Promoting the dispersion of graphene and crystallization of poly (lactic acid) with a freezing-dried graphene/PEG masterbatch

For poly (lactic acid) (PLA) nanocomposites, improving the dispersion of nanofillers and promoting the crystallization rates of PLA matrix are crucial to the final properties. Here, we proposed a facile “freezing-dried masterbatch” strategy to fulfill the two goals simultaneously in the preparation of PLA/graphene composites. After graphene oxide (GO) sheets are dispersed in poly (ethylene glycol) (PEG) aqueous solution and hydrazine hydrate is added to transform GO sheets into graphene sheets, the resulting mixture was freezing-dried to get the masterbatch of PEG and graphene. By simply melt blending the masterbatch with pristine PLA, PLA composites with excellent mechanical properties and thermal stability are prepared. For example, with 0.25 wt % of graphene, the composite prepared using the freezing-dried masterbatch has a tensile stress of 61.6 MPa, a tensile modulus of 1256 MPa, and a toughness value of 4.86 MJ/m3. The values are respectively 50.9, 125.5, 200.0% higher than that of the control sample of PLA-PEG and 11.5, 25.5, 124.0% higher than that of PLA composite prepared by directly blending with 5 wt % PEG and 0.25 wt % graphene. Morphological observations and crystallization behavior investigations reveal that graphene shows well dispersion in PLA composites, and the crystallinity and crystallization rates of PLA are greatly improved, which may be the reason for the improved mechanical properties.