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1.
The high‐density polyethylene (HDPE)/barium sulfate (BaSO4) nanocomposites had been successfully prepared by melt‐blending. Nonisothermal melt‐crystallization kinetics of neat HDPE and HDPE/BaSO4 nanocomposites was investigated with differential scanning calorimetry under different cooling rates. The nonisothermal crystallization behavior was analyzed by Ozawa, Avrami, and combined Ozawa–Avrami methods. It was found that the Ozawa method failed to describe the nonisothermal crystallization behavior of neat HDPE and HDPE/BaSO4 nanocomposites. The modified Avrami method by Jeziorny was only valid for describing the middle stage of crystallization but was not able to describe the later stage of neat HDPE and HDPE/BaSO4 nanocomposites crystallization. The value of Avrami exponent n for neat HDPE ranged from 3.3 to 5.7 and for HDPE/BaSO4 nanocomposites ranged from 1.8 to 2.5. It is postulated that the values of n close to 3 are caused by spherulitic crystal growth with heterogeneous nucleation, whereas simultaneous occurrence of spherulitic and lamellar crystal growth with heterogeneous nucleation account for lower values of n. The combined Ozawa–Avrami method by Mo and coworkers (Polym. Eng. Sci., 37(3) , 568 (1997)) was able to satisfactorily describe the crystallization behavior of neat HDPE and HDPE/BaSO4 nanocomposites. In addition, the activation energy of nonisothermal crystallization was determined using the Kissinger (J. Res. Natl. Bur. Stand., 57(4) , 217 (1956)) method, showing that the crystallization activation energy of HDPE/BaSO4 nanocomposites was lower than that of neat HDPE. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers  相似文献   

2.
The effect of the addition of 50 nm spherical alumina nanoparticles with hydrophilic or hydrophobic surfaces on the morphology of syndiotactic polypropylene (sPP) was investigated. The filler content in the nanocomposites was 3 wt%. Polarized Optical Microscopy and Small Angle Light Scattering (SALS) studies showed that sPP and the nanocomposites form hedrites. The addition of alumina nanoparticles significantly increased the number of hedrites. A higher number of nucleation sites in the nanocomposites promote a higher crystallization rate, and thus hedritic growth was stopped at the early stage of crystallization. Quantitative evaluations by SALS analysis show that the object size is decreased by not only the crystallization conditions but also the presence of Al2O3 nanoparticles. A small amount of Al2O3 nanoparticles did not noticeably affect the crystallinity of sPP, but increased the melting point. Transmission Electron Microscopy images showed that the lamellar thickness did not change significantly with the incorporation of nanoparticles. The lamella thickness, however, depends on cooling rates. X-ray diffraction characterization indicated that the sPP and the nanocomposites were crystallized in disordered “form I”. The incorporation of alumina nanoparticles had a small effect on the crystal structure of syndiotactic polypropylene.  相似文献   

3.
The melting/crystallization behavior and isothermal crystallization kinetics of high‐density polyethylene (HDPE)/barium sulfate (BaSO4) nanocomposites were studied with differential scanning calorimetry (DSC). The isothermal crystallization kinetics of the neat HDPE and nanocomposites was described with the Avrami equation. For neat HDPE and HDPE/BaSO4 nanocomposites, the values of n ranges from 1.7 to 2.0. Values of the Avrami exponent indicated that crystallization nucleation of the nanocomposites is two‐dimensional diffusion‐controlled crystal growth. The multiple melting behaviors were found on DSC scan after isothermal crystallization process. The multiple endotherms could be attributed to melting of the recrystallized materials or the secondary lamellae caused during different crystallization processes. Adding the BaSO4 nanoparticles increased the equilibrium melting temperature of HDPE in the nanocomposites. Surface free energy of HDPE chain folding for crystallization of HDPE/BaSO4 nanocomposites was lower than that of neat HDPE, confirming the heterogeneous nucleation effect of BaSO4. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers  相似文献   

