Effect of isotacticity distribution on crystallization kinetics of polypropylene

The crystallization kinetics of isotactic polypropylene (iPP) depends not only on the undercooling but also on its microstructure characteristics. In this paper the effect of isotacticity distribution on the isothermal kinetics of iPPs in the crystallization regime III was examined by differential scanning calorimetry. The microstructure features of two commercial film grade iPPs were characterized with temperature rising elution fractionation and size exclusion chromatography. The results indicated that, although the overall isotacticities and molecular weights of two iPPs were similar, their isothermal crystallization kinetics displayed marked differences due to the disparity in isotacticity distributions. With increasing molecular weight of components containing crystallizable units, the isothermal crystallization rate exhibited a higher temperature dependence. When the isotactic defects in polypropylene chains increase with the molecular weight of components, both the fold surface free energy σ_e and the work of chain folding q decreases, in spite of the higher molecular weight. © 2002 Society of Chemical Industry     

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 and nonisothermal crystallization kinetics of nylon-11

Analysis of the isothermal, and nonisothermal crystallization kinetics of Nylon-11 is carried out using differential scanning calorimetry. The Avrami equation and that modified by Jeziorny can describe the primary stage of isothermal and nonisothermal crystallization of Nylon-11. In the isothermal crystallization process, the mechanism of spherulitic nucleation and growth are discussed; the lateral and folding surface free energies determined from the Lauritzen–Hoffman equation are ς = 10.68 erg/cm² and ς_e = 110.62 erg/cm²; and the work of chain folding q = 7.61 Kcal/mol. In the nonisothermal crystallization process, Ozawa analysis failed to describe the crystallization behavior of Nylon-11. Combining the Avrami and Ozawa equations, we obtain a new and convenient method to analyze the nonisothermal crystallization kinetics of Nylon-11; in the meantime, the activation energies are determined to be −394.56 and 328.37 KJ/mol in isothermal and nonisothermal crystallization process from the Arrhonius form and the Kissinger method. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2371–2380, 1998     

稀土荧光PA6等温结晶动力学的研究

采用差示扫描量热法研究了稀土荧光PA6的等温结晶过程。结果表明,PA6的结晶速率随着荧光粉含量的增加而增加,稀土荧光PA6的Avrami指数随着结晶温度的增加而增加。稀土荧光PA6结晶时的表观活化能随着荧光粉含量的增加而增加,荧光粉的加入对PA6链段的运动起阻碍作用。     

高流动抗冲PP的结晶特性及结晶动力学

采用X射线衍射仪、差示扫描量热仪和偏光显微镜研究了5种高流动抗冲聚丙烯(PP)树脂的结晶特性和结晶动力学。结果发现：国产试样的结晶度与晶粒尺寸明显不同于进口试样;在等温结晶条件下。总结晶速率常数和总结晶速率随结晶温度的增加而下降,而结晶半值期增加;在所研究的温度范围内。所有试样的Avrami指数基本为2～3的非整数;在133℃以下,5^#试样的球晶生长速率明显高于其他试样,但在相同结晶温度时,国产试样的总结晶速率大于进口试样。5种试样在抗冲击性能上的差异归因于它们在结晶特性和结晶动力学方面的不同。     

Studies on simultaneous crystallization of polypropylene/nylon 12 blends

The effect of the morphology of polypropylene (PP)/nylon 12 (PA12) blends on their crystallization behaviour is studied using differential scanning calorimetry and scanning electron microscopy. In PP/ maleated polypropylene (PP-MA)/PA12=65/10/25 blend, simultaneous phase (PA12) is smaller than 0.5 μm, PP crystallizes first and its crystals induce the crystallization of PA12. When some of the PA12 particles are larger than 0.5 μm, this part of PA12 crystallizes first. Then this part of the PA12 crystals induces the crystallization of PP, and PP crystals induced the crystallization of PA12 fine droplets in turn.     

Study on the viscosity of polypropylene composites filled with different size and size distribution CaCO3

Two kinds of different size calcium carbonates are blended and filled into polypropylene in 30 wt%. The melting viscosity of PP composites samples is measured by capillary extrusion rheometer at 230°C. The results show that the melt viscosity of PP composites evidently decreased when that was filled with the blending 325 and 1,500 mesh CaCO₃ and the 1,500 mesh proportion in fillers was from 20 to 60 wt%. The viscosity in the low shear velocity decreased more than that in the high shear velocity. The shear viscosity of single filler and filler samples with the size distribution at the different temperature was studied by capillary extrusion rheometer. The results show that the flow activation energy and the flow activation entropy of composites filled with the size distribution filler increased. The change of the flow activation entropy and the model of the efficient arrangement of the structure are used to explain the phenomenon in melting viscosity decrease of PP filled with the size distribution fillers. A structural model of composites that filled with the size distribution fillers was set up. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

