Degree Of Miscibility Research Articles

Miscibility, melting and crystallization of poly(ε-caprolactone) and poly (vinyl formal) blend

Solution cast blends of poly(e-caprolactone) [PCL] and poly(vinyl formal) [PVF] from dichloromethane was investigated for miscibility by Differential Scanning Calorimetry [DSC], Fourier Transform Infrared Spectroscopy [FTIR] and optical microscopy. Melting (Tm) and crystallization (Tc) temperatures were for the PCL fraction while the glass transition temperature (Tg) was for PVF fraction in the blends. Blends with 20 wt% and less PCL showed a depression in Tm and Tc. Depression in Tc indicated that during the non-isothermal crystallization process, the presence of PVF decreased the PCL segments migrating to the crystallite-melt interface thus reducing the nucleation rate, growth rate and the thickness of the lamella resulting in a depressed Tm. Crystallinity (Xc) decreased gradually with decreasing content of PCL in the blend and was due to the dilution of PCL by PVF. A depressed Tg was observed for 10 wt% PCL blend and remained the same for all other blend compositions. These observations suggested that this blend system has very low degree of miscibility. The degree of miscibility increased at low polyester concentration. FTIR spectra of the blends with low polyester concentrations showed changes in the C=O, O-H and C-O-C regions in the blended PVF and PCL spectra. Optical microscopy showed phase separation in the melt and in the PCL spherulites.

Conductive Polyaniline/Poly (Epichlorohydrin-co-Ethylene Oxide) Blends Prepared in Solution

Blends of poly (epichlorohydrin-co-ethylene oxide) rubber (Zeon Hydrin® C2000L) and polyaniline doped with dodecylbenzenesulfonic acid (PAni-DBSA), containing different weight fractions of PAni were cast from solution. Solubility parameters for both PAni-DBSA and Hydrin® were calculated and found to be comparable, favouring some degree of miscibility. Conductive transparent films were formed by casting onto PTFE substrates. Conductivities of cast films were found to be in the region of 10−7 S.cm−1 for 1% wt PAni-DBSA. Electrical conductivities increased as the wt % of PAni-DBSA was increased, showing a percolation threshold as low as 1% wt with highest conductivity achieved at 50%. Decomposition steps of conductive blends were investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermal stability of the blends was influenced by the ratio of PAni-DBSA to Hydrin®. The effect of composition on the glass transition in the blends was determined using thermomechanical analysis (TMA).

Miscibility and physical properties of conducting poly(urea‐urethane) thermoplastic elastomers

AbstractA series of amine‐terminated polyaniline oligomer (OPA)‐based conducting poly(urea‐urethane) thermoplastic elastomers (PUUs) was synthesized by two‐stage solution polymerization and characterized by FTIR. Various percentages of OPA were introduced into PUUs as chain extenders to form hard segments of PUUs with urea‐linkages. Spectroscopic and differential scanning calorimetry, as well as dynamic mechanical analysis, were conducted to elucidate the interaction and degree of miscibility between hard and soft segments, which were related to the stress–strain properties of PUUs. The hydrogen bonding index (HBI) measured by FTIR was employed to show the degree of interchain hydrogen bonding. Copolymer films with higher OPA content exhibit higher HBI and the degree of miscibility is significantly improved. The resultant conducting copolymers have higher tensile strength, higher Young's modulus, and lower elongation at break, because of the long rigid structure of OPA and the increase in the number of hydrogen bonds among the copolymers blocks. Incorporating OPA in PUUs increases the mass of the residue at temperatures over 600°C, according to thermogravimetric analysis. The conductivity of PUUs is found to range from 0.83 S/cm for neat OPA to 6.11 × 10−5 S/cm for PUUs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3803–3810, 2007

Miscibility and Properties of Acid-Treated Multi-Walled Carbon Nanotubes/Polyurethane Nanocomposites

