Molecular modeling simulations to predict compatibility of poly(vinyl alcohol) and chitosan blends: a comparison with experiments

Molecular modeling simulations are the most important tools to predict blend compatibility of polymers that are otherwise difficult to predict by experimental means. Conflicting reports have been reported on the blend compatibility of poly(vinyl alcohol), PVA, and chitosan, CS polymers. Since both the polymers are widely used in pharmaceutics as drug-loaded particulates and as separation membranes, we felt it necessary to investigate their compatibility over the practical range of compositions. In this paper, we attempt to study the compatibility of PVA and CS polymers using molecular modeling strategies to understand the interactions between CS and PVA polymers to predict their compatibility from atomistic simulations. Flory-Huggins interaction parameter, chi, was computed at 298 K to assess the blend compatibility at different ratios of the component polymers. Miscibility was observed for blends below 50% of PVA, while immiscibility was prevalent at compositions between 50 and 90% PVA. Computed results confirmed the experimental findings of dynamic mechanical thermal analysis, suggesting the validity of modeling strategies employed. Plots of Hildebrand solubility parameter and cohesive energy density calculated at 298 K supported these findings. The chi values for blends, which satisfied the criteria of miscibility of polymers computed by atomistic simulations, agreed with the solubility criteria related to order parameters calculated from mesoscopic simulations. Miscibility between PVA and CS polymers is attributed to hydrogen bond formation and to an understanding of which of the interacting groups of CS, i.e., -CH2OH or -NH2, are responsible in blend miscibility. This was further confirmed by molecular dynamics simulations of radial distribution functions for groups or atoms that are tentatively involved in interactions. These results are correlated well to obtain more realistic information about interactions involved as a function of blend composition. Computed free-energy from the mesoscopic simulation for blends reached equilibrium, particularly when the simulation was performed at higher time step, indicating stability of the blend system at certain compositions.     

Compatibility of poly(ethylene oxide)–poly(vinyl acetate) blends

The compatibility of poly(ethylene oxide)–poly(vinyl acetate) (PEO-PVA) blends was examined at five compositions covering the complete range. Samples were prepared by coprecipitation and solution casting. Dynamic mechanical properties were studied at 110 Hz between ?120 and 65°C for dry, quenched, and annealed samples. The study also included tensile testing at 25°C, examination of blend morphology, and DSC measurements at elevated temperatures. Optical microscopy revealed that crystallization of PEO proceeds essentially unhindered at up to 25% poly(vinyl acetate) content by weight. Higher levels of this component drastically reduce spherulite size, and at the highest PVA compositions there was no evidence of crystallization. Thermomechanical spectra of quenched and annealed samples indicate limited mixing of the two components except for the higher (>75%) PVA compositions. Tensile properties show a mutual reinforcement at 10-25% PVA content due to possible polymer segment association. The melting-point depression of PEO is significant above 25% PVA and has been attributed to morphological changes of the PEO crystalline phase.     

Structure and compatibility of poly(vinyl alcohol)-silk fibroin (PVA/SA) blend films

The structure and compatibility of poly(vinyl alcohol)-silk fibroin (PVA/SF) blend films were analyzed by differential scanning calorimetry (DSC), thermomechanical (TMA) and thermogravimetric (TGA) analysis, x-ray diffractometry, and scanning (SEM) and transmission (TEM) electron microscopy. DSC curves of PVA/SF blend films showed a major endothermic peak at 220°C, along with a peak at 280°C. These endotherms were assigned to the thermal decomposition of the ordered PVA elements and to the thermal degradation of silk fibroin, respectively. The PVA/SF blends behaved in a manner intermediate to the pure components, as suggested by both contraction expansion and sample weight retention properties recorded by TMA and TGA measurements. The IR absorption spectra of the blends were identified as purely a composite of the absorption bands characteristic of both PVA and SF pure polymers. The X-ray diffraction patterns of PVA/SF blends showed overlapping spacing due to PVA and SF. A dispersed phase formed by spherical particles of 3–7 μm diameter was observed by SEM and TEM. All these findings suggest that PVA and SF are incompatible. © 1994 John Wiley & Sons, Inc.     

New chitin-based polymer hybrids, 1. Miscibility of poly(vinyl alcohol) with chitin derivatives

As a new class of biopolymer-based hybrid materials, the present paper describes the binary blends of a modified chitin and poly(vinyl alcohol) (PVA) which are miscible in the whole range of compositions. The blend films were prepared by the solvent cast method from a homogeneous aqueous solution of PVA and a chitin derivative having poly(2-methyl-2-oxazoline) side chains. Miscibility between PVA and poly(2-methyl-2-oxazoline) homopolymer was also revealed. Differential scanning calorimetry and FT-IR analyses were used to investigate the blends.     

