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1.
The nonisothermal crystallization kinetics of poly(vinylidene fluoride) (PVDF) in PVDF/MMT, SiO2, CaCO3, or PTFE composites was investigated through differential scanning calorimetry measurements. The enhanced nucleation of PVDF in its nanocomposites with four types of nanoparticle, and their impact on the crystallization kinetics and melting behaviors were discussed. The modified Avrami method and combined Ozawa–Avrami approaches successfully described the primary crystallization of PVDF in nanocomposite samples under the nonisothermal crystallization process. The activation energy was determined according to the Friedman method and it was quite fit with the results of the analysis according to the modified Avrami model and a combined Ozawa–Avrami model.  相似文献   

2.
Poly(vinylidene fluoride)/silica (PVDF/SiO2) hybrid composite films were prepared via sol–gel reactions from mixtures of PVDF and tetraethoxysilane in dimethylacetamide. Their morphology, crystalline structure, and thermal, mechanical, and electrical properties were examined. For morphology measurements, scanning electron microscopy and optical microscopy were applied. X‐ray diffraction and infrared analyses showed that the crystalline structure of PVDF was not changed much by the addition of SiO2, indicating that there was no interaction between PVDF and SiO2. With increasing SiO2 content, the melting temperature rarely changed, the degree of crystallinity and the dielectric constant decreased, and the decomposition temperature slightly increased. A PVDF/SiO2 hybrid composite film with 5 wt % SiO2 exhibited balanced mechanical properties without a severe change in the crystalline structure of PVDF, whereas for the hybrid composites with higher SiO2 contents (>10 wt %), the mechanical properties were reduced, and the spherulite texture of PVDF was significantly disrupted by the presence of SiO2 particles. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 19–30, 2002  相似文献   

3.
The peculiar thermal behavior of four PTFE/PMMA (Polymethylmethacrylate) core–shell nanoparticle samples, marked DV2M1, DV2M2, DV2M4, and DV2M6, was studied by combined differential scanning calorimetry and thermogravimetric analysis. The melting process of the PTFE in the various samples, subjected to annealing and thermal treatments, does not change. In contrast, a complex fractionated crystallization‐type behavior for the PTFE component was observed. The nanocomposite produced by the PMMA shell fluidification features a perfect dispersion of the nanometric PTFE cores. In these conditions, only one crystallization exotherm at very high undercooling is observed, possibly deriving from the homogeneous nucleation mechanism. In contrast, when high temperature thermal treatments cause the decomposition with partial loss of the PMMA shell and allows some cores to get in contact and merge, a crystallization process structured into several components is observed. This behavior indicates that different nucleation mechanisms are active, possibly involving the participation of distinct types of active nuclei with distinct crystallization efficiencies. Finally, when the PMMA shell amount is substantially reduced by the thermal degradation, only the expected crystallization process at moderate undercooling (310 °C) is observed, corresponding to the bulk crystallization induced by the most efficient heterogeneous nuclei. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 548–554, 2010  相似文献   

4.
Poly(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  相似文献   

5.
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  相似文献   

6.
The effect of organo‐modified clay (Cloisite 93A) on the crystal structure and isothermal crystallization behavior of isotactic polypropylene (iPP) in iPP/clay nanocomposites prepared by latex technology was investigated by wide angle X‐ray diffraction, differential scanning calorimetry and polarized optical microscopy. The X‐ray diffraction results indicated that the higher clay loading promotes the formation of the β‐phase crystallites, as evidenced by the appearance of a new peak corresponding to the (300) reflection of β‐iPP. Analysis of the isothermal crystallization showed that the PP nanocomposite (1% C93A) exhibited higher crystallization rates than the neat PP. The unfilled iPP matrix and nanocomposites clearly shows double melting behavior; the shape of the melting transition progressively changes toward single melting with increasing crystallization temperature. The fold surface free energy (σe) of polymer chains in the nanocomposites was lower than that in the PP latex (PPL). It should be reasonable to treat C93A as a good nucleating agent for the crystallization of PPL, which plays a determinant effect on the reduction in σe during the isothermal crystallization of the nanocomposites. The activation energy, ΔEa, decreased with the incorporation of clay nanoparticles into the matrix, which in turn indicates that the nucleation process is facilitated by the presence of clay. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1927–1938, 2010  相似文献   