不同二氧化钛含量的PET非等温结晶动力学研究

用DSC、非等温结晶动力学方法研究了PET切片中不同二氧化钛含量对其结晶性能的影响。结果表明:适量的二氧化钛在聚合过程中起成核剂作用,随着切片中二氧化钛含量的增加,聚合物结晶速度加快,质量分数超过0.33％时,对熔体成核结晶有阻滞作用。结晶能力在冷却速率和二氧化钛含量变化时基本不变,说明二氧化钛的加入对聚合物的结晶能力影响不大。不同二氧化钛含量不同冷却速率的Avrami指数平均值都在4.0以上,可以认为结晶以均相成核为主,三维生长。     

PBT非等温结晶动力学

用差示扫描量热法研究聚对苯二甲酸丁二酯（PBT）的非等温结晶动力学，并分别用Ozawa,Jeziorny和考虑综合因素法来处理PBT的非等温结晶数据。结果表明，PBT非等温结晶过程与Ozawa动力学方程相吻合，但不符合用Jeziorny方法处理的Avrami动力学方程；综合考虑温度和结晶程度对聚合物结晶速度的影响。PBT非等温结晶过程符合结晶动力学方程。     

Quantitative estimation of crystallization kinetics in GeGaS and Au-doped GeGaS glass-ceramics

Ge_26.7Ga₈S_65.3 (GGS) and 0.1% Au-doped Ge_26.7Ga₈S_65.3 (GGS-Au) glasses were prepared and annealed at a temperature that is 20 K higher than their respective glass transition temperature in order to create chalcogenide glass-ceramics. X-ray diffraction results showed that, thermal annealing can induce large amount of the crystal growth in the pure glass but this can be significantly suppressed by Au doping in the glass, which is in agreement with the previous results. We further employed various calorimetric methods, together with Mauro-Yue-Ellison-Gupta-Allan viscosity model, to investigate their crystallization kinetics. The crystal growth rate at annealing temperature of 723 K was quantitatively deduced to be 2.5 × 10⁻⁸ μm/s in Au-doped GGS, which is about 20 times slower than that in the pure GGS with a growth rate of 4.7 × 10⁻⁷ μm/s.     

聚苯硫醚的等温结晶动力学

采用光学解偏振法结晶速率仪研究了聚苯硫醚(PPS)的等温结晶动力学.结果表明:PPS的结晶速率随结晶温度的升高,先增大后减小,并在160℃左右达到最大结晶速率,约为0.471 7 s-1.PPS的Avrami指数为2.20～2.93,表明PPS是以异相成核或非热成核的方式三维生长形成球状结晶.在偏光显微镜放大400倍的...     

Isothermal and nonisothermal melt‐crystallization kinetics of syndiotactic polystyrene

Analyses of the isothermal and nonisothermal melt kinetics for syndiotactic polystyrene have been performed with differential scanning calorimetry, and several kinetic analyses have been used to describe the crystallization process. The regime II→III transition, at a crystallization temperature of 239°, is found. The values of the nucleation parameter K_g for regimes II and III are estimated. The lateral‐surface free energy, σ = 3.24 erg cm^?2, the fold‐surface free energy, σ_e = 52.3 ± 4.2 erg cm^?2, and the average work of chain folding, q = 4.49 ± 0.38 kcal/mol, are determined with the (040) plane assumed to be the growth plane. The observed crystallization characteristics of syndiotactic polystyrene are compared with those of isotactic polystyrene. The activation energies of isothermal and nonisothermal melt crystallization are determined to be ΔE = ?830.7 kJ/mol and ΔE = ?315.9 kJ/mol, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2528–2538, 2002     

纳米Al_2O_3改性聚丙烯的非等温结晶动力学

采用差示扫描量热法研究了聚丙烯(PP)及PP/纳米Al_2O_3复合材料的非等温结晶动力学。结果表明:纳米Al_2O_3有异相成核的作用,使PP的结晶峰温升高;PP的半结晶时间随纳米Al_2O_3含量增大而减小;纳米粒子的填充使PP的结晶活化能(△E)增大,含纳米Al_2O_3质量分数为2%的PP的△E最大。     

Nonisothermal and isothermal crystallization kinetics of nylon‐12

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 (σ) 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     

小本体聚丙烯及其接枝丙烯酰胺的非等温结晶动力学

采用DSC方法测试了小本体聚丙烯（PP）及其接枝丙烯酰胺（PP-g-AM）非等温结晶过程的释热情况,并对两组实验数据分别运用Jeziorny法和Mo法进行了处理和比较.结果表明,两种方法均可准确地描述PP及PP-g-AM的非等温结晶过程.PP接枝前后Avrami指数n无明显改变,表明两者结晶机理基本相同;由Jeziorny法得到接枝产物的校正晶体增长速率常数Z_c略大于纯PP的Z_c;由Mo法计算得出,PP-g-AM的F(T)值略小于纯PP的F（T）,表明接枝物的相对结晶速率略大于纯PP的相对结晶速率.     