Polypeptide-synthetic polymer hybrids, 1. Miscibility of poly(vinyl alcohol) with poly(sodium α,β-D,L-aspartate)

The present paper describes materials of polypeptide-commodity polymer hybrids from poly(vinyl alcohol) (PVA) and poly(sodium α,β-D ,L -aspartate) ( 1 ). Miscible blend films of polypeptide 1 and PVA were prepared by the solvent-cast method from a homogeneous aqueous solution. Differential scanning calorimetry. Fourier transform infrared, and scanning electron microscopy combined with energy dispersive X-ray spectroscopy (EDX) were used to investigate the blends. It was revealed that 1 and PVA are miscible in a wide range of compositions.     

Study of the miscibility of poly(styrene-co-4-vinylbenzoic acid) with poly(ethyl methacrylate) or with poly[ethyl methacrylate-co-(2-N,N-dimethylaminoethyl) methacrylate] by inverse gas chromatography

Poly(styrene) is immiscible with poly(ethyl methacrylate). The introduction of a small amount of 4-vinylbenzoic acid units along poly(styrene) chains (PS-VBA) enhanced its miscibility with poly(ethyl methacrylate) (PEMA) or with poly[ethyl methacrylate-co-(2-N,N-dimethylaminoethyl) methacrylate] (PEMA-DAE), as observed from the appearance of a single composition dependent glass transition temperature for each binary system using inverse gas chromatography. The negative values of the apparent polymer-polymer interaction parameter, chi(23)app, determined with different families of molecular probes, for three blend compositions and over a range of temperature confirm quantitatively the miscibility of these blends. The chi(23)app values for PEMA(PS-VBA) and (PEMA-DAE)-(PS-VBA) blends are dependent of the chemical nature of the probes, the temperature and the blend composition.     

Poly(ether ether ketone)/poly(aryl ether sulfone) blends: Melt rheological behavior

Dynamic rheological measurements were carried out on blends of poly(ether ether ketone) (PEEK)/poly(aryl ether sulfone) (PES) in the melt state in the oscillatory shear mode. The data were analyzed for the fundamental rheological behavior to yield insight into the microstructure of PEEK/PES blends. A variation of complex viscosity with composition exhibited positive–negative deviations from the log‐additivity rule and was typical for a continuous‐discrete type of morphology with weak interaction among droplets. The point of transition showed that phase inversion takes place at composition with a 0.6 weight fraction of PEEK, which agreed with the actual morphology of these blends observed by scanning electron microscopy. Activation energy for flow, for blend compositions followed additive behavior, which indicated that PEEK/PES blends may have had some compatibility in the melt. Variation of the elastic modulus (G′) with composition showed a trend similar to that observed for complex viscosity. A three‐zone model used for understanding the dynamic moduli behavior of polymers demonstrated that PEEK follows plateau‐zone behavior, whereas PES exhibits only terminal‐zone behavior in the frequency range studied. The blends of these two polymers showed an intermediate behavior, and the crossover frequency shifted to the low‐frequency region as the PEEK content in PES increased. This revealed the shift of terminal‐zone behavior to low frequency with an increased PEEK percentage in the blend. Variation of relaxation time with composition suggested that slow relaxation of PEEK retards the relaxation process of PES as the PEEK concentration in the blend is increased because of the partial miscibility of the blend, which affects the constraint release process of pure components in the blend. A temperature‐independent correlation observed in the log–log plots of G′ versus loss modulus (G″) for different blend systems fulfilled the necessary condition for their rheological simplicity. Further, the composition‐dependent correlations of PEEK/PES blends observed in a log–log plot of G′ versus G″ showed that the blends are either partially miscible or immiscible and form a discrete‐continuous phase morphology. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1548–1563, 2004     

Effect of poly(vinyl acetate) (PVAc) on thermal behavior and mechanical properties of poly(3-hydroxybutyrate)/poly(propylene carbonate) (PHB/PPC) blends

To assess the compatibility of blends of synthetic poly(propylene carbonate) (PPC), with a natural bacterial poly(3-hydroxybutyrate) (PHB), a simple casting procedure of blend was used. poly(3-hydroxybutyrate)/poly(propylene carbonate) blends are found to be incompatible according to DSC and DMA analysis. In order to improve the compatibility and mechanical properties of PHB/PPC blends, poly(vinyl acetate) (PVAc) was added as a compatibilizer. The effects of PVAc on the thermal behavior, morphology, and mechanical properties of 70PHB/30PPC blend were investigated. The results show that the melting point and the crystallization temperature of PHB in blends decrease with the increase of PVAc content in blends, the loss factor changes from two separate peaks of 70PHB/30PPC blend to one peak of 70PHB/30PPC/12PVAc blend. It is also found that adding PVAc into 70PHB/30PPC blend can decrease the size of dispersed phase from morphology analysis. The result of tensile properties shows that PVAc can increase the tensile strength and Young’s modulus of 70PHB/30PPC blend, and both the elongation at break and the tensile toughness increase significantly with PVAc added into 70PHB/30PPC.     

