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

摘要: Metallocene polyethylene (mPE) fractions are recognized as being more homogeneous with respect to short-chain branch (SCB) distribution compared unfractionated mPEs. Differential scanning calorimetry and polarized optical microscopy (POM) were used study the influences of SCB content on crystallization kinetics, melting behavior, crystal morphology four butyl-branched mPE fractions. The parent studied was also investigated for comparative purposes, showed a much simpler behavior their during cooling experiments. Ozawa equation successfully analyze nonisothermal kinetics exponent n decreased from about 3.5 2 temperature declined each fraction, indicating crystal-growth geometry changed three-dimensional two-dimensional. For isothermal crystallization, fraction lesser exhibited higher (T c ) window. results Avrami analysis values around 3 (with minor variation), which implied that is pseudo-three-dimensional. Both activation energies determined Kissinger Arrhenius-type equations, respectively. Double peaks observed both nonisothermally or isothermally crystallized specimens. high-melting peak confirmed induced via annealing effect heating scans. Hoffman-Weeks plot inapplicable in obtaining equilibrium m °) fraction. relationship between T C , approximately = (°C) + 8.3. POM indicated crystals formed under conditions did not exhibit typical spherulitic result high content.