A Study On The Epitaxial Crystallization Of The Poly(L-lactide)/Isotactic Polypropylene System

The regulation of material structure is always a hot issue in the field of today's materials science. To meet the needs of practical applications with the structure regulation material is the main purpose of material science. Epitaxial crystallization as an important means of regulating the material structure has a very significant advantage. But the main mechanism of epitaxial crystallization has always been controversial. To address this issue we selected double helix epiphytic system poly(L-lactide) (PLLA)/isotactic polypropylene (iPP) to study the internal relations of epitaxial crystallization.We studied the epitaxial internal relation of the PLLA/iPP system by studying the epitaxial crystallization of PLLA on the highly oriented iPP film substrate. The highly oriented iPP film has a strong nuclear ability to the cold crystallization of PLLA, making it forming regular lamellae, which is significantly different from the spherulite morphology formed on the common glass or silicon substrates. However, the epitaxial crystallization in this system is not heteroepitaxy as predicted. There is no strict dimensional and orientational matching between PLLA and iPP. The interaction between the supercooled PLLA layer and the substrate crystalline layer that generates a layer of PLLA chains oriented at right angles to the iPP ones. From the much lesser density of the second population of lamellae, it is reasonable to consider that this population results from a PLLA/PLLA interaction:the oblique lamellae must, in some way, be the daughters of the initial orthogonal PLLA lamellae.In addition, after studying the melting recrystallization behavior of iPP in the PLLA/iPP blend stretch system, we found that highly oriented PLLA has a relatively strong induction to the crystallization of iPP from melt. The iPP crystals have strong orientation after recrystallization with the existence of the highly oriented PLLA crystals, making the iPP molecular chains parallel to the stretching direction. Since the epitaxial crystallization between PLLA and iPP is a kind of soft epitaxy, and there is not strict crystal structure match between PLLA and iPP, the relationship of the molecular chain alignment state between the two components in bulk before heattreatment has a relatively large impact on the iPP recrystallization behavior, resulting in this phenomenon, which is significant for the study of the mechanism of epitaxy.