Dynamics of a poly(isoprene)/poly(vinyl ethylene) blend revisited: Component polymer relaxation and blend behavior

Motivated by recent molecular dynamics simulation studies of miscible blends of dynamically disparate polymers, we have revisited the experimentally measured dielectric relaxation in a 50/50 blend of poly(isoprene) and poly(vinyl ethylene) (PI/PVE). In contrast to efforts to explain the dielectric loss in PI/PVE blends in terms of a distribution of local environments leading to a broad distribution of segmental relaxation times (the so-called concentration fluctuation model), our analysis indicates that there is no evidence for significant broadening of the relaxation processes in the component polymers upon blending. Rather, we find that the dielectric loss of the 50/50 PI/PVE blend can be represented as a sum of α- and β-relaxation processes for the component polymers represented with Havriliak-Negami functions whose shape and relaxation strength are consistent with those obtained for the pure PI and PVE melts. The α-relaxation process for the PVE component was found to be dramatically influenced by blending, moving to much higher frequency with moderate narrowing, while the α-relaxation process for the PI component shifted to somewhat lower frequency with slight broadening, consistent with our MD simulations of a model blend and 2D NMR measurements on PI/PVE blends. In contrast, the β-processes in the PVE and PI components were found to be essentially uninfluenced by blending, with the latter accounting for the significant high-frequency loss observed in the PI/PVE blend.     

Effect of PEO‐PPO‐PEO copolymer on the mechanical and thermal properties and morphological behavior of biodegradable poly (L‐lactic acid) (PLLA) and poly (butylene succinate‐co‐L‐lactate) (PBSL) blends

A blend of two biodegradable and semi‐crystalline polymers, poly (L‐lactic acid) (PLLA; 70 wt%) and poly (butylene succinate‐co‐L‐lactate) (PBSL; 30 wt%), was prepared in the presence of various polyethylene oxide‐polypropylene oxide‐polyethylene oxide (PEO‐PPO‐PEO) triblock copolymer contents (0.5, 1, 2 wt%). Mechanical, thermal properties, and Fourier transform infrared (FTIR) analysis of the blends were investigated. It was found that the addition of copolymer to PLLA/PBSL improved the fracture toughness of the blends as shown by mode I fracture energies. It was supported by morphological analysis where the brittle deformation behavior of PLLA changed to ductile deformation with the presence of elongated fibril structure in the blend with copolymer system. The glass transition temperature (T_g), melting temperature (T_m) of PLLA, and PBSL shift‐closed together indicated that some compatibility exists in the blends. In short, PEO‐PPO‐PEO could be used as compatibilizer to improve the toughness and compatibility of the PLLA/PBSL blends. Copyright © 2010 John Wiley & Sons, Ltd.     

Miscibility and properties of poly(l-lactic acid)/poly(butylene terephthalate) blends

Binary blends of poly(l-lactide) (PLLA) and poly(butylene terephthalate) (PBT) containing PLLA as major component were prepared by melt mixing. The two polymers are immiscible, but display compatibility, probably due to the establishment of interactions between the functional groups of the two polyesters upon melt mixing. Electron microscopy analysis revealed that in the blends containing up to 20% of poly(butylene terephthalate), PBT particles are finely dispersed within the PLLA matrix, with a good adhesion between the phases. The PLLA/PBT 60/40 blend presents a co-continuous multi-level morphology, where PLLA domains, containing dispersed PBT units, are embedded in a PBT matrix. The varied morphology affects the mechanical properties of the material, as the 60/40 blend displays a largely enhanced resistance to elongation, compared to the blends with lower PBT content.     

