Effect of silver nanoparticles on the dynamic crystallization behavior of nylon‐6

The effect of introducing silver nanoparticles on the rheological properties and dynamic crystallization behavior of nylon‐6 was investigated. The nanocomposites showed slightly higher viscosity than pure nylon‐6 in the low‐frequency range even at an extremely low loading level of the silver particles (0.5–1.0 wt %). The nanoparticles had a more noticeable effect on the storage modulus than on the loss modulus of a nylon‐6 melt and reduced its loss tangent. They increased the crystallization temperature of nylon‐6 by about 14 °C and produced a sharper crystalline peak. The silver nanoparticles promoted the crystallization of nylon‐6, and their effect on the dynamic crystallization of nylon‐6 at 200 °C was more notable at a lower shear rate and at 190 °C at a higher frequency. Nylon‐6 produced large spherulitic crystals, but the nanocomposites showed a grainy structure. In addition, the silver nanoparticles reduced the fraction of the α‐form crystal but increased that of the γ‐form crystal. The nanocomposites crystallized at 190 °C showed a lower melting temperature than nylon‐6 by about 3 °C, whereas the nanocomposites crystallized at 200 °C showed almost the same melting temperature. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 790–799, 2004     

Effect of MMT,SiO2, CaCO3, and PTFE nanoparticles on the morphology and crystallization of poly(vinylidene fluoride)

The crystallization and melting behaviors of poly (vinylidene fluoride) (PVDF) with small amount of nanoparticles (1 wt %), such as montmorillonite (MMT), SiO₂, CaCO₃, or polytetrafluoroethylene (PTFE), directly prepared by melt‐mixing method were investigated by scanning electron microscopy (SEM), polarizing optical microscopy, Fourier transform infrared spectroscopy, wide angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC). The nanoparticle structure and the interactions between PVDF molecule and nanoparticle surface predominated the crystallization behavior and morphology of the PVDF. Small amount addition of these four types of nanoparticles would not affect the original crystalline phase obtained in the neat PVDF sample (α phase), but accelerated the crystallization rate because of the nucleation effect. In these four blend systems, MMT or PTFE nanoparticles could be well applied for PVDF nanocomposite preparation because of stronger interactions between particle surface and PVDF molecules. The nucleation enhancement and the growth rate of the spherulites were decreased in the order SiO₂ > CaCO₃ > PTFE > MMT. The melting and recrystallization of PVDF was found in MMT addition sample, because of the special ways of ordering of the PVDF chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Nucleation of isotactic polypropylene crystallization by gold nanoparticles

Nucleation of isotactic polypropylene (iPP) crystallization by gold (Au) nanoparticles was studied. Regardless of their size, 4.3, 8.8, 28.3, and 84.5 nm, all particles were able to nucleate spherulites when deposited on the iPP surface. However, when added and melt‐mixed with iPP, only the smallest particles affected significantly the iPP bulk crystallization. Au nanoparticles larger than 4.3 nm, at the concentration of 0.001 wt %, did not influence the crystallization of iPP. Contrary to this, 0.001 and 0.005 wt % of Au nanoparticles having the size of 4.3 nm increased crystallization temperature of the iPP by 7–8 °C and decreased markedly the sizes of polycrystalline aggregates. Aggregation of Au nanoparticles in the polymer matrix was evidenced by electron microscopy and contributed to their decreased effectiveness in the nucleation of iPP crystallization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 469–478, 2010     

Rheological properties of ferrite nanocomposites based on nylon‐66

Effects of ferrite nanoparticles (0.1–20 wt %) on the rheological and other physical properties of nylon‐66 were investigated. The presence of ferrite nanoparticles less than 1 wt % increased the crystallization temperature (T_c) by 4.2 °C with ferrite content, but further addition decreased T_c. The onset temperature of degradation was increased by 7.3 °C at only 0.1 wt % loading of ferrite, after which the thermal stability of nylon‐66 was decreased with ferrite content. The incorporation of ferrite nanoparticles more than 5 wt % increased the dynamic viscosity (η′) with the loading level. Further, it produced notably shear thickening behavior in the low frequency, after which high degree of shear thinning was followed with ferrite content. In the Cole–Cole plot, the nanocomposites with ferrite lower than 5 wt % presented a single master curve, while further addition gave rise to a deviation from the curve. The relaxation time (λ) was increased with ferrite content and the difference of λ between nylon‐66 and its nanocomposite was greater at lower frequency. The tensile strength was a little increased up to 1 wt % loading, after which it was decreased with increasing the loading level. In addition, the introduction of the nanoparticles increased tensile modulus and decreased the ductility with ferrite content. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 371–377, 2006     