4.
Nonisothermal crystallization of poly(N‐methyldodecano‐12‐lactam) (MPA) was investigated using DSC method at cooling rates of 2–40 K/min. With increasing cooling rate, crystallization exotherms decreased in magnitude and shifted toward lower temperatures. Subsequent heating runs (10 K/min) showed an exotherm just above Tg, which increased in magnitude with the rate of preceding cooling run, corresponding to the continuation of primary crystallization interrupted as the system crossed Tg on cooling. Kinetic evaluation by the Avrami method gave values of exponent n close to 2.0, suggesting two‐dimensional crystal growth combined with heterogeneous nucleation. The Tobin method, covering the intermediate range of relative crystallinities, provided n ? 2.20, suggesting possible partial involvement of homogeneous nucleation at later stages of nonisothermal crystallization. The crystallization rate parameter k1/n showed a linear dependency on cooling rate for both methods, the Tobin values being slightly higher. The Ozawa approach failed to provide reasonable values of the kinetic exponent m of MPA. The Augis–Bennet method was used to determine the effective activation energy of the entire nonisothermal crystallization process of MPA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 564–572, 2005  相似文献   

5.
Differential scanning calorimeter (DSC) and X‐ray diffraction methods were used to investigate the isothermal and nonisothermal crystallization behavior and crystalline structure of syndiotactic polystyrene (sPS)/clay nanocomposites. The sPS/clay nanocomposites were prepared by mixing the sPS polymer solution with the organically modified montmorillonite. DSC isothermal results revealed that introducing 5 wt% of clay into the sPS structure causes strongly heterogeneous nucleation, inducing a change of the crystal growth process from mixed three‐dimensional and two‐dimensional crystal growth to two‐dimensional spherulitic growth. The activation energy of sPS drastically decreases with the presence of 0.5 wt% clay and then increases with increasing clay content. The result indicates that the addition of clay into sPS induces the heterogeneous nucleation (a lower ΔE) at lower clay content and then reduces the transportation ability of polymer chains during crystallization processes at higher clay content (a higher ΔE). We studied the non‐isothermal melt‐crystallization kinetics and melting behavior of sPS/clay nanocomposites at various cooling rates. The correlation among crystallization kinetics, melting behavior and crystalline structure of sPS/clay nanocomposites is discussed. Polym. Eng. Sci. 44:2288–2297, 2004. © 2004 Society of Plastics Engineers.  相似文献   

6.
BACKGROUND: The technological development of poly(ε‐caprolactone) (PCL) is limited by its short useful lifespan, low modulus and high crystallinity. There are a few papers dealing with the crystallization behavior of carbon nanotube‐reinforced PCL composites. However, little work has been done on the crystallization kinetics of melt‐compounded PCL/multiwalled carbon nanotube (MWNT) nanocomposites. In this study, PCL/MWNT nanocomposites were successfully prepared by a simple melt‐compounding method, and their morphology and mechanical properties as well as their crystallization kinetics were studied. RESULTS: The MWNTs were observed to be homogeneously dispersed throughout the PCL matrix. The incorporation of a very small quantity of MWNTs significantly improved the storage modulus and loss modulus of the PCL/MWNT nanocomposites. The nonisothermal crystallization behavior of the PCL/MWNT nanocomposites exhibits strong dependencies of the degree of crystallinity (Xc), peak crystallization temperature (Tp), half‐time of crystallization (t1/2) and Avrami exponent (n) on the MWNT content and cooling rate. The MWNTs in the PCL/MWNT nanocomposites exhibit a higher nucleation activity. The crystallization activation energy (Ea) calculated with the Kissinger model is higher when a small amount of MWNTs is added, then gradually decreases; all the Ea values are higher than that of pure PCL. CONCLUSION: This paper reports for the first time the preparation of high‐performance biopolymer PCL/MWNT nanocomposites prepared by a simple melt‐compounding method. The results show that the PCL/MWNT nanocomposites can broaden the applications of PCL. Copyright © 2008 Society of Chemical Industry  相似文献   

