Morphology and properties of poly(vinylidene fluoride)/silicone rubber blends

Blends of poly(vinylidene fluoride) (PVDF) and silicone rubber (SR) were prepared through melt mixing. The morphology, rheology, crystallization behavior, mechanical properties, dynamic mechanical properties and thermal properties of the PVDF/SR blends were investigated. The blend with 9 wt % of SR showed spherical shape of disperse phase whereas the blend with 27 wt % of SR resulted in irregular shape of rubber phase. The rheology showed that the complex viscosity and storage modulus of the blends decreased with increasing the SR content. The mechanical properties of the blends were decreased with increasing the SR content but that were significantly improved after dynamical vulcanization. The crystallization temperature of PVDF phase in PVDF/SR blends was increased. The incorporation of SR improved the thermal stability of PVDF/SR blends, and the temperature at 10% mass loss of the blends increased to about 489°C compared with 478°C of the pure PVDF. The mass of residual char in experiment of the blends was lower than that obtained in theory. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39945.     

Spherulitic morphology and growth of poly(vinylidene fluoride)/poly(3-hydroxybutyrate-co-hydroxyvalerate) blends by optical microscopy

Poly(vinylidene fluoride) (PVDF) and poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV), both semicrystalline polymers, are miscible as shown by the single glass transition temperature over the entire composition range. Morphology of PVDF/PHBV blends was investigated by optical microscopy under two different crystallization conditions. PVDF showed the spherulitic morphology at 150 °C in the PVDF/PHBV blends, where PHBV acted as the noncrystallizing component. PHBV also showed the spherulitic morphology within the matrix of the pre-existing PVDF crystals when PVDF/PHBV blends were quenched from the melt to the crystallization temperature below the melting point of PHBV. The spherulitic growth of PHBV was investigated as the function of both blend composition and crystallization temperature.     

Transition behavior of poly(vinylidene fluoride)/poly(ethyl methacrylate) blends

Previous work has shown evidence that PMMA and PEMA are miscible with PVF₂. The present paper examines in detail the behavior of PEMA/PVF₂ blends by thermal analysis and dynamic mechanical testing. All transitions and relaxations are affected by blond composition but in a complex manner owing to the crystallization of PVF₂ from blends rich in this component. Inadequacies of the simple two-phase picture of semi-crystalline polymers is believed responsible for some of the transitional behavior observed here. The melting point depression observed for PVF₂ was found to be consistent with an exothermic heat of mixing for this pair comparable in value to that found for PPMA/PVF₂/All evidence here are consistent with the previous conclusion of miscibility for these systems.     

The crystallization and transition behavior of poly(vinylidene fluoride)/copoly(chlorotriofluorethylene-vinylidene fluoride) blends

Thermal analysis of solution precipitated blends of two crystallizable polymers, poly(vinylidene fluoride) (PVDF) and copoly(chlorotrifluorethylene-vinylidene fluoride) (copoly(CTFE-VDF)), has been carried out to study the transition temperatures, crystallinity, and crystallization rates. PVDF crystallizes over the whole blend composition either during precipitation from solution or upon cooling from the melt. The high degree of crystallinity attained, higher than in PVDF by itself, suggests the occurrence of partial PVDF-copolymer cocrystallization. The melt crystallization temperature, decreasing with cooling rate, is lower in PVDF-rich blends than for lean blends. However, the heat of crystallization increases with cooling rate, suggesting that the crystal composition depends on crystallization rate. No significant melting temperature depression due to blending was observed. However, the blends glass transition (T_g) changes linearly with composition, but less than expected by any mixing rule applicable to compatible systems. Annealing of the blends above T_g results in an additional crystalline phase consisting mainly of the copolymer. The amount of these crystals increases with PVDF content, due to partial cocrystallization and kinetic effects. The addition of the copolymer to PVDF results in a volume-filling spherulitic structure consisting of spherulites which decrease in size with increasing copolymer content.     

