Showing papers on "Miscibility published in 2008"

Hydrogen-bonding in polymer blends

Abstract: Hydrogen bonding in polymer blends is a topic of great interest to polymer scientists because such systems have many potential applications. Introducing functional groups to one component to make it capable of forming hydrogen bonds to another, thereby enhancing the miscibility of otherwise immiscible blends, is one of the major achievements during the past 20 years of polymer science. The Painter–Coleman association model generally describes these interactions accurately. This Review discusses in detail the effects of hydrogen bonding on the miscibility and thermal properties of polymer blend systems.

Effects of ion solvation on the miscibility of binary polymer blends.

Abstract: We study the effects of adding salt ions on the miscibility of a binary blend of polymers having different dielectric constants. The competition between the preference of the ions to be solvated by the component of the higher dielectric constant and the entropic tendency for the ions to be distributed uniformly results in nontrivial effects on the miscibility. We first study the thermodynamics of the polymer blend−ion mixture using a simple Born model in a uniform dielectric medium of the average composition of the polymer blend. We then study the effect of local enrichment of the higher dielectric constant polymer near the ion. We find that when the dielectric constants of the polymers are both low, adding salt decreases the miscibility, while when the dielectric constants of the polymers are both high, the addition of salt enhances the miscibility. When the blend consists of a high dielectric constant polymer and a low dielectric constant polymer, miscibility is decreased if the low dielectric constant component is the majority and is increased if the high dielectric constant component is the majority. The effect becomes significant at ion concentrations corresponding to an order of one ion per polymer chain. The quantitative change in the effective χ parameter depends on the functional form of the composition dependence of the dielectric constant of the mixture. We also illustrate the difference between fixed ion concentration and fixed chemical potential of the ions.

Determination of CO2 Minimum Miscibility Pressure from Measured and Predicted Equilibrium Interfacial Tensions

Abstract: Accurate determination of the minimum miscibility pressure (MMP) of a crude oil−CO2 system at the actual reservoir temperature is required in order to determine whether CO2 flooding is immiscible o...

Self-Assembly through Competitive Interactions of Miscible Diblock Copolymer/Homopolymer Blends: Poly(vinylphenol-b-methyl methacrylate)/Poly(vinylpyrrolidone) Blend

Abstract: We have investigated a new type A-b-B/C blend system, poly(vinylphenol-b-methyl methacrylate)/ poly(vinylpyrrolidone) (PVPh-b-PMMA)/PVP, where PVPh-b-PMMA block (A-b-B) copolymer, PVPh/PVP (A/C), and PMMA/PVP (B/C) blends are all miscible through hydrogen bond interaction or dipole-dipole interaction. Because of the significantly stronger hydrogen bond interaction between PVPh and PVP than that between PVPh and PMMA, this miscible PVPh-b-PMMA copolymer becomes immiscible up on blending with 20-60 wt % PVP (27-56 wt % PMMA in the blend system) and can self-assemble to form ordered morphologies. Results from small-angle X-ray scattering (SAXS) and TEM consistently indicate that different compositions of PVPh-b-PMMA/PVP blends induce different microphase separation structures such as hexagonal and lamellar phases. However, sharp and multiple orders of diffraction are absent from the SAXS profiles, indicating relatively limited sizes of the ordered domains. Large polydispersity in the molecular weight of PVP and small differences in the interaction parameters of the three components of PVPh, PMMA, and PVP are attributed to be the main reasons that limit the microphase separation in this blend system.

Blends of Polybenzimidazole and Poly(vinylidene fluoride) for Use in a Fuel Cell

Abstract: We report a new blend system consisting of an amorphous polymer polybenzimidazole (PBI) and a semicrystalline polymer poly(vinylidene fluoride) (PVDF) A systematic investigation of the blend pair in various compositions using Fourier transform infrared (FT-IR) spectroscopy provides direct evidence of specific hydrogen bonding interaction involving the N−H groups of PBI and the >CF2 groups of PVDF Blending shows a maximum 30 cm-1 frequency shift in the N−H stretching band of PBI and also the existence of a partial double bond character in the PVDF chain Differential scanning calorimetry (DSC) study proves the miscibility of these polymers in a wider composition range The decrease of the Tg with increasing PVDF in the blend and also the decrease of both the Tm and Tc with increasing PBI in the blend attribute the miscibility of the blend systems The PA doping level of the blend membranes improves significantly as a result of the hydrophobic nature of the PVDF component

