Showing papers on "Miscibility published in 1997"

Preparation and Mechanical Properties of Polypropylene−Clay Hybrids

Abstract: Polypropylene (PP)−clay hybrids (PPCH) have been prepared by simple melt-mixing of three components, i.e., PP, maleic anhydride modified polypropylene oligomers (PP-MA), and clays intercalated with stearylammonium. The dispersibility of 10-A-thick silicate layers of the clays in the hybrids was investigated by using a transmission electron microscope and X-ray diffractometer. It is found that there are two important factors to achieve the exfoliated and homogeneous dispersion of the layers in the hybrids: (1) the intercalation capability of the oligomers in the layers and (2) the miscibility of the oligomers with PP. Almost complete hybrids were obtained in the case where the PP-MA has both intercalation capability and miscibility. The hybrids exhibit higher storage moduli compared to those of PP especially in the temperature range from Tg to 90 °C. The highest relative storage modulus at 80 °C of the hybrid based on a mica and the miscible PP-MA is as high as 2.0 to that of PP and is 2.4 to that of the ...

Miscibility and Crystallization of Poly(β-hydroxybutyrate) and Poly(p-vinylphenol) Blends

Abstract: The miscibility and crystallization behavior of poly(beta-hydroxybutyrate) (PHB) and poly(p-vinylphenol) (PVPh) blends were studied by differential scanning calorimetry and optical microscopy (OM). The blends exhibit a single composition-dependent glass transition temperature, characteristic of miscible systems, A depression of the equilibrium melting temperature of PHB is observed. The interaction parameter values obtained from analysis of the melting point depression are of large negative values, which suggests that PHB and PVPh blends are thermodynamically miscible in the melt. Isothermal crystallization kinetics in the miscible blend system PHB/PVPh was examined by OM. The presence of the amorphous PVPh component results in a reduction in the rate of spherulite growth of PHB. The spherulite growth rate is analyzed using the Lauritzen-Hoffman model, The isothermally crystallized blends of PHB/PVPh were examined by wide-angle X-ray diffraction and smell-angle X-ray scattering (SAXS). The long period obtained from SAXS increases with the increase in PVPh component, which implies that the amorphous PVPh is squeezed into the interlamallar region of PHB.

Miscibility and crystallization of poly(L-lactide)/poly(ethylene glycol) and poly(L-lactide)/poly(ε-caprolactone) blends

Abstract: Miscibility and Crystallization of Poly( L -lactide)/Poly(ethylene glycol) and Poly( L -lactide)/Poly(e-caprolactone) Blends

FTIR and FT-Raman Studies of Partially Miscible Poly(methyl methacrylate)/Poly(4-vinylphenol) Blends in Solid States

Abstract: The miscibility of poly(4-vinylphenol) (PVPh) and poly(methyl methacrylate) (PMMA) blends has been investigated by FTIR and FT-Raman spectroscopy. Although both techniques provide evidence for the ...

Hydrogen-Bonding Strength in the Blends of Polybenzimidazole with BTDA- and DSDA-Based Polyimides

Abstract: Blends of solutions of poly[2,2‘-(m-phenylene)-5,5‘-bibenzimidazole] (PBI) with poly(amic acids) (PAA's) synthesized from BTDA (3,3‘,4,4‘-tetracarboxybenzophenone dianhydride) and DSDA (3,3‘,4,4‘-tetracarboxydiphenyl sulfone dianhydride) with 3,3‘-DDSO2 (3,3‘-diaminodiphenyl sulfone), 4,4‘-DDSO2 (4,4‘-diaminodiphenyl sulfone), 4,4‘-MDA (4,4‘-methylenedianiline), and 4,4‘-ODA (4,4‘-oxydianiline) were prepared in DMAc solvent and transformed into PBI/polyimide (PI) blends by curing at higher temperatures than the Tgs of the blends. The blend systems used in this study were all miscible; evidences for miscibility were optically clear film, a synergistic single Tgs at all compositions, and frequency shifts of the functional groups intermediate between those of the constituents. The strength of intermolecular interaction between PBI and various polyimides were measured by means of DSC, DMTA, and FT-IR. From the analyzed data based on the Tg diagram, the Fox equation, the k values in Gordon−Taylor equation, and...

