Influences of halloysite nanotubes on crystallisation behaviour of polylactide

Abstract

The aim of this study was to investigate influences of halloysite nanotubes (HNTs) on the (i) isothermal and (ii) non-isothermal crystallisation kinetics of polylactide (PLA) by differential scanning calorimetry (DSC) analyses, and (iii) crystallinity of injection moulded and then annealed specimens by DSC and X-ray diffraction (XRD) analyses. Nanocomposites were compounded using melt mixing technique via twin screw extrusion. Owing to basically very effective heterogeneous nucleation effect, addition of HNTs resulted in significant increases in the crystallinity of PLA under all three cases. Crystallisation time parameters and Avrami rate constants indicated that crystallisation rate increased under isothermal crystallisation, while it decreased under non-isothermal crystallisation due to the delayed conformational mobility of PLA chains by the physical barrier actions of HNTs. Avrami exponent also revealed that two-dimensional growth mechanism of crystallites transformed into three-dimensional growth during non-isothermal crystallisation, while there was no change during isothermal crystallisation. Crystallinity determinations of the injection moulded and then annealed specimens indicated that, the highest crystallinity degree of PLA, i.e. 47%, could be reached by the addition of only 1 wt-% HNT.