Phase transformation and enhancement of toughness in polyvinylidene fluoride by onium salts

We study the effect of onium salts (benzyl triphenyl phosphonium chloride, BTPC; tetrabutyl ammonium perchlorate, TAP) on the crystallization of polyvinylidene fluoride (PVDF) from a melt. The β phase of PVDF crystals is polar and has excellent piezoelectric properties, in contrast to the nonpolar α phase. Processing of PVDF results in the formation of predominantly α‐phase crystals. Different amounts of the onium salts were melt‐mixed into PVDF using a micro‐compounder. PVDF containing about 0.5 wt % of BTPC is found to have predominantly β‐phase crystals in compression molded PVDF films, with an increase in the melting temperature by about 7 °C. A significant increase in the toughness of PVDF is obtained by the addition of BTPC. Polarizing microscopy indicates that the onium salts act as nucleating agents and result in significant reduction in spherulite size. Similar results were observed for samples prepared with TAP. The results of the study indicate a facile method for producing β‐phase PVDF films. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1339–1344, 2011     

Poly(vinylidene fluoride)/clay nanocomposites prepared by melt intercalation: Crystallization and dynamic mechanical behavior studies

The preparation and properties of poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported for the first time. PVDF/clay nanocomposites were prepared by melt intercalation with organophilic clay. The composites were characterized with X‐ray diffraction, differential scanning calorimetry, and dynamic mechanical analysis. X‐ray diffraction results indicated intercalation of the polymer into the interlayer spacing. PVDF in the nanocomposites crystallized in the β form. Differential scanning calorimetry nonisothermal curves showed an increase in the melting and crystallization temperatures along with a decrease in crystallinity, as evidenced by the melting and crystallization peaks. Isothermal crystallization studies showed an enhanced rate of crystallization with the addition of clay, as evidenced by a reduction in the crystallization time. Dynamic mechanical analysis indicated significant improvements in the storage modulus over a temperature range of ?100 to 150 °C. The tan δ peak signifying the glass‐transition temperature of PVDF shifted to higher temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1682–1689, 2002     

Morphologies and crystalline forms of polyvinylidene fluoride membranes prepared in different diluents by thermally induced phase separation

We have studied the morphologies and crystalline forms of polyvinylidene fluoride (PVDF) membranes separately prepared in four different diluents bearing >C?O groups, namely 1,2‐propylene glycol carbonate (PGC), dimethyl phthalate (DMP), diphenyl ketone (DPK), and dibutyl phthalate (DBP), by the thermally induced phase separation (TIPS) method. The permittivities of the diluents and PVDF were measured to compare the different PVDF–diluent systems. The results showed the permittivity of PGC to be much greater than that of PVDF, and those of DMP and DBP to be lower than that of PVDF. The permittivity difference between DPK and PVDF was not apparent above 120 °C. On cooling mixtures with a PVDF concentration of 10 wt %, PVDF crystallization was observed in the PVDF–DMP, PVDF–DBP, and PVDF–PGC systems, while liquid–liquid phase separation occurred in the PVDF–DPK system. A cross‐section of the PVDF–PGC membrane presented smooth PVDF particles in the β‐phase crystalline form. Those of the PVDF–DMP and PVDF–DBP membranes presented PVDF particles consisting of a fibrillar network in the α‐phase. The PVDF–DPK membrane preferentially adopted an α‐phase bicontinuous channel structure. When the concentration of PVDF was 60 wt %, the cross‐sections of the above four membranes revealed PVDF polyhedra, among which the PVDF–DMP, PVDF–DBP, and PVDF–DPK membranes retained the α‐phase crystalline form, and the diffraction peak of the α‐phase became visible in the X‐ray diffraction (XRD) spectrum of the PVDF–PGC membrane. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Crystallization-induced composition inhomogeneities in PVDF/PMMA blends