Interactions of ionic liquids with polysaccharides. VI. Pure cellulose nanoparticles from trimethylsilyl cellulose synthesized in ionic liquids

Abstract: Trimethylsilyl cellulose (TMSC) can be efficiently synthesized with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) by applying the ionic liquids (ILs) 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium chloride, and 1-butyl-3-methylimidazolium chloride as reaction medium, yielding pure biopolymer derivatives with degrees of substitution (DS) up to 2.89. Cosolvents, for example, chloroform, could be used to adjust the viscosity of the system and to achieve the miscibility of the components. During the synthesis of highly functionalized derivatives precipitation of the TMSC occurred, which simplifies the recycling of the IL. The high tendency of TMSC toward the formation of supermolecular structures was exploited for the formation of nanoparticles studying a simple dialysis process. Amazingly, pure cellulose nanoparticles can be obtained by dissolving TMSC in tetrahydrofurane or N,N-dimethyl acetamide and dialysis against water. FTIR spectroscopy confirmed the complete removal of the TMS functions during this process. Scanning electron microscopy, dynamic light scattering, atomic force microscopy, and particle size distribution analysis showed that cellulose particles down to a size of 170 nm are accessible in this simple manner. The nanoparticle suspensions exhibit viscosities in the range of water. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4070–4080, 2008

Cellulose alkyl ester/poly( ε -caprolactone) blends: characterization of miscibility and crystallization behaviour

Abstract: Cellulose valerate (CV)/poly(e-caprolactone) (PCL) blends were investigated to clarify the effect of the degree of substitution (DS) of the cellulose ester component on the miscibility. CVs of DS > 2.15 were miscible with PCL in their amorphous states, as judged from the detection of a single T g by differential scanning calorimetry (DSC). This result and other complementary data for cellulose acetate (CA), propionate (CP), and butyrate (CB) blends with PCL made up a miscibility map as a function of the number N of carbons in the normal acyl substituent as well as of DS. CB of N = 4 and CV of N = 5, the ester side-chains of which make a higher similarity in chemical structure with a repeating unit of PCL, were found to be miscible with the aliphatic polyester at a comparatively lower DS; the critical butyryl DS of ∼1.85 being still lower than 2.15. For PCL-rich compositions of CB(DS > 2.0)/PCL and CV(DS > 2.2)/PCL blends, isothermal melt-crystallization behaviour was characterized by calorimetry and polarized optical microscopy. The CB and CV components gave rise to a marked diminution of the crystallization rate of PCL, as a result of the diluent action of the cellulose esters in the respective miscible, molten mixtures. Through a quantitative analysis of the kinetics, it is suggested regarding the supramolecular morphology that the bulky cellulose esters would be trapped not only on the fold surfaces but also on the growth faces of PCL lamellar crystals, to form a non-crystalline mixed polymer phase in the crystal boundary regions.

Thermorheological properties of LLDPE/LDPE blends

Abstract: The thermorheological behavior of a number of linear low-density polyethylene and low-density polyethylene (LLDPE/LDPE) blends was studied with emphasis on the effects of long chain branching. A Ziegler–Natta, LLDPE (LL3001.32) was blended with four LDPEs having distinctly different molecular weights. The weight fractions of the LDPEs used in the blends were 1, 5, 10, 20, 50, and 75%. Differential scanning calorimetry (DSC) analysis has shown that all blends exhibited more than one crystal type. At high LDPE weight fractions, apart from the two distinct peaks of the individual components, a third peak appears which indicates the existence of a third phase that is created from the co-crystallization of the two components. The linear viscoelastic characterization was performed, and mastercurves at 150 °C were constructed for all blends to check miscibility. In addition, Van Gurp Palmen, zero-shear viscosity vs composition, Cole–Cole, and the weighted relaxation spectra plots were constructed to check the thermorheological behavior of all blends. In general, good agreement is found among these various methods. The elongational behavior of the blends was studied using a uniaxial extensional rheometer, the SER universal testing platform from Xpansion Instruments. The blends exhibit strain-hardening behavior at high rates of deformation even at LDPE concentrations as low as 1%, which suggests the strong effect of branching added by the LDPE component.

