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.     

Suppression of AC conductivity by crystalline transformation in poly(vinylidene fluoride)/carbon nanofiber composites

Poly(vinylidene fluoride) (PVDF) is an important ferroelectric semi-crystalline polymer with multiple-phase behavior. In this study, remarkable effects of the various crystalline structures of PVDF nanocomposites on alternating current (AC) conductivity were discovered using carbon nanofibers (CNF). It was found that the transformation from α-phase to β-phase in PVDF, induced by the addition of CNFs, had a surprisingly suppressive effect on the AC conductivity of the nanocomposites. These unexpected results indicate that the decline in conductivity occurs after re-crystallization treatment (annealing) of the nanocomposites, and the reduction levels increase with increasing amounts of CNFs. Interestingly, the AC conductivity of annealed 5 wt% CNF/PVDF composites becomes even lower than that of re-crystallized nanocomposites with 3 wt% CNFs. These findings are believed to be very significant for fabrication and long-term service of PVDF composites in industry, which often involves exposure to repeated thermal cycling.     

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     

Toughening effect of poly(methyl methacrylate) on an immiscible poly(vinylidene fluoride)/polylactide blend

In this work, a mutually miscible third polymer, poly(methyl methacrylate) (PMMA), was incorporated into an immiscible poly(vinylidene fluoride)/polylactide (PVDF/PLA) blend (weight ratio 70:30). It was found that incorporation of PMMA in an appropriate amount (30–60 wt%) induced a marked improvement in fracture toughness. A five times enlargement of the elongation at break can be achieved by introducing 30 wt% PMMA. In order to understand the underlying toughening mechanism, SEM, dynamic mechanical analysis (DMA), XRD and DSC were applied to study the variations in morphology, the interaction between the three components and the crystallization behavior. SEM micrographs showed that the PMMA preferred to locate at the interface of PVDF and PLA, which was attributed to the mutual miscibility of PVDF with PMMA and PLA. Furthermore, a variety of thermal characteristics such as T_g and T_m induced by the entanglement of PVDF, PMMA and PLA at the interface were illustrated in DMA and DSC curves. Obviously, the interface consisting of the entanglement of PVDF, PLA and PMMA acted as a linkage to improve interfacial adhesion, which was regarded as the main toughening mechanism. This work provides a potential strategy to realize the interfacial enhancement of an immiscible blend via the incorporation of a mutually miscible third polymer. © 2016 Society of Chemical Industry     

Thermal and spectroscopic studies of poly(N‐vinyl pyrrolidone)/poly(vinyl alcohol) blend films

Poly(N‐vinyl pyrrolidone) (PVP) and poly (vinyl alcohol) (PVA) homopolymers and their blended samples with different compositions were prepared using cast technique and subjected to X‐ray diffraction (XRD) measurements, infrared (IR) spectroscopy, ultraviolet/visible spectroscopy, and thermogravimetric analysis (TGA). XRD patterns of homopolymers and their blended samples indicated that blending amorphous materials, such as PVP, with semicrystalline polymer, such as PVA, gives rise to an amorphous structure with two halo peaks at positions identical to those found in pure PVP. Identification of structure and assignments of the most evident IR ‐ absorption bands of PVP and PVA as well as their blends in the range 400–2000 cm^?1 were studied. UV–vis spectra were used to study absorption spectra and estimate the values of absorption edge, E_g, and band tail, E_e, for all samples. Making use of Coats‐Redfern relation, thermogravimetric (TG) data allowed the calculation of the values of some thermodynamic parameters, such as activation energy E, entropy ΔS^#, enthalpy ΔH, and free energy of activation ΔG^# for different decomposition steps in the samples under investigation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Crystal transformation and thermomechanical properties of poly(vinylidene fluoride)/clay nanocomposites

The crystal transformation and thermomechanical properties of melt‐intercalated poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported in this study. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study the thermal properties of PVDF and its nanocomposites with various clay concentrations. The incorporation of clay in PVDF results in the formation of β‐form crystals of PVDF. DSC study of melting behavior suggested the presence of only α‐phase crystals in neat PVDF and both α‐ and β‐phase crystals in the nanocomposite. This conclusion was corroborated by findings from Fourier‐transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD). Dynamic mechanical analysis (DMA) indicated significant improvements in storage modulus over a temperature range of 20–150 °C. The coefficient of thermal expansion (CTE) decreases with increasing clay loading. Copyright © 2004 Society of Chemical Industry     

Tensile,stress-strain and creep rupture properties of poly (vinyl chloride)/poly(neopentyl glycol adipate)/poly(vinylidene fluoride) blends