Composition profiles develop around growing PVDF spherulites in a blend with PMMA. These profiles assume stationary courses after a certain crystallization time provided that the overall degree of crystallinity is not too high. The composition-dependent growth rate and the diffusion-controlled remove of the surplus PMMA from the spherulite surface are then in a stationary equilibrium. The internal structure of the spherulites will then be homogeneous, too. Upon isothermal crystallization of a PVDF/PMMA = 60/40 (wt %) blend at 160°C for at least 4 h, the spherulites internal degree of crystallinity x_c as related to the PVDF fraction obeys the inequality 55 wt % ≤ x_c ≤ 84 wt %. The overall PMMA content within the spherulites as averaged over its whole inside has been determined by IR microscopy. It amounts to about 15 wt %. In contrast, the PMMA content of the amorphous phase within the spherulites (averaged again over its whole inside) ranges between 28 and 52 wt %. This composition jumps at the spherulite surface to 52 wt %. From the slope of the composition profiles outside the spherulites that have a width of more than 50 μm, the effective chain diffusion coefficient in blends as averaged over both components can be calculated to amount to (250 ± 100) μm²h⁻¹. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2923–2930, 1998     

Thermal,crystallization, mechanical,and rheological characteristics of poly(trimethylene terephthalate)/poly(ethylene terephthalate) blends

Blends of poly(trimethylene terephthalate) (PTT) and poly(ethylene terephthalate) in the amorphous state were miscible in all of the blend compositions studied, as evidenced by a single, composition‐dependent glass‐transition temperature observed for each blend composition. The variation in the glass‐transition temperature with the blend composition was well predicted by the Gordon–Taylor equation, with the fitting parameter being 0.91. The cold‐crystallization (peak) temperature decreased with an increasing PTT content, whereas the melt‐crystallization (peak) temperature decreased with an increasing amount of the minor component. The subsequent melting behavior after both cold and melt crystallizations exhibited melting point depression behavior in which the observed melting temperatures decreased with an increasing amount of the minor component of the blends. During crystallization, the pure components crystallized simultaneously just to form their own crystals. The blend having 50 wt % of PTT showed the lowest apparent degree of crystallinity and the lowest tensile‐strength values. The steady shear viscosity values for the pure components and the blends decreased slightly with an increasing shear rate (within the shear rate range of 0.25–25 s^?1); those of the blends were lower than those of the pure components. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 676–686, 2004     

Crystallization studies of isotactic polypropylene containing nanostructured polyhedral oligomeric silsesquioxane molecules under quiescent and shear conditions

Crystallization studies at quiescent and shear states in isotactic polypropylene (iPP) containing nanostructured polyhedral oligomeric silsesquioxane (POSS) molecules were performed with in situ small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC). DSC was used to characterize the quiescent crystallization behavior. It was observed that the addition of POSS molecules increased the crystallization rate of iPP under both isothermal and nonisothermal conditions, which suggests that POSS crystals act as nucleating agents. Furthermore, the crystallization rate was significantly reduced at a POSS concentration of 30 wt %, which suggests a retarded growth mechanism due to the molecular dispersion of POSS in the matrix. In situ SAXS was used to study the behavior of shear‐induced crystallization at temperatures of 140, 145, and 150 °C in samples with POSS concentrations of 10, 20, and 30 wt %. The SAXS patterns showed scattering maxima along the shear direction, which corresponded to a lamellar structure developed perpendicularly to the flow direction. The crystallization half‐time was calculated from the total scattered intensity of the SAXS image. The oriented fraction, defined as the fraction of scattered intensity from the oriented component to the total scattered intensity, was also calculated. The addition of POSS significantly increased the crystallization rate during shear compared with the rate for the neat polymer without POSS. We postulate that although POSS crystals have a limited role in shear‐induced crystallization, molecularly dispersed POSS molecules behave as weak crosslinkers in polymer melts and increase the relaxation time of iPP chains after shear. Therefore, the overall orientation of the polymer chains is improved and a faster crystallization rate is obtained with the addition of POSS. Moreover, higher POSS concentrations resulted in faster crystallization rates during shear. The addition of POSS decreased the average long‐period value of crystallized iPP after shear, which indicates that iPP nuclei are probably initiated in large numbers near molecularly dispersed POSS molecules. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2727–2739, 2001     