7.
To enhance the crystallization kinetics of poly(lactic acid) (PLA), fibrous sepiolite was explored for nucleating the crystallization of PLA. PLA/sepiolite nanocomposites were prepared via the melt‐extrusion method. The effect of sepiolite on the crystallization behavior, spherulite growth and crystal structure of PLA were investigated by means of differential scanning calorimetry (DSC), polarized optical microscope (POM), wide angle X‐ray diffraction (WAXD), Fourier transform infrared (FTIR), and scanning election microscope (SEM). On the basis of DSC and POM results, the overall crystallization kinetics of PLA/sepiolite nanocomposites were significantly enhanced leading to higher crystallinity and nucleation density, faster spherulite growth rate (G) and lower crystallization half‐time (t1/2) compared with the neat PLA. Under non‐isothermal conditions, the PLA blend comprising 1.0 wt% of sepiolite still revealed two crystallization peaks upon cooling at a rate of 35°C/min. Above phenomena strongly suggested that sepiolite was an effective nucleating agent for PLA. FTIR and WAXD analyses confirmed that the crystal structure of PLA matrix was the most common α‐form. SEM micrographics illustrated the fine three‐dimensional spherulite structures with the lath‐shape lamellae regularly arranged in radial directions. POLYM. ENG. SCI., 55:1104–1112, 2015. © 2014 Society of Plastics Engineers  相似文献   

8.
The effects of silver (Ag) nanoparticles on the physical properties of syndiotactic PP (sPP) were investigated concentrating on the isothermal melt crystallization behavior under shear. sPP with 5 wt % Ag nanoparticles presented higher crystallization temperature (Tc) and heat of crystallization (ΔHc) than pure sPP. At 90°C, the Ag nanoparticles had little effect on the induction time of crystallization but a little increased the half‐time (t1/2) for the crystallization. At 100°C, however, the induction time was decreased with increasing the Ag content and the t1/2 was decreased up to the Ag content of 0.5 wt %. DSC melting endotherms exhibited double melting peaks when crystallized at 90°C under shear but a single melting peak when crystallized at 100°C. The WAXD patterns exhibited that the presence of Ag nanoparticles did not produce any change in the crystal structure of sPP. The tensile strength of sPP is little changed up to the Ag content of 0.1 wt % but it was decreased with further addition. In addition, the introduction of less than 0.1 wt % Ag increased the elongation at break, but further addition decreased it abruptly. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

9.
The kinetics of crystallization have been studied for a series of novel poly(ether ether sulfide)s based on a biphenyl moiety in the backbone (Mn = 14.3K, 19.1K), referred to as biphenyl sulfide (Tg = 142°C, Tm = 347°C) and phenyl moieties in the backbone (Mn = 8.1K, 19.9K, 34K), referred to as phenyl sulfide (Tg = 100°C, Tm = 243°C). Isothermal melt crystallization kinetics were analyzed based on the Avrami equation. Avrami exponents close to three were obtained for the phenyl sulfides, independent of molecular weight or crystallization temperature, which implies growth of three-dimensional spherulitic superstructures following heterogeneous nucleation. For the biphenyl sulfides, values closer to 2 were obtained for the exponent, also independent of molecular weight or crystallization temperature, which could imply the incomplete development of three-dimensional superstructures following heterogeneous nucleation. Nonisothermal crystallization kinetics were also studied by cooling from the melt; in all cases studied, the Ozawa analysis could not well describe the evolution of crystallinity, probably because of the inapplicability of some of the inherent assumptions in this type of analysis. The data were analyzed using the conventional form of the Avrami equation, which yielded good fits. This semiquantitative method of analysis yields a reduced rate constant that was found to increase with increasing cooling rate and decreasing molecular weight. The results of the isothermal and nonisothermal crystallization studies carried out on the poly(ether ether sulfide)s have been compared wherever possible to the results available for PPS and PEEK.  相似文献   

