Spherulitic Morphology and Crystallization Kinetics of Poly(vinylidene fluoride)/Poly(vinyl acetate) Blends

Spherulitic morphology and crystallization kinetics of the blends of poly(vinylidene fluoride) (PVDF) and poly(vinyl acetate) (PVAc) prepared by solution casting films have been investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results suggested that PVAc was mainly segregated into the interlamellar and/or interfibrillar regions due to the volume-filling spherulitic morphology observed. As for the results of crystallization kinetics, it was found that both the PVDF spherulitic growth rate (G ^PVDF) and the overall crystallization rate constant (k _n ) were depressed with either the addition of PVAc component or the increase of crystallization temperature (T _c). The kinetics retardation was attributed to the decrease in PVDF molecular mobility and dilution of PVDF concentration due to the addition of PVAc, which has a higher glass transition temperature (T _g).     

The crystallization of a copoly(chlorotrifluorethylene-vinylidene fluoride) from the amorphous rubbery state

A random copoly(chlorotrifluorethylene-vinylidene fluoride) in the ratio of 3 : 1 was annealed at the temperature range of T_g < T < T_m. The copolymer slowly crystallizes, attaining a rather low ultimate degree of crystallinity, depending on the annealing temperature, in the form of randomly distributed ribbonlike lamellae. The crystallites' melting temperatures are much lower than those of the corresponding homopolymers, increasing with annealing temperature and time. The crystallization kinetics, analyzed using the Avrami equation, indicates the formation of small, low-ordered crystallites. The crystallization process results in a dramatic increase in the elastic modulus at T > T_g. Annealing of stretched samples results in oriented crystallization at much higher rates than in the unstretched material, without markedly affecting the ultimate degree of crystallinity. The oriented crystallites, distributed in an isotropic amorphous matrix, exhibit lower thermal stability than the corresponding unoriented crystals. Their melting temperatures increase with annealing time; however, they decrease with the extent of stretching, suggesting a strong kinetic effect on the crystallites' degree of order.     

Compatibility of poly(vinylidene fluoride) (PVDF)/polyamide 12 (PA12) blends

Poly(vinylidene fluoride) (PVDF)/polyamide 12 (PA12) blends showed new peaks in XRD profile with increasing PA12 and the crystallinity of PA12 significantly decreased with the addition of PVDF. PVDF showed three relaxation regions at about −40, 40, and 100°C, respectively, and glass transition temperature (T_g ) of PA12 increased in blends (10.8→30.14°C) and α‐relaxation of PVDF decreased from 100.26 to 86.46°C. Complex viscosities (η*) vs. composition curve showed a great positive deviation in PVDF‐rich and a small negative deviation in PA12‐rich blends. The N—H and C=O stretching band of PA12 shifted slightly toward higher wavelength, and from curve‐fitted data the area of hydrogen‐bonded C=O stretching bands of PA12 decreased with the addition of PVDF, especially in the 30/70 blend, implying the existence of interactions between the β‐hydrogen atom of PVDF and amide carbonyl group of PA12 in the blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1374–1380, 2000     

High-performance poly(vinylidene fluoride)-polyamide 11/lithium niobate nanocomposites for the applications in air filtration

To overcome the fiber-spinning problem of poly(vinylidene fluoride) (PVDF) because of its high melt viscosity and rapid crystallization, polyamide 11 (PA11) with excellent melt spinning capability and good electret properties is incorporated to prepare blends by melt mixing. Their crystal structure, morphology, electrical polarization properties, and melt spinning performance are systematically characterized by various techniques. It is found that the incorporation of PA11 reduces the crystallinity of PVDF, increases its thermally stimulated discharge current, and reduces its viscosity. Therefore, the blends show much better melt spinning capability. For such blends, the addition of outstanding inorganic electret materials, lithium niobate (LiNbO₃, LN) nanoparticles is found to further improve the materials’ electret properties. Such a strategy is proved to be successful in melt spinning PVDF electrets into fine fibers, which is beneficial to their applications in air filtration and other related fields. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48957.     

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.     

