Characterization of the dual crystal population in an isothermally crystallized homogeneous ethylene-1-octene copolymer

Abstract

The melting of a homogeneous ethylene-1-octene copolymer after isothermal crystallization is discussed based on DSC and time-resolved SALS, SAXS and WAXD data. Two melting peaks appear in DSC suggesting the presence of two crystal fractions. All crystals grow in a lamellar habit and there is no evidence for fringed micellar or isolated block-like crystals. The high melting fraction crystallizes while segregating comonomer-rich parts into separate regions where in a later stage the low melting fraction crystallizes. The data support the view of lamellae that grow via the secondary nucleation of crystalline blocks from a preexisting layer-like mesomorphic phase with preservation of the mesomorphic layer thickness. The stability of these blocks increases due to sintering, forming lamellae that melt slightly above the crystallization temperature. The high melting fraction is generated from those lamellae that are able to reduce the crystalline-amorphous interfacial tension.