Showing papers on "Miscibility published in 2001"

Preparation and characterization of chitosan/poly(vinyl alcohol) blend fibers

Abstract: Chitosan and poly(vinyl alcohol) blend fibers were prepared by spinning their solution through a viscose-type spinneret at 25°C into a coagulating bath containing aqueous NaOH and ethanol. The influence of coagulation solution composition on the spinning performance was discussed, and the intermolecular interactions of blend fibers were studied by infrared analysis (IR), X-ray diffraction (XRD), and scanning electron micrograph (SEM) and by measurements of mechanical properties and water-retention properties. The results demonstrated that the water-retention properties and mechanical properties of the blend fibers increase due to the presence of PVA in the chitosan substract, and the mechanical strength of the blends is also related to PVA content and the degree of deacetylation of chitosan. The best mechanical strength values of the blend fibers, 1.82 cN/d (dry state) and 0.81 cN/d (wet state), were obtained when PVA content was 20 wt % and the degree of deacetylation of chitosan was 90.2%. The strength of the blend fibers, especially wet tenacity could be improved further by crosslinking with glutaraldehyde. The water-retention values (WRV) of the blend fibers were between 170 and 241%, obviously higher than pure chitosan fiber (120%). The structure analysis indicated that there are strong interaction and good miscibility between chitosan and poly(vinyl alcohol) molecular resulted from intermolecular hydrogen bonds. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2558–2565, 2001

Studies of Miscibility Behavior and Hydrogen Bonding in Blends of Poly(vinylphenol) and Poly(vinylpyrrolidone)

Abstract: Polymer blends of poly(vinylphenol) (PVPh) with poly(vinylpyrrolidone) (PVP) were prepared by solution casting from the N,N-dimethylformamide (DMF) solution. Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and solid-state nuclear magnetic resonance (NMR) were used to investigate the hydrogen bonding and miscibility behavior of the blend. This PVPh/PVP blend system has a single glass transition temperature over the entire composition range, indicating that this blend is able to form a miscible phase due to the formation of inter-hydrogen bonding between the hydroxyl of PVPh and the carbonyl of PVP. Furthermore, FTIR and solid-state NMR were used to study the hydrogen-bonding interaction between the PVPh hydroxyl group and the PVP carbonyl group at various compositions. According to the Painter−Coleman association model (PCAM), the interassociation constant for the PVPh/PVP blend is significantly higher than the self-association constant of PVPh, revealing that the t...

Miscibility and Hydrogen Bonding in Blends of Poly(vinylphenol-co-methyl methacrylate) with Poly(ethylene oxide)

Abstract: Blends of poly(vinylphenol-co-methyl methacrylate) (PVPh-co-PMMA) with poly(ethylene oxide) (PEO) were prepared by solution casting from tetrahydrofuran (THF) solution. The miscibility behavior and hydrogen bonding of blends were investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and solid-state nuclear magnetic resonance (NMR). Experimental results indicate that PEO was miscible with PVPh-co-PMMA as shown by the existence of single composition-dependent glass transition temperatures over the entire composition range by DSC. In addition, a negative polymer-polymer interaction energy density "B" was calculated based on the melting depression of PEO using the Nishi-Wang equation. Solid-state NMR reveals single-exponential decay of proton spin-lattice relaxation times in the rotating frame (T1F H ) in the amorphous PVPh-co- PMMA phase. Furthermore, FTIR and solid-state NMR results reveal that at least three competing equilibria are present in the blend; self-association of PVPh-co-PMMA copolymer (hydroxyl-hydroxyl and hydroxyl-carbonyl) and hydroxyl-ether interassociation between PVPh and PEO. Quantitative results show that although the hydroxyl-ether interassociation is favored at room temperature, the hydroxyl-carbonyl self-association dominates at higher temperatures (>70 °C). The Painter-Coleman association model (PCAM) can predict three interacting functional groups based on our experimental results at various temperatures.