Conformational Entropy Contributions to the Glass Temperature of Blends of Miscible Polymers.

Abstract: Because of negligible contributions of combinatorial entropy, miscibility of polymers is attributed predominantly to favorable (exothermic) enthalpic effects of mixing, i.e., to strong interactions between the blend components, which have to overcome the cohesive forces acting within the components. Miscibility of amorphous polymers usually is associated with the presence of a single glass temperature of the blend. Although stronger hetero-contact interactions are thermodynamically required for polymer miscibility, the majority of miscible binary polymer blends exhibit negative deviations of the glass temperature from values predicted by the free volume or flexible bond additivity rules, suggesting a looser packing within those blends. A reasonable explanation assumes that binary hetero-contact formation within the blend may be accompanied by local interchain orientation contributing consequently to conformational entropy changes. The smaller the induced interchain orientation by hetero-contact formation, the larger the mobility in the neighborhood of the contacts and the probability of related conformational entropy changes, causing an equivalent increase of the "free volume" within the blend, i.e., a corresponding decrease of the blend Tg, which finally can be situated below the values predicted by the additivity rules. Vice versa, the corresponding argument will hold for blends with higher interchain orientation induced by intensive exothermic hetero-contact forces.

The influence of stereoregularity on the miscibility of poly(propylene)s

Abstract: The melt miscibility of atactic poly(propylene) (a-PP) with isotactic (i-PP) and syndiotactic poly(propylene) (s-PP), respectively, is investigated by diffusion experiments ofi-PP/a-PP/i-PP or s-PP/a-PP/s-PP sandwich specimens using polarized light microscopy. It is shown that the system a-PP/i-PP is miscible in the melt, whereas for the system a-PP/s-PP no evidence for melt mixing is found. Pressure-volume-temperature (PVT) measurements of the three poly(propylene)s are carried out in order to determine the characteristic parameters of the Flory-Orwoll-Vrij equation-of-state theory. Theoretical predictions using the solubility parameter concept are in agreement with the observed miscibility behavior of the blends. Differences in the cohesive energy densities of a-PP and i-PP on the one side, and s-PP on the other side, are found to be responsible for the phase behavior of the mixtures of poly(propylene)s with different stereoregularity.

Functional Group Accessibility in Hydrogen-Bonded Polymer Blends. 2. Miscibility Map of 2,3-Dimethylbutadiene- stat-vinylphenol Blends with Ethylene-stat-vinyl acetate

Abstract: An experimental miscibility map for 2,3-dimethylbutadiene-stat-4-vinylphenol (DMBVPh) blends with ethylene-stat-vinyl acetate (EVA) is obtained and compared to theoretical calculations. The number of hydrogen-bonded carbonyl groups in these systems is measured by FTIR spectroscopy and some systematic trends are apparent. It is shown that the miscibility of DMBVPh/EVA blends is much more sensitive to the difference in solubility parameters than to the degree of hydrogen bonding. However, the contribution from hydrogen bonding in these mixtures is important and is significantly influenced by screening effects. A simple correlation for the dependence of the screening effect on the average spacing of functional groups in a chain is proposed and tested.

Solid-state relaxations in linear low-density (1-octene comonomer), low-density, and high-density polyethylene blends