10.
Nonisothermal melt‐crystallization behavior of syndiotactic polypropylene (sPP) compounded with 5% by weight (wt %) of some inorganic fillers [i.e., kaolin, talcum, marl, titanium dioxide (TiO2), and silicon dioxide (SiO2)] and 1 wt % of some organic fillers, which are some sorbital derivatives (i.e., DBS, MDBS, and DMDBS) was investigated and reported for the first time. It was found that the ability of these fillers to nucleate sPP decreased in the following sequence: DBS > talcum > MDBS > SiO2 ~ kaolin ~ DMDBS > marl > TiO2, with DBS being able to shift the crystallization exotherm by ~ 18°C on average, while TiO2 was able to shift the crystallization exotherm by only ~ 6°C on average, from that of neat sPP. The Avrami analysis revealed that the Avrami exponent for sPP compounds varied between 2.9 and 4.3, with the values for neat sPP varying between 3.1 and 6.8. Lastly, the Ziabicki's crystallizability of sPP compounds was greater than that of neat sPP, suggesting an increase in the crystallization ability of sPP as a result of the presence of these fillers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 245–253, 2005  相似文献   

11.
Differential scanning calorimetry, combined with Avrami theory, was used to investigate the kinetics of three steps of the complex crystallization process of poly(N‐methyldodecano‐12‐lactam) (MPA): (1) primary melt crystallization at respective crystallization temperature (Tc), (2) additional crystallization at 30°C, and (3) recrystallization at 54°C. Kinetics of the three steps was discussed with respect to Tc. The Avrami exponent n of primary melt crystallization decreased between 2.5 and 1.9 in the range of Tc values of ?10 to 20°C, which suggests heterogeneous nucleation, followed by two‐dimensional growth, with a larger involvement of homogeneous thermal nucleation at greater supercoolings. The crystallization rate constant k decreased with increasing Tc. The value of n = 1.5 for additional crystallization implies a two‐dimensional diffusion‐controlled crystal growth with a suppressed nucleation phase. For Tc values ranging from ?10 to 0°C and 0 to 20°C, k showed weak and quite strong decreasing dependencies on Tc, respectively. The recrystallization mechanism involved partial melting of primary crystallites and two‐dimensional rearrangement of chains into a more perfect structure. The rate of this process was almost independent of Tc. The values of activation energies were derived for the three steps of MPA crystallization using the Arrhenius equation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 279–293, 2004  相似文献   

12.
The nonisothermal crystallization kinetics of polyoxymethylene (POM), polyoxymethylene/Na–montmorillonite (POM/Na–MMT), and polyoxymethylene/organic–montmorillonite (POM/organ–MMT) nanocomposites were investigated by differential scanning calorimetry at various cooling rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the nonisothermal crystallization process of POM/Na–MMT and POM/organ–MMT nanocomposites. The difference in the values of the exponent n between POM and POM/montmorillonite nanocomposites suggests that the nonisothermal crystallization of POM/Na–MMT and POM/organ–MMT nanocomposites corresponds to a tridimensional growth with heterogeneous nucleation. The values of half‐time and the parameter Zc, which characterizes the kinetics of nonisothermal crystallization, show that the crystallization rate of either POM/Na–MMT or POM/organ–MMT nanocomposite is faster than that of virgin POM at a given cooling rate. The activation energies were evaluated by the Kissinger method and were 387.0, 330.3, and 328.6 kJ/mol for the nonisothermal crystallization of POM, POM/Na–MMT nanocomposite, and POM/organ–MMT nanocomposite, respectively. POM/montmorillonite nanocomposite can be as easily fabricated as the original polyoxymethylene, considering that the addition of montmorillonite, either Na–montmorillonite or organ–montmorillonite, may accelerate the overall nonisothermal crystallization process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2281–2289, 2001  相似文献   