7.
The structural and thermal behavior of PVDF/ZnO nanocomposites have been investigated by employing scanning electron microscopy (SEM),TEM, DSC, powder X-ray diffraction (XRD), thermally stimulated discharge current (TSDC), and transient current techniques. SEM/TEM observation indicated the homogeneous dispersion of functionalized ZnO nanoparticles throughout PVDF matrix. DSC shows that the crystallinity is influenced by the presence of ZnO nanoparticles in the PVDF matrix because the filler acts as efficient nucleating agent to facilitate PVDF crystallization. DSC results indicated the enhancement of the glass transition temperature (T g), melting temperature (T m) and crystallization temperature (T c) of nanocomposites compared to pristine PVDF. XRD shows that the full-width at half maximum decreases with increasing ZnO content, which is attributed to the improvement in crystallinity. The incorporation of ZnO nanoparticles influences the modification of polarization process in PVDF as observed by means of TSDC and transient current study.  相似文献   

8.
Poly(vinylidene fluoride) (PVDF) chains with the same expanded state were obtained by dissolving PVDF resin in good solvent. Then, the crystallization of PVDF chains from mixed solvents composed of its good solvent and nonsolvent was investigated. N,N‐dimethylformamide (DMF) and ethanol were used as good solvent and nonsolvent of PVDF, respectively. The crystalline phases of PVDF were characterized by Fourier transform infrared (FTIR) spectroscopy and wide angle X‐ray diffraction (WAXD). For the crystallization of PVDF chains from mixed solvents, low ethanol content favored the formation of β phase, while high ethanol content resulted predominantly in the α phase. Different crystallization morphology was observed from the scanning electron microscopy (SEM) images. The obvious spherulite morphology disappeared with the increase in ethanol content in mixed solvent. According to thermal analyses, the crystallized PVDF from mixed solvents with high ethanol content had lower onset melting temperatures than that from low ethanol content. Smaller lamellar thickness calculated from WAXD data reasoned the low onset melting temperatures. The above results indicated that the crystallization of PVDF chains from mixed solvent was a “controlled” process by ethanol content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 575–581, 2010  相似文献   

9.
The cold crystallization at temperature Tcc (melting > Tcc > glass transition) and the postmelting crystallization of polylactic acid plasticized by compressed carbon dioxide (CO2) were studied using a high-pressure differential scanning calorimeter. The kinetics of the two kinds of crystallization were evaluated by the Avrami equation as a function of pressure at certain temperatures. The effects of using talc as a nucleation agent on the two types of crystallization under pressure were also investigated. The results show that compressed CO2 increased the mobility of the polymer chains in solid state, resulting in an increased rate of cold crystallization. The decreased rate of postmelting crystallization was mainly in the nucleation-controlled region, which indicates that the number of nuclei was decreased by the compressed CO2. The growth rate of the two crystallization types followed the Avrami equation, but the kinetics of each depended upon temperature and pressure. The inclusion of talc accelerated postmelting crystallization but had little effect on cold crystallization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2630–2636, 2008  相似文献   

10.
In a previous work, the roles of low‐loading, that is, 1 vol %, nano‐SiO2 particles on the tribological behavior of short carbon fibers (SCFs)/polytetrafluoroethylene (PTFE)/graphite filled polyetheretherketone (PEEK) were studied. In the present work, the effects of nanoparticle content, varying from 1 to 4 vol %, on the structure and the tribological performance of the composite was investigated. The polished cross sections of the composites were inspected using a scanning electron microscope (SEM). The incorporated nanoparticles significantly reduce the friction coefficients of the composite. With low pressure‐sliding velocity (pv) factors, nanoparticle agglomerates seem to exert an abrasive effect on SCF, and thereby lead to high wear rates. Under such conditions, an increase in nanoparticle content decreases the wear resistance. With high pv factors, the nanoparticles remarkably improve the wear resistance of the composite and the nanoparticle contents do not play an important role on the wear resistance. The worn surfaces, transfer films and wear debris of the composites were analyzed. The tribological mechanisms were discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 801–811, 2010  相似文献   