Nanocomposites based on polyurethane and acid-treatment multi-walled carbon nanotubes (A-MWNTs) are prepared by solution blending. The surface of the MWNTs was modified by acid treatment to incorporated functional groups. The modified MWNTs exhibited improved dispersion in organic solvents and miscibility with the PU matrix. The derivatives of MWNTs were characterized by Fourier transform infrared (FT-IR) spectroscopy, Transmission electron microscopy (TEM) and Raman spectroscopy. The thinning and defects of the A-MWNT from the surface etching of acid treatment can be clearly seen from TEM pictures and Raman spectra, respectively. The interaction and degree of miscibility between the MWNTs and the PU matrix is examined using FT-IR, modulated differential scanning calorimeter (MDSC), TEM and atomic force microscopy (AFM). The hydrogen bonding index (HBI) measured by FT-IR was employed to show the degree of interchange hydrogen bonding. Composites films with higher A-MWNT content exhibit higher HBI and the degree of miscibility is significantly improved. The resultant composites have higher tensile strength, higher Young’s modulus and lower elongation at break because of the rigid structure of A-MWNT and the increase in the number of hydrogen bonds among the composites. Incorporating A-MWNT in composites increases the mass of the residue at temperatures over 600 °C, according to thermo gravimetric analysis (TGA). An A-MWNT percentage of 20 wt %, the electric conductivity approached 6.2×10−2 S/cm.

Effects of polydimethylsiloxane concentration on properties of polyurethane/polydimethylsiloxane hybrid dispersions

AbstractA series of waterborne polyurethane (WPU) derived from isophorone isocyanate and poly(tetramethylene glycol) were modified by hydroxyl‐terminated polydimethylsiloxane (HPMS). The solutions were then cast into films named as PUHS. Rheological behavior of the emulsions were studied using Rheometer and morphology was studied with transmission electron microscope. Meanwhile, the casting films were prepared from the WPU/HPMS hybrid dispersions, and their glass transition behavior, miscibility, water resistance, and medium resistance were studied with differential scanning calorimeter (DSC), wide‐angle X‐ray diffraction (WAXD), and so on. The results revealed that the emulsions' particle size decreases with increasing HPMS content and the particles are more easily affixed to each other when the HPMS content is more than 15%, and emulsions are endowed with pseudoplasticity and thixotropy. WAXD and DSC figures manifested that the casting films all exhibited a certain degree of miscibility. The degrees of crystallinity (xc) decreased with increasing HPMS content, and the PUHS films were almost amorphous. It is noticed that water and medium absorption increased in the HPMS/PU compared to pure PU, which demonstrate that the membrane surfaces have excellent water and chemical medium repellency. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5538–5544, 2006

Recycling poly(ethylene terephtalate) wastes: Properties of poly(ethylene terephtalate)/polycarbonate blends and the effect of a transesterification catalyst

The article addresses the issue of recycling of poly(ethylene terephtalate) (PET) by melt blending with polycarbonate (PC). PET/PC blends containing various amounts of the immiscible polymers were prepared in a twin-screw extruder. Selected compositions were also prepared in the presence of an Sn-based catalyst to assess the influence of transesterification during melt mixing. The degree of miscibility in the blends was studied using differential scanning calorimetry, scanning electron microscopy, and mechanical testing. PET/PC blends exhibit enhanced tensile properties in comparison to neat components for compositions of PET higher than 50% and these properties are improved by the addition of a transesterification catalyst. The PET/PC blend containing 20 wt% of PC, prepared with stannous octoate, shows the smallest size of the dispersed phase because of transesterification reactions that generate copolymer molecules at the interface between the immiscible polymers. The melting temperature of PET is decreased with the increase of the PC content in blends extruded in the presence of the catalyst. Also, the temperatures of the cold crystallization of PET are higher than those of similar blends without added catalyst. Both features give rise to better molding properties because of a shortening of the cooling time in the range of 50–90 wt% of PET. POLYM. ENG. SCI. 46:1378–1386, 2006. © 2006 Society of Plastics Engineers

Investigation of rubber–rubber blends miscibility

Polybutadiene rubber, poly(styrene-co-butadiene) rubber, natural rubber, and their blends were investigated to estimate the degree of miscibility of components in the blends. The morphology of a rubber–rubber blend controls its rheological properties and glass transition behavior. Therefore, two different measuring techniques were used: rheological characterization of blends by the rubber process analyzer (RPA) and temperature modulated differential scanning calorimetry (TMDSC). To study the dependence of complex viscosity on blend composition, two commonly used empirical mixing rules were applied: the log-additivity mixing rule and the quadratic mixing rule. Viscoelastic properties of the examined samples were described by mechanical and relaxation spectra. Since the RPA measurements cannot be performed in a wide frequency range, the experimental results cannot offer a complete overview. Also, the quantitative analysis using the differential of the heat capacity, dCp/dT, versus the temperature signal from TMDSC did not allow to calculate the weight fraction of the interface for all types of the blends under investigation. However, the combination of the two techniques applied provided complementary information on blend morphology and rubber–rubber miscibility. POLYM. ENG. SCI. 46:1649–1659, 2006. © 2006 Society of Plastics Engineers.