Effect of silicon dioxide on crystallization and melting behavior of polypropylene

The crystallization and melting behavior of isotactic polypropylene (iPP) and polypropylene copolymer (co‐PP) containing silicon dioxide (SiO₂) were investigated by differential scanning calorimeter (DSC). SiO₂ had a heterogenous nucleating effect on iPP, leading to a moderate increase in the crystallization temperature and a decrease in the half crystallization time. However, SiO₂ decreased the crystallization temperature and prolonged the half crystallization time of co‐PP. A modified Avrami theory was successfully used to well describe the early stages of nonisothermal crystallization of iPP, co‐PP, and their composites. SiO₂ exhibited high nucleation activity for iPP, but showed little nucleation activity for co‐PP and even restrained nucleation. The iPP/SiO₂ composite had higher activation energy of crystal growth than iPP, indicating the difficulty of crystal growth of the composite. The co‐PP/SiO₂ composite had lower activation energy than co‐PP, indicating the ease of crystal growth of the composite. Crystallization rates of iPP, co‐PP, and their composites depended on the nucleation. Because of its high rate of nucleation, the iPP/SiO₂ composite had higher crystallization rate than iPP. Because of its low rate of nucleation, the co‐PP/SiO₂ composite had lower crystallization rate than co‐PP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1889–1898, 2006     

Influence of crystallization conditions on crystal morphology and size of CaCO3 and their effect on pressure filtration

The temperature, supersaturation, seeding procedure, stirring speed and other parameters were varied in crystallization experiments of calcium carbonate performed in aqueous solutions to control size, particle size distribution and morphology of the particles. Particle size information was obtained by focused beam reflectance measurements and the Coulter Counter Multisizer. Crystals of CaCO₃ could be crystallized as spherical polycrystalline particles of the vaterite polymorph, needle‐like crystals of aragonite and both cube‐like and novel plate‐like crystals of calcite. Filtration experiments for calcium carbonate, performed at a constant pressure difference of 2 bar, show that spherical particles with a larger size show better filterability and that spheres with a wider size distribution, as a result of high supersaturation and nucleation, give higher average cake resistance values. Comparing different particle morphologies, plate‐like crystals and needle‐like crystals show worse filterability than spherical particles and cube‐like particles. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Nonisothermal crystallization kinetics and morphology of self‐seeded syndiotactic 1,2‐polybutadiene

Subsequent melting behavior after isothermal crystallization at different temperatures from the isotropic melt and nonisothermal crystallization kinetics and morphology of partially melting sPB were carried out by differential scanning calorimetry (DSC), polarized light microscopy (POM), respectively. Triple melting‐endothermic peaks were observed for the polymer first isothermally crystallized at temperatures ranging from 141 to 149°C, respectively, and then followed by cooling at 10°C/min to 70°C. Comparing with the nonisothermal crystallization from the isotropic melt, the nonisothermal crystallization for the partially melting sPB characterized the increased onset crystallization temperature, and the sizes of spherulites became smaller and more uniform. The Tobin, Avrami, Ozawa, and the combination of Avrami and Ozawa equations were applied to describe the kinetics of the nonisothermal process. Both of the Tobin and the Avrami crystallization rate parameters (K_T and K_A, respectively) were found to increase with increase in the cooling rate. The parameter F(T) for the combination of Avrami and Ozawa equations increases with increasing relative crystallinity. The Ziabicki's kinetic crytallizability index G_Z for the partially melting sPB was found to be 3.14. The effective energy barrier Δ? describing the nonisothermal crystallization of partially melting sPB was evaluated by the differential isoconversional method of Friedman and was found to increase with an increase in the relative crystallinity. At the same time, Hoffman‐Lauritzen parameters (U and K_g) are evaluated and analyzed from the nonisothermal crystallization data by the combination of isoconversional approach and Hoffman‐Lauritzen theory. The K_g value obtained from DSC technique was found to be in good agreement with that obtained from POM technique. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1479–1491, 2006     

Non‐isothermal crystallization kinetics of poly(L‐lactide)

The non‐isothermal crystallization kinetics of poly( L ‐lactide) (PLLA) in comparison with a polylactide stereocopolymer (PLA₉₈) containing 98% L ‐lactyl and 2% D ‐lactyl units were investigated using differential scanning calorimetry to examine the effect of the configurational structure. Avrami, Ozawa and Liu models were applied to describe the crystallization process. The Avrami analysis exhibited two stages in non‐isothermal crystallization, while the Ozawa and Liu models did not successfully describe the crystallization behaviour. The activation energy was calculated with Kissinger's method. The energy barrier was found to be the same for PLLA and PLA₉₈ with a value of 126 kJ mol^?1. Copyright © 2010 Society of Chemical Industry     

PA1212的结晶动力学研究

采用DSC方法研究了PA1212的非等温和等温结晶动力学。Avrami方程可以适用PA1212的等温结晶过程,其Avrami指数为2．51～2．87,等温结晶活化能为-131．9 kJ/mol;在非等温结晶过程中,结晶速率随降温速率的增大而提高,综合利用Avrami方程和Ozawa方程得到Avrami指数与Ozawa指数的比值为1．31～1．49,非等温结晶活化能为-87．96 kJ/mol。结果表明,与其他聚酰胺相比,PA1212较容易结晶。