Crystallization Behavior Of PVDF Research Articles

Structure and Properties of PVDF/PA6 Blends Compatibilized by Ionic Liquid-Grafted PA6.

Compatibilization of immiscible blends is critically important for developing high-performance polymer materials. In this work, an ionic liquid, 1-vinyl-3-butyl imidazole chloride, grafted polyamide 6 (PA6-g-IL(Cl)) with a quasi-block structure was used as a compatibilizer for an immiscible poly(vinylidene fluoride) (PVDF)/PA6 blend. The effects of two PA6-g-IL(Cl)s (E-2%-50K and E-8%-50K) on the morphology, crystallization behavior, mechanical properties, and surface resistance of the PVDF/PA6 blend were investigated systematically. It was found that the two types of PA6-g-IL(Cl)s had a favorable compatibilization effect on the PVDF/PA6 blend. Specifically, the morphology of the PVDF/PA6 = 60/40 blend transformed from a typical sea-island into a bicontinuous structure after incorporating E-8%-50K with a high degree of grafting (DG). In addition, the tensile strength of the PVDF/PA6/E-8%-50K blend reached 66 MPa, which is higher than that of PVDF, PA6 and the PVDF/PA6 blend. Moreover, the PVDF/PA6/E-8%-50K blend exhibited surface conductivity due to the conductive path offered by the bicontinuous structure and conductive ions offered by grafted IL(Cl). Differential scanning calorimetry (DSC) and wide-angle X-ray diffractometry (WAXD) results revealed that PA6-g-IL(Cl) exhibits different effects on the crystallization behavior of PVDF and PA6. The compatibilization mechanism was concluded to be based on the fact that the nongrafted PA6 blocks entangled with the PA6 chains, while the ionic liquid-grafted PA6 blocks interacted with the PVDF chains. This work offers a new strategy for the compatibilization of immiscible polymer blends.

On the miscibility of PVDF/PMMA polymer blends: Thermodynamics, experimental and numerical investigations

In this paper the miscibility of PVDF/PMMA blends was studied using different approaches: experimental tests, thermodynamics and numerical simulation. The first part of this study is devoted to the experimental work and aims to investigate the miscibility of blends by different experimental techniques. First, blends of PVDF/PMMA at different ratios were compounded and characterized using physico-chemical and rheological methods. The effect of PMMA content on the crystallization behavior of PVDF in the blend was experimentally investigated. At a second stage, the thermodynamic interaction parameter of Flory-Huggins was evaluated as a function of the PMMA proportion in the blends based on the experimental data related to the PVDF melting point and enthalpy. Besides, a numerical method has been developed using Fluent Ansys software to describe the coalescence phenomenon under different scenarios of viscosity ratios and grain sizes of polymers. The confrontation of the code simulation results with the experimental and thermodynamic approaches has shown a good agreement for reproducing the behavior of miscible polymers as well as their aptitude to form a homogeneous blend.

Shear induced crystallization in different polymorphic forms of PVDF induced by surface functionalized MWNTs in PVDF/PMMA blends.

Shear induced crystallization in PVDF/PMMA blends, especially at higher fractions of PMMA, can be quite interesting in understanding the structure-property correlation and processing of these blends. In a recent submission (Phys. Chem. Chem. Phys., 2014, 16, 2693-2704), we clearly demonstrated, using dielectric spectroscopy, that the origin of segmental relaxations concerning the crystalline segments of PVDF in PVDF/PMMA blends in the presence of MWNTs (multiwalled nanotubes) was strongly contingent on the size of the crystallite. We now understand that the fraction of PMMA in the blends governs the origin of polymorphism in PVDF. This motivated us to systematically study the effect of shear on the crystallization behavior of PVDF especially in blends with different polymorphic forms of PVDF. Two model blends were selected; one with a mixture of α and β crystals and the other predominantly rich in α crystals. Initially, physical ageing, at different oscillation frequencies (1 rad s(-1) and 0.1 rad s(-1)), was monitored by melt rheology and subsequently, the effect of steady shear was probed in situ without changing the history of the samples. Intriguingly, the rate of crystallization was observed to be significantly higher for higher oscillation frequencies, which essentially suggest that shear has induced crystallization in the blends. More interestingly, the effect of steady shear was more pronounced in the blends rich in α crystals (bigger crystallites as observed from SAXS) and at lower oscillation frequencies.