Approaching criticality in polymer-polymer systems

The interfacial width of polyolefins blends has been probed as a function of distance away from the critical point by using neutron reflectivity. For strongly immiscible polymer pairs, the width of the interface increases slowly when the degree of immiscibility is decreased and the interfacial width varies with the interaction parameter chi of the polymers. Closer to the critical point the dependence on the degree of miscibility becomes stronger and the way in which the interfacial width diverges, as criticality is approached, is related to both the chain length and chi. The self-consistent field theory numerical calculations, with the additional contribution due to capillary waves, provides a good description of the width of the interface between two polymer bulk phases in particular at intermediate values of the degree of immiscibility.

Enhanced Matrimid membranes for pervaporation by homogenous blends with polybenzimidazole (PBI)

We have demonstrated that the incorporation of a small amount of polybenzimidazole (PBI) into Matrimid polyimide can significantly stabilize Matrimid's polymeric chains for high-temperature pervaporation and remarkably enhance the separation factor/selectivity and flux/permeance for the dehydration of tert-butanol/water mixtures. The strong interactions between the carbonyl group of Matrimid and the N H group of PBI are the cause for the enhanced chain stability, while the hydrophilic nature of PBI and the close chain packing may be the reasons for the high separation performance. Data from DSC, TMA, DMA and FTIR confirm that the PBI/Matrimid blends studied are miscible in molecular level, but the degree of miscibility apparently decreases with an increase in PBI. It is found that annealing plays an important role on membrane structure and separation performance. Not only can it induce chains rearrangement towards a dense packing and the formation of charge transfer complexes (CTC), but also significantly improve separation factor and selectivity. Pervaporation experiments conducted at room and elevated temperatures all indicate that the blend membrane with 3.55 wt.% PBI has the best separation performance, which is consistent with the smallest d-space value measured by XRD. In addition, both DMA and pervaporation experiments verify that the blending of a small amount of PBI with Matrimid can efficiently overcome the plasticization of Matrimid at high temperature operation.

Bioartificial materials based on blends of dextran and poly(vinyl alcohol- co-acrylic acid)

Bioartificial polymeric materials based on blends of dextran and poly(vinyl alcohol- co-acrylic acid) P(VA- co-AA) were prepared in the form of films and characterised to evaluate the miscibility of the natural component with the synthetic one. The idea of this work was to compatibilise PVA and dextran by introducing carboxylic groups along the PVA chains. The copolymer was synthesised and characterised in our laboratories. The results evidenced that the copolymer had an appropriate molecular weight and the content of PAA in the copolymer was 45% (weight). Then, films with different composition ratios were prepared by solution casting and analysed by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), chemical imaging analysis and mechanical tests. The results obtained indicated that the introduction of carboxylic groups along the PVA chains had a positive effect on the miscibility degree of the synthetic component with the biological one.

Crystallization Behavior of Poly(l-lactic acid) Nanocomposites: Nucleation and Growth Probed by Infrared Spectroscopy

Time-lapsed Fourier transform infrared (FTIR) spectroscopy was employed to probe chain conformational changes during the isothermal crystallization of poly(l-lactic acid), PLLA, and its nanocomposites from the melt. To study the effect of clay exfoliation extent on the crystallization behavior of PLLA, intercalated and exfoliated nanocomposites were fabricated by solution casting two commercially available organoclays with different degrees of matrix miscibility. By solely varying the degree of miscibility between the organic modifier and the polymer matrix, fully intercalated and exfoliated nanocomposites were obtained. This system allowed us to systematically investigate the effect of degree of clay exfoliation on the chain conformational changes during the crystallization process. In the case of neat PLLA, interchain interactions preceded intrachain interactions during the crystallization. Conversely, the exfoliated nanocomposites exhibited an opposite behavior in that 103 helix formation and backbone ...

