Efficient Gas Barrier and Antibacterial Properties of Poly(lactic acid) Nanocomposites: Functionalization with Phytic Acid-Cu(II) Loaded Layered Clay

Poly(lactic acid) (PLA) represents one of the most promising and attractive bio-based polymers for green packaging. However, toughness, gas barrier and antibacterial properties of pure PLA films cannot compete with those of traditional petroleum-based active packaging plastics. To fill this gap, utilization of excellent chelating properties of phytic acid (PA), functionalized layered double hydroxides (LDHs@PA-Cu(II)) was firstly synthetized via facile deposition and chelation of one-step assembled PA-Cu(II) coordination compounds on the surface of layered clay. Furthermore, LDHs@PA-Cu(II)/PLA nanocomposites were prepared by blending LDHs@PA-Cu(II) and pure PLA via solution casting evaporation process. After adding only 1 wt % LDHs@PA-Cu(II), elongation at break and tensile strength increase by 53.0% and 18.9%, respectively, and the oxygen relative permeability decreases by 28.0%. Due to the strong interface interaction and heterogenous nucleation, the reinforcement effect of LDHs@PA-Cu(II) at low loadings is remarkable. Meanwhile, owing to the antibacterial activity of PA-Cu(II) coatings, the antibacterial rate (against Escherichia coli) of LDHs@PA-Cu(II) exceeds 99.99%. Furthermore, the corresponding LDHs@PA-Cu(II)/PLA nanocomposites also show outstanding antibacterial properties, which will be a promising candidate for active packaging application.

Mussel-inspired nano-silver loaded layered double hydroxides embedded into a biodegradable polymer matrix for enhanced mechanical and gas barrier properties

In this paper, a facile, green and mussel-inspired method is presented to prepare silver loaded layered double hydroxides (Ag-LDHs@PDA and Ag-LDHs@TA–Fe(iii)) using a pre-synthesis polydopamine (PDA)/tannic acid (TA)–Fe(iii) layer as a nanoscale guide and PDA/TA itself as a reducing reagent to form uniform silver nanoparticles (AgNPs) on the surface of modified LDHs. Meanwhile, another kind of LDH, Ag-LDHs(PVP), was prepared via the direct reduction of the precursor [Ag(NH₃)₂]⁺ with polyvinyl pyrrolidone (PVP). And three kinds of Ag-LDHs/poly(ε-caprolactone) (PCL) nanocomposite were prepared by blending Ag-LDHs and pure PCL via a solution casting method to obtain homogeneous films. It is shown that the obtained AgNPs are distributed on the LDH surfaces uniformly. And the high loading and medium size of the AgNPs present in Ag-LDHs(PVP) give it the best antibacterial properties. However, compared with Ag-LDHs(PVP), the better dispersibilities of Ag-LDHs@PDA and Ag-LDHs@TA–Fe(iii) contribute to the greater aspect ratios of Ag-LDHs in the matrices, resulting in an increase in the number of tortuous paths for gas diffusion. Meanwhile, Ag-LDHs@PDA and Ag-LDHs@TA–Fe(iii) have stronger interactions with the PCL matrix, which is favorable for the existence of less interface defects in the matrix, resulting in an improvement in the mechanical and gas barrier properties. Therefore, mussel-inspired antibacterial Ag-LDHs/PCL nanocomposites show preferable mechanical and gas barrier properties.

A facile, green and mussel-inspired method is presented to prepare Ag loaded LDHs using a pre-synthesis PDA/TA–Fe(iii) layer as a nanoscale guide and PDA/TA itself as a reducing reagent to form uniform AgNPs on the surface of modified LDHs.