of the three axes. The extent to which the modulation of the physical properties in general, but the stability in various environments in particular, is possible by the formation of three-component blends, such as those formed between P(HB-HV), cellulose acetate butyrate and poly(alkylene adipate) plasticisers, is discussed.     

Interfacial tension in polymer blends

Theoretical models of the interfacial tension coefficient in polymer blends, v₁₂, were evaluated. A new working relation was derived that makes it possible to compute v₁₂ from the chemical structure of two polymers. The calculations involve determination of the dispersive, polar and hydrogen-bonding parts of the solubility parameter from the tabulated group and bond contributions. The computed values of v₁₂ for 46 blends were found to follow the experimental ones with a reasonable scatter of ± 36%. Next, the experimental methods of v₁₂-measurements were critically examined. Although many have been developed for low viscosity Newtonian fluids, most are irrelevant to industrial polymeric systems. For the present studies two were selected. Values of v₁₂ were measured using the so-called “capillary breakup method,” and a newly developed method based on the retraction rate of deformed drop.