Alkyne-Functional Homopolymers and Block Copolymers through Nitroxide-Mediated Free Radical Polymerization of 4-(Phenylethynyl)styrene

Nitroxide-mediated polymerization of the alkyne-functional monomer 4-(phenylethynyl)styrene allows the preparation of homopolymers and block copolymers with narrow molecular weight distributions. At higher conversions, side reactions, including addition of mediating nitroxides to alkyne groups, lead to broader molecular weight distributions. While differential scanning calorimetry suggests that poly((4-phenylethynyl)styrene) blocks of moderate molecular weight have a fair degree of miscibility with polystyrene, reaction of the pendant alkyne groups of these copolymers with dicobalt octacarbonyl leads to microphase-segregated cobalt-functional materials.

Miscibility and Crystallization Behaviors of Polyamide 6/Polytetrafluoroethylene Blends

Summary: The miscibility and crystallization behaviors of polyamide 6 (PA 6)/polytetrafluoroethylene (PTFE) blends, prepared via reactive extrusion, are systematically investigated by means of wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). WAXD measurements show that no co-crystallization occurred between two components, while DSC and DMTA measurements suggest that a certain degree of miscibility between them might exist due to the formation of some copolymers during the reactive extrusion. DMTA curves for the pure PA 6 sample and PA 6/PTFE blends with various compositions.

Effect of inorganic salts on crystallization of poly(ethylene glycol) in frozen solutions

The effect of inorganic salts on eutectic crystallization of poly(ethylene glycol) (PEG) 1500–20,000 in frozen solution was studied to model the polymer and inorganic salt interaction in freeze-dried formulations. Thermal analysis of an aqueous PEG 3000 solution showed a eutectic PEG crystallization exotherm at approximately −47 °C and a subsequent PEG crystal melting endotherm at −14.9 °C. Addition of sodium chloride prevented the PEG crystallization in the freeze-concentrated solution surrounding ice crystals. Higher concentration NaCl was required to retain higher molecular weight PEG in the amorphous state. Various inorganic salts prevented the PEG crystallization to varying degrees depending mainly on the position of the anion in the Hofmeister's lyotropic series. Some salting-in and ‘intermediate’ salts (NaSCN, NaI, NaBr, NaCl, LiCl, KCl, and RbCl) inhibited the crystallization of PEG 7500 in frozen solutions. On the other hand, salting-out salts (NaH 2PO 4, Na 2HPO 4, Na 2SO 4, and NaF) did not show an apparent effect on the PEG crystallization. Some salting-out salts induced PEG crystallization in PEG and sucrose combination frozen solutions. The varying abilities of salts to prevent the PEG crystallization in frozen solutions strongly suggested that the solutes had different degrees of miscibility in the freeze-concentrates.

Nano-structured Langmuir–Blodgett mixed films of titanyl(IV) phthalocyanine and bis(neopentylimido)perylene: Unique degree of miscibility

Langmuir and Langmuir–Blodgett (LB) films of mixed titanyl(IV) phthalocyanine (TiOPc)–bis (neopentylimido)perylene (BNPTCD) were fabricated and characterized. The surface pressure–area isotherms ( π– A) of the mixed Langmuir films were recorded and revealed an unusual expansion of the surface area per molecule. The expansion is attributed to the interpenetration of the BNPTCD in the space available between adjacent Pc macrocycles preventing molecular stacking and forcing the expansion. This effect is a result of the high degree of mixing between species in the floating monolayer. This assumption was further supported by means of surface enhanced Raman scattering (SERS) mapping technique that proved the absence of large segregated domains in the LB film, in other words, the absence of phase separated regions, in agreement with a unique degree of miscibility.

Miscibility studies on poly(ethylene glycol)/dextran blends in aqueous solutions by dilute solution viscometry

AbstractMiscibility of poly(ethylene glycol) (PEG) with dextran (Dx) was investigated by dilute solution viscometry. Dilute solution viscosity measurements were made on ternary systems, polymer (1)/polymer (2)/solvent (H2O), for four different average molecular weights of PEG and Dx. The intrinsic viscosity and viscometric interaction parameters were experimentally measured for the binary (solvent/polymer) as well as for the ternary systems by classical Huggins equation. Degree of miscibility of these polymer systems was estimated on the basis of the four following criteria: (1) the sign of the ΔkAB, (2) the sign of α, (3) the sign of ΔB, and (4) the sign of the μ. Based on the sign convention involved in these criteria, immiscibility was observed in most systems. The miscibility of all these systems in accordance with the interactions between the unlike polymer chains rather the polymer–solvent interactions were investigated depending on molecular weight of polymer sample. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 453–460, 2004

Effect of the Particle Size in Dispersions on the Properties of Waterborne Polyurethane/Casein Composites