Crystalline Morphology and Crystallization Kinetics of Melt-miscible Crystalline/Crystalline Polymer Blends of Poly（vinylidene fluoride） and Poly（butylene succinate-co-24mol% hexamethylene succinate）

Poly（vinylidene fluoride） （PVDF） and poly（butylene succinate-co-24 mol% hexamethylene succinate） （PBHS）, both crystalline polymers, formed melt-miscible crystalline/crystalline polymer blends. Both the characteristic diffraction peaks and nonisothermal melt crystallization peak of each component were found in the blends, indicating that PVDF and PBHS crystallized separately. The crystalline morphology and crystallization kinetics of each component were studied under different crystallization conditions for the PVDF/PBHS blends. Both the spherulitic growth rates and overall isothermal melt crystallization rates of blended PVDF decreased with increasing the PBHS composition and were lower than those of neat PVDF, when the crystallization temperature was above the melting point of PBHS component. The crystallization mechanism of neat and blended PVDF remained unchanged, despite changes of blend composition and crystallization temperature. The crystallization kinetics and crystalline morphology of neat and blended PBHS were further studied, when the crystallization temperature was below the melting point of PBHS component. Relative to neat PBHS, the overall crystallization rates of the blended PBHS first increased and then decreased with increasing the PVDF content in the blends, indicating that the preexisting PVDF crystals may show different effects on the nucleation and crystal growth of PBHS component in the crystalline/crystalline polymer blends.     

Poly(phenylene sulfide)/low‐melting‐point metal composites. I. Transient viscoelastic properties and crystallization kinetics

Poly(phenylene sulfide)/low‐melting‐point metal composites (PPSMs) with various loading levels were prepared by melt compounding. The nonisothermal crystallization behavior and transient viscoelastic properties were characterized by the DSC, POM, DMA, and parallel‐plate rheometer. The results reveal that the low‐melting‐point metal (LMPM) particles show nice dispersion at relative low content levels (< 30 wt %). The PPSMs composites present dual characteristics of both the filled polymer composite and polymer blend system in their transient viscoelastic behaviors, which results in occurrence of the stress overshoots with long relaxation time and nonzero residual stress especially at high shear levels. During the crystallization process, the presence of those deformable LMPM droplets facilitates the crystallization kinetics of PPS because of their flow‐promoting action. On the other hand, the LMPM has no heterogeneous nucleating effect and, only plays the role of inert filler, which results in the degradation of the crystal structure of PPS. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 677–690, 2008     

Rheological properties and crystallization behavior of multi‐walled carbon nanotube/poly(ε‐caprolactone) composites

Multi‐walled carbon nanotube/poly(ε‐caprolactone) composites (PCLCNs) were prepared by melt compounding. The rheology, nonisothermal crystallization behavior, and thermal stability of PCLCNs were, respectively, investigated by the parallel‐plate rheometer, differential scanning calorimeter, and TGA. Cole–Cole plots were employed successfully to detect the rheological percolation of PCLCNs under small amplitude oscillatory shear. PCLCNs present a low percolation threshold of about 2–3 wt % in contrast to that of clay‐based nanocomposites. The percolated nanotube network is very sensitive to the steady shear deformation, and is also to the temperature, which makes the principle of time‐temperature superposition be invalid on those percolated PCLCNs. Small addition of nanotube cannot improve the thermal stability of PCL but can increase crystallization temperature remarkably due to the nucleating effect. As the nanotube is much enough to be percolated, however, the impeding effect becomes the dominant role on the crystallization, and the thermal stability increases to some extent. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3137–3147, 2007     

Crystallization and morphology of poly(vinylidene fluoride)/poly(3‐hydroxybutyrate) blends. II. Morphology and crystallization kinetics by time resolved X‐ray scattering