Miscibility of ethanol in diesel fuels

Abstract: Whereas the use of ethanol in gasoline is widely practiced as a means to reduce vehicle exhaust emissions, similar use of ethanol in diesel is not widely accepted. Barriers to the use of ethanol in diesel fuel include limited miscibility at lower temperatures and need for minor variations in fuel delivery systems to account for the different physical properties of ethanol as compared to diesel. An understanding of the phase behavior is necessary to achieve benefits and avoid problems when ethanol is used in diesel. The miscibilities of ethanol in eight diesel fuels having a wide variation in compositions were evaluated. Aromatic contents and intermediate distillate temperatures had a significant impact on miscibility limits. An emphasis was placed on the transition in phase behavior from gasoline, where phase behavior problems are consistently avoided, to US-2D diesel fuel, where phase behavior is considered a barrier to implementation. An empirical correlation was developed for predicting upper critical ...

Miscibility and shape memory property of poly(vinyl chloride)/thermoplastic polyurethane blends

Abstract: The miscibility and the shape memory effect of PVC blends with segmented thermoplastic polyurethanes (TPUs), synthesized from diol-terminated polycaprolactone (PCL), hexamethylene diisocyanate, 4,4′-dihydroxy biphenyl, were studied. PVC was miscible with PCL segment in TPU and the glass transition temperature of this miscible amorphous domain varied smoothly with composition. When PVC was blended with TPU by the weight ratio of 8/2, the hysterisis in repeated cyclic tensile test was reduced compared with PVC. However, in 6/4 blends, unrecoverable permanent deformation was increased compared with PVC. Dynamic mechanical properties were examined to explain these results.

Miscibility and phase structure of binary blends of poly(L‐lactide) and poly(vinyl alcohol)

Abstract: Blend films of poly(L-lactide) (PLLA) and poly(vinyl alcohol) (PVA) were obtained by evaporation of hexafluoroisopropanol solutions of both components. The component interaction, crystallization behavior, and miscibility of these blends were studied by solid-state NMR and other conventional methods, such as Fourier transform infrared (FTIR) spectra, differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD). The existence of two series of isolated and constant glass-transition temperatures (Tg's) independent of the blend composition indicates that PLLA and PVA are immiscible in the amorphous region. However, the DSC data still demonstrates that some degree of compatibility related to blend composition exists in both PLLA/atactic-PVA (a-PVA) and PLLA/syndiotactic-PVA (s-PVA) blend systems. Furthermore, the formation of interpolymer hydrogen bonding in the amorphous region, which is regarded as the driving force leading to some degree of component compatibility in these immiscible systems, is confirmed by FTIR and further analyzed by 13C solid-state NMR analyses, especially for the blends with low PLLA contents. Although the crystallization kinetics of one component (especially PVA) were affected by another component, WAXD measurement shows that these blends still possess two isolated crystalline PLLA and PVA phases other than the so-called cocrystalline phase. 13C solid-state NMR analysis excludes the interpolymer hydrogen bonding in the crystalline region. The mechanical properties (tensile strength and elongation at break) of blend films are consistent with the immiscible but somewhat compatible nature of these blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 762–772, 2001

A dynamic mechanical and thermal analysis of unplasticized and plasticized poly(vinyl alcohol)/methylcellulose blends

Abstract: The miscibility of poly(vinyl alcohol) (PVA)/methylcellulose (MC) blends was investigated over the entire composition range using the dynamic mechanical analyzer (DMA) and the differential scanning calorimeter (DSC). On the basis of the glass transition temperature, determined by DMA, one could conclude that the blends exhibited some miscibility below 80 wt % of MC and a good miscibility above 80 wt % of MC. The highest depressions of the melting and crystallization temperatures of the blends compared to those of PVA, determined via DSC analysis, were observed for MC contents greater than 80 wt %. The miscibility between PVA and MC can be attributed to the hydrogen bonds formed between the two components. The DMA studies showed that water is a good plasticizer for PVA and poly(ethylene glycol) 400 (PEG 400), a good plasticizer for MC. The inclusion of both water and PEG 400 in the blends revealed a synergistic plasticizing effect, which resulted in an increased miscibility between PVA and MC over a greater range of MC compositions (>60 wt %). The elongations of PVA, MC, and their blends were found to increase with the addition of PEG 400, but the tensile strengths to decrease. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1825–1834, 2001