Spectroscopic and thermal studies of PS/PVAc blends

Abstract: Polystyrene and polyvinyl acetate (PS/PVAc) films were blended with different contents using casting method. The effect of PS content on PVAc blends was investigated by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Ultra violet and visible studies (UV/VIS), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Significant changes in FT-IR, XRD and DSC analysis are observed which reveals an interactions between the two polymers and PS/PVAc blends had good or certain miscibility. XRD scans show some changes in the intensity and the height of the amorphous halos with increased PS. UV/VIS analysis revealed that the optical band gap decreases with increasing content of PS from 5 to 4.11 eV. A single glass transition temperature for each blend was observed, this DSC results supported that the miscibility existed in the blend. The apparent activation energy (E) of the blends was evaluated using TGA analysis. The value of E was increased with the increase of PS content.

On the Correlation between Miscibility and Solubility Properties of Energetic Plasticizers/Polymer Blends: Modeling and Simulation Studies

Abstract: In this paper, systems for which miscibility (hydroxyl-terminated polybutadiene–dioctyl adipate or HTPB–DOA) or immiscibility (HTPB–diethylene glycol dinitrate or HTPB–DEGDN) have been firmly established were used to test the usefulness of an atomistic molecular mechanics model. Two specific aspects were discussed: miscibility assessment of a plasticizer/polymer blend, and predictions of the enthalpy of vaporization. Simulations were carried out using Amorphous Cell and Discover packages of the Material Studio software using Compass force field for all calculations. A good agreement has been found for miscibility observations of blends, and for solubility parameter, density, and derived enthalpy of vaporization for pure substances. Therefore, the approach proposed in this work is a useful tool to provide insights on miscibility and properties of a given polymer/plasticizer blend. In addition, it is a promising technique to help in screening among several plastic bonded explosive (PBX) formulations prior to real experimental tests.

Immiscibility-miscibility phase transitions in blends of poly(L-lactide) with poly(methyl methacrylate)

Abstract: BACKGROUND: The nature of phase transitions and apparently irreversible phase homogenization upon heating in blends of biodegradable poly(L-lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were proven using differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy and 1H NMR spectroscopy. The complex phase behaviour in this blend system is puzzling and is a matter of debate; this study attempts to clarify the true nature of the phase behaviour. RESULTS: A PMMA/PLLA blend is immiscible at ambient temperature but can become miscible upon heating to higher temperatures with an upper critical solution temperature (UCST) at 230 °C. The blends, upon rapid quenching from the UCST, can be frozen into a quasi-miscible state. In this state, the interaction strength was determined to be χ12 = − 0.15 to − 0.19, indicating relatively weak interactions between the PLLA ester and PMMA acrylic carbonyl groups. CONCLUSION: The absence of chemical exchange reactions above the UCST and phase reversibility back to the original phase separation morphology, assisted by solvent re-dissolution, in the heat-homogenized PLLA/PMMA blend was shown. Verification of UCST behaviour, phase diagrams and solvent-assisted phase reversibility were experimentally demonstrated in PMMA/PLLA blends. Copyright © 2008 Society of Chemical Industry

Miscibility, Melting, and Crystallization Behavior of Poly(hydroxybutyrate) and Poly(D,L-lactic acid) Blends

Abstract: Melting behavior and crystal morphology of poly(3-hydroxybutyrate)-poly(D,L-lactic acid) (PHB-RPLA) blends with various compositions have been investigated by modulated temperature differential scanning calorimetry (mt-DSC), polarized optical thermomicroscopy (POTM), modulated force thermomechanometry (mf-TM), and small angle X-ray scattering (SAXS) Thermal properties were investigated after fast cooling crystallization treatment Multiple melting peak behavior was observed for all polymers mt-DSC data revealed that PHB-RPLA blends undergo melting-recrystallization-remelting during heating, as evidenced by exothermic peaks in the nonreversing heat capacity A decrease in degree of crystallinity due to significant melt-recrystallization was observed for blends PHB-RPLA showed different crystal morphologies for various compositions POTM results showed that the crystallization rates and sizes of spherulites were significantly reduced as RPLA content increased mf-TM results confirmed miscibility of these two polymers SAXS data provided evidence of lamella thickness of blends, which increased with increasing RPLA content

Preparation, swelling and electro-mechano-chemical behaviors of a gelatin-chitosan blend membrane.