The development of the morphology in poly(vinylidene fluoride)/poly(3‐hydroxybutyrate) (PVDF/PHB) blends upon isothermal and anisothermal crystallization is investigated by time‐resolved small‐ and wide‐angle X‐ray scattering. The components are completely miscible in the melt but crystallize separately; they crystallize stepwise at different temperatures or sequentially with isothermal or anisothermal conditions, respectively. The PVDF crystallizes undisturbed whereas PHB crystallizes in a confined space that is determined by the existing supermolecular structure of the PVDF. The investigations reveal that composition inhomogeneities may initially develop in the remaining melt or in the amorphous phases of the PVDF upon crystallization of that component. The subsequent crystallization of the PHB depends on these heterogeneities and the supermolecular structure of PVDF (dendritically or globularly spherulitic). PHB may form separate spherulites that start to grow from the melt, or it may develop “interlocking spherulites” that start to grow from inside a PVDF spherulite. Occasionally, a large number of PVDF spherulites may be incorporated into PHB interlocking spherulites. The separate PHB spherulites may intrude into the PVDF spherulites upon further growth, which results in “interpenetrating spherulites.” Interlocking and interpenetrating are realized by the growth of separate lamellar stacks (“fibrils”) of the blend components. There is no interlamellar growth. The growth direction of the PHB fibrils follows that of the existing PVDF fibrils. Depending on the distribution of the PHB molecules on the interlamellar and interfibrillar PVDF regions, the lamellar arrangement of the PVDF may contract or expand upon PHB crystallization and the adjacent fibrils of the two components are linked or clearly separated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 974–985, 2004     

Intercalated poly(vinylidene fluoride)/clay nanocomposites: Structure and properties

The preparation and characterization of melt‐intercalated poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported. Organophilic clay (clay treated with dimethyl dihydrogenated tallow quaternary ammonium chloride) was used for the nanocomposite preparation. The composites were characterized with X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). XRD results indicated the intercalation of the polymer in the interlayer spacing. The incorporation of clay in PVDF resulted in the β form of PVDF. DSC nonisothermal curves showed an increase in the melting and crystallization temperatures along with a decrease in crystallinity. Isothermal crystallization studies show an enhanced rate of crystallization with the addition of clay. DMA indicated significant improvements in the storage modulus over a temperature range of ?100 to 150 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 31–38, 2003     

Crystallization and morphology of poly(vinylidene fluoride)/poly(3‐hydroxybutyrate) blends. III. Crystallization and phase diagram by differential scanning calorimetry

The crystallization of poly(vinylidene fluoride) (PVDF)/poly(3‐hydroxybutyrate) (PHB) blends was studied with differential scanning calorimetry, from which the phase diagram was derived. Strong miscibility was underlined by the large negative Flory–Huggins interaction parameter (?0.25). The crystallization of the blend components differed remarkably. Whereas PVDF always crystallized in the surroundings of a homogeneous melt, PHB crystallized in a volume that was confined by the already existing PVDF spherulites, partly in their surroundings and partly inside. Under isothermal conditions, PVDF usually crystallized regularly in three dimensions with predominant quench‐induced athermal nucleation. The Avrami exponent for PVDF dendritic spherulitic growth was, however, distinctly smaller than that for compact growth, and this revealed the two‐dimensional lamellar growth inside. This deviation from ideal Avrami behavior was caused by the development of compositional inhomogeneities as PVDF crystallization proceeded, and this decelerated the kinetics. PHB crystallized three‐dimensionally with mixed thermal and athermal nucleation outside the PVDF spherulites. Inside the PVDF spherulites, PHB crystallization proceeded in a fibrillar fashion with thermal nucleation; the growth front followed the amorphous paths inside the dendritic PVDF spherulites. The crystallization was faster than that in the melt of uncrystallized PVDF. Solid PVDF acts possibly heterogeneously nucleating, accelerating PHB crystallization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 287–295, 2005     

Crystallization behavior and hydrophilicity of poly (vinylidene fluoride) (PVDF)/poly (styrene-<Emphasis Type="Italic">co</Emphasis>-acrylonitrile) (SAN) blends

Poly (styrene-co-acrylonitrile) (SAN) is a hydrophilic non-crystalline copolymer, which is initially used in this paper to improve the hydrophilicity of poly (vinylidene fluoride) (PVDF). Investigation of the crystallization behavior of PVDF/SAN blends showed that the samples presented only α phase regardless of SAN content as cooling from the melt. A double-melting phenomenon was related to the perfection or crystal size of PVDF crystals. As the SAN content is increasing, crystallization of PVDF was limited, leading to a decreased crystallinity and lamellar growth. Besides, the hydrophilicity of PVDF was improved by blending with SAN. The sample containing 70 wt.% SAN performed a similar surface property of the neat SAN owing to the besieging of the PVDF phase by SAN. Observed from the cross section of the blends, PVDF/SAN blends were partially miscible with less than 50 wt.% SAN addition. As the SAN content was more than 50 wt.%, the crystalline PVDF particles clearly dispersed in the amorphous matrix.     

