Constructing robust chain entanglement network, well-defined nanosized crystals and highly aligned graphene oxide nanosheets: Towards strong, ductile and high barrier Poly(lactic acid) nanocomposite films for green packaging

It is a great challenge to develop a feasible strategy for reconciling barrier performance and mechanical ductility of environmentally friendly poly(lactic acid) (PLA) in the application of packaging industry. In the current study, the combination of manipulating the amorphous chain entanglement network of PLA and constructing "dual barrier walls" of highly aligned GONSs and well-defined PLA crystals simultaneously enhanced barrier properties and ductility of PLA nanocomposite films via "biaxial stretching-constrained annealing" method. The intense extensional field during biaxial stretching induced highly aligned GONSs as the first barrier wall and regulated the amorphous chain entanglement network. Constrained annealing promoted the growth and perfection of PLA crystals as the second effective barrier wall and strengthened amorphous chain entanglement network to some extent. More interestingly, GONSs were first verified as contributors to stabilize the enhanced amorphous chain entanglement network of PLA and benefited for the mechanical ductility of PLA nanocomposite films. As a result, this synergetic structure manifested excellent comprehensive ability in ameliorating the intrinsic drawbacks of brittle and poor barrier PLA films, exhibiting low oxygen permeability coefficient of 0.712 x 10-14 cm3 cm cm- 2 s- 1 Pa- 1, excellent ductility with elongation at break of 147.8%, high yield strength of 83.1 MPa and good dimensional stability with deformation ratio of as low as 3%. The as-prepared PLA nanocomposite films with excellent comprehensive properties hold great potential prospects in the application of packaging industry. The methodology proposed here opens up a new avenue to fabricate environmentally friendly PLA films for promoting the sustainable development of packaging industry.