Preparation and characterization of electrospun poly(vinylidene fluoride)/poly(methyl methacrylate) membrane

In this work, nanofibrous poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) membranes with different PMMA contents from 10 wt% to 20 wt% were prepared by electrospinning. The morphology of resultant membranes was investigated using scanning electron microscopy. It was found that the morphology of PVDF/PMMA electrospun nanofibers in the membrane was highly dependent on the solvent used during the electrospinning process. PVDF/PMMA nanofibers with beads were formed in the electrospun membrane when N, N-dimethylformamide (DMF) solvent was used due to its low evaporation rate. Uniform PVDF/PMMA nanofibers without beads in the electrospun membranes were obtained by DMF–acetone mixed solvent. The crystallization behavior of PVDF in the electrospun PVDF/PMMA membranes was investigated using differential scanning calorimetry and Fourier transform infrared spectroscopy. The β form crystalline structure was the major crystalline phase of PVDF in electrospun PVDF/PMMA membranes, and PMMA may suppress the formation of α crystalline phase of PVDF. The crystallinity degree of PVDF in the electrospun PVDF/PMMA membranes was lower than that of the electrospun PVDF membrane, and the annealing could effectively improve the crystallinity degree of PVDF in electrospun membranes. Moreover, it was found that the annealing has no adverse effect on the low density, high porosity, and water vapor permeability of electrospun membranes.

Induced formation of polar phases in poly(vinylidene fluoride) by cetyl trimethyl ammonium bromide

Poly(vinylidene fluoride) (PVDF) has been widely used as transducers, actuators,and sensors due to its exceptional electroactive properties among polymer materials and the electroactive properties of PVDF heavily depend on its polymorphs. The effects of cetyl trimethyl ammonium bromide (CTAB) on the crystallization behavior of PVDF during isothermal crystallization and annealing process were studied, and the results showed that the polar phases (β, γ) were induced by CTAB when PVDF was isothermally crystallized at 145–160 °C. Increasing the isothermal crystallization temperature resulted in an increased γ-phase formation with a concomitant decrease of α and β phases. A 100 % γ-phase formation occurred when the sample isothermally crystallized at 155 and 160 °C. The crystalline phase transition of the sample annealed at 160 °C for various time revealed that CTAB induced the transformation from α to γ′ phase and a higher concentration of CTAB resulted in shorter transformation time, as well as higher transformation degree.

Facile and effective promotion of β crystalline phase in poly(vinylidene fluoride) via the incorporation of imidazolium ionic liquids

AbstractIn this study, a facile and efficient protocol to enhance the β‐phase content of poly(vinylidene fluoride) (PVDF) is developed, in which the effect of room temperature ionic liquids (RTILs), including [1‐butyl‐3‐methylimidazolium (bmim)][PF6], [bmim][BF4], [bmim][FeCl4] and [bmim][Cl], on the crystallization behavior of PVDF is investigated. The resulting PVDF/RTIL hybrids are characterized by Fourier transform infrared (FTIR) spectroscopy, XRD, polarized optical microscopy (POM) and DSC. The FTIR spectroscopy and XRD results show that the fraction of β‐phase, F(β), is significantly enhanced by the incorporation of RTILs, specifically from 49.2% for neat PVDF to 92.6% for hybrid filled with 15 wt% [bmim][PF6]. The analysis of the crystallization behavior based on the DSC tests reveals that the degree of crystallinity increases with incorporation of RTILs, implying that RTILs could act as directing agents to facilitate the crystallization process, which is further evidenced by the POM results. In addition, the non‐isothermal crystallization kinetics of PVDF and PVDF/RTIL composites are investigated by means of DSC and the results indicate that the addition of the RTILs significantly influences the mechanism of nucleation and growth of PVDF crystallites. © 2013 Society of Chemical Industry

Study on the Nonisothermal Crystallization Kinetics of Poly(Vinylidene Fluoride)/Tributyl Citrate Blends Via Thermally Induced Phase Separation

The nonisothermal crystallization kinetics of poly (vinylidene fluoride) (PVDF) in PVDF/tributyl citrate (TBC) blends having undergone thermally induced phase separation were investigated through differential scanning calorimetry measurements. Ozawa theory, Mo's method and Kissinger model were used to analyze the kinetics of the nonisothermal crystallization process. The Ozawa theory failed to describe the crystallization behavior of PVDF in the PVDF/TBC blends, whereas the Mo model was able to describe the nonisothermal crystallization process fairly well. The crystallization activation energy was determined by the Kissinger method, and was in the range of 90–165 kJ/mol.

