Isothermal crystallization kinetics of polypropylene by differential scanning calorimetry. I. Experimental conditions

Reliable isothermal crystallization kinetic studies can be achieved by differential scanning calorimetric techniques only under restricted conditions. In the case of isotactic polypropylene, our results indicate that those conditions are met in the range of 3°C below the isothermal crystallization temperature T_c. Experimentally, it is only in this range when the complete crystallization peak can be registered by the DSC and depicted in a thermogram. Just around this temperature interval, the Avrami exponent n = 3 for bulk crystallization, whereas for any other test the isothermal temperature T_it, nonisothermal conditions prevail and the Avrami exponent deviates from the expected value. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 970–978, 2004     

Isothermal crystallization kinetics of high‐flow nylon 6 by differential scanning calorimetry

The isothermal crystallization kinetics have been investigated with differential scanning calorimetry for high‐flow nylon 6, which was prepared with the mother salt of polyamidoamine dendrimers and p‐phthalic acid, an end‐capping agent, and ε‐caprolactam by in situ polymerization. The Avrami equation has been adopted to study the crystallization kinetics. In comparison with pure nylon 6, the high‐flow nylon 6 has a lower crystallization rate, which varies with the generation and content of polyamidoamine units in the nylon 6 matrix. The traditional analysis indicates that the values of the Avrami parameters calculated from the half‐time of crystallization might be more in agreement with the actual crystallization mechanism than the parameters determined from the Avrami plots. The Avrami exponents of the high‐flow nylon 6 range from 2.1 to 2.4, and this means that the crystallization of the high‐flow nylon 6 is a two‐dimensional growth process. The activation energies of the high‐flow nylon 6, which were determined by the Arrhenius method, range from ?293 to ?382 kJ/mol. The activation energies decrease with the increase in the generation of polyamidoamine units but increase with the increase in the content of polyamidoamine units in the nylon 6 matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Crystallization study on absorbable poly(p‐dioxanone) polymers by differential scanning calorimetry

An investigation was carried out on the crystallization behavior of p‐dioxanone polymers using differential scanning calorimetry (DSC). Kinetic analyses were performed on data collected primarily during isothermal crystallization. Isothermal data were treated within the framework of the classical Avrami equation. Using this approach, both the Avrami exponent, n, and the crystallization half‐time, t_1/2, were evaluated and their implications are discussed for each system studied. It is shown that a small change in the polymer's composition greatly affects the crystallization kinetics, as well as the crystallizability of the materials. Additionally, nonisothermal crystallization under controlled heating and cooling rates was explored. In the case of cooling from the melt, the Ozawa theory and the recently proposed Calculus method were employed to describe the nonisothermal crystallization kinetics. In view of our results, the validity of these two estimation techniques for determining important kinetic and morphological parameters is also discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 742–759, 2001     

Isothermal crystallization and chain mobility of poly(L-lactide)

Isothermal melt crystallization of poly(L-lactide) (PLLA) has been studied in the temperature range of 90 to 135°C. A maximum in crystallization kinetic was observed around 105°C. A transition from regime II to regime III is present around 115°C. The crystal morphology is a function of the degree of undercooling. At crystallization temperatures (T_c) below 105°C, further crystallization occurs upon heating; this behavior is not detected for T_c above 110°C. The analysis of the heat capacity increment at glass transition temperature (T_g) and of dielectric properties of PLLA indicates the presence of a fraction of the amorphous phase which does not relax at the T_g, and the amount of this so-called rigid amorphous phase is a function of T_c. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 911–919, 1997     

聚丙烯/超支化聚酯酰胺共混物的等温结晶动力学

将超支化聚酯酰胺(HBPEA)与聚丙烯(PP)挤出共混,得到PP/HBPEA共混物。利用差示扫描量热法研究了HBPEA改性PP的结晶行为和等温结晶动力学。结果表明:Avrami方程适用于研究PP/HBPEA共混物的等温结晶动力学,Avrami指数为1.48~2.11,晶体的生长方式为二维盘状方式。加入HBPEA可加快PP的结晶速率,在不同等温结晶温度条件下,HBPEA为0.4 phr时可使半结晶速率提高到纯PP的1.3~2.0倍。使用Hoffmann-Lauritizen理论计算了端表面自由能,发现加入HBPEA可降低垂直于分子链方向的界面自由能,促进PP链折叠,提高PP的结晶能力。     

