Preparation of hybrid composites of PLLA using GO/PEG masterbatch and their characterization

Nanocomposites of poly(ethylene glycol) (PEG) reinforced with graphene oxide (GO), prepared by drying their ultrasonically homogenized aqueous solution, were incorporated in poly(l-lactic acid) (PLLA) via melt extrusion. Raman spectroscopy revealed that the employed method increased GO’s structural defects due to exfoliation and allowed PEG to penetrate its layers. Hydrogen bonding interactions were identified in the hybrids by Fourier transform infrared spectroscopy (FTIR), whereas differential scanning calorimetry (DSC) tests showed that GO promoted PEG’s crystallization by increasing its crystallization temperature (Tc) and degree of crystallinity (Xc). The combination of nucleant and plasticizer in the hybrids increased PLLA’s Tc and melting temperature and a new band, associated with crystalline domains, appeared in their FTIR spectra. The Avrami kinetic model was implemented on DSC data to understand the isothermal crystallization behavior of PEG/PLLA blend, as well as of the system GO/PEG/PLLA. It was highlighted that GO is an effective nucleating agent for plasticized PLLA since, under the examined conditions, it enhances its crystallization rate and transforms the disk-like to sphere-like crystal formation and the two-dimensional to three-dimensional crystal growth. Furthermore, GO increased the crystallization activation energy values of plasticized PLLA due to segment transportation obstruction and transformed the double-melting peak into single after isothermal crystallization. Thermogravimetric analysis showed that GO did not enhance the heat resistivity of plasticized PLLA.