13.
Through differential scanning calorimetry, the crystallization kinetics of syndiotactic polypropylene (sPP) nanocomposites with organically modified layered silicates has been investigated in both nonisothermal and isothermal conditions. A strong influence on the thermal behavior is exerted by the compatibilizer agent (low molecular weight isotactic polypropylene‐g‐maleic anydrhyde, iPP‐g‐MA), which increases the crystallization rate of sPP. A further strong increase in the crystallization rate is observed upon increasing the OLS content in the sample. The kinetics data have been analyzed through the Ozawa, Avrami, and Tobin methods, the first of them resulted ineffective in describing our data. Morphological analyses have been performed by polarized optical microscopy and atomic force microscopy. Spherulitic morphology is observed for neat sPP; for the sample containing only the compatibilizer the spherulites grow around the iPP‐g‐MA particles, revealing their nucleating effect on sPP crystallization; for the nanocomposites the spherulitic morphology is lost: the texture appears globular, compact; inside the globules lamellae are present, parallel one to the other. POLYM. ENG. SCI., 46:1433–1442, 2006. © 2006 Society of Plastics Engineers  相似文献   

14.
Polyamide 11 (PA 11)/silica nanocomposites were prepared via in situ melt polymerization by the dispersion of hydrophobic silica in 11‐aminoundecanoic acid monomer. Their isothermal crystallization process and melting behaviors were analyzed by differential scanning calorimetry. The isothermal crystallization kinetics was analyzed by the Avrami equation. The obtained data showed that the model of nucleation and growth of PA 11 was not affected after the incorporation of silica and was a mixture with two‐dimensional, circular, three‐dimensional growth with thermal nucleation. Double and single melting peaks were observed depending on the crystallization temperature. The equilibrium melting point of samples was evaluated, and the spherulites growth kinetics parameters and fold surface free energy were further calculated according to the classical theories. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011  相似文献   

15.
Isothermal and nonisothermal crystallization behavior for PEKK(T) was studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and electron diffraction (ED). In the isothermal crystallization process, the Avrami parameters obtained were n = 2.33–2.69, which shows crystal growth of two‐dimensional extensions consistent with our observations by TEM. The lamellar thickness increases with the crystallization temperature of PEKK(T) crystallized isothermally from the melt. However, for the nonisothermal crystallization of PEKK(T), the results from the modified Avrami analysis show two different crystallization processes. Avrami exponents n1 = 3.61–5.30, obtained from the primary crystallization process, are much bigger than are the secondary n2 = 2.26–3.04 and confirmed by the observation of the spherulite morphology. PEKK(T) crystallized isothermally from the melt possesses the same crystal structure (Form I) as that from nonisothermal melt crystallization. The results from TEM observation show that the spherulite radius decreases with an increasing cooling rate. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3431–3438, 2001  相似文献   

16.
1,2‐Syndiotactic polybutadiene was synthesized at ?30°C using the catalyst system CrCl2(dmpe)2‐MAO. The syndiotactic index of the butadiene sequences, expressed as a percentage of syndiotactic pentads [rrrr], was evaluated by 13C‐NMR measurements. WAXD and SAXS techniques were employed to characterize the crystalline structure of the polymer. The thermal behavior of the polybutadiene was investigated by differential scanning calorimetry. The isothermal crystallization kinetics were described by means of the Avrami equation, which suggested a three‐dimensional growth of crystalline units, developed by heterogeneous nucleation, followed by a secondary crystallization stage. Polybutadiene isothermally crystallizes from the melt according to regime II of crystallization described by Lauritzen–Hoffman secondary nucleation theory. Nonisothermal crystallization kinetics were elaborated using the Ziabicki and Avrami methods modified by Jeziorny. The equilibrium melting temperature was calculated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1680–1687, 2004  相似文献   