Abstract: Swelling, states of water, morphology, stability in the aqueous solution, and electro-mechano-chemical bending behaviors of the gelatin–chitosan blend system were studied in order to clarify the potential use of this blend system as an actuator. The gelatin–chitosan blend system was prepared in order to avoid dissolution of the pure chitosan in an aqueous medium and the rigidity and easy degradation of the pure gelatin in the swollen state. The blend systems showed improved material properties: the vacuum-dried blend sample at the G75/C25 (w/w, gelatin–chitosan) ratio showed ∼6 times swelling (in distilled water, at neutral pH and room temperature), ∼5 times stability (in distilled water), and ∼6 times bending (at 6 V/53 mm and in a 0.02 M NaCl aqueous solution) as compared to pure gelatin. These enhanced properties could be explained by the introduction of free –OH, –NH2, and –NHOCOCH3groups of the amorphous chitosan in the blend and the network structure through the electrostatic interactions between the ammonium (–NH3+) ions of the chitosan and the carboxylate (–COO−) ions of the gelatin. The scanning electron microscopy (SEM) micrographs of the surfaces of the blend films showed homogeneous and smooth surfaces due to the good miscibility between gelatin and chitosan. However, a different morphology from the fractured surface was found between the pure gelatin and blend systems which showed condensed and foliaceous morphologies, respectively. The leafy morphology indicates a large and homogeneous pore structure, which would cause increased ion diffusion into the gel and might lead to increased bending.

Miscibility, crystallization, and mechanical properties of poly(3‐hydroxybutyrate) and poly(propylene carbonate) biodegradable blends

Abstract: Nine blends of poly(3-hydroxybutyrate) (PHB) and poly(propylene carbonate) (PPC), biodegradable polyester, and pure sample films were prepared with the ratio of PHB/PPC ranging from 90/10 to 10/90 by codissolving these two polyesters in chloroform and casting the mixture. The miscibility, crystallization, melting behavior, morphology, and mechanical properties of the blends have been studied by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), wide angle X-ray diffraction (WAXD), polarizing optical microscopy (POM), and scanning electron micrograph (SEM). The results indicated that PHB showed complete miscibility with PPC for PHB/PPC 30/70, 20/80, and 10/90, as evidenced by the only one composition-dependent glass transitions (Tg) of blends, and the Tgs close to the values calculated using the Fox equation. However, PHB showed immiscibility with PPC for the other six blends, as shown by the existence of almost unchanged Tg of PHB at about 2°C. According to the DSC analysis, the crystallization of PHB was suppressed by blending with abundant PPC. This result is consistent with results obtained from X-ray and POM results. Some interaction between the two macromolecules was confirmed by using FTIR analysis. SEM graphs showed that the blends containing PHB ≤ 30 wt % tend to form a more compact structure, and no obvious phase separation was found. The brittleness of PHB was improved apparently by blending with PPC. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Miscibility and Hydrogen-Bonding Behavior in Organic/Inorganic Polymer Hybrids Containing Octaphenol Polyhedral Oligomeric Silsesquioxane

Abstract: In this study, we investigated the miscibility behavior and mechanism of interaction of poly(methyl mechacrylate) (PMMA), poly(vinyl pyrrolidone) PVP, and PMMA- co-PVP blends with octa(phenol)octasilsequioxane (OP-POSS). For the PMMA/OP-POSS binary blend, the value of the association constant ( K A = 29) was smaller than that in the poly(vinyl phenol) (PVPh)/PMMA ( K A = 37.4) and ethyl phenol (EPh)/PMMA ( K A = 101) blend systems, implying that the phenol groups of the OP-POSS units in the PMMA/OP-POSS blends interacted to a lesser degree with the CO groups of PMMA than they did in the other two systems. In addition, the ionic conductivity of a LiClO4/PMMA- co-PVP polymer electrolyte was increased after blending with OP-POSS.

Structure and Properties of Blend Films Prepared from Castor Oil-Based Polyurethane/Soy Protein Derivative

Abstract: We successfully prepared a series of transparent blend films from castor oil-based polyurethane (PU) and p-phenylene diamine soy protein (PDSP). The miscibility, morphology, and properties of the blend films were investigated with Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, scanning electron microscopy, moisture adsorption, thermal degradation, and tensile testing. The results revealed that the PDSP exhibited certain miscibility with PU varied its content from 10 to 80 wt % and also showed the strong hydrogen-bond and chemical cross-linking interactions lied between PU and PDSP. With an increase in the PU content, the elongation at break, thermal stability, and water resistance were improved whereas the tensile strength and Young’s modulus decreased. It is worth noting that modified soy protein could be blended with hydrophobic polyurethane to obtain the blend films having good mechanical properties and optical transmittance.