Calorimetric and dielectric study on poly(trimethylene terephthalate)/polycarbonate blends

Poly(trimethylene terephthalate) (PTT)/polycarbonate (PC) blends with different compositions were prepared by melt blending. The miscibility and phase behavior of melt-quenched and cold-crystallized blends were studied using differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy. The blends of all compositions display only one glass transition (T _g ) in both states. The melting temperature and the crystallinity of PTT in the blend decrease with increasing PC content. The dielectric results for the melt-quenched blends, for PC content up to 60 wt.%, exhibited two merged relaxation peaks during the heating scan; the lower temperature relaxation peak represent the normal glass-transition (α) relaxation of the mixed amorphous phase and the higher temperature relaxation due to the new-constrained mixed amorphous phase after crystallization. Cold-crystallized blends displayed only one glass transition α-relaxation whose temperatures varied with composition in manner similar to that observed by DSC. The dielectric α-relaxation of cold crystallized blends has been analyzed. Parameters relating to relaxation broadening, dielectric relaxation strength, and activation energy were quantified and were found to be composition dependent. The PTT/PC blends could be considered as two-phase system, a crystalline PTT phase and a mixed amorphous phase consisting of a miscible mixture of the two polymers. However, the crystallinity was only detected for blends containing greater than 40 wt.% PTT.     

Crystallization behavior and hydrophilicity of poly(vinylidene fluoride)/poly(methyl methacrylate)/poly(vinyl pyrrolidone) ternary blends

Ternary blends composed of matrix polymer poly(vinylidene fluoride) (PVDF) with different proportions of poly(methyl methacrylate) (PMMA)/poly(vinyl pyrrolidone) (PVP) blends were prepared by melt mixing. The miscibility, crystallization behavior, mechanical properties and hydrophilicity of the ternary blends have been investigated. The high compatibility of PVDF/PMMA/PVP ternary blends is induced by strong interactions between the carbonyl groups of the PMMA/PVP blend and the CF₂ or CH₂ group of PVDF. According to the Fourier transform infrared and wide‐angle X‐ray difffraction analyses, the introduction of PMMA does not change the crystalline state (i.e. α phase) of PVDF. By contrast, the addition of PVP in the blends favors the transformation of the crystalline state of PVDF from non‐polar α to polar β phase. Moreover, the crystallinity of the PVDF/PMMA/PVP ternary blends also decreases compared with neat PVDF. Through mechanical analysis, the elongation at break of the blends significantly increases to more than six times that of neat PVDF. This confirms that the addition of the PMMA/PVP blend enhances the toughness of PVDF. Besides, the hydrophilicity of PVDF is remarkably improved by blending with PMMA/PVP; in particular when the content of PVP reaches 30 wt%, the water contact angle displays its lowest value which decreased from 91.4° to 51.0°. Copyright © 2011 Society of Chemical Industry     

Interactions in poly(vinylidene fluoride)/poly(methyl methacrylate-co-ethyl methacrylate) blends

Summary The interaction parameters B for blends of poly(vinylidene fluoride) (PVDF) with poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA) and five methyl methacrylate/ ethyl methacrylate copolymers (PMEMA) were determined by measurements of melting point depression of PVDF. The B values are negative, indicating an attractive intermolecular interaction. The intramolecular interaction parameter between MMA and EMA segments in PMEMA was found to be +3.25 cal/cm³, indicating a repulsive interaction between different monomer segments in the copolymer.     

Phase behavior of poly(ε-caprolactone)/ poly (vinylidene fluoride) blends

The miscibility of blends of poly (ε-caprolactone) (PCL)/poly(vinylidene fluoride) (PVDF) was studied by measuring the cloud point, melting point depression and crystallization kinetics. Lower critical solution temperature (LCST) behavior was observed at PCL-rich compositions, whilst it was not observed at high compositions of PVDF. However it is possible that an LCST could exist below the melting point of PVDF. From analysis of the melting point depression, the Flory interaction parameter x₁₂, was calculated from the Nishi-Wang equation and the value was found to be-1.5. The crystallization rate of PCL increased with increasing amount of PVDF in the blend. The spinodal curve for PCL/PVDF blends was simulated by using the lattice-fluid theory.     

The crystalline morphology of poly(vinylidene fluoride)/poly(methylmethacrylate) blends

Poly(vinylidene fluoride), PVF₂, as well as blends of PVF₂ with poly(methyl methacrylate), PMMA, develop a variety of crystalline morphologies at low undercoolings. Both the α and γ crystal forms grow from the melt and the former undergoes a solid-solid phase transition to the latter, though its morphology remains unaltered. Three melting temperatures which decrease with increasing PMMA content are observed. Hoffman-Weeks analysis shows the equilibrium melting points of the blends to be depressed. Using these equilibrium values, the thermodynamic interaction energy density is calculated to go from ?5.40 × 10⁶ to ?2.96 × 10⁷ j/m³ as the blend composition goes from 40.1 volume percent to pure PVF₂. The band periodicity in the α form spherulites increases with crystallization temperature and PMMA content and it appears to be from a lamellar reorientation process with an apparent activation energy of 322 cal/mole. Electron diffraction patterns taken along the radial direction in a given spherulite reveal lamellar twisting which causes the banded appearance. Light scattering results suggest that the lamellar are formed into rod-like structures on a local scale but that on a larger scale they develop a disoriented spherulitic morphology.     

Study of crystal structure and properties of poly(vinylidene fluoride)/graphene composite fibers

Poly(vinylidene fluoride) (PVDF) nascent composite fibers were prepared through the melt-spinning method with different graphene (GE) contents, following which post-stretched composite fibers were obtained using a post-stretching process under thermal treatment condition. The effects of GE content and post-stretching ratio on the crystal structure and properties of the fibers were investigated in order to obtain PVDF composite fibers with high β crystal content and high hydrophobicity and oleophilicity. The results indicated that the addition of GE led to some extent to an improvement in the content of β crystals and the orientation of crystals. Furthermore, the addition of GE obviously improved the mechanical properties, hydrophobicity and oleophilicity of nascent composite fibers. The post-stretching ratio had a significant influence on the transition of the crystal phase from α to β and the orientation of crystals. In addition, the post-stretching played a positive role in enhancement of mechanical properties and hydrophobicity. When 5 wt% GE was added and the post-stretching ratio was 6, PVDF composite fibers with high β crystal content, super-oleophilicity and high hydrophobicity could be obtained. The β crystal content of PVDF composite fibers could reach 62.8%, oil contact angle was 0° and water contact angle was 116.0°. © 2021 Society of Industrial Chemistry.     

Crystallization behavior of poly(vinylidene fluoride)/montmorillonite nanocomposite

The crystallization behavior of poly(vinylidene fluoride)/montmorillonite (PVDF/MMT) nanocomposite was investigated by using differential scanning calorimeter (DSC), polarizing optical microscope (POM), and X‐ray diffraction. The results showed that the crystallization behavior of PVDF was changed by adding MMT in PVDF matrix. The MMT layers in PVDF acted as effective nucleation agents. It is observed that the crystallization temperature of PVDF/MMT nanocomposite was higher than that of PVDF at various cooling rates. The value of half‐time of crystallization showed that the crystallization rate of PVDF/MMT nanocomposite was faster than that of PVDF at a given cooling rate. The addition of MMT hindered the growth of spherulite. Nonisothermal crystallization data was analyzed using Avrami, Ozawa, and Jeziorny method. The Jeziorny method successfully described the nonisothermal crystallization behaviors of PVDF/MMT nanocomposite. The MMT loading was favorable to produce the piezoelectric β phase in the PVDF matrix. The α phase coexisted with the β phase in the PVDF/MMT nanocomposite. For this polymorphic structure, a possible explanation was proposed based on the variable temperature X‐ray diffraction, DSC, and POM experiments. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Piezo- and pyroelectricity in polymer blends of poly(vinylidene fluoride)/poly(methyl methacrylate)

