Miscibility and morphology of binary crystalline blends of poly(L-lactide) and poly(butylene adipate)

Abstract

Poly(L-lactide)/poly(butylene adipate) (PLLA/PBA) crystalline/crystalline blends with different weight ratios (from 90/10 to 20/80) were prepared using a solution blend method. According to the differential scanning calorimetry (DSC) results and the optical microscopy (OM) images, PLLA was partially miscible with PBA. The crystallization morphologies of the PLLA/PBA blends formed in a high-temperature region and in a low-temperature region were studied separately. In the high-temperature region, Maltese-cross spherulites, banded spherulites and branched structures were observed by changing the weight ratio and the thickness of the specimen. The distribution of PLLA and PBA in these morphologies was determined using polarized OM, which utilized a hot stage. Additionally, the thickness of the PLLA lamella, which was determined from the DSC results, decreased slightly with increasing PBA concentration. In the low-temperature region, the effect of PLLA on the morphologies of PBA was studied. In PBA-rich blends, the morphology of the PBA crystal was not significantly affected by PLLA. However, in PLLA-rich blends, PBA formed fragments because solid PLLA restricted the growth of the PBA crystal. The thickness of the PBA lamella, which was determined from the DSC results, decreased with increasing PLLA concentration. The morphology of PLLA/PBA crystalline/crystalline system reveals abundant morphologies in different crystallization condition. Neat PLLA and PBA usually show Maltese-cross spherulites. However, banded spherulites and branched structures of blends formed in high-temperature region in this work. In addition, fragments morphology is discovered in low-temperature region. These different morphologies are related to the changes of crystallization environment caused by crystalline/crystalline blending.