Poly (vinyl chloride), PVC, and poly(vinylidene fluoride), PVDF, are incompatible polymers. Poly(neopentyl glycol adipate), PDPA, is miscible with both PVC and PVDF. With PDPA acting as a compatibilizer between PVC and PVDF. compatible PVC/PDPA/PVDF blends can be formed at PVDF content of about less than 50wt%. Above 50wt% PVDF the ternary blends exist in two phases exhibiting two glass transition temperatures, T_g, PVC is the main contributor to the mechanical strength while PDPA and PVDF contribute to the elastic properties of these blends. A compatible blend of 55/22.5/22.5 wt% PVC/PDPA/PVDF exhibiting one single T_g appears to show an interesting balance of the properties of the blend components.     

Largely restricted nucleation effect of carbon nanotubes in a miscible poly(vinylidene fluoride)/poly(butylene succinate) blend

The crystallization behaviors of miscible poly(vinylidene fluoride)/poly(butylene succinate) (PVDF/PBS) and its blend composites with carbon nanotubes (CNTs) during non‐isothermal and isothermal processes were investigated. The results showed that CNTs acted as heterogeneous nucleation agents and further improved the nucleation ability of PBS and PVDF in blends. However, compared with the nucleation effects of CNTs in PBS/CNT or PVDF/CNT binary composites, the nucleation effect of CNTs in miscible PVDF/PBS was largely restricted and nucleation efficiency was lowered. A reasonable explanation about the restricted nucleation ability of CNTs was studied from the viewpoint of interfacial interactions between polymer components and CNTs, in which a preferential affinity of CNTs to PBS was found. Further combined with the preparation method, it is proposed that PVDF chains adsorbed on the CNT surface in the master batch were peeled off from the CNTs by incorporated PBS chains, due to the better interaction between PBS and CNTs. Finally, the PVDF chains at the interface were diluted by PBS, and most of the CNT surface was covered by PBS chains, giving rise to the nucleation of PBS on the CNTs. On the other hand, unremoved PVDF still adsorbed on the CNT surface and crystallized. Compared with PVDF/CNT and PBS/CNT binary composites, the nucleation density in the ternary composites was greatly lowered, resulting in restricted nucleation effects of CNTs. On the other hand, the preferable adsorption of PBS on CNTs induced an apparent phase fluctuation in the PVDF/PBS blend composites, which also reflected the selective adsorption of PBS on the CNT surface. © 2016 Society of Chemical Industry     

Membrane formation of poly(vinylidene fluoride)/poly(methyl methacrylate)/diluents via thermally induced phase separation

The role of the single diluents and mixed diluents on the poly (vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend membranes via thermally induced phase separation (TIPS) process was investigated. The crystallization behaviors of PVDF in the diluted samples were examined by differential scanning calorimetry. The melting and crystallization temperatures of those diluted PVDF blend were decreased with the enhanced interactions between polymer chains and diluent molecules. The crystallinity of PVDF in the diluent was always higher than that obtained in PVDF blend sample. This can be explained by the dilution effects, which increased the average spatial separation distances between crystallizable chains. Thus, the PVDF crystallization was favored. Additionally, solid‐liquid (S‐L) phase separation occurred in the quenched samples. Illustrated by scanning electron microscopy, inter‐ and intraspherulitic voids were formed in the ultimate membranes, which related to the polymer/diluent interactions, the kinetics of crystallization and diluent rejection from the growing crystal. The porosity of the PVDF blend membranes obtained from the mixed diluents was higher than those obtained from the single diluent samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of flow history on poly(vinylidine fluoride) crystalline phase transformation

This study was devoted to the effect of extensional flow during film extrusion on the formation of the β‐crystalline phase and on the piezoelectric properties of the extruded poly(vinylidine fluoride) (PVDF) films after cold drawing. The PVDF films were extruded at different draw ratios with two different dies, a conventional slit die and a two‐channel die, of which the latter was capable of applying high extensional flow to the PVDF melt. The PVDF films prepared with the two‐channel die were drawn at different temperatures, strain rates, and strains. The optimum stretching conditions for the achievement of the maximum β‐phase content were determined as follows: temperature = 90°C, strain = 500%, and strain rate = 0.083 s^?1. The samples prepared from the dies were then drawn under optimum stretching conditions, and their β‐phase content and piezoelectric strain coefficient (d₃₃) values were compared at equal draw ratios. Measured by the Fourier transform infrared technique, a maximum of 82% β‐phase content was obtained for the samples prepared with the two‐channel die, which was 7% higher than that of the samples prepared by the slit die. The d₃₃ value of the two‐channel die was 35 pC/N, which was also 5 pC/N higher than that of the samples prepared with the slit die. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

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.     