Compatible polymer blends of poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) can be used as suitable model systems for investigating the relationship between the physico-chemical structure of polymers and their piezo- and pyroelectric activity. The structure of PVDF/PMMA blends can be varied over a very wide range which can lead to a strong influence on the piezo- and pyroelectric activity and the corresponding coefficients d₃₁ and g₃. The values of d₃₁ and g₃ were found to vary over nearly five decades whereas the normalized coefficients $\text{d}{}_{31}\text{P}$ and $\text{g}{}_3\text{P}$ remain largely unaffected. This emphasizes the importance of the molecular processes causing the macroscopic polarization P during the poling procedure. For a given polarization P and a given temperature T the properties of the polymer matrix, however, are far less important for the values obtained for d₃₁ and g₃. The experimental results were compared with theoretical predictions based on models which were recently developed by Tashiro et al., Broadhurst et al. and by Mopsik et al.. Considering the appropriate scope of each model a good agreement between theory and experiment is observed and general contradictions have not been found.     

Investigation on crystallization behavior and hydrophilicity of poly(vinylidene fluoride)/poly(methyl methacrylate)/poly(vinyl pyrrolidone) ternary blends by solution casting

Ternary blends composed of matrix polymer poly(vinylidene fluoride) (PVDF) with different proportions of poly(methyl methacrylate) (PMMA)/poly(vinyl pyrrolidone) (PVP) blends were prepared by solution casting. The crystallization behavior and hydrophilicity of ternary blends were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and contact angle test. According to morphological analysis, the surface was full of typical spherulitic structure of PVDF and the average diameter was in the order of 3 μm. The samples presented predominantly β phase of PVDF by solution casting. It indicated that the size of surface spherulites and crystalline phase had little change with the PMMA or PVP addition. Moreover, FTIR demonstrated special interactions among the ternary polymers, which led to the shift of the carbonyl stretching absorption band of PVP. On the other hand, the melting, crystallization temperature, and crystallinity of the blends had a little change compared with the neat PVDF in the first heating process. Except for the content of PVP containing 30 wt %, the crystallinity of PVDF decreased remarkably from 64% to 33% and the value of t_1/2 was not obtained. Besides, the hydrophilicity of PVDF was remarkably improved by blending with PMMA/PVP, especially when the content of PVP reached 30 wt %, the water contact angle displayed the lowest value which decreased from 98.8° to 51.0°. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Melting and crystallization behaviour of the poly(vinylidene fluoride)/poly(monobenzyl itaconate) blends

Summary Melting and crystallization behaviour of blends of poly(vinylidene fluoride)(PVF₂) and poly(monobenzyl itaconate) (PMBzI) have been analyzed as a function of the composition in the range 100-40% PVF₂. Using the Hoffman-Week plot we have not found an equilibrium melting point depression in all the blends studied. However, the addition of PMBzI to pure PVF₂ leads to an increase in its crystallization rate. The results suggest that both polymers are incompatible and that PMBzI acts as nucleating agent in the PVF₂ crystallization.     

Miscibility and morphology of poly(vinylidene fluoride)/poly[(vinylidene fluoride)‐ran‐trifluorethylene] blends

This study presents an investigation of the effect of the different crystalline phases of each blend component on miscibility when blending poly(vinylidene fluoride) (PVDF) and its copolymer poly[(vinylidene fluoride)‐ran‐trifluorethylene] [P(VDF–TrFE)] containing 72 mol % of VDF. It was found that, when both components crystallized in their ferroelectric phase, the PVDF showed a strong effect on the crystallinity and phase‐transition temperature of the copolymer, indicating partial miscibility in the crystalline state. On the other hand, immiscibility was observed when both components, after melting, were crystallized in their paraelectric phase. In this case, however, a decrease in crystallization temperatures suggested a strong interaction between monomers in the liquid state. Blend morphologies indicated that, in spite of the lack of miscibility in the crystalline state, there is at least miscibility between PVDF and P(VDF–TrFE) in the liquid state, and that a very intimate mixture of the two phases on the lamellar level can be maintained upon crystallization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1362–1369, 2002     

Dielectric behavior of polymer blends based on poly(vinylidene fluoride)

Dielectric properties of polymer blends based on PVDF and two amorphous polymers, i.e. poly(vinyl acetate) and poly(methyl methacrylate), have been studied at different frequencies in the temperature range between –150 and +150°C. The novelty of this work lies in the way of planning the polymer blends compositions, which have been prepared according to a statistical design proposed by Scheffé. The purpose is to obtain an empirical equation capable of reproducing the behavior of these systems. From the results obtained after applying the model to the values of the glass transition temperature of PVDF in these polymer blends, it is possible to draw conclusions about their compatibility.     