Miscible blends of poly(ethylene oxide) with brush copolymers of poly(vinyl alcohol)‐graft‐poly(l‐lactide)

Even though poly(ethylene oxide) (PEO) is immiscible with both poly(l ‐lactide) (PLLA) and poly(vinyl alcohol) (PVA), this article shows a working route to obtain miscible blends based on these polymers. The miscibility of these polymers has been analyzed using the solubility parameter approach to choose the proper ratios of the constituents of the blend. Then, PVA has been grafted with l ‐lactide (LLA) through ring‐opening polymerization to obtain a poly(vinyl alcohol)‐graft‐poly(l ‐lactide) (PVA‐g‐PLLA) brush copolymer with 82 mol % LLA according to ¹H and ¹³C NMR spectroscopies. PEO has been blended with the PVA‐g‐PLLA brush copolymer and the miscibility of the system has been analyzed by DSC, FTIR, OM, and SEM. The particular architecture of the blends results in DSC traces lacking clearly distinguishable glass transitions that have been explained considering self‐concentration effects (Lodge and McLeish) and the associated concentration fluctuations. Fortunately, the FTIR analysis is conclusive regarding the miscibility and the specific interactions in these systems. Melting point depression analysis suggests that interactions of intermediate strength and PLOM and SEM reveal homogeneous morphologies for the PEO/PVA‐g‐PLLA blends. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1217–1226     

Morphology control of sulfonated poly(ether ketone ketone) poly(ether imide) blends and their use in proton-exchange membranes

Polymer blends based on sulfonated poly(ether ketone ketone) (SPEKK) as the proton-conducting component and poly(ether imide) (PEI) as the second component were considered for proton-exchange membranes (PEMs). The PEI was added to improve the mechanical stability and lower the water swelling in the fuel cell environment. Membranes were cast from solution using N-methyl-2-pyrrolidone (NMP) and dimethylacetamide (DMAc). The ternary, polymer/polymer/solvent, phase diagram was determined to provide guidance on how to control the morphology during solvent casting of blend membranes.

For blends of SPEKK (ion-exchange capacity = 2 mequiv/g) with PEI as the minority component, the morphology consisted of dispersed particles of 0.5–6 μm. Larger particles were achieved by increasing the PEI content and/or lowering the casting temperature. High-temperature annealing after solution casting did not affect the morphology of blend membranes, due to the low mobility and compatibility of the two polymers.

The possible use of SPEKK/PEI blends in PEMs is discussed in terms of existing theories of ion transport in polymers.     

PH effects in the complex formation and blending of poly(acrylic acid) with poly(ethylene oxide)

The effect of pH on the complex formation between poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) has been studied in aqueous solutions by turbidimetric and fluorescent methods. It was shown that the formation of insoluble interpolymer complexes is observed below a certain critical pH of complexation (pH(crit1)). The formation of hydrophilic interpolymer associates is possible above pH(crit1) and below a certain pH(crit2). The effects of polymer concentrations in solution and PEO molecular weight as well as inorganic salt addition on these critical pH values were studied. The polymeric films based on blends of PAA and PEO were prepared by casting from aqueous solutions with different pHs. These films were characterized by light transmittance measurements and differential scanning calorimetry. The existence of the pH value above which the polymers form an immiscible blend was demonstrated. The transitions between the interpolymer complex, miscible blend, and immiscible blend caused by pH changes are discussed. The recommendations for preparation of homogeneous miscible films based on compositions of poly(carboxylic acids) and various nonionic water-soluble polymers are presented.     

Mechanical, morphological and biodegradation studies of microwave processed nanostructured blends of some bio-based oil epoxies with poly (vinyl alcohol)

Bioresource based blends exploit the synergy between polymers derived from renewable resource and commercial polymers to obtain desirable physical, mechanical, and biodegradable properties. With the aim to develop a sustainable resource based biodegradable mulch films, nanostructured blends of epoxies of linseed oil (LOE) and dehydrated castor oil (DCOE) with poly (vinyl alcohol) (PVA) were prepared in the weight ratios of 20/80, 50/50 and 80/20. Microwave-assisted blending was used for the synthesis of DCOE/LOE blends with PVA and the results were compared with conventional solution blending using FT-IR, TGA-DTA and optical measurements. The results revealed that microwave-assisted blending proved to be an efficient method for the formation of compatible blends in a short span of time as compared to conventional solution blending. Transmission electron microscopy (TEM) analysis of DCOE/PVA and LOE/PVA blends synthesized by microwave-assisted method confirmed the formation of a nanostructured blend. Scanning electron microscopy (SEM), respirometry and mechanical measurements were carried out to compare the morphology, biodegradability, and the mechanical strength of DCOE/PVA and LOE/PVA blends. It was observed that DCOE/PVA blends exhibited higher biodegradability, better mechanical properties, and lower moisture absorption characteristics as compared to LOE/PVA blends. The mechanical strength, moisture absorption, and biodegradability of these blends were also compared with blends of other bioresource based polymers such as sugarcane bagasse (SCB), waste gelation (WG), apple peal (AP), and starch/glycerol with PVA, as available from the cited literature in the text.     