17.
Titanium dioxide (TiO2) nanoparticles were pretreated with excessive toluene‐2,4‐diisocyanate (TDI) to synthesize TDI‐functionalized TiO2 (TiO2‐NCO), and then polymeric nanocomposites consisting of polyamide 6 (PA6) and functionalized‐TiO2 nanoparticles were prepared via a melt compounding method. The interfacial interaction between TiO2 nanoparticles and polymeric matrix has been greatly improved due to the isocyanate ( NCO) groups at the surface of the functionalized‐TiO2 nanoparticles reacted with amino groups ( NH2) or carboxyl ( COOH) groups of PA6 during the melt compounding and resulted in higher tensile and impact strength than that of pure PA6. The nonisothermal crystallization kinetics of PA6/functionalized TiO2 nanocomposites was investigated by differential scanning calorimetry (DSC). The nonisothermal crystallization DSC data were analyzed by the modified‐Avrami (Jeziorny) methods. The results showed that the functionalized‐TiO2 nanoparticles in the PA6 matrix acted as effective nucleation agents. The crystallization rate of the nanocomposites obtained was faster than that of the pure PA6. Thus, the presence of functionalized‐TiO2 nanoparticles influenced the mechanism of nucleation and accelerated the growth of PA6 crystallites. POLYM. COMPOS., 35:294–300, 2014. © 2013 Society of Plastics Engineers  相似文献   

18.
Thermal behavior of polylactic acid (PLA)/nanosilica nanocomposites prepared via bulk ring opening polymerization from lactide was investigated by differential scanning calorimetry and thermogravimetric analysis (TGA). Both unmodified nanosilica and modified by surface treatments with different amounts of two distinct silanes were used. Samples containing pure silica show enhanced crystallization processes; with silane‐modified silica this effect is magnified, especially in the case of materials with high loadings of epoxy silane. Nonisothermal crystallization temperatures become higher and isothermal crystallization kinetics show a marked increase of Kinetic constant (Kc). TGA analyses show that, when pure nanosilica is present, nanocomposites have a thermal stability far greater than the one of standard PLA, starting their degradation at temperatures up to 70°C higher than the ones of pure PLA. When silanes are present, thermal stability lowers as silane content increases, but it is anyway higher than the one of the pure polymer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

19.
Nonisothermal crystallization behavior of poly(butylene terephthalate) (PBT) was investigated by means of differential scanning calorimetry. The nonisothermal crystallization kinetic process was analyzed and relative kinetic parameters were obtained with the Avrami and Liu–Mo equations. The results demonstrate a heterogeneous nucleation mechanism. It was found that the nonisothermal primary crystallization of PBT was composed of two courses. Course I corresponded to the two‐dimensional formation process of the lamellae, and the corresponding relative crystallinity (Xt) was less than 15%. Course II was concerned with the three‐dimensional growth process of the spherulite, and Xt changed from 15 to 90%. The secondary crystallization began when Xt was greater than 90%. According to the Flynn–Wall–Ozawa equation, the activation energies for course I, course II, and secondary crystallization were calculated to be ?120, ?210, and ?100 kJ/mol, respectively. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

20.
Investigation of crystallization behavior and kinetics of thermoplastic elastomer nanocomposites was the subject of limited works because of complexities associated with semiexperimental modeling of such phenomenon in a system containing components having completely different behavior in the molten state. Nonisothermal crystallization kinetics of dynamically vulcanized PA6/NBR/HNTs thermoplastic elastomer nanocomposites was mathematically modeled applying well‐known Avrami, Ozawa, and Mo theoretical models to the differential scanning calorimetry data gathered at various cooling rates. It was found that HNTs contribute as nucleating agents to the crystallization kinetics and cause acceleration of crystallization. Activation energy of the crystallization was calculated by correlating the crystallization peak temperature with the cooling rate using Kissinger model. It was found that Mo equation could properly describe nonisothermal crystallization kinetics of the PA6/NBR/HNTs thermoplastic elastomer nanocomposites. This was recognized from the obtained parameters of Mo equation in terms of HNTs loading level, which suggested a higher rate for dynamic crystallization. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46488.  相似文献   

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