Two kinds of aqueous dispersions were prepared from waterborne polyurethane (WPU) and its prepolymer by mixing (M) and grafting (G) with 10 wt % casein, respectively. The resulting dispersions were characterized by using a rotary viscometer and a particle size distribution meter, indicating that the viscosity, Z average size, and polydispersity of the dispersions increased with an increase of the casein content, and the average particle size of the M dispersions (ca. 30−50 nm) was much lower than that of the G dispersions (ca. 50−150 nm). Polyurethane/casein composite sheets were prepared from the dispersions M and G, coded as sheets M and G, respectively. The structure and properties of the sheets were characterized by using infrared spectroscopy, scanning electron microscopy, ultraviolet spectrophotometry, dynamic mechanical analysis, and tensile testing. The results revealed that the sheets M and G all exhibited a certain degree of miscibility, and their tensile strength was much higher than that of th...

Fracture behavior at partially miscible polymer interfaces

AbstractThe fracture behavior for the partially miscible polystyrene/poly (styrene‐r‐4‐bromostyrene) (PS/PBS) interface is analyzed as a function of miscibility. This is achieved by measuring the fracture energy at PS/PBS interfaces over a range of molecular weights (1370 < N < 7144; N is the degree of polymerization) and annealing conditions (150 < T < 200°C) at varying degrees of miscibility (controlled by ƒ, the volume fraction of brominated repeat units in PBS). Correlations between fracture energy, mutual diffusion coefficient (measured using Rutherford backscattering spectroscopy), and the Flory‐Huggins interaction parameter (χ) are presented. It is shown that the fracture energy, Gc, increases as annealing temperature increases and N and ƒ decrease. The presence of two miscibility‐mediated interdiffusion/fracture regimes is postulated depending upon the value of N*χ, where \documentclass{article}\pagestyle{empty}\begin{document}$N^* = \frac{{2N_{PS} N_{PBS} }}{{N_{PS} + N_{PBS} }}$\end{document}. (I) When N*χ < 2, the system is miscible, Gc is high, and the fracture mechanism is crazing; (II) When N*χ > 2, the system exhibits a miscibility gap, interdiffusion is thermodynamically limited, which results in a decreased Gc, which continues to decrease with increasing ƒ. No crazes are observed in regime II and fracture occurs via chain pullout. Polym. Eng. Sci. 44:929–939, 2004. © 2004 Society of Plastics Engineers.

Properties of crosslinked casein/waterborne polyurethane composites

AbstractWaterborne polyurethane (WPU) and casein (1 : 1 by weight) were blended at 90°C for 30 min, and then were crosslinked by adding 1–10 wt % ethanedial to prepare a series of sheets. Their structure and properties were characterized by using infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical analysis, and tensile testing. The results indicated that crosslinked blend sheets exhibited a certain degree of miscibility, and exhibited much higher tensile strength and water resistivity than did the WPU, casein, and the uncrosslinked blend from WPU and casein. When the ethanedial content was 2 wt %, the tensile strength and elongation at break of crosslinked sheets achieved 19.5 MPa and 148% in the dry state, and 5.0 MPa and 175% in the wet state, respectively. A 2 wt % content of ethanedial plays an important role in the enhancement of mechanical properties, thermal stability, and water resistivity of the blends of WPU and casein as a result of intermolecular crosslinking. This work provided a new protein plastic with good water resistivity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 332–338, 2004

Networks and blends of polyaniline and polyurethane: correlations between composition and thermal, dynamic mechanical and electrical properties

The combination of the electrical conducting properties of polyaniline (Pani) with the mechanical performance of polyurethanes (PU) was accomplished through the interconnection of the two polymers via condensation of a NCO terminated PU prepolymer and the amine groups of polyaniline. The crosslinking density of the resulting networks was set by the proportion between the two components, since the PU length was kept constant (Mw=40,000, Mn=23,000). The composition range Pani/PU spanned from 1 to 30%. Blends of the same composition were prepared for comparison purposes. Taking into account the IR absorption shifts, DMTA spectra, electrical conductivity results and computer generated optimized chain conformation, a morphological interpretation is proposed in which Pani chains form a continuous percolating phase dispersed in a polyurethane matrix, linked together by an interphase, with a certain degree of miscibility. This interphase would be responsible for the connectivity between the two components and the good mechanical properties observed. Electrical conductivity of the networks was in the 10−4S/cm range.