Poly(vinylidene fluoride)–acrylic rubber partially miscible blends: Phase behavior and its effects on the mechanical properties

A phase diagram of poly(vinylidene fluoride) (PVDF) and acrylic rubber (ACM) was plotted, and the effects of the extent of miscibility on the mechanical properties of the polymer blends were examined. A compressible, regular solution model was used to forecast the phase diagram of this blend. The model prediction, the lower critical solution temperature (LCST) over the upper critical solution temperature (UCST), was done qualitatively according to the experimentally determined phase diagram by differential scanning calorimetry (DSC), optical microscopy, and rheological analysis. These experimental methods showed that this system was miscible in ACM‐rich blends (>50% ACM) and partially miscible in PVDF‐rich blends. A wide‐angle X‐ray diffraction study revealed that PVDF/ACM blends such as neat PVDF had a characteristic α‐crystalline peak. The partially miscible blends displayed up to 350% elongation at break; this was a significant increment of this parameter compared to that of neat PVDF(20%). However, the miscible blends showed elongation of up to 1000% [again, a remarkable increase compared to chemically crosslinked ACM (220%)] and displayed excellent mechanical properties and tensile strength and a large elongation at break. For the miscible and partially miscible blends, two different mechanisms were responsible for this improvement in the mechanical properties. It was suggested that in the partially miscible blends, the rubbery depletion layer between the spherulite and the conventional rubber cavitations mechanism were responsible for the increase in the elongation at break, whereas for the miscible blends, the PVDF spherulite acted as a crosslinking junction. The stretched part of the tensile samples in the partially miscible blends showed characteristic β‐crystalline peaks in the Fourier transform infrared spectra, whereas that in the miscible blends showed α‐crystalline peaks. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1247‐1258, 2013     

Formation of multilayer poly(acrylic acid)/poly(vinylidene fluoride) composite membranes for pervaporation

Dual‐ and multilayer composite membranes, consisting of poly(acrylic acid) (PAA) and poly(vinylidene fluoride) (PVDF), were synthesized by the plasma‐induced polymerization technique. The dual‐layer membrane had a dense PAA layer grafted onto a microporous PVDF substrate, whereas in the multilayer membranes, the grafted PAA and the PVDF layers were arranged in an alternating sequence (e.g., PAA/PVDF/PAA and PAA/PVDF/PAA/PVDF/PAA). These membranes were used in a pervaporation process to separate ethanol–water solutions. For the dual‐layer membranes, the results indicated that the separation factor increased and the permeation flux decreased with increasing amounts of grafted PAA. For the case of grafting yield < 0.6 mg/cm², the composite membrane demonstrated poor separation. As the grafting yield reached 0.85 mg/cm², a sharp increase of the separation factor was observed. For the multilayer membranes, the pervaporation performances were very good, with high separation factors (on the order of 100) and reasonable permeation fluxes over a wide ethanol concentration range. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2266–2274, 2004     

Miscibility and surface crystal morphology of blends containing poly(vinylidene fluoride) by atomic force microscopy

The miscibility and surface crystalline structure of blends containing poly(vinylidene fluoride) (PVDF) composed of and γ phases were investigated by atomic force microscopy (AFM) and differential scanning calorimeter (d.s.c.) measurements. It was found that the surface crystalline phase of PVDF and the degree of surface enrichment of a lower surface free energy component in a blend might strongly be affected by the magnitude of the intermolecular interaction, even though the blend is miscible. Also, the segmental interaction parameters was determined by combining the T_m depression of PVDF in a blend and the binary interaction model. According to the binary interaction model, the introduction of a carboxyl group for miscible [poly(methyl methacrylate)/PVDF] and [poly(vinyl acetate)/PVDF] blends decreased their miscibility.