11.
The effects of the inclusion of silver (Ag) nanoparticles on the physical properties, the crystallization behavior under shear, and the consequential crystalline morphology of poly(vinylidene fluoride) (PVDF) were investigated. Ag nanoparticles were melt compounded with PVDF in weight fractions of 20, 50, and 90 wt % (15.3 vol %). In the melt rheology, the presence of 20 wt % Ag nanoparticles had little effect on the dynamic viscosity of PVDF, but further addition increased it with the loading level. In Cole–Cole plot, all the melts gave a single master curve independent of the presence of Ag nanoparticles. As Ag loading level was increased, the overall crystallization process under shear was accelerated by reducing both induction time and crystallization time. The degree of acceleration was more notable at higher crystallization temperatures. The induction time and the crystallization time of 90 wt % loaded nanocomposites were promoted by 53.5 and 3.7%, respectively, at 145 °C and by 62 and 26.3%, respectively, at 160 °C, compared with those of pure PVDF. For the isothermal crystallization measured by differential scanning calorimeter, the critical Ag concentration, where overall crystallization was not promoted by further addition, occurred between 50 and 90 wt %. Both wide angle X‐ray diffraction profiles and Fourier transform infrared spectra of the samples crystallized under shear displayed the peaks for only α‐form crystals without new peak or peak shift regardless of the Ag loading and crystallization temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010  相似文献   

12.
The confinement effects introduced by nanoparticles have been reported to influence the phase behaviors thus the properties of polymer nanocomposites. In this study, molecular dynamics and crystallization behaviors of polyethylene (PE) composited with three types of silica (SiO2) nanoparticles, namely unmodified SiO2, hydrophobically modified SiO2, SiO2‐APTES (3‐aminopropyltriethoxysilane) and SiO2‐PTES (n‐propyltriethoxysilane), were systematically investigated via a combination of DSC, XRD and 1H solid‐state NMR measurements. The suppressions in crystallization and chain mobilities of PE rank in the order of unmodified SiO2 < SiO2‐APTES < SiO2‐PTES due to the increasing interfacial interactions between PE and SiO2 nanoparticles. Additionally, independent of polymer–nanoparticle interactions, a silica network forms for all three kinds of nanocomposites when SiO2 content reaches 83 wt %. The mobilities of polymer chains are severely restricted by such a percolated network structure, leading to a turning point in the crystallization ability of nanocomposites and a new crystallization peak at 45 °C lower than that of pure PE. The synergetic effects of interfacial interactions and filler network on polymer crystallization have been thoroughly studied in this work, which will provide guidance on modifying and designing nanocomposites with controlled properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 498–505  相似文献   

13.
Nylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with organically modified montmorillonite (MMT). The organic MMT layers were exfoliated in a nylon‐66 matrix as confirmed by wide‐angle X‐ray diffraction (WAXD) and transmission electron microscopy. The presence of MMT layers increased the crystallization temperature of nylon‐66 because of the heterogeneous nucleation of MMT. Multiple melting behavior was observed in the nylon‐66/MMT nanocomposites, and the MMT layers induced the formation of form II spherulites of nylon‐66. The crystallite sizes L100 and L010 of nylon‐66, determined by WAXD, decreased with an increasing MMT content. High‐temperature WAXD was performed to determine the Brill transition in the nylon‐66/MMT nanocomposites. Polarized optical microscopy demonstrated that the dimension of nylon‐66 spherulites decreased because of the effect of the MMT layers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2861–2869, 2003  相似文献   

14.
The crystallization of poly(vinylidene fluoride) (PVDF) during thermally induced solid–liquid phase separation leads to supermolecular structures in PVDF/montmorillonite (MMT)/diphenyl ketone dilutions with various poly(methyl methacrylate) (PMMA) contents. The presence of MMT had a significant nucleation enhancement on the β-PVDF crystals along with the MMT surfaces, and subsequently the α-PVDF crystals formed between MMT layers. The mechanism of the PVDF crystallization in the dilution was studied by DSC, POM, FTIR, and SEM results. A small amount of PMMA incorporation (0.3 wt%) improved the dispersion of MMT in the mixture, leading to the highest nucleation effect on the PVDF crystals. This result proves that PMMA chains acted as a good interfacial agent for PVDF and MMT nanoparticles. A well-interconnected supermolecular morphology formed in the dilutions resulted in a higher tensile strength. When the PMMA content was over 1.5 wt% in the dilution, the excessive amorphous PMMA chains would hinder the crystallization of PVDF; subsequently, less interconnected PVDF lamellae structures lowered the tensile strength.  相似文献   

15.
Poly(butylene terephthalate) (PBT) was blended with nanoscale fully vulcanized acrylic rubber (FVAR) powders in a twin extruder, and the FVAR powders were dispersed well in PBT from scanning electron microscopy (SEM) and transmission electron microscope (TEM) investigation. The isothermal crystallization kinetics of PBT/FVAR blends were investigated by differential scanning calorimeter (DSC) and simulated by Avrami model. Equilibrium melting temperature was estimated by the nonlinear Hoffman-Weeks relation. The active energy (ΔE) and nucleation parameters (Kg) increased with the addition of FVAR, suggesting that FVAR particles hindered the crystallization; however more content FVAR had a lower ΔE and Kg because FVAR powders acted as heterogeneous nuclei in the nucleation of crystallization and facilitated the crystallization of PBT. The crystallization ability followed the order: PBT > PBT/FVAR6 > PBT/FVAR3 > PBT/FVAR1 when undercooling was considered.  相似文献   

16.
The influence of low contents of a liquid crystalline polymer on the crystallization and melting behavior of isotactic polypropylene (iPP) was investigated using electron and optical microscopy, differential scanning calorimetry, and X-ray diffraction. In pure iPP, the α modification was found, whereas for iPP/Vectra blends at Vectra concentration <5%, both α and β forms were observed. The amount of β phase varied from 0.23 to 0.16. Optical microscopy showed that Vectra was able to nucleate both α and β forms. Non-isothermal crystallization produces a material with a strong tendency for recrystallization of the α and β forms (αα′ and ββ′ recrystallization) leading to double endotherms for both crystalline forms in DSC thermograms. Melting thermograms after isothermal crystallization at low temperatures showed a similar behavior. At values of Tc > 119 °C for the α form and Tc > 125 °C for the β form, only one melting endotherm was observed because enough perfect crystals, not susceptible to recrystallization, were obtained. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1949–1959, 2004  相似文献   

17.
X‐ray diffraction methods and differential scanning calorimetry were used to investigate the crystalline structure and crystallization kinetics of syndiotactic polystyrene (sPS)/clay nanocomposites. X‐ray diffraction data showed the presence of polymorphism in sPS/montmorillonite (MMT) nanocomposites, which was strongly dependent on the processing conditions (premelting temperature and cooling rate) of the sPS/MMT nanocomposites and on the content of MMT in the sPS/MMT nanocomposites. The α‐crystalline form could be transformed into β‐crystalline forms at higher premelting temperatures. The nonisothermal melt‐crystallization kinetics and melting behavior of the sPS/MMT nanocomposites were also studied at various cooling rates. The correlation of the crystallization kinetics, melting behavior, and crystalline structure of the sPS/MMT nanocomposites was examined. The results indicated that the addition of a small amount of MMT to sPS caused a change in the mechanism of nucleation and the crystal growth of the sPS crystallite. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 560–570, 2003  相似文献   

18.
The influence of ZnO nanoparticles on the crystalline structures of nylon‐6 under different crystallization conditions (annealing at different temperatures from the amorphous solid, isothermal crystallization from the melt at different temperatures, and crystallization from the solution) has been examined with differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared. ZnO nanoparticles can induce the γ‐crystalline form in nylon‐6 when it is cooled from the melted state and annealed from the amorphous solid. This effect of ZnO nanoparticles increases with decreasing particle size and changes under different crystallization conditions. The effects of ZnO nanoparticles on the crystallization kinetics of nylon‐6 have also been studied with DSC. The results show that ZnO nanoparticles have two competing effects on the crystallization of nylon‐6: inducing the nucleation but retarding the mobility of polymer chains. Finally, the melting behavior of the composites has been investigated with DSC, and the multiple melting peaks of composites containing ZnO nanoparticles and pure nylon‐6 are ascribed to the reorganization of imperfect crystals. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1033–1050, 2003  相似文献   