Abstract: Extensive thermal and relaxational behavior in the blends of linear low-density polyethylene (LLDPE) (1-octene comonomer) with low-density polyethylene (LDPE) and high-density polyethylene (HDPE) have been investigated to elucidate miscibility and molecular relaxations in the crystalline and amorphous phases by using a differential scanning calorimeter (DSC) and a dynamic mechanical thermal analyzer (DMTA). In the LLDPE/LDPE blends, two distinct endotherms during melting and crystallization by DSC were observed supporting the belief that LLDPE and LDPE exclude one another during crystallization. However, the dynamic mechanical β and γ relaxations of the blends indicate that the two constituents are miscible in the amorphous phase, while LLDPE dominates α relaxation. In the LLDPE/HDPE system, there was a single composition-dependent peak during melting and crystallization, and the heat of fusion varied linearly with composition supporting the incorporation of HDPE into the LLDPE crystals. The dynamic mechanical α, β, and γ relaxations of the blends display an intermediate behavior that indicates miscibility in both the crystalline and amorphous phases. In the LDPE/HDPE blend, the melting or crystallization peaks of LDPE were strongly influenced by HDPE. The behavior of the α relaxation was dominated by HDPE, while those of β and γ relaxations were intermediate of the constituents, which were similar to those of the LLDPE/HDPE blends. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1633–1642, 1997

Blends of poly(∈-caprolactone) with cellulose alkyl esters: effect of the alkyl side-chain length and degree of substitu tion on miscibility

Abstract: Cellulose alkyl esters, CELL- OCOCnH2n+1(n = 1 ∼ 6), were synthesized by a homogeneous reaction of cotton cellulose with different acyl chlorides in N,N-dimethylacetamide--lithium chloride solution. The miscibility of the esterified celluloses with poly(∈-caprolactone) (PCL) was investigated, mainly through thermal analysis by differential scanning calorimetry (DSC). A polymer pair, cellulose butyrate (CB)/PCL, showed the highest miscibility of all the binary blends examined here; this is usual when relatively high-substituted esters (DS ≥ 2.0) are used as the respective component. The butyl ester derivatives with DS ≤ 1.5 showed poor miscibility with PCL

The role of transesterification on the miscibility in blends of polycarbonate and liquid crystalline copolyester

Abstract: Transesterification mechanisms and rate in blends of polycarbonate (PC) and random liquid crystalline polyester copoly(oxybenzoate-p-terephthalate) at molar ratio 40/60 (P46) were studied through a five-component diad analysis and with 13C and 1H-13C nuclear magnetic resonance spectroscopy. It was found that the ester-ester interchange in the two polymers took place within 15 min when the blend was annealed at 260 °C in vacuum. In the annealed blend, the Bisphenol A unit in polycarbonate reacted first with the terephthalate unit and then with the oxybenzoate unit in copoly(oxybenzoate-p- terephthalate). As the transesterification in the blend continued for about 1 h, the forming of diad Bisphenol A-oxybenzoate exceeded that of diad Bisphenol A-terephthalate. This large loss (57%) of the diad oxybenzoate-oxybenzoate caused the disappearance of the liquid crystalline phase in the blend. In sharp contrast to the originally immiscible blend of PC and P46 (two distinctive glass transition temperatures), the large loss of the liquid crystalline diad resulted in complete miscibility in the annealed blend, as evidenced by the appearance of a single glass transition temperature in the differential scanning calorimetry measurement.

Phase Behavior of Isotactic Polypropylene−Poly(ethylene/ethylethylene) Random Copolymer Blends

Abstract: The melt-state phase behavior of isotactic polypropylene (i-PP) blended with a series of poly(ethylene/ethylethylene) random copolymers has been investigated using small-angle neutron scattering (SANS). These PEExx copolymers, where xx is the percentage of ethylethylene (EE) units, were prepared by hydrogenation of anionically polymerized polybutadienes with controlled amounts of 1,2 addition. Random phase approximation (RPA) fits to the scattering data for blends of i-PP with a deuterated, low molecular weight PEE90 at 180 °C indicate a statistical segment length for i-PP that is 10% less than that reported previously. Scattering from blends of i-PP with higher molecular weight PEE90 and PEE73 at 180 °C can be quantitatively fit using the RPA theory with χ as the only adjustable parameter, indicating melt miscibility. PEE46 and PEE62 are strongly and marginally immiscible, respectively, with i-PP at 180 °C. These results establish a “window” in EE content in which these random copolymers can form single ...

