Structural Change by Annealing

The higher ductility of polyethylene nascent powders suggested the coexistence of less entangled amorphous phases located between the crystalline and amorphous phases [26,47]. This arises from the nonequilibrium crystallization during polymerization. Therefore, the polymerization temperature affects the structure and the morphology of the nascent powder. 

120 °C [46]. At 7], = 80 C (Fig. 8.12a), the typical lamellar morphology of an MGC or SGC is not observed. Rather, the crystalline domains of 15 nm are distributed throughout the powder. At 100 C, the crystalline and amorphous phases are aggregated and the crystalline domain size increases (Fig. 8.12b). Above 120 °C, the lamellar structure appeared (Fig. 8.12c). 

From H-NMR analysis, the crystallinity decreases and exhibits a minimum value around 60 °C, then increases as the temperature increases. These decrement and subsequent increment in crystallinity coincide with those of the reflection intensities observed for the variable-temperature WAXD profile. Heating produces maximum crystallinity at about 120 °C followed by the abmpt drops in crystallinity, which is attributed to the sample melting. These temperatures of the maximum crystallinity coincide well with the temperatures at which the lamellae appear in the TEM observations. These results indicate that the lamellar formation originates from melt recrystallization during annealing. 

---