Gradient Interphase between Reactive Epoxy and Glassy Thermoplastic from Dissolution Process, Reaction Kinetics, and Phase Separation Thermodynamics

Abstract: Planar interfaces have been prepared by assembling high-Tg thermoplastics such as poly(phenylene ether) (PPE) or poly(ether imide) (PEI) and epoxy−amine networks at different conversions of the epoxy groups, Xe, followed by a complete curing. Direct evidence of the structure of the interfacial regions was made by means of electron microscopies, SEM and TEM, and atomic force microscopy, after a complete curing of the epoxy−amine. The morphologies of the interfaces are explained from the competition between the dissolution process of a thermoplastic by nonreactive solvent and the thermodynamics and the kinetics of reactive epoxy−amine/thermoplastic system. If the phase diagram indicates that the epoxy−amine/thermoplastic system is nonmiscible, the interface remains very thin (<20 nm). In the opposite, a gap range of miscibility controlled by the polymerization rate allows a diffusion of the comonomers into the thermoplastic layer and its further dissolution. As a consequence, 100−400 μm thick interphases ca...

Miscibility and mechanical properties of tetrafunctional epoxy resin/phenolphthalein poly(ether ether ketone) blends

Abstract: Phenolphthalein poly(ether ether ketone) (PEK-C) was found to be miscible with uncured tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM), which is a type of tetrafunctional epoxy resin (ER), as shown by the existence of a single glass transition temperature (Tg) within the whole composition range. The miscibility between PEK-C and TGDDM is considered to be due mainly to entropy contribution. Furthermore, blends of PEK-C and TGDDM cured with 4,4′-diaminodiphenylmethane (DDM) were studied using dynamic mechanical analysis (DMA), Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). DMA studies show that the DDM-cured TGDDM/PEK-C blends have only one Tg. SEM observation also confirmed that the blends were homogeneous. FTIR studies showed that the curing reaction is incomplete due to the high viscosity of PEK-C. As the PEK-C content increased, the tensile properties of the blends decreased slightly and the fracture toughness factor also showed a slight decreasing tendency, presumably due to the reduced crosslink density of the epoxy network. SEM observation of the fracture surfaces of fracture toughness test specimens showed the brittle nature of the fracture for the pure ER and its blends with PEK-C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 598–607, 2001

Effects of nitrolignin on mechanical properties of polyurethane–nitrolignin films

Abstract: Polyurethane-nitrolignin (PUNL), a new network polymer, was synthesized from a castor oil based–polyurethane (PU) prepolymer and nitrolignin (NL) with a weight-average molecular weight of 20.6 × 104 and a content of 1.4–10%. The structure and miscibility of PUNL films prepared by solution casting were investigated by infrared spectroscopy and transmission electron microscopy. The results indicated that PUNL2 film, which had a 2.8% NL content, was the most miscible, and its tensile strength (σb) and breaking elongation (ϵb) were 2 times higher than that of PU film. The crosslink densities of PUNL films increased with the increase of NL content until about 3%, similar to the variety of the mechanical properties. Thermogravimetric analysis revealed that the thermal stability of PUNL films was slightly higher than that of PU. Covalent bonds occurred between PU prepolymer and the NL in the PUNL films, forming crosslink networks, which resulted in the enhancement of mechanical properties and thermal stability. NL has a far higher reactivity with PU than nitrocellulose. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1213–1219, 2001