Investigations of transesterification in PC/PBT melt blends and the proof of immiscibility of PC and PBT at completely suppressed transesterification

Abstract: The miscibility of polycarbonate PC and poly(butylene terephthalate) PBT is controversially discussed in the literature. Partial miscibility has been generally found in melt blends of the two polymers. However, in solution cast blends they were found to be immiscible. It is known that the transesterification takes place in the melt. Copolyesters formed by the transesterification change the compatibility of PC and PBT. In this work PC/PBT melt blends of various composition were investigated in dependence on the copolyester content by means of DSC and NMR. It can be shown that the time regime of the thermal treatment in the melt determines the transesterification degree. The PBT crystallization behavior is strongly influenced by both the PC and copolyester content. The glass transition temperatures of the PBT-rich and PC-rich phase approach each other with the increasing copolyester content. The analysis of the glass transition behavior permits the conclusion that PC and PBT are inherently immiscible provided that the copolyester content is exactly zero. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2161–2168, 1997

Rheological properties for binary blends of i-PP and ethylene-1-hexene copolymer

Abstract: The dynamic viscoelastic properties for binary blends consisting of an isotactic polypropylene (i-PP) and an ethylene-1-hexene copolymer (EHR) were investigated in both solid and molten states to reveal the relation between miscibility in the molten state and the morphology in the solid state In this study, two types of EHRs were employed: “ethylene-rich” EHR and “1-hexene-rich” EHR The blend of i-PP and EHR of 30 mol % 1-hexene content shows a very long time relaxation due to the phase separation in the molten state The blend film shows two separate glass-relaxation processes associated with those of the pure components These indicate that the blend shows phase-separated morphology in the solid state as well as in the molten state On the other hand, dynamic moduli in the molten state of the blends of i-PP and EHR of 57 mol % 1-hexene were found to be intermediate between those of individual pure components Furthermore, the apparent activation energy of the blends is constant and is identical with those of i-PP and the EHR The blend films show a single glass-relaxation process at the temperatures between those of the pure components, indicating that the EHR molecules are incorporated in the amorphous region of i-PP in the solid state Accordingly, it was found that the polymer miscibility in the molten state for the i-PP/EHR blends directly affects the morphology in the solid state © 1997 John Wiley & Sons, Inc J Appl Polym Sci 63: 467–474, 1997

Thermosetting polymer blends of unsaturated polyester resin and poly(ethylene oxide). II. Hydrogen‐bonding interaction, crystallization kinetics, and morphology

Abstract: Hydrogen-bonding interaction between the two components of the poly(ethylene oxide) (PEO)/oligoester (OER) blends and the PEO/crosslinked unsaturated polyester resin (PER) blends was found to be an important driving force to the miscibility of these polymer blends. Its strength is approximately as strong as the self-association of hydroxyl groups in either the pure OER or the pure PER. The crystallization kinetics and morphology of PEO in PEO/PER blends was remarkably affected by crosslinking. It was found that the overall crystallization rate of PEO in PEO/PER blends is larger than that in PEO/OER blends at the crystallization temperature investigated, which was considered to be the result of nucleation controlling mechanism. With decreasing PEO content, the regular shape of PEO spherulites turns irregular in PEO/ OER blends, whereas in PEO/PER blends, the birefrigent spherulites turns into dendritic structures. Raising the crystallization temperature favors the formation of dendritic textures in PEO/PER blends.

Analysis of the density and the enthalpy of poly(epsilon-caprolactone)-polycarbonate blends: Amorphous phase compatibility and the effect of secondary crystallization

