Assembly Of Layered Double Hydroxides/Polymer Composite Films Toward Oxygen/Water Barrier Property

Polymer films have been applied as packaging materials due to their light-weight, low-cost and good processability, but their application as gas barrier materials is restricted because of relatively high gas permeability. In order to meet the extreme requirements for gas barrier materials, a wide variety of hybrid materials containing polymer and two-dimensional ?2D? inorganic platelets have been designed and fabricated. Since the infilling of high-oriented platelets into polymer matrix would induce a long diffusion length and strong resistance to permeating gas, considerable efforts have been devoted to the synthesis of organic-inorganic composites as gas barrier materials. Nevertheless, for such a brick-and-mortar structure, the diffusion of gas molecules is only suppressed in the normal direction of the films, i.e., the gas diffusion parallel to the inorganic platelets is non-restricted. Furthermore, the diffusion of water molecule through gas barrier films was normally out of consideration, which is unfavorable for food/drug preservation. In order to resolve the above issues, in this study, layered double hydroxides ?LDHs? with different structure were used as building block to fabricate multilayer films with polymer matrix via alternate spin-coating technique. The resulting films exhibit ultrahigh gas and water molecule barrier behavior, excellent mechanical and thermal stability. The detailed researches are as follows:?1? A hierarchical LDH ?H-LDH? material was synthesized via the following three-step route:hydrothermal synthesis of plate-like LDH ?P-LDH?, calcination at 450? to produce metal oxide ?MMO?, followed by a rehydration treatment in sodium hydroxide solution. Subsequently, the multilayer films were fabricated by alternate spin-coating technique with H-LDH and polymer chitosan ?CTