Crystallization kinetics and melting behavior of metallocene short-chain branched polyethylene fractions

被引:28
作者
Chiu, FC [1 ]
Fu, Q
Peng, Y
Shih, HH
机构
[1] Chang Gung Univ, Dept Chem & Mat Engn, Tao Yuan 333, Taiwan
[2] Sichuan Univ, Dept Polymer Sci & Mat, Sichuan 610065, Peoples R China
[3] Ind Technol Res Inst, Union Chem Labs, Hsinchu 300, Taiwan
关键词
metallocene catalysts; polyethylene; crystallization; morphology;
D O I
10.1002/polb.10094
中图分类号
O63 [高分子化学(高聚物)];
学科分类号
070305 ; 080501 ; 081704 ;
摘要
Metallocene polyethylene (mPE) fractions are recognized as being more homogeneous with respect to short-chain branch (SCB) distribution as compared with unfractionated mPEs. Differential scanning calorimetry and polarized optical microscopy (POM) were used to study the influences of SCB content on the crystallization kinetics, melting behavior, and crystal morphology of four butyl-branched mPE fractions. The parent mPE of the studied fractions was also investigated for comparative purposes. mPE fractions showed a much simpler crystallization behavior as compared with their parent mPE during the cooling experiments. The Ozawa equation was successfully used to analyze the nonisothermal crystallization kinetics of the fractions. The Ozawa exponent n decreased from about 3.5 to 2 as the temperature declined for each fraction, indicating the crystal-growth geometry changed from three-dimensional to two-dimensional. For isothermal crystallization, the fraction with a lesser SCB content exhibited a higher crystallization temperature (T-c) window. The results from the Avrami equation analysis showed the exponent n values were around 3 (with minor variation), which implied that the crystal-growth geometry is pseudo-three-dimensional. Both of the activation energies for nonisothermal and isothermal crystallization were determined for each fraction with Kissinger and Arrhenius-type equations, respectively. Double melting peaks were observed for both nonisothermally or isothermally crystallized specimens. The high-melting peak was confirmed induced via the annealing effect during heating scans. The Hoffman-Weeks plot was inapplicable in obtaining the equilibrium melting temperature (T(m)degrees) for each fraction. The relationship between T-c and T-m for the fractions is approximately T-m = T-c (degreesC) + 8.3. The POM results indicated that the crystals of parent or fractions formed under cooling conditions did not exhibit the typical spherulitic morphology as a result of the high SCB content. (C) 2002 John Wiley Sons, Inc.
引用
收藏
页码:325 / 337
页数:13
相关论文
共 43 条
[1]   INFLUENCE OF MOLECULAR-WEIGHT ON THE MELTING AND PHASE-STRUCTURE OF RANDOM COPOLYMERS OF ETHYLENE [J].
ALAMO, RG ;
CHAN, EKM ;
MANDELKERN, L ;
VOIGTMARTIN, IG .
MACROMOLECULES, 1992, 25 (24) :6381-6394
[2]   Kinetics of phase change I - General theory [J].
Avrami, M .
JOURNAL OF CHEMICAL PHYSICS, 1939, 7 (12) :1103-1112
[3]  
AVRAMI M, 1941, J CHEM PHYS, V9, P17
[4]  
Avrami M., 1940, J CHEM PHYS, V8, P212
[5]  
Bensason S, 1996, J POLYM SCI POL PHYS, V34, P1301, DOI 10.1002/(SICI)1099-0488(199605)34:7<1301::AID-POLB12>3.0.CO
[6]  
2-E
[8]   Non-isothermal crystallization and multiple melting behavior of syndiotactic polystyrene - Pre-melting temperature effects [J].
Chiu, FC ;
Peng, CG ;
Fu, Q .
POLYMER ENGINEERING AND SCIENCE, 2000, 40 (11) :2397-2406
[9]   Structural and morphological inhomogeneity of short-chain branched polyethylenes in multiple-step crystallization [J].
Chiu, FC ;
Wang, Q ;
Fu, Q ;
Honigfort, P ;
Cheng, SZD ;
Hsiao, BS ;
Yeh, FJ ;
Keating, MY ;
Hsieh, ET ;
Tso, CC .
JOURNAL OF MACROMOLECULAR SCIENCE-PHYSICS, 2000, B39 (03) :317-331
[10]  
CLAS SD, 1987, J POLYM SCI A, V25, P3150