19.
Silica (SiO2) nanoparticles and silica/calcium carbonate (SiO2/CaCO3) core–shell nanocomposites were prepared by sol–gel technique as fillers for papermaking application. Semi-burned rice straw ash (SBRSA), as waste material, was used to prepare the targeted fillers. Preparation of SiO2 nanoparticles and SiO2/CaCO3 nanocomposites was carried out using Na2SiO3 solution that was prepared from SBRSA and CaCO3 nanoparticles of 30–70 nm. The targeted SiO2/CaCO3 nanocomposites were prepared with different molar ratio of SiO2:CaCO3 1:15, 1:10 and 1:5. The percentage of silica increased from 62.5% to 82.9% by thermal treatment of SBRSA at 800 °C for 2 h. The prepared SiO2 nanoparticles and SiO2/CaCO3 nanocomposites were characterized by using XRD, XRF, TEM, FT-IR and Zeta potential. The results indicate that a pure semi-crystalline SiO2 nanoparticle and semi-crystalline shell of SiO2 coated CaCO3 core particles were produced. The work extended also to investigate the effect of the prepared fillers on physical, mechanical and optical properties of paper.Application of the prepared SiO2 nanoparticles and SiO2/CaCO3 nanocomposites improved the optical properties of paper (brightness, whiteness and opacity) but it slightly reduced the mechanical properties when compared to commercial precipitated CaCO3 (PCC) filler.The results showed that the retention of SiO2 nano-particles was highly increased. The retention of the prepared nanocomposites increased along with increasing of SiO2:CaCO3 molar ratio.  相似文献   

20.
The thermal, morphological and optical studies of BaSO4 and MMT (nanoclay) embedded in PVDF were investigated. Nanocomposites samples of PVDF–BaSO4–MMT were prepared by varying the loadings (1–4 mass%) in case of BaSO4 and MMT nanomaterials, respectively. Polyvinylidene fluoride–barium sulfate-montmorillonite (PVDF–BaSO4–MMT) nanocomposites were prepared by solvent-mixing technique. Nanoparticles were synthesized by in situ deposition technique with the help of nonionic polymeric surfactant, and the particle size of nanoparticles was recognized by scanning electron microscopy (SEM) analysis which confirms that the particle has diameter of 80–90 nm. As prepared, nanocomposites films (thickness, 25 μm) were characterized by Fourier transform infrared microscopy (FTIR), SEM and electron diffraction spectroscopy (EDS). FTIR shows that all the chemical constituents were present in the nanocomposites, whereas SEM analysis suggested that the nanofillers dispersed well in polymer matrix and EDS showed the elemental composition of nanocomposite samples. Thermal properties of nanocomposites were studied by using TG/DTA/DTG. TG/DTA studies showed decomposition temperature of pure PVDF is 473.5 °C. The decomposition temperature (T d) of nanocomposites was increased by 93 °C in case of nanocomposites with addition of both BaSO4 and MMT nanomaterials. The difference in the thermal degradation temperature was found to be 1.2% higher in case of addition of BaSO4 nanoparticle as compared to nanoclay. The obtained transparent nanocomposite films were characterized by using UV–Vis spectrophotometer which shows that transparencies of nanocomposites are maintained in visible region, the intensity of absorption band in UV region is increased with the addition of BaSO4 nanoparticles, while in case of addition of nanoclay the UV region does not show drastic changes. Addition of both nanoparticle and nanoclay shows higher absorption in comparison with the individual samples. But further, doubling the amount of nanoparticle and nanoclay shows decrease in UV absorption. Overall, the results of thermal studies show that the incorporation of BaSO4 and MMT could significantly improve the thermal properties of nanocomposites.  相似文献   

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