Influence of lamellar thickness on the transformation in isotactic polybutylene-1/carbon nanotube nanocomposites

Probing the transformation from crystalline form II with 11/3 helical structure to form I with 3/1 helical structure in PB-1 and its nanocomposites is of great importance in both scientific fields and commercial applications. The influence of lamellar thickness on the transformation from form II to form I in isotactic polybutylene-1 (PB-1)/ carbon nanotube (CNT) nanocomposites was investigated by differential scanning calorimetry (DSC), polarized optical microscope (POM) and small-angle X-ray scattering (SAXS) techniques. The crystallization kinetics of PB-1/CNT nanocomposites at different isothermal temperatures (Tc) indicates that CNT significantly accelerates the nucleation and growth of form II, acting as heterogeneous nucleating agent. However, the influence of CNT on the form II-I transformation strongly relies on the lamellar thickness formed at different Tc, verified by the change of melting points (Tm) and the SAXS results of form I. The addition of CNT accelerates the transformation and elevates the Tm of completed form I when the Tc is lower than ∼ 88◦C, while slows the transformation and slightly decreases the Tm when the Tc is higher than ∼ 88◦C. This is probably due to the fact that the incorporation of CNT facilitates the increase of lamellar thickness of form II formed at lower Tc but decreases the lamellar thickness of form II formed at higher Tc. Our study illustrates that the lamellar thickness is one of the key points to determine the transformation from form II to form I in PB-1.