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Isothermal Crystallization Kinetics (isothermal + crystallization_kinetics)
Selected AbstractsIsothermal Crystallization Kinetics of Poly(, -caprolactone) with Tetramethyl Polycarbonate and Poly(styrene- co -acrylonitrile) Blends Using Broadband Dielectric SpectroscopyMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2006Samy A. Madbouly Abstract Summary: Phase behavior and isothermal crystallization kinetics of poly(, -caprolactone) (PCL) blends with tetramethyl polycarbonate (TMPC) and poly(styrene- co -acrylonitrile) with 27.5 wt.-% acrylonitrile content have been investigated using broadband dielectric spectroscopy and differential scanning calorimeter. An LCST-type phase diagram has been observed for PCL/SAN blend while all the different blend compositions of PCL/TMPC were optically clear without any phase separation structure even at high temperatures up to 300,°C. The composition dependence of Tgs for both blends has been well described by the Gordon-Taylor equation. The phase diagram of PCL/SAN was theoretically calculated using the Flory-Huggins equation considering that the interaction parameter is temperature and composition dependent. The equilibrium melting point of PCL depressed in the blend and the magnitude of the depression was found to be composition dependent. The interaction parameters of PCL with TMPC and SAN could not be calculated from the melting point depression based on Nishi-Wang approach. The isothermal crystallization kinetics of PCL and in different blends was also investigated as a function of crystallization temperature using broadband dielectric spectroscopy. For pure PCL the rate of crystallization was found to be crystallization temperature (Tc) dependent, i.e., the higher the Tc, the lower the crystallization rate. The crystallization kinetics of PCL/TMPC blend was much slower than that of PCL/SAN at a constant crystallization temperature. This behavior was attributed to the fact that PCL is highly interacted with TMPC than SAN and consequently the stronger the interaction the higher the depression in the crystallization kinetics. It was also attributed to the different values of Tg of TMPC (191,°C) and SAN (100,°C); therefore, the tendency for crystallization decreases upon increasing the Tg of the amorphous component in the blend. The analysis of the isothermal crystallization kinetics was carried out using the theoretical approach of Avrami. The value of Avrami exponent was almost constant in the pure state and in the blends indicating that blending simply retarded the crystallization rate without affecting the crystallization mechanism. Dielectric constant, ,,, of pure PCL, blends of PCL/TMPC,=,80/20 and PCL/SAN,=,80/20 as a function of crystallization time at 47,°C and 1 kHz. [source] Isothermal crystallization kinetics and melting behaviors of nanocomposites of poly(trimethylene terephthalate) filled with nano-CaCO3JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Mingtao Run Abstract The isothermal crystallization and subsequent melting behavior of poly(trimethylene terephthalate) (PTT) composites filled with nano-CaCO3 were investigated at designated temperatures with differential scanning calorimetry. The Avrami equation was used to fit the isothermal crystallization. The Avrami exponents were determined to be 2,3 for the neat PTT and PTT/CaCO3 composites. The particles of nano-CaCO3, acting as nucleating agents in the composites, accelerated the crystallization rate, with the half-time of crystallization decreasing or the growth rate constant (involving both nucleation and growth rate parameters) increasing. The crystallization activation energy calculated from the Arrhenius formula was reduced as the nano-CaCO3 content increased from 0 to 2%, and this suggested that nano-CaCO3 made the molecular chains of PTT easier to crystallize during the isothermal crystallization process. Subsequent melting scans of the isothermally crystallized composites exhibited triple or double melting endotherms: the greater the content was of nano-CaCO3, the lower the temperature was of the melting peak. The degree of crystallization deduced from the melt enthalpy of composites with the proper concentration of nano-CaCO3 was higher than that of pure PTT, but it was lower when the nano-CaCO3 concentration was more than 2%. The transmission electron microscopy pictures suggested that the dispersion state of nano-CaCO3 particles in the polymer matrix was even when its concentration was no more than 2%, whereas some agglomeration occurred when its concentration was 4%. Polarized microscopy pictures showed that much smaller or less perfect crystals formed in the composites because of the interaction between the molecular chains and nano-CaCO3 particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Mechanistic Investigation into the Unique Orientation Textures of Poly(vinylidene fluoride) in Blends with Nylon 11MACROMOLECULAR RAPID COMMUNICATIONS, Issue 10 2003Yongjin Li Abstract Self-seeded crystallization experiments were carried out to detect the mechanism of the unique orientation behavior of poly(vinylidene fluoride) (PVDF) in oriented PVDF/nylon 11 blends. It was found that primary nuclei have no effects on the final orientation textures adopted by PVDF. The results show that the PVDF crystal orientation in the oriented blends is determined in the early stage of crystal growth, thus a trans crystallization mechanism is preferred. Isothermal crystallization kinetics for the self-seeded and non-self-seeded crystallization at 145,°C. [source] Nonisothermal and isothermal crystallization kinetics of nylon-12JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Neil L. A. McFerran Abstract The isothermal and nonisothermal crystallization behavior of Nylon 12 was investigated using differential scanning calorimetry (DSC). An Avrami analysis was used to study the isothermal crystallization kinetics of Nylon 12, the Avrami exponent (n) determined and its relevance to crystal growth discussed and an activation energy for the process evaluated using an