Melting and crystallization of linear polyethylene (HDPE, high-density polyethylene) and its blends with poly(ethylene-α-olefin) copolymers has been the subject of many studies in recent years. The final properties of such polymers depend on the volume fraction of the crystalline domains as well as on their size and structure. During crystallization from quiescent melt these polymers usually form thin lamellar crystals. These lamellae are arranged in stacks, with layers of amorphous material being inserted between the crystalline lamellae. Because amorphous and crystalline layers in lamellar stacks exhibit different electron densities, the small-angle X-ray scattering (SAXS) patterns and the derived correlation functions are commonly used in polymer morphology characterization. These functions allow for determination the values of the long period (L_P), the crystalline and amorphous layer thickness (l_C and l_A respectively) and the local volume fraction crystallinity (Φ_L). Φ_L can be obtained from the correlation functions in two different ways. Both methods have their own prerequisites and limitations. Moreover, application of the correlation functions requires subtraction of contribution due to electron density fluctuations and realization a number of corrections of measured intensities.

The present paper shows all steps necessary in the evolution of the correlation function and the extraction of structural data from this function. In the application part of this study the correlation functions derived from time-resolved SAXS experiments using synchrotron radiation are used to describe the structural changes of blends of HDPE and a homogeneous copolymer of ethene-1-octene. The structural changes were observed during cooling at a rate 10^o C per minute from the melt to room temperature and during subsequent heating at the same rate from room temperature to melting temperature.

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