Mechanical, optical and barrier properties of PLA-layered silicate nanocomposites coated with organic plasma polymer thin films

Abstract

In the frame of the efforts that are nowadays provided to develop new environmentally-friendly products as biosourced alternative to petrochemical polymers, we investigated in this work new PLA-based materials for packaging applications obtained by combining bulk and surface modifications of PLA substrates. Four PLA-based nanocomposites were prepared by adding organo-modified layered silicates (either Cloisite® 30B or Cloisite® 20A) and a nucleating agent, i.e. N,N’-ethylenebisstearamide (EBS). The combination of EBS with CL30B led to very good nanofiller dispersion into PLA-clay nanocomposite while allowing, unlike neat PLA, to preserve the structural and thermal properties of PLA under plasma treatment. Based on this study, PLA/CL30B/EBS nanocomposites have been selected to investigate their surface modification that consisted in depositing on this substrate an organic barrier coating, i.e. an ethyl lactate plasma polymer film (ELPPF) synthesized by plasma polymerization of ethyl lactate. The PLA/CL30B/EBSELPPF system allowed increasing the tensile modulus from 3800 MPa (uncoated film) to 5200 MPa at high power plasma while preserving the ultimate mechanical properties. In addition, optical properties study showed that PLA/CL30B/EBS-ELPPF is also the best UV-B protective material while keeping a good transparency. Finally, the oxygen transmission rate was reduced by 53% with respect to neat PLA. All properties of final material are discussed as a function of the characteristics of PLA-clay nanocomposite substrate, of the ethyl lactate plasma polymer film (ELPPF) and of the substrate/plasma film interface.