Degradation of polymer mixtures. IV. Blends of poly(vinyl acetate) with poly(vinyl chloride) and other chlorine-containing polymers

The degradation of the binary polymer blends, poly(vinyl acetate)/poly(vinyl chloride), poly(vinyl acetate)/poly(vinylidene chloride) and poly(vinyl acetate)/polychloroprene has been studied by using thermal volatilization analysis, thermogravimetry, evolved gas analysis for hydrogen chloride and acetic acid, and spectroscopic methods. For the first two systems named, strong interaction occurs in the degrading blend, but the polychloroprene blends showed no indication of interaction. In the PVA/PVC and PVA/PVDC blends, hydrogen chloride from the chlorinated polymer causes substantial acceleration in the deacetylation of PVA. Acetic acid from PVA destabilizes PVC but has little effect in the case of PVDC because of the widely differing degradation temperatures of PVA and PVDC. The presence of hydrogen chloride during the degradation of PVA results in the formation of longer conjugated sequences, and the regression in sequence length at high extents of deacetylation found for PVA degraded alone is not observed.     

Miscibility and surface characterization of a poly(vinylidene fluoride)‐poly(vinyl methyl ketone) blend by inverse gas chromatography

The miscibility of blends of semicrystalline poly(vinylidene fluoride)(PVF₂) and poly(vinyl methyl ketone) (PVMK) along with surface characterization were investigated using the inverse gas chromatography method (IGC), over a range of blend compositions and temperatures. Three chemically different families, alkanes, acetates, and alcohols, were utilized for this study. The values of the PVF₂‐PVMK interaction parameters were found to be slightly positive for most of the solutes used, although some degree of miscibility was found at all compositions. Miscibility was greatest at a 50:50 w/w composition of the blend. The interaction parameters obtained from IGC are in excellent agreement with those obtained using calorimetry on the same blends. The calculated molar heat of sorption of alkanes, acetates, and alcohols into the blend layer reveal the impact of the combination of dispersive and hydrogen bonding forces on the interaction of solutes with the blend's backbone. The dispersive component of the surface energy was found to range from 18.70–64.30 mJ/m² in the temperature range of 82–163 °C. A comparison of the blend's surface energy with that of mercury and other polymers is given. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1155–1166, 2000     

Investigating the homogeneity of nylon-6 and polyvinyl alcohol blend

Viscosity measurements were used for measuring the rheological behavior of the nylon-6 and polyvinyl alcohol (PVA) blends in solution and hence their compatibility. The change of different viscosities of various blend compositions showed straight line, curve linear, and S-shape. The effect of concentration of one polymer over the other is also explained. This behavior is explained on the basis of the miscibility of the polymers in various blend compositions. The article is published in the original.     

Compatibility of poly(vinyl chloride) with polyalkyleneoxides. II. Poly(propylene oxide) and poly(tetramethylene oxide)

This study [Part II of a series dealing with the compatibility of polyalkyleneoxides with poly(vinyl chloride)] examines blends of PVC with poly(propylene oxide) (PPrO) and poly(tetra-methylene oxide) (PTMO), covering the entire composition range. Morphological, dynamic mechanical and thermal properties investigated indicate that PVC/PPrO blends are incompatible, whereas the PVC/PTMO system shows miscibility in the melt. For this polyblend and at high polyether compositions where the Hoffman–Weeks analysis can be applied, T_m equilibrium data allow the determination of the thermodynamic interaction parameter, χ₁₂ = ?0.15. Experimental compatibility data of all polyether-PVC pairs investigated in Parts I and II are also used to test various blend miscibility prediction schemes, using solubility parameter theory and recent theory on copolymer-copolymer miscibility.     

Miscibility of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) blends by transesterification

The effects of transesterification on the miscibility of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) were studied. Blends were obtained by solution precipitation at room temperature to avoid transesterification during blend preparation. The physical blends and transesterified products were analyzed by wide-angle x-ray scattering, differential scanning calorimetry, and nuclear magnetic resonance spectroscopy. It was found that the physical blends are immiscible and when the extent of transesterification reaches 50% of the completely randomized state, independent of blend composition, the blends are not crystallizable and show a single glass transition temperature between those of starting polymers. The interchange reactions were significantly influenced by annealing temperature and time but negligibly by blend composition. © 1996 John Wiley & Sons, Inc.