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1.
The morphology of crystals, isothermal and non-isothermal crystallization of poly(methylene terephthalate) (PMT) have been investigated by using polarized optical microscopy and differential scanning calorimeter (DSC). The POM photographs displayed only several Maltese cross at the beginning short time of crystallization indicating that some spherulites had been formed. The crystal cell belonged to the Triclinic crystal systems and the cell dimensions were calculated from the WAXD pattern. The commonly used Avrami equation and that modified by Jeziorny were used, respectively, to fit the primary stage of isothermal and non-isothermal crystallization. The Ozawa theory was also used to analyze the primary stage of non-isothermal crystallization. The Avrami exponents n were evaluated to be in the range of 2-3 for isothermal crystallization, and 3-4 for non-isothermal crystallization. The Ozawa exponents m were evaluated to be in the range of 1-3 for non-isothermal crystallization in the range of 135-155 °C. The crystallization activation energy was calculated to be −78.8 kJ/mol and −94.5 kJ/mol, respectively, for the isothermal and non-isothermal crystallization processes by the Arrhenius’ formula and the Kissinger’s methods. 相似文献
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Lourdes Franco 《European Polymer Journal》2003,39(8):1575-1583
Isothermal and nonisothermal crystallization kinetics of polyester 64 have been investigated by means of differential scanning calorimetry and optical microscopy. The Avrami analysis has been performed to obtain the kinetic parameters of primary crystallization. These indicate a three-dimensional spherulitic growth on heterogeneous nuclei for the isothermal crystallization, whereas an sporadic nucleation becomes dominant in the nonisothermal crystallization. The maximum crystallization rate of polyester 64 was deduced to take place at a temperature close to −3 °C. Polarizing light microscopy showed that spherulites with a negative birefringence are formed during isothermal crystallization, whereas transmission electron microscopy indicates that the b crystallographic axis is aligned parallel to the spherulitic radius. 相似文献
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Meritxell Martínez‐Palau Lourdes Franco Jordi Puiggalí 《Journal of Polymer Science.Polymer Physics》2008,46(2):121-133
The crystallization behavior of a new sequential polyester constituted by glycolic acid and 4‐hydroxybutyric acid has been studied under nonisothermal conditions. Nonisothermal melt crystallization has been followed by means of hot‐stage optical microscopy (HSOM), with experiments performed at different cooling rates. Two crystallization regimes have been found, which is in good agreement with previous isothermal studies and with the different spherulitic morphologies that were observed. The kinetics of both glass and melt crystallizations has also been studied by differential scanning calorimetry (DSC) and considering the typical Avrami, Ozawa, and Cazé analyses. Only the last gave Avrami exponents, which were in good agreement with those measured under isothermal conditions, suggesting a spherulitic growth with a predetermined nucleation. Isoconversional data of melt and glass nonisothermal crystallizations have been combined to obtain the Hoffman and Lauritzen parameters. Results again indicate the existence of two crystallization regimes with nucleation constants close to those deduced from isothermal DSC experiments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 121–133, 2008 相似文献
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MELTING CRYSTALLIZATION BEHAVIOR OF NYLON 66 总被引:2,自引:0,他引:2
Qing-xin Zhang Zhi-shen Mo State Key Laboratory of Polymer Physics & Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China 《高分子科学》2001,(3):237-246
