Confined PEO crystallisation in immiscible PEO/PLLA blends

Abstract

The thermal and morphological properties of PEO/PLLA blends have been widely studied, and the kinetics of PLLA crystallisation have been very well described. However, their miscibility is still a subject of controversy and PEO crystallisation behaviour in these blends is not completely understood. In this paper, the miscibility of PEO/PLLA blends was studied over a wide molar range (5 to 163 kDa and 11 to 199 kDa, for PEO and PLLA, respectively). DSC, DMA, and POM results indicate that PEO/PLLA blends are immiscible over the entire composition range of the molar masses studied. Moreover, the PLLA content of the blends crystallises under cooling at a constant rate from melting to form a continuous crystalline phase, such as a crystal network, even for blends with low PLLA content. Therefore, the PEO phase is confined in the interlamellae and interspherulite regions and a confined and fractional type of crystallisation occurs as the density of the PLLA crystalline phase increases (with increasing PLLA content in the blends). XRD and SAXS data showed that both PLLA and PEO influence each other's crystallisation. While the presence of PEO induces PLLA crystallisation in the α-form, PLLA acts as a template for PEO crystallisation.