Impact of Ionic Liquid-Modified Multiwalled Carbon Nanotubes on the Crystallization Behavior of Poly(vinylidene fluoride)

The impact of pristine multiwalled carbon nanotubes (MWCNTs), an ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], and the ionic liquid-modified MWCNTs (IL-MWCNTs) on the crystallization behavior of melt-crystallized poly(vinylidene fluoride) (PVDF) has been investigated. Pristine MWCNTs accelerate crystallization of PVDF as an efficient nucleation agent, while the formed crystals are mainly nonpolar α crystal form with few polar β crystals. Incorporation of only ionic liquid results in depression of the PVDF melt crystallization rate due to the miscibility of IL with PVDF but leads to a higher content of polar crystals (β and γ forms) than MWCNTs. The ionic liquid and MWCNTs show significant synergetic effects on both the nucleation and the formation of polar crystals for PVDF by melt crystallization. Addition of IL-MWCNTs not only improves the MWCNTs dispersion in PVDF matrix but also increases the overall crystallization rate of PVDF drastically. More important, the melt-crystallized PVDF nanocomposites with IL-MWCNTs show 100% polar polymorphs but no α crystal forms. To the best of our knowledge, this is the first report on the achievements of full polar crystal form in the melt-crystallized PVDF without mechanical deformation or electric field. The IL to MWCNTs ratio and the IL-MWCNTs loading content effects on the crystallization behavior of PVDF in the nanocomposites were also studied. It is considered that the specific interactions between >CF2 with the planar cationic imidazolium ring wrapped on the MWCNTs surface lead to the full zigzag conformations of PVDF; thus, nucleation in polar crystals (β and γ forms) lattice is achieved and full polar crystals are obtained by subsequent crystal growth from the nuclei.

Crystallization behavior of poly (vinylidene fluoride)/multi-walled carbon nanotubes nanocomposites

The non-isothermal and isothermal crystallization of poly (vinylidene fluoride) (PVDF)/multiple-walled carbon nanotubes (MWNTs) composites containing pristine (MWNT1) and carboxyl group (–COOH) functionalized MWNT (MWNT2) were investigated. The effects of MWNT on the crystallization behavior of PVDF were dependent on the dispersion state of MWNT. Pristine MWNT could increase the nucleation due to better dispersion, and thus, PVDF/MWNT1 composites exhibited higher crystallization peak temperatures (Tcps) and crystallinities (Xcs) compared with PVDF/MWNT2 composites. Meanwhile, the formation of MWNT network confined the growth of crystals. For the isothermal crystallization, MWNT acted as nucleating agents, and the crystallization rate constant k was increased with the addition of MWNT. Besides, the half crystallization time, t0.5, was remarkably shortened with the increase of MWNT content, especially for the pristine MWNT.

Effect of multiwalled carbon nanotubes on crystallization behavior of poly(vinylidene fluoride) in different solvents

AbstractIn this study, the poly(vinylidene fluoride) (PVDF)—multiwalled carbon nanotubes (MWNTs) composites have been prepared by solution casting in two different solvents: dimethyl sulfoxide (DMSO) and dimethylacetamide (DMAc). Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimeter (DSC) results showed that the crystal phases of PVDF are quite different in the two solvents. When DMSO is used as the solvent, the PVDF crystalline phases could be greatly alternated from α‐form to β‐form by the incorporation of MWNTs. While the crystalline structure of PVDF hardly change in the case of DMAc. The DSC and polarized optical microphotographs implied that MWNTs not only act as nucleating agents for PVDF but also confine the crystallization of PVDF. Besides, it was found that the storage modulus (E′) of the composites were significantly enhanced with an appropriate content of MWNTs. And when using DMSO as the solvent, one relaxation process emerges in the loss tan δ (loss factor) curves of the neat PVDF and PVDF/MWNTs composites, while it was not observed in the DMAc system. The obtained results revealed that varing solvents have different effects on the crystallization behavior of PVDF with the addition of MWNTs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Characterization of poly(vinylidene fluoride)/Na+‐MMT composites: An investigation into the β‐crystalline nucleation effect of Na+‐MMT

