Morphology and Crystallization Kinetics of Melt Miscible Polyolefin Blends

Abstract

Blends of copolymers of ethylene/hexene (9 CH3/1 000 C) and ethylene/butene (77 CH3/1 000 C) synthesized with metallocene catalysts were prepared by co‐precipitation from solution. A phase diagram for this blend had been obtained in a preceding work, where the blends were found to be miscible in the melt with a characteristic upper critical solution temperature (UCST). In this work, the successive self‐nucleation and annealing (SSA) thermal fractionation method revealed that both pure copolymers, even though they had been prepared by metallocene catalysis, displayed a very broad distribution of short chain branching. The thermal behavior of the pure copolymers and their blends revealed that co‐crystallization effects were present within each phase and that molecular fractionation during crystallization can prevail when the materials are slow cooled from the melt. A crystallization kinetics study was performed by differential scanning calorimetry (DSC) and it revealed a strong competition between crystallization and phase segregation. Upon cooling from a one phase melt, phase segregation precedes crystallization if the crystallization temperature (Tc) is high. On the other hand when low crystallization temperatures are employed, the amount of phase segregation that can be achieved before crystallization is limited. Transmission electron microscopy (TEM) allowed the observation of the lamellar morphology and their aggregation state. In specially prepared samples, the relative lamellar frequency of isothermally crystallized material was employed to ascertain whether the blend under consideration was within the one or the two phase region of the blends phase diagram.Crystallization half‐time for isothermally crystallized PEB/PEH blends quenched to the crystallization temperature from 170 °C.magnified imageCrystallization half‐time for isothermally crystallized PEB/PEH blends quenched to the crystallization temperature from 170 °C.

The effect of the mixed external donors on the sequence length distribution of polypropylene

“…Generally, it is believed that lamellae thickness is related to the isotactic sequence distribution of polymer. There is a good correspondence between the SSA and the TREF techniques 39. The results of SSA are coincident with the results of high‐resolution 13 C‐NMR, TREF, and xylene solvent fractionation, but SSA can provide important quantitative information about the lamellar thickness distribution 29, 32.…”

“…There is a good correspondence between the SSA and the TREF techniques. 39 The results of SSA are coincident with the results of high-resolution 13 C-NMR, TREF, and xylene solvent fractionation, but SSA can provide important quantitative information about the lamellar thickness distribution. 29,32 With the increase of separation temperature, the component separated by TREF shows higher melting temperature and longer crystalline sequence length after SSA treatment.…”

Effect of small amount of ultra high molecular weight component on the crystallization behaviors of bimodal high density polyethylene

“…This technique is based on the sequential application of self-nucleation and annealing steps to a polymer sample originally devised by Fillon et al [32,44,45] and has been widely used to analyze the chain structures of semi-crystallized polymers such as PE and PP [46][47][48][49][50][51]. For a SSA fractionated polymer sample, the final DSC heating run will reveal a distribution of melting points induced by thermal treatment indicating the heterogeneous nature of the chain structures of the polymer.…”

Thermal fractionation and properties of different polyethylene/wax blends

“…[14][15][16][17][18][19][20][21][22] Mu †ller and Arnal 23 summarized these results and they observed that, in thermal fractionation, the polymer chains are never physically separated, and therefore the technique is sensitive to linear and uninterrupted chain sequences. This implies that thermal fractionation is equally sensitive to both intra-and intermolecular defects.…”