Abstract: The dependency of the density of poly(epsilon-caprolactone)-polycarbonate (PCL-PC) blends on composition has been studied. PCL/PC blends are typical of miscible blends containing crystallizable components, and miscibility is therefore considered with respect to the amorphous phase. In literature, a single glass transition temperature is reported for the PCL-PC system; however, the exact dependency on amorphous phase composition is not clear. For quenched amorphous blends, we found the Fox equation to be appropriate in order to describe the glass transition temperature as a function of composition. For amorphous samples containing low amounts of PCL (less than or equal to 40 wt %), an increase in the density of the blend over that of a linear average of the densities of amorphous PC and PCL was observed experimentally. This is indicative of significant interactions in the blend. For samples containing greater than or equal to 50 wt % PCL, crystallization of PCL has to be accounted for in the analysis of the density. It is shown that the experimental density data can only be described satisfactorily by assuming that secondary crystallization of PCL does not lead to an increase of the overall blend density. This is attributed to the rigid and volume filling primary crystalline structure at room temperature, i.e., below the melting point of PCL. Excess density is present in the amorphous phase of the PCL/PC blend over the whole range of composition; therefore, specific interactions exist in the amorphous phase of the blend over the whole range of composition. (C) 1997 John Wiley & Sons, Inc.

Casting solvent effect on crystallization behavior of poly(vinyl acetate)/poly(ethylene oxide) blends: DSC study

Abstract: Poly(vinyl acetate) (PVAc)/poly(ethylene oxide) (PEO) blends were prepared by casting from either benzene or chloroform. The solvent effects on the crystallization behavior and thermodynamic properties of the blends were studied by the differential scanning calorimeter (DSC). Two grades of PEO with different molecular weights (PEO200 with Mw = 200,000 g/mol and PEO2 with Mn = 2000 g/mol) were used in this work. The thermal analysis revealed that the blends cast from either benzene or chloroform were miscible in the molten state. The crystallization of PEO in the benzene-cast blends was more easily suppressed than it was in the chloroform-cast blends. Furthermore, the benzene-cast blends showed a greater negative value of Flory-Huggins interaction parameter than those cast from chloroform in the PVAc/PEO200 poly-blend system. It was supposed that the benzene-cast blends had more homogeneous morphology. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 411–421, 1997

Thermosetting polymer blends of unsaturated polyester resin and poly(ethylene oxide). I. Miscibility and thermal properties

Abstract: The miscibility and thermal properties of polyethylene oxide(PEO)/oligoester resin (OER) blends and PEO/crosslinked polyester (PER) blends were studied by differential scanning calorimetry (DSC). The effect of quenching process on the crystallization behavior of PEO for these two systems were investigated and discussed in details. It has been found that a single, composition dependent glass transition temperature (Tg) was observed for all the blends, indicating that the two systems are miscible in the amorphous state at overall compositions. From the melting point depression of PEO, the interaction parameter χ12 for PEO/OER blends and that for PEO/PER blends were found to be −1.29 and −2.01, respectively. The negative values of χ12 confirmed that both PEO/OER blends and PEO/PER blends are miscible in the molten state. Quenching process has a greater hindrance on the crystallization of PEO/OER blends than on that of PEO/PER blends. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3161–3168, 1997

A DSC Study of Miscibility and Phase Separation in Crystalline Polymer Blends of Phenolphthalein Poly(ether ether sulfone) and Poly(ethylene oxide)

Abstract: The miscibility of blends of phenolphthalein poly(ether ether sulfone) (PES-C) and poly(ethylene oxide) (PEO) was established on the basis of the thermal analysis results. Differential scanning calorimetry (DSC) studies showed that the PES- C/PEO blends prepared by casting from N,N-dimethylformamide (DMF) possessed a single, composition-dependent glass transition temperature (Tg), and thus that PES- C and PEO are miscible in the amorphous state at all compositions at lower tempera- ture. At higher temperature, the blends underwent phase separation, and the PES-C/ PEO blend system was found to display a lower critical solution temperature (LCST) behavior. The phase separation process in the blends has also been investigated by using DSC. Annealed at high temperatures, the PES-C/PEO blends exhibited signifi- cant changes of thermal properties, such as the enthalpy of crystallization and fusion, temperatures of crystallization and melting, depending on blend composition when phase separation occurred. These changes reflect different characteristics of phase structure in the blends, and were taken as probes to determine phase boundary. From both the thermal analysis and optical microscopy, the phase diagram of the blend system was established. q 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1383- 1392, 1997