Thermal properties and non‐isothermal crystallization behavior of poly(trimethylene terephthalate)/poly(lactic acid) blends

Thermal properties and non‐isothermal melt‐crystallization behavior of poly(trimethylene terephthalate) (PTT)/poly(lactic acid) (PLA) blends were investigated using differential scanning calorimetry and thermogravimetric analysis. The blends exhibit single and composition‐dependent glass transition temperature, cold crystallization temperature (T_cc) and melt crystallization peak temperature (T_mc) over the entire composition range, implying miscibility between the PLA and PTT components. The T_cc values of PTT/PLA blends increase, while the T_mc values decrease with increasing PLA content, suggesting that the cold crystallization and melt crystallization of PTT are retarded by the addition of PLA. The modified Avrami model is satisfactory in describing the non‐isothermal melt crystallization of the blends, whereas the Ozawa method is not applicable to the blends. The estimated Avrami exponent of the PTT/PLA blends ranges from 3.25 to 4.11, implying that the non‐isothermal crystallization follows a spherulitic‐like crystal growth combined with a complicated growth form. The PTT/PLA blends generally exhibit inferior crystallization rate and superior activation energy compared to pure PTT at the same cooling rate. The greater the PLA content in the PTT/PLA blends, the lower the crystallization rate and the higher the activation energy. Moreover, the introduction of PTT into PLA leads to an increase in the thermal stability behavior of the resulting PTT/PLA blends. Copyright © 2011 Society of Chemical Industry     

Effect of poly(vinylidene fluoride) polymorphic structures on the crystallization behavior of poly(butylene succinate)

The detail information of both α and β form poly(vinylidene fluoride) (PVDF) crystal effect on the crystallization behavior of poly(butylene succinate) (PBS) were systematically studied. The results show that β form PVDF can obviously improve the melt‐crystallization temperature of PBS during the nonisothermal crystallization process. Both crystallization time span and spherulitic size of PBS decrease with the increasing amount of β form PVDF, which enhances the primary nucleation of PBS. But α form PVDF shows no nucleating effect on PBS crystallization, exhibiting as almost unchanged T_c values for α form PVDF‐blended PBS samples. The intrinsic mechanism for the nucleating effect of β form PVDF on PBS was proposed to be the epitaxial crystallization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40991.     

Non-isothermal crystallization behavior of poly(vinylidene fluoride)/ethylene–vinyl acetate copolymer blends

Non-isothermal crystallization behavior of poly(vinylidene fluoride) (PVDF) and ethylene–vinyl acetate (EVA) copolymer and their binary blends with different blending ratios were investigated by the use of differential scanning calorimetry (DSC). With the increasing cooling rates, PVDF, EVA and their binary blends showed wide crystallization temperature range and high crystalline enthalpy. Jeziorny and Mo’s models were applied to calculate non-isothermal crystallization kinetics parameters of neat PVDF, EVA and their binary blends. By Jeziorny method, the crystallization process of neat PVDF, EVA and PVDF/EVA = 7/3 blend can be divided into two parts: primary and secondary crystallization processes. The Avrami exponent n ₁ indicated that the primary crystallization process was a mixture model of three-dimensional and two-dimensional space extensions. In comparison, PVDF/EVA = 5/5 and PVDF/EVA = 3/7 blends showed a single crystallization process. Through Mo’s analysis, faster cooling rate was demanded to reach higher relative crystallinity. Crystallization rate coefficient (CRC) was used to describe the effect of crystallization rates on the interaction between PVDF and EVA. CRC reached a maximum value when the mass ratio of PVDF and EVA was 7/3. The maximum CRC values of PVDF system and EVA system were 98.1 and 179.9 h^?1, respectively. The activation energy was closely related to the extent of conversion and the neat samples had a maximum value of crystallization activation energy. This was consistent with the observation for the parameters from Jeziorny analysis and could be correlated to the heterogeneous nucleation.     

