Evaluation of the crystallization kinetics and melting of polypropylene and metallocene‐prepared polyethylene blends

Abstract

The kinetics of the isothermal crystallization of a polypropylene (PP) random copolymer containing 5 mol % ethylene, a metallocene linear low-density polyethylene (m-LLDPE) with 3.3 mol % hexene-1 as a comonomer, and three blends were studied with differential scanning calorimetry at temperatures sufficiently high to prevent any crystallization of m-LLDPE. The analysis was carried out with the Avrami equation. The overall crystallization rate and the equilibrium melting temperature of the PP copolymer decreased with increasing amounts of m-LLDPE in the blends. The former was attributed to the effect of m-LLDPE in reducing the number of primary nuclei, and the latter was attributed to a lowering of the fold surface energy due to the limited partial miscibility of the blend components.

The melting of poly ( l -lactic acid)

“…The melting of polymers is different from that of low molar mass materials in that melting generally occurs over a wider temperature range and is dependent on thermal history [1]. The presence of multiple melting endotherms is common and has been observed with many semicrystalline polymers, copolymers and blends [1][2][3][4]. A variety of effects have been invoked to explain the phenomenon, to the presence of more than one crystallographic form (polymorphism) [5], to the presence of melting/re-crystallisation and re-melting [6]; to changes in morphology [7], to lamellar thickening and crystal perfecting [8,9], to changes in orientation [10] and to the effect of molecular weight distribution [11].…”

Effects of reactive melt mixing on the morphology and thermal behavior of linear low‐density polyethylene/rubber blends

“…Although the Avrami equation was developed for studying the crystallization process in pure polymers, various articles describe the use of this equation for studying the crystallization behavior of polymer blends 16, 18, 26. However, here it was used merely as a fitting equation for DSC isothermal data of the blends; Z and n parameters, obtained with high correlation coefficients, should be considered as fitting parameters and compared.…”

“…The morphology was analyzed with transmission electron microscopy (TEM), and the obtained particle size distributions were compared; the thermal properties were determined with differential scanning calorimetry (DSC). The crystallization behavior, determined with DSC isothermal measurements, was analyzed on the basis of the Avrami equation17–19 to compare the primary composite constant rate of crystallization ( Z ) and exponent of time ( n ); the mechanical properties were determined by dynamic mechanical thermal analysis (DMTA).…”

The interrelationships between microstructure and melting, crystallization and thermal degradation behaviors of fractionated ethylene/1-butene copolymer

“…According to the Gibbs-Thomson relationship (Eq. 6), it is possible to determine the lamellae thickness (L c ) of different fractions [48,53,54]:…”