Crystallization of polyformals: 1. Crystallization kinetics of poly(1,3-dioxolane)

Poly(1,3-dioxolane) fractions ranging in molecular weight from 8800 to 120 000 have been isothemally crystallized in the temperature range 25–41°C. From the dilatometric isotherms, the Avrami exponent is an integral number, 3, and is independent of temperature and molecular weight. The level of crystallinity is dependent on molecular weight and there is a change from ～55% for the highest molecular weight fraction to ～80% for the lowest molecular weight fraction. The overall crystallization rate temperature coefficient was studied using two dimensional nucleation theory and it was found that the interfacial free energies do not change with molecular weight. However, the usual plots are nonlinear in the whole range of crystallization temperatures. For the high crystallization temperatures the slope is about twice the low crystallization temperature slope, this change being related to a morphological transition.     

Effect of crystallization temperature on crystal modifications and crystallization kinetics of poly(L‐lactide)

The crystalline structure of poly(L ‐lactide) (PLLA) have been found to quite depend on the crystallization temperatures (T_cs), especially in the range of 100?120°C, which is usually used as the crystallization temperature for the industrial process of PLLA. The analysis of wide‐angle X‐ray diffraction and Fourier transformed infrared spectroscopy revealed that 110°C is a critical temperature for PLLA crystallization. At T_c < 110°C and T_c ≥ 110°C, the α′ and α crystals were mainly produced, respectively. Besides, the structural feature of the α′‐form was illustrated, and it was found that the α′‐form has the larger unit cell dimension than that of the α‐form. Moreover, the crystallization kinetics of the α′ and α crystals are different, resulting in the discontinuousness of the curves of spherulite radius growth rate (G) versus T_c and the half time in the melt‐crystallization (t_1/2) versus T_c investigated by Polarized optical microscope and Differential scanning calorimetry, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization of poly(butylene terephthalate)/poly(ethylene octene) blends: Isothermal crystallization

Poly(ethylene‐octene) (POE), maleic anhydride grafted poly(ethylene‐octene) (mPOE), and a mixture of POE and mPOE were added to poly(butylene terephthalate) (PBT) to prepare PBT/POE, PBT/mPOE, and PBT/mPOE/POE blends by a twin‐screw extruder. Observation by scanning electron microscopy revealed improved compatibility between PBT and POE in the presence of maleic anhydride groups. The melting behavior and isothermal crystallization kinetics of the blends were studied by wide‐angle X‐ray diffraction and differential scanning calorimeter; the kinetics data was delineated by kinetic models. The addition of POE or mPOE did not affect the melting behavior of PBT in samples quenched in water after blending in an extrude. Subsequent DSC scans of isothermally crystallized PBT and PBT blends exhibited two melting endotherms (T_mI and T_mII). T_mI was the fusion of the crystals grown by normal primary crystallization and T_mII was the melting peak of the most perfect crystals after reorganization. The dispersed second phase hindered the crystallization; on the other hand, the well dispersed phases with smaller size enhanced crystallization because of higher nucleation density. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

聚丁二酸丁二醇酯的等温结晶动力学研究

采用差示扫描量热仪(DSC)对聚丁二酸丁二醇酯(PBS)的等温结晶动力学进行了研究,并用Avrami方程对实验数据进行了量化分析。研究结果表明:在等温结晶时,PBS倾向于以均相成核的三维生长方式结晶,并通过偏光显微镜进行了验证;同时,随着结晶温度的升高,PBS的结晶速率常数K值下降,半结晶时间t1/2延长。     

Isothermal and nonisothermal crystallization of poly(aryl ether ketone ketone) with all‐para phenylene linkage

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     

含较高立构缺陷聚乳酸的非等温结晶动力学

用非等温结晶动力学研究了聚乳酸(PLA)的结晶行为,利用Hoffman-Weeks外推法以及Baur等提出的方程反推出PLA中的右旋组分摩尔分数为7.2%.较高的右旋组分摩尔分数是PLA结晶过程中成核速率低的主要因素.添加质量分数为2%滑石粉等成核剂后,PLA结晶速率没有明显提高;含10%滑石粉的PLA结晶速率略上升,...     

