Insight on the striking influence of the chain architecture on promoting the exfoliation of clay in a polylactide matrix during the annealing process
The influence of the topological structure of polylactide (PLA) chains on the microstructure of PLA–organically modified clay (OMC) nanocomposites was studied. Here, an OMC with a hydroxyl group-containing modifier (I.34TCN) was used as the nanofiller. According to the results from the XRD and TEM measurements, the change in the dispersed states of the OMC with star-shaped PLA (PLA3-x) was totally different from that with linear PLA (PLA1-1) during annealing at high temperature. A transition from the intercalated to the exfoliated structure appeared in the simple PLA3-x/OMC mixture during the annealing process, but the intercalated structure was retained in the PLA1-1/OMC system. The enhanced exfoliation of the OMC in the PLA3-x matrix was attributed to the spatial limitation of the star-shaped PLA3-x, which made the intercalated interlayer swell. As a result, the concentration of PLA3-x chains within the layers of the OMC was lower than that of the outside bulk, and so, more PLA3-x chains diffused into the interlayers of the clay until the clay sheets separated (exfoliation state). Furthermore, the exfoliation extent of the OMC in the star-shaped PLA3-x/OMC composites strongly influenced the glass transition temperature (Tg) of star-shaped PLA3-x.