Analysis of isothermal and nonisothermal crystallization kinetics of nylon 66 was carried out using differentialscanning calorimetry (DSC). The commonly used Avrami equation and that modified by Jeziorny were used, respectively, tofit the primary stage of isothermal and nonisothermal crystallizations of nylon 66, In the isothermal crystallization process,mechanisms of spherulitic nucleation and growth were discussed. The lateral and folding surface free energies determinedfrom the Lauritzen-Hoffman treatment are σ= 9.77 erg/cm~2 and σ_e= 155.48 erg/cm~2, respectively; and the work of chainfolding is q = 33.14 kJ/mol. The nonisothermal crystallization kinetics of nylon 66 was analyzed by using the Mo methodcombined with the Avrami and Ozawa equations. The average Avrami exponent n was determined to be 3.45, Theactivation energies (ΔE) were determined to be -485.45 kJ/mol and -331.27 kJ/mol, respectively, for the isothermal andnonisothermal crystallization processes by the Arrhenius and the Kissinger methods. 相似文献
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Nonisothermal crystallization kinetics and spherulite morphology of poly(trimethylene terephthalate)
The nonisothermal melt crystallization behavior of poly(trimethylene terephthalate) (PTT) was investigated using the DSC technique. PTT peak exothermic crystallization temperature was found to move to lower temperatures as the cooling rate was increased. The modified Avrami equation exponent, n, was 4 when the cooling rates were between 5 and 15 °C/min, indicating a thermal nucleation and a three-dimensional spherical growth mechanism. When the cooling rate was increased to 25 °C/min, n gradually decreased to near 3, implying the nucleation mechanism changed to an athermal mode. PTT nonisothermal crystallization behavior could also be analyzed using the Ozawa equation and the combined equations of Ozawa and Avrami with very good fit of the data.PTT spherulite morphologies and the sign of the birefringence depended strongly on the spherulite's growth temperature. When the growth temperature was decreased from 222 to 170 °C, the spherulite changed from a saturation-type dendritic morphology to one with a colorful banded texture; the sign of the birefringence also changed in the following order: from a weakly positive spherulite → mixed spherulite → weakly negative spherulite → negative spherulite → positive spherulite → negative spherulite → positive spherulite. 相似文献
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低密度聚乙烯/乙丙烯三元共聚(LDPE/EPO)共混体系的结晶动力学 总被引:2,自引:0,他引:2
用DSC方法研究了LDPE/EPO共混体系的等温及非等温结晶动力学,对LDPE/EPO共混体系的等温结晶动力学研究表明,共混物是三维生长的异相成核,共混物在各个结晶温度下的结晶过程都是以方式K_g(Ⅱ)进行的.采用联系Avrami方程和Ozawa方程导出的新非等温结晶动力学方程,处理了LDPE/EPO共混体系,得到了非等温结晶过程的一些基本参数,新方程很好地描述了此共混体系的非等温结晶动力学过程. 相似文献
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Synthesis and non‐isothermal crystallization kinetics of poly(ethylene terephthalate)‐co‐poly(propylene glycol) copolymers 下载免费PDF全文
Poly(ethylene terephthalate)‐co‐poly(propylene glycol) (PET‐co‐PPG) copolymers with PPG ratio ranging from 0 to 0.90 mol% were synthesized by the melt copolycondensation. The intrinsic viscosity, structure, non‐isothermal crystallization behavior, nucleation and spherulitic growth of the copolymers were investigated by Ubbelohde viscometer, Proton Nuclear Magnetic Resonance (1H‐NMR), differential scanning calorimetry, and polarized optical microscopy, respectively. The non‐isothermal crystallization process of the copolymers was analyzed by Avrami, Ozawa, Mo's, Kissinger, and Dobreva methods, respectively. The results showed that the crystallizability of PET was apparently enhanced with incorporating a small amount of PPG, which first rose and then reduced with increasing amount of PPG in the copolymers at a given cooling rate. The crystallization mechanism was a three‐dimensional growth with both instantaneous and sporadic nucleation. Particularly, PET‐co‐PPG containing 0.60 mol% PPG exhibited the highest crystallizability among all the copolymers. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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一种研究聚合物非等温结晶动力学的方法 总被引:19,自引:2,他引:17
作者基于多年对聚合物结晶动力学方面研究的工作积累,联合Avrami方程和Ozawa方程,提出了一种研究聚合物非等温结晶动力学的新方法.该方法既克服了使用Ozawa方程所获得的数据点过少,常常出现非线性,不能获得可靠的动力学参数的缺点,又克服了使用经Jeziorny修正的Avrami方程所获得的表观Avrami指数无法准确预测非等温过程成核生长机理的缺点.该方法已成功用于多种聚合物体系,被国内外学者引用数百次,已成为研究聚合物非等温结晶动力学一种有效方法. 相似文献
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The effect of self-seeding nucleation on the crystallization behavior of poly(trimethylene terephthalate) (PTT) was studied.