Electrospun fiber membranes from blends of poly(vinylidene fluoride) with fouling‐resistant zwitterionic copolymers

Nonwoven super‐hydrophobic fiber membranes have potential applications in oil–water separation and membrane distillation, but fouling negatively impacts both applications. Membranes were prepared from blends comprising poly(vinylidene fluoride) (PVDF) and random zwitterionic copolymers of poly(methyl methacrylate) (PMMA) with sulfobetaine methacrylate (SBMA) or with sulfobetaine‐2‐vinylpyridine (SB2VP). PVDF imparts mechanical strength to the membrane, while the copolymers enhance fouling resistance. Blend composition was varied by controlling the PVDF‐to‐copolymer ratio. Nonwoven fiber membranes were obtained by electrospinning solutions of PVDF and the copolymers in a mixed solvent of N,N‐dimethylacetamide and acetone. The PVDF crystal phases and crystallinities of the blends were studied using wide‐angle X‐ray diffraction and differential scanning calorimetry (DSC). PVDF crystallized preferentially into its polar β‐phase, though its degree of crystallinity was reduced with increased addition of the random copolymers. Thermogravimetry (TG) showed that the degradation temperatures varied systematically with blend composition. PVDF blends with either copolymer showed significant increase of fouling resistance. Membranes prepared from blends containing 10% P(MMA‐ran‐SB2VP) had the highest fouling resistance, with a fivefold decrease in protein adsorption on the surface, compared to homopolymer PVDF. They also exhibited higher pure water flux, and better oil removal in oil–water separation experiments. © 2018 Society of Chemical Industry     

Thermal behaviour of polyethylene‐block‐poly(methyl methacrylate) block copolymer: effect of multiple heating and cooling rates versus mathematical artefact

The melting and crystallization behaviours of a polyethylene‐block‐poly(methyl methacrylate) (PE‐b‐PMMA) diblock copolymer and a PE homopolymer were investigated using multiple heating and cooling rate differential scanning calorimetry (DSC) experiments, and modelling of the crystallization kinetics and lamellar thickness distribution. This new model was first validated applying literature and experimental data. The model‐predicted morphology (n = 3.2) closely matched the spherulitic morphology (n = 3), which was determined using polarized optical microscopy. For each experimental cooling rate, the model predicted diblock copolymer crystallinity that well matched the entire DSC crystallinity curve, notably for an Avrami–Erofeev index of n = 2; and apparent crystallization activation energy that hardly varied with the cooling rates used, relative crystallinity (α), and crystallization temperature or time. This disfavours the concept of variable activation energy. The use of the right crystallization model and parameter estimation algorithm is important for addressing the mathematical artefact. Under non‐isothermal cooling, the PE‐b‐PMMA diblock copolymer, as per the model prediction, crystallized without confinement (n ≠ 1), preserving the cylindrical structure. From the characteristic shapes of the crystallization function f(α(T)) versus 1/T and crystallization rate versus α plots, the resulting T_cmax and narrow α_max range can guide the search for an appropriate crystallization model. The overall treatment illustrated in this study is not restricted to a PE homopolymer and a PE‐b‐isotactic PMMA block copolymer. It can be generally applied to crystalline homopolymers and copolymers (alternating, random and block), as well as their blends. The block copolymers and blends can be crystalline–amorphous as well as crystalline–crystalline. © 2014 Society of Chemical Industry     

Thermal studies of blends of poly(phenylene sulfide) (PPS) with poly(phenylene sulfide sulfone) (PPSS) and with poly(phenylene sulfide ether) (PPSE)

The miscibilities of poly(phenylene) sulfide/poly(phenylene sulfide sulfone) (PPS/PPSS) and poly(phenylene) sulfide/poly(phenylene sulfide ether) (PPS/PPSE) blends were invesigated in terms of shifts of glass transition temperatures T_g of pure PPS, PPSS, a dn PPSE. The crystallization kinetics of PPS/PPSS blends was also studied as a function of molar composition. The PPS/PPSS and PPS/PPSE blends are respectively partially and fully miscible. PPSE shows a plasticizing effect on PPS as does PPS on PPSS, which necessarily improves te processibility in the respective systems. We can control T_g and melting temperature T_m of PPS by varying amounts of PPSE in blends. The melt crystallization temperature T_mc of PPS/PPSE blends was higher than that of the PPSE homopolymer. Therefore, these blends require shorter cycle times in processing than pure PPSE. The overall rate of crystallization for PPS/PPSS blends follows the Avrami equation with an exponent ?2. The maximal rate of crystallization for PPS/PPSS blends occurs at a temperatre higher by 10°C than that for PPS, while the crystallization half time t_1/2 is 4 times shorter. In the cold crystallization range, crystal growth rates increase and Avrami exponents decrease significantly as the temperature increases.     