Arrhenius type expression. The Lauritzen and Hoffman analysis was used to examine the spherulitic growth process of the primary crystallization stage of Nylon 12. The surface-free energy and work of chain folding were calculated using a procedure reported by Hoffmann and the work of chain folding per molecular fold (,) and chain stiffness of Nylon 12 (q) was calculated and compared to values reported for Nylons 6,6 and 11. The Jeziorny modification of the Avrami analysis, Cazé and Chuah average Avrami parameter methods and Ozawa equation were used in an attempt to model the nonisothermal crystallization kinetics of Nylon 12. A combined Avrami and Ozawa treatment, described by Liu, was used to more accurately model the nonisothermal crystallization kinetics of Nylon 12. The activation energy for nonisothermal crystallization processes was determined using the Kissinger method for Nylon 12 and compared with values reported previously for Nylon 6,6 and Nylon 11. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Effect of ,-nucleating agents on crystallization and melting behavior of isotactic polypropyleneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Wenchang Xiao Abstract Two kinds of ,-nucleating agents, named a rare earth complex (WBG) and a N,N,-dicyclohexylterephthalamide (TMB5), were introduced into isotactic polypropylene (iPP), and their effect on crystallization and melting behavior of iPP was comparatively investigated. Wide angle X-ray diffraction measurements revealed that both the two additives were highly effective in inducing , modification. At their respective optimum concentrations of 0.08 wt % for WBG and 0.06 wt % for TMB5, the relative amount of ,-form calculated by Turner-Jones equation both exceeds 92%. However, the isothermal crystallization kinetics investigated by differential scanning calorimetry demonstrated that WBG had more pronounced effect than TMB5 in accelerating the overall crystallization rate. The Lauritzen,Hoffman theory analysis also revealed that WBG was more effective not only in increasing the nucleus number but also in accelerating the growth rate of crystallization. After completing isothermal crystallization process, the subsequent melting behavior examination suggested that the addition of WBG expanded the upper limit temperature of forming , modification, and therefore was more effective in delaying the ,-, transformation than TMB5. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Isothermal Crystallization Kinetics of Poly(, -caprolactone) with Tetramethyl Polycarbonate and Poly(styrene- co -acrylonitrile) Blends Using Broadband Dielectric SpectroscopyMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2006Samy A. Madbouly Abstract Summary: Phase behavior and isothermal crystallization kinetics of poly(, -caprolactone) (PCL) blends with tetramethyl polycarbonate (TMPC) and poly(styrene- co -acrylonitrile) with 27.5 wt.-% acrylonitrile content have been investigated using broadband dielectric spectroscopy and differential scanning calorimeter. An LCST-type phase diagram has been observed for PCL/SAN blend while all the different blend compositions of PCL/TMPC were optically clear without any phase separation structure even at high temperatures up to 300,°C. The composition dependence of Tgs for both blends has been well described by the Gordon-Taylor equation. The phase diagram of PCL/SAN was theoretically calculated using the Flory-Huggins equation considering that the interaction parameter is temperature and composition dependent. The equilibrium melting point of PCL depressed in the blend and the magnitude of the depression was found to be composition dependent. The interaction parameters of PCL with TMPC and SAN could not be calculated from the melting point depression based on Nishi-Wang approach. The isothermal crystallization kinetics of PCL and in different blends was also investigated as a function of crystallization temperature using broadband dielectric spectroscopy. For pure PCL the rate of crystallization was found to be crystallization temperature (Tc) dependent, i.e., the higher the Tc, the lower the crystallization rate. The crystallization kinetics of PCL/TMPC blend was much slower than that of PCL/SAN at a constant crystallization temperature. This behavior was attributed to the fact that PCL is highly interacted with TMPC than SAN and consequently the stronger the interaction the higher the depression in the crystallization kinetics. It was also attributed to the different values of Tg of TMPC (191,°C) and SAN (100,°C); therefore, the tendency for crystallization decreases upon increasing the Tg of the amorphous component in the blend. The analysis of the isothermal crystallization kinetics was carried out using the theoretical approach of Avrami. The value of Avrami exponent was almost constant in the pure state and in the blends indicating that blending simply retarded the crystallization rate without affecting the crystallization mechanism. Dielectric constant, ,,, of pure PCL, blends of PCL/TMPC,=,80/20 and PCL/SAN,=,80/20 as a function of crystallization time at 47,°C and 1 kHz. [source] Effect of CO2 on crystallization kinetics of poly(ethylene terephthalate)POLYMER ENGINEERING & SCIENCE, Issue 2 2003Mitsuko Takada The effect of CO2 on the isothermal crystallization kinetics of poly(ethylene terephthalate), PET, was investigated using a high-pressure differential scanning calorimeter (DSC), which performed calorimetric measurements while keeping the polymer in contact with presurized CO2. It was found that the crystallization rate followed the Avrami equation with values of the crystallization kinetic constant dependent on the crystallization temperature and concentration of CO2 in PET. The presence of CO2 in the PET increased its overall crystallization rate. CO2 also decreased the glass transition temperature, Tg, and the melting temperature, Tm. As a result, the observed changes in crystallization rate caused by CO2 can be qualitatively predicted from the magnitude of Tg depression and that of the equilibrium melting temperature, Tm0. [source] | ||||||||||