Morphology and crystallization behavior of poly(vinylidene fluoride)/poly(methyl methacrylate)/methyl salicylate,and benzophenone systems via thermally induced phase separation

Poly(vinylidene fluoride) (PVDF) blend microporous membranes were prepared by PVDF/poly(methyl methacrylate) blend (with mass ratio = 70/30) via thermally induced phase separation. Benzophenone (BP) and methyl salicylate (MS) were used as diluents. The phase diagram calculations were carried out in terms of a pseudobinary system, considering the PVDF blend to be one component. The crytallization behaviors of PVDF in the dilutions were detected by differential scanning calorimetry measurement. In these two systems, the melting and crystallization temperatures leveled off in the low polymer concentration (<40 wt %), but shifted to a higher temperature when the polymer concentration >40 wt %. The calculated crystallinity of PVDF for samples with low polymer concentrations was greater than those with high polymer concentrations, because of the limited mobility of polymer chains at a high polymer concentration. The membrane structure as determined by scanning electron microscopy depended on the phase separation mechanism. The quenched samples mainly illustrated the occurrence of crystallization on the same time scale as the liquid–liquid phase separated, resulting in the obvious spherulitic structure with small pores in the spherulites. As the polymer concentration increased, the size of the spherulites and pores within the spherulite was decreased. The evaluated porosity for BP diluted system was higher than that for MS diluted system, and decreased with the increased polymer concentration. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 248–260, 2009     

高β相聚偏氟乙烯基复合体系的制备及压电性能

为了提高聚偏氟乙烯(PVDF)的压电性能,需要寻找有效的途径来提高PVDF的电活性相(β相)含量。 通过水热法成功合成了Ag、ZnO以及二者复合(Ag-ZnO)的3种类型纳米粒子,并与PVDF共混形成PVDF复合薄膜。 通过表征PVDF复合材料的形貌,结晶性能和压电性能,可以发现Ag-ZnO复合纳米粒子的协同作用可以有效提高PVDF的结晶性能和压电性能。 此外,通过单轴拉伸可以使得所有PVDF膜的β相含量得到进一步提高,其中拉伸后的PVDF/Ag-ZnO纳米颗粒(P-C)的β相物质的量分数最高,达到70.0％,最佳的压电系数(d₃₃)达到了31.0 pC/N。     

Crystallization and morphology of poly(vinylidene fluoride)/poly(3‐hydroxybutyrate) blends. I. Spherulitic morphology and growth by polarized microscopy

The development of the poly(3‐hydroxybutyrate) (PHB) morphology in the presence of already existent poly(vinylidene fluoride) (PVDF) spherulites was studied by two‐stage solidification with two separate crystallization temperatures. PVDF formed irregular dendrites at lower temperatures and regular, banded spherulites at elevated temperatures. The transition temperature of the spherulitic morphology from dendrites to regular, banded spherulites increased with increasing PVDF content. A remarkable amount of PHB was included in the PVDF dendrites, whereas PHB was rejected into the remaining melt from the banded spherulites. When PVDF crystallized as banded spherulites, PHB could consequently crystallize only around them, if at all. In contrast, PHB crystallized with a common growth front, starting from a defined site in the interfibrillar regions of volume‐filling PVDF dendrites. It formed by itself dendritic spherulites that included a large number of PVDF spherulites. For blends with a PHB content of more than 80 wt %, for which the PVDF dendrites were not volume‐filling, PHB first formed regular spherulites. Their growth started from outside the PVDF dendrites but could later interpenetrate them, and this made their own morphology dendritic. These PHB spherulites melted stepwise because the lamellae inside the PVDF dendrites melted at a lower temperature than those from outside. This reflected the regularity of the two fractions of the lamellae because that of those inside the dendrites of PVDF was controlled by the intraspherulitic order of PVDF, whereas that from outside was only controlled by the temperature and the melt composition. The described morphologies developed without mutual nucleating efficiency of the components. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 873–882, 2003