AbstractPoly(vinylidene fluoride)(PVDF)/Na+‐MMT composites have been successfully prepared utilizing sodium montmorillonite (Na+‐MMT) via N,N‐dimethylformamide (DMF) solution mixing. The dispersion of Na+‐MMT layers in composites were investigated by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The effect of adding Na+‐MMT on crystallization behavior of PVDF was specifically studied. The β‐crystalline nucleation effect of Na+‐MMT was investigated and confirmed by differential scanning calorimetry (DSC), XRD, and Fourier transform infrared (FTIR) results. The interaction between PVDF and the surface of Na+‐MMT layers in DMF solution was confirmed by UV‐Vis absorbency. The effect of adding Na+‐MMT on rheological and electrical properties of PVDF/Na+‐MMT composites were also determined. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 903–911, 2009

Crystallization behavior of poly(vinylidene fluoride)/montmorillonite nanocomposite

AbstractThe 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

Crystalline Phase Formation of Poly(vinylidene fluoride) from Tetrahydrofuran/N,N‐dimethylformamide Mixed Solutions

The present work focused on the effect of the interactions between poly(vinylidene fluoride) (PVDF) chains and solvent molecules on the structure and crystallization behavior of PVDF in films obtained by solution casting. In a single solvent system, the film cast from the good solvent of N,N‐dimethylformamide (DMF), showed dominantly β‐phase crystals with the highest PVDF crystallinity (50.6%) and the largest spherulite size, about 4 μm, at the top surface. The samples deposited from good swelling agents, such as tetrahydrofuran (THF) and methyl ethyl ketone (MEK), exhibited mainly the original α phase with some amount of β‐phase crystals; the crystallization behavior and the morphology of the surface were similar to the original PVDF resin, because of the only partially dissolved PVDF chains in these two solvents. In a mixed solvent system (THF/DMF), the β phase formation linearly increased as the DMF component increased, determined by Fourier transform infrared spectroscopy (FTIR) techniques, owing to increased interactions between PVDF chains and DMF molecules. The film surface consisted of β spherulites with average size of about 3 μm, which were smaller than those grown from pure DMF, because of the increased crystallization rate in the mixed solvent.

Crystallization behavior of PVDF in PVDF‐DMP system via thermally induced phase separation

AbstractThe crystallization behavior of PVDF (poly (vinylidene) fluoride) in PVDF‐dimethylphthalate(DMP) system was investigated in the liquid–liquid (L–L) phase separation region, solid–liquid (S–L) phase separation region and different quenching conditions via thermally induced phase separation (TIPS). Differential scanning calorimetry (DSC) indicated the crystallinity of PVDF in PVDF‐DMP system increased in the early stage of phase separation and polymer‐rich phase crystallized completely in the late stage of phase separation. The scanning electron microscopy (SEM) showed the different quenching temperatures had effects on the spherulite size of polymer rich phase and the ultimate membrane structure in the different phase separation regions. The wide angle X‐ray diffraction (WAXD) was used to quantify the crystal structure of PVDF in PVDF‐DMP system. The α‐phase PVDF was obtained when the system quenched to different temperatures above 40°C, and the area of diffraction peaks changed when quenching temperatures changed. While the β‐phase PVDF was formed when PVDF‐DMP system was quenched form liquid nitrogen and crystallized for 24 h in 25°C water bath. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3714–3719, 2006

Crystallization of poly(vinylidene fluoride)-SiO2 hybrid composites prepared by a Sol-gel process

Organic-inorganic hybrid composites consisting of poly(vinylidene fluoride) (PVDF) and SiO2 were prepared through a sol-gel process and the crystallization behavior of PVDF in the presence of SiO2 networks was investigated by spectroscopic, thermal and x-ray diffraction measurements. The hybrid composites obtained were relatively transparent, and brittleness increased with increasing content of tetraethoxysilane (TEOS). It was regarded from FT-IR and DSC thermal analyses that at least a certain interaction existed between PVDF molecules and the SiO2 networks. X-ray diffraction measurements showed that all of the hybrid samples had a crystal structure of PVDFγ-phase. Fresh gel prepared from the sol-gel reaction showed a very weak x-ray diffraction peak near 2θ=21° due to PVDF crystallization, and intensity increased gradually with time after gelation. The crystallization behavior of PVDF was strongly affected by the amount of SiO2 networks. That is, SiO2 content directly influenced preference and disturbance for crystallization. In polymer-rich hybrids, SiO2 networks had a favorable effect on the extent of PVDF crystallization. In particular, the maximum percent crystallinity of PVDF occurred at the content of 3.7 wt% SiO2 and was higher than that of pure PVDF. However, beyond about 10 wt% SiO2, the crystallization of PVDF was strongly confined.