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.     

Crystallization and vitrification effect in a poly(styrene)-g-poly(ethylene oxide) graft copolymer

Crystallization and solid state structure of a poly(styrene)-graft-poly(ethylene oxide) (PS-g-PEO) graft copolymer with crystallizable side chains were studied using simultaneous small angle X-ray scattering/wide angle X-ray scattering/differential scanning calorimetry (SAXS/WAXS/DSC). It is found that the glass transition temperature (T_g) of PS main chain is remarkably higher than that of PS homopolymer. The start cooling temperature (T_o) has a great influence on crystallization of the PEO side-chain. When the graft copolymer is cooled from the temperature above T_g, phase separation is suppressed due to the low mobility of the PS main chain and the homogeneous melt is vitrified. The unfavorable conformation of the rigid main chain results in a single crystallization peak and lower crystallinity. When PS-g-PEO is only heated to a temperature lower than the T_g and then cooled, phase separation is retained. Both the PEO side chains with high and low crystallizability can crystallize in the phase-separated state, leading to double crystallization peaks and higher crystallinity. The effect of solvent on crystallization of the graft copolymer was also examined. It is observed that addition of toluene reduces the T_g of the PS main chain and leads to the disappearance of the vitrification effect.     

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     

Understanding of intermolecular interaction in PVDF/PTW blends: Crystallization behavior,thermal, and dynamic mechanical properties

Poly(vinylidene fluoride) (PVDF)/ poly(ethylene–butylacrylate–glycidyl methacrylate) (PTW) blends were directly prepared by melt blending and the interaction and properties of PVDF/PTW blends were explored systematically. The crystallization behavior, thermal stability, dynamic mechanical property, and morphological features of PVDF/PTW blends with different ratios have been studied by XRD, attenuated total reflection Fourier transform infrared spectroscopy, differential scanning calorimeter analysis (DSC), thermal gravimetric analysis (TGA), dynamic mechanical analysis, and polarized optical microscopy (POM). The results showed that the crystalline structure of neat PVDF was dominantly α‐phase crystalline and the incorporation of PTW had no effect on the crystalline structure of PVDF in the PVDF/PTW blends. And T_g of PVDF in PVDF/PTW blends shifted to higher temperature compared with that of neat PVDF, indicating the weak interaction between PVDF and PTW, which was corresponding to DSC and TGA results. An increase in the coarseness and ring‐band spacing observed from POM further substantiated the weak interaction between PVDF and PTW. This work provided a way for preparing improved properties of PVDF/PTW blends for the coating material. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43908.     

Effect of multi‐walled carbon nanotubes on crystallization,thermal, and mechanical properties of poly(vinylidene fluoride)

Composites were prepared by solution blending poly(vinylidene fluoride) (PVDF) and multi‐walled carbon nanotubes (MWNTs). Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) results showed that the crystalline structure of PVDF was changed by the addition of MWNTs and a MWNTs‐induced crystal transformation from α‐phase to β‐phase of PVDF was confirmed. With differential scanning calorimeter (DSC) and dynamic mechanic thermal analysis (DMA) techniques, thermal and mechanical properties of the composite films were examined. As the DSC results showed, addition of MWNTs would lead to the increased cooling crystallization temperature (T_c), implying that MWNTs nanoparticles could act as nucleating agents, which is further proved with the help of polarized optical microphotographs. On the other hand, the decreasing of D_d (degree of crystallinity) implied that the MWNTs networks can confine the crystallization of PVDF. Through the curve analysis of the dynamic mechanical measurements, it was found that the storage modulus (E′) is significantly enhanced, revealing that a strong interaction should exist between PVDF and MWNTs. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Effect of the compatibility on dielectric performance and breakdown strength of poly(vinylidene fluoride)/low‐density polyethylene blends