Differential scanning calorimetry (DSC) indicated that the crystallization temperature of PTT notably increased after self-seeding
nucleation. Avrami equation was applied in the analysis of the isothermal crystallization process of PTT. The resulting average
value of the Avrami exponent at n = 3.34 suggests that primary crystallization may correspond to a three-dimensional spherulitic growth. Self-seeding nucleation,
leading to a decrease in active energy for crystallization and chain folding work, promotes the overall crystallization process
of PTT.
Translated from Acta Polymerica Sinica, 2006, (3): 414–417 (in Chinese) 相似文献
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Crystallization kinetics of polypropylene with hyperbranched polyurethane acrylate being used as a toughening agent 总被引:1,自引:0,他引:1
The crystallization kinetics of polypropylene (PP) with hyperbranched polyurethane acrylate (HUA) being used as a toughening agent was studied by isothermal and nonisothermal differential scanning calorimetry (DSC). The presence of a small amount of HUA (2-7%) remarkably influences the crystallizability of PP. An addition of HUA leads to an increase in the number of effective nuclei, thus resulting in an increase of crystallization rate and a stronger trend of instantaneous three-dimensional growth. For isothermal crystallization, Avrami exponents were determined to be about 2.97 for pure PP and 3.51 for the HUA/PP blend containing 5% HUA (HUA-PP). The half crystallization time (t1/2) of pure PP was measured to be 8.43 min, while being 3.28 min for HUA-PP at the crystallization temperature of 132 °C. The nonisothermal crystallization kinetics of HUA/PP blends was analyzed by Avrami, Ozawa and Kissinger methods. It has also been proved that an addition of HUA could increase the crystallization rate of PP. Moreover, the crystallization activation energies of pure PP and HUA-PP were estimated by Kissinger and Friedman methods. 相似文献
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Minqiao Ren Jianbin Song Chunlei Song Huiliang Zhang Xiaohong Sun Qingyong Chen Hongfang Zhang Zhishen Mo 《Journal of Polymer Science.Polymer Physics》2005,43(22):3231-3241
The crystallization kinetics of biodegradable poly(butylene succinate‐co‐adipate) (PBS/A) copolyester was investigated by using differential scanning calorimetry (DSC) and polarized optical microscopy (POM), respectively. The Avrami and Ozawa equations were used to analyze the isothermal and nonisothermal crystallization kinetics, respectively. By using wide‐angle X‐ray diffraction (WAXD), PBS/A was identified to have the same crystal structure with that of PBS. The spherulitic growth rates of PBS/A measured in isothermal conditions are very well comparable with those measured by nonisothermal procedures (cooling rates ranged from 0.5 to 15 °C/min). The kinetic data were examined with the Hoffman–Lauritzen nucleation theory. The observed spherulites of PBS/A with different shapes and textures strongly depend on the crystallization temperatures. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3231–3241, 2005 相似文献
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Xiaowen Cui 《European Polymer Journal》2005,41(12):3060-3068
A study on isothermal and nonisothermal crystallization kinetics of odd-odd polyamide 9 11 was carried out by differential scanning calorimetry (DSC). The equilibrium melting temperature of polyamide 9 11 was determined to be 199.1 °C. The Avrami equation was adopted to describe isothermal crystallization of polyamide 9 11. Nonisothermal crystallization was analyzed using both the Avrami relation modified by Jeziorny and the equation suggested by Mo. The isothermal and nonisothermal crystallization activation energies of polyamide 9 11 were determined to be −310.9 and −269.0 kJ/mol using the Arrhenius equation and the Kissinger method, respectively. 相似文献