Phase transformation mechanisms and piezoelectric properties of poly(vinylidene fluoride)/montmorillonite composite

Poly(vinylidene fluoride) (PVDF)/montmorillonite (MMT) composite with different MMT contents were prepared by solutions‐casting method. The effects of MMT on crystalline structure, morphology, dielectric property, piezoelectric property and phase transformation mechanism were studied. The results showed that acted as effective nucleation agents, the orientation of MMT were almost parallel to the surface of the film. The beta phase in the PVDF matrix was increased and the alpha phase was decreased. Relative dielectric constant and loss of the composite were increased with the increasing of MMT. The d₃₃ was also increased with MMT, which reached a maximum (5.8pC/N) with 2.0 wt % MMT. The mechanisms of changes in phase transformation and piezoelectric property were proposed based on experiment results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Melt rheology and mechanical crystal transformation in an immiscible blend with poly(vinylidene fluoride) matrix

Effect of immiscible polyamide 6 (PA6) on the melt rheology and stretch‐induced crystal transformation of poly (vinylidene fluoride) (PVDF) matrix is reported. PA6 is dispersed as submicron droplets in the PVDF matrix, responsible for significant enhancement in the melt elasticity. Nevertheless, crystallization habits of PVDF matrix from melt are little affected by submicron PA6 droplets, and the α‐form of PVDF prevails in the blends. Upon mechanical stretching, the α‐form is converted to the β‐form, which is remarkably reduced with the increasing of PA6 content in the blends. It could be correlated with the decreased tensile stress in the presence of submicron PA6 droplets that act as stress concentrators. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43499.     

Grafting poly(vinyl amine-co-acrylic acid)s on poly(vinylidene fluoride) membranes

In this study, N-vinylacetamide (NVA) was graft-polymerized and graft-copolymerized with acrylamide (AAm) onto plasma-activated surfaces. The polymer compositions of the grafted layer were estimated from X-ray photoelectron spectroscopy spectra. N-vinylacetamide was enriched in the grafted polymers in all regions of the monomer compositions. The primary amine groups could be densely introduced on the surface by hydrolyzing the grafted poly(vinylacetamide-co-acrylamide). © 1994 John Wiley & Sons, Inc.     

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.     

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 separation structure in poly(vinyl alcohol)/silk fibroin blend films

Blend films of a commercial poly(vinyl alcohol) (a-PVA) derived from vinyl acetate and silk fibroin (SF) obtained from degummed silk were prepared by mixing the aqueous solutions of both samples. A plain weave structure was recognized only in the blend films, whereas no structure was found for the superimposed films of both samples. The phase separation structure of the blend films was examined by microscopic observations elongation, tensile tests, and IR measurements. The microphase separation region increased with increase in the degree of polymerization of the PVA. In the IR spectra of the blend films with high PVA contents cast under certain conditions, the absorption peak attributed to the cross-β-form conformation of SF appeared strongly. Gelatin, a water-soluble and natural polymer, was also used for comparison with SF. The ternary phase diagram in an a-PVA/gelatin/H₂O system was obtained experimentally and the critical point was used to estimate the interaction parameter between PVA and gelatin molecules. The phase separation structure and the interaction between PVA and SF molecules were also discussed taking into consideration the results of the a-PVA/gelatin system. © 1998 SCI.     

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     

Doubly oriented β-form films of poly(vinylidene fluoride)

PVDF sheets, rapidly quenched, were (1) two-step transversely stretched at various temperatures and (2) stretched at various temperatures, rolled at room temperature and then annealed. The orientation patterns of the β-form crystal (which contains the polar b-axis) in these films were analysed on the basis of X-ray diffraction photographs taken with flat and cylindrical cameras. In the case of (1), when both of the two-step transversely stretching temperatures were below 100°C, a doubly oriented film with the plar b-axis oriented parallel to the film surface was obtained. In the case of (2), when the stretching temperature was below 100°C, the sheets then rolled without annealing, another doubly oriented film with the polar b-axis preferentially oriented at 30° to the film surface was obtained. On the other hand, when these films were annealed above 100°C, or the stretching temperatures were above 100°C, orientation patterns in which the polar b-axis was partially rotated through 60° were obtained. The orientation mechanisms of these films are discussed using the measurements of the lattice spacings of the β-form crystal.