Immiscible polymer blends with high dielectric constant (ε) and improved breakdown strength (E_b) performance were obtained by composing poly(vinylidene fluoride) (PVDF) with low‐density polyethylene (LDPE) or the LDPE grafted with maleic anhydride (LDPE‐g‐MAH) through melt‐blending way. The dielectric properties of these blends were emphasized for considering the compatibility effect on the energy storage application. Interface morphology, co‐continuity behavior, and grafted ratio were simultaneously investigated to detect the compatibility enhancement after introducing MAH. Results showed that the MAH positively improved the dielectric properties. Both the measured E_b of PVDF/LDPE and PVDF/LDPE‐g‐MAH blends showed a minimum value at v^PVDF = 50 vol % because of the worst compatibility; meanwhile, higher E_b of PVDF/LDPE‐g‐MAH than that of PVDF/LDPE blend was observed owing to the better compatibility. For considering the effect interface morphology on the dielectric performance, layer‐structure films composing with pure PVDF and LDPE layers were further constructed and studied. It was revealed that the layered structure could be treated as a helpful way to improve ε and E_b for immiscible polymer blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42507.     

Investigation of the structural,thermal, mechanical,and optical properties of poly(methyl methacrylate) and poly(vinylidene fluoride) blends

In this investigation, poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF) blends (w/w) were prepared in a Brabender (South Hackensack, NJ) plasticorder with a thermoplastic mixing chamber (type W60) preheated at 180°C. These blends were further converted into films by a conventional solution casting method and characterized with Fourier transform infrared spectroscopy, differential scanning calorimetry, X‐ray diffraction, mechanical property measurements, impact strength testing, ultraviolet–visible spectroscopy, refractive‐index measurements, and contact‐angle study. The Fourier transform infrared results indicated that the compatibility between these two systems resulted from hydrogen bonding between the carbonyl group of PMMA and the CH₂ group of PVDF. The thermal analysis showed depressions in the glass‐transition temperature, melting temperature, and crystallization temperature. The heat of crystallization increased with an increase in the PVDF content in the blend. An increase in the heat of crystallization meant an increase in the crystallinity. An increase in the cooling rate increased the crystallization rate. The improvement in the mechanical properties of the blend films indicated that the observed behavior was ascribable to a more coherent structure of the blends due to strong specific interactions between PMMA and PVDF chains. The impact strength analysis revealed a substantial increase in the impact strength from 21.64 to 38.52 J/m. Optical absorption spectra suggested the presence of an optical band gap energy that increased with an increase in the PVDF content in the blend. The contact angle against water increased with the PVDF content in the blend film, and this was caused by the hydrophobicity of PVDF due to the CF₂ group of PVDF. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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.     

Microphase separation and crystallization in mixtures of polystyrene-poly(methyl methacrylate) diblock copolymer and poly(vinylidene fluoride)

This study examined the microdomain structures and the crystallization behavior in binary blends consisting of an asymmetric block copolymer and a homopolymer using small-angle X-ray scattering, optical microscopy and differential scanning calorimetry. A polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) was mixed with a low molecular weight poly(vinylidene fluoride) (PVDF), where the PS-b-PMMA had a 0.30 wt fraction of the PMMA block. At a PVDF concentration of <13.0 wt%, the PVDF was completely miscible with the PMMA microdomains, and the blends had a cylindrical structure. The addition of PVDF altered the morphology from a PMMA-cylindrical structure to a lamellar structure and finally to a PS-cylindrical structure. When the PVDF concentration was <23.0 wt%, the PVDF was distributed uniformly within the PMMA microdomains. After adding more PVDF, some of the PVDF was locally dissolved in the middle of the PMMA microdomains. The addition of PVDF also affected the ordered microstructure in the blends, leading to a well-defined microdomain structure. However, PVDF crystallization significantly disturbed the pre-existing microdomain structure, resulting in a poorly ordered morphology. In the blends, PVDF had unique crystallization behavior as a result of the space constraints imposed by the microdomains.