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Isothermal melt-crystallization, glass transition and melting behavior of poly(l-lactide) (PLLA) with different molecular weights were investigated by using differential scanning calorimetry. Analysis by Avrami equation showed that crystallization was initiated by heterogeneous nucleation, followed by 3-dimensional growth. The maximum reciprocal half-time of crystallization (1/t1/2) was detected at 105 °C. Double endothermic peaks were observed around the glass transition for PLLA with intermediate crystallinities, indicating the coexistence of bulk-like and confined amorphous regions. Double-melting behavior was analyzed and combined with the equilibrium melting temperature evaluation by non-linear Hoffman-Weeks extrapolation, from which a value of 207.6 °C was deduced for PLLA of infinite molecular weight. Lauritzen-Hoffman theory was employed to analyze the crystallization kinetics. Regime II-III transition was found to occur at 120 °C for PLLA of lower molecular weight. The crystal morphology was also examined by scanning electron microscopy through chemical etching method. 相似文献
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Liang Song 《Polymer Degradation and Stability》2009,94(4):632-637
Biodegradable poly(butylene succinate) (PBSU)/functional multi-walled carbon nanotubes (f-MWNTs) nanocomposite were prepared by melt compounding. Nonisothermal crystallization and subsequent melting behavior, isothermal crystallization kinetics, spherulitic morphology, and crystal structure of neat PBSU and its nanocomposite were studied by differential scanning calorimetry, optical microscopy and wide angle X-ray diffraction in detail. The presence of f-MWNTs has a significant heterogeneous nucleation effect on the crystallization and morphology of PBSU, resulting in that the crystallization is enhanced during both nonisothermal and isothermal crystallization in the nanocomposite. Moreover, the crystal structure of PBSU is not modified by f-MWNTs in the nanocomposite. The thermogravimetric analysis illustrates an improvement in thermal stability of PBSU by around 10 °C in the presence of f-MWNTs compared with that of neat PBSU. 相似文献
19.
Shuwen Peng 《European Polymer Journal》2003,39(7):1475-1480
Isothermal crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was investigated by means of differential scanning calorimetry and polarized optical microscopy (POM). The Avrami analysis can be used successfully to describe the isothermal crystallization kinetics of PHBV, which indicates that the Avrami exponent n=3 is good for all the temperatures investigated. The spherulitic growth rate, G, was determined by POM. The result shows that the G has a maximum value at about 353 K. Using the equilibrium melting temperature (448 K) determined by the Flory equation for melting point depression together with U∗=1500 cal mol−1, T∞=30 K and Tg=278 K, the nucleation parameter Kg was determined, which was found to be 3.14 ± 0.07 × 105 (K2), lower than that for pure PHB. The surface-free energy σ=2.55×10−2 J m−2 and σe=2.70±0.06×10−2 J m−2 were estimated and the work of chain-folding (q=12.5±0.2 kJ mol−1) was derived from σe, and found to be lower than that for PHB. This implies that the chains of PHBV are more flexible than that of PHB. 相似文献
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Effect of multi-walled carbon nanotubes on non-isothermal crystallization kinetics of polyamide 6 总被引:2,自引:0,他引:2
The non-isothermal crystallization behaviors of multi-walled carbon nanotubes (MWNTs)/polyamide 6 (PA6) composites were investigated by differential scanning calorimetry (DSC). Three methods, namely, Avrami, Ozawa and Mo, were carried out to analyze the non-isothermal crystallization data. The results showed that the MWNTs in PA6 acted as effective nucleation agents. However the crystallization rate of composites obtained was lower than that of the neat PA6. It is indicated that the presence of MWNTs influenced the mechanism of nucleation and the growth of PA6 crystallites. 相似文献