The use of differential scanning calorimetry to study polymer crystallization kinetics

A Tektronix-31 programmable calculator interfaced to a Perkin Elmer differential scanning calorimeter, model 2, substantially improves the accuracy of measuring the time-dependent development of the degree of crystallinity (× 10) and hence improves the quality of the rate data. Storing energy flow data at preset time intervals directly into the memory of the calculator improves the accuracy of the measurement of time, and enables the evaluation of the onset of crystallization and the baseline of the calorimeter initially. This substantially improves the measurement of the degree of crystallinity developing with time by integrating the energy flow data over the time interval from the onset of crystallization. Polyethylene samples are studied since their rate constants have a marked temperature dependence which enables the accuracy of the analytical procedure to be assessed. Primary and secondary crystallization processes are separated.     

Rigid amorphous phase and low temperature melting endotherm of poly(ethylene terephthalate) studied by modulated differential scanning calorimetry

The rigid amorphous phase, the low temperature melting endotherm, and their development with thermal treatment in poly(ethylene terephthalate) (PET) were investigated by means of modulated differential scanning calorimetry. The differential of the reversing heat capacity and nonreversing heat flow signals were used to analyze the behavior of the glass transition and the low temperature melting endotherm. With increasing annealing time, the increment of the heat capacity at the glass‐transition temperature decreased and the increment of heat capacity at the annealing temperature increased. It was suggested that the origin of the low temperature melting endotherm mainly resulted from the transition of the rigid amorphous fraction for the PET used. The glasslike transition of the rigid amorphous fraction occurred between the glass transition and melting. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2779–2785, 2001     

Isothermal crystallization kinetics of anhydrous sodium acetate nucleated poly(ethylene terephthalate)

Studies on the isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) nucleated with anhydrous sodium acetate were carried out. The nucleated agent had succeeded in promoting greater rates of crystallization in PET. A study of the melting behavior of the samples revealed that the nucleating agents promoted formation of thinner lamellae. The equilibrium melting temperature (T) of samples was determined using linear and nonlinear Hoffman Weeks procedure. The nonlinear Hoffman Week's procedure was found to be inapplicable in the current study. The Lauritzen‐Hoffman secondary nucleation theory was applied to determine the nucleation parameter (K_g), fold surface energy (σ_e), and work of chain folding (q). σ_e and q decreased on addition of nucleating agent. The approximate and exact form of the Lauritzen Z‐test was used to determine the operating regime. The operating regime was found to be primarily regime II for the range of temperatures studied. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Isothermal crystallization kinetics and spherulite morphologies of poly(lactic acid)/ethylene acrylate copolymer blends

Isothermal crystallization kinetics and spherulite morphologies of partially immiscible blends of poly(lactic acid) (PLA) and ethylene acrylate copolymer (EAC) were investigated by differential scanning calorimetry (DSC) and polarized optical microscopy. The DSC data obtained was analyzed using the Avrami equation. Crystallization kinetics of PLA from the melt was strongly influenced by the blend composition and the crystallization temperature. At a given crystallization temperature, the overall crystallization rate value was greater in the blends than in PLA suggesting that the presence of EAC enhanced crystallization of PLA. Polarized optical micrographs showed that the crystallization of PLA initially took place at the PLA/EAC interface. At high EAC content (>1 wt %), EAC domains acted as hindrance to crystallization reducing the overall crystallization rate of PLA in the blends. Based on the DSC analysis, the crystallization rate was maximum when PLA blend with 1 wt % EAC was isothermally crystallized at 103 °C. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45487.     

Isothermal and nonisothermal crystallization kinetics of a semicrystalline copolyterephthalamide based on poly(decamethylene terephthalamide)

The isothermal and nonisothermal crystallization kinetics of a semicrystalline copolyterephthalamide based on poly(decamethylene terephthalamide) (PA‐10T) was studied by differential scanning calorimetry. Several kinetic analyses were used to describe the crystallization process. The commonly used Avrami equation and the one modified by Jeziorny were used, respectively, to describe the primary stage of isothermal and nonisothermal crystallization. The Avrami exponent n was evaluated to be in the range of 2.36–2.67 for isothermal crystallization, and of 3.05–5.34 for nonisothermal crystallization. The Ozawa analysis failed to describe the nonisothermal crystallization behavior, whereas the Mo–Liu equation, a combination equation of Avrami and Ozawa formulas, successfully described the nonisothermal crystallization kinetics. In addition, the value of crystallization rate coefficient under nonisothermal crystallization conditions was calculated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 819–826, 2004     

Use of differential scanning calorimetry in measuring the thermal decomposition of mineral carbonates occurring in coal

Differential scanning calorimetry (d.s.c.) was used to measure in nitrogen the enthalpies of decomposition of mineral carbonates occurring in coal, namely magnesite, siderite, calcite, dolomite and ankerite. Measured values were compared with calculated values, and reasonable agreement was obtained provided that heat losses from the sample were minimized. In air, magnesite, dolomite, ankerite and calcite afforded large negative contributions to the calorific value of coals, whereas siderite produced a small positive calorific contribution.     

Nonisothermal crystallization kinetics of nucleated poly(ethylene terephthalate)

Studies of the nonisothermal crystallization kinetics of poly(ethylene terephthalate) nucleated with anhydrous sodium acetate were carried out. The chemical nucleating effect was investigated and confirmed with Fourier transform infrared and intrinsic viscosity measurements. The Avrami, Ozawa, and Liu models were used to describe the crystallization process. The rates of crystallization, which initially increased, decreased at higher loadings of the additive. The activation energy, calculated with Kissinger's method, was lower for nucleated samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The preparation of ultra narrow molecular weight distribution poly(ethylene glycol)s by fractional crystallization from solution

The preparation of very narrow molecular weight distribution poly(ethylene glycol) (PEG) was investigated by fractional crystallization from solution. Fractionation experiments were conducted from the solutions of 1500, 2000, and 3000 molecular weight PEG in n‐butanol/n‐heptane mixtures. Size Exclusion Chromatography and Differential Scanning Calorimetric studies were performed for the characterization of fractions prepared at different crystallization temperatures and times. By suitable choice of these experimental parameters it was possible to obtain PEG fractions with M_w/M_n ≤ 1.05. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1999–2005, 2001     

Crystallization behavior and isothermal crystallization kinetics of polylactide/polystyrene-b-polybutadiene-b-polystyrene blends compatibilized with poly(styrene-ran-methyl acrylate)

The morphology, non-isothermal and isothermal crystallization behavior, and spherulite growth of polylactide (PLA)/polystyrene-b-polybutadiene-b-polystyrene (SBS) blends were investigated in the presence of a poly(styrene-ran-methyl acrylate) (S–MA) compatibilizer synthesized using surfactant-free emulsion copolymerization. Scanning electron microscopy revealed that the SBS dispersed-phase became more uniform and refined as the amount of S–MA compatibilizer was increased from 0 to 3 wt%. Calorimetric characterization of the non-isothermal and isothermal crystallization behavior analyzed using Avrami theory shows that the SBS in PLA shows plasticization and dilution effects simultaneously. When the PLA matrix chains do not move easily and/or its effective crystallization time window is narrow, the plasticization effect of the SBS is more significant. However, when the PLA matrix chains move more easily and/or its crsytallization window is wide, the dilution effects effect of the SBS is more notable. After the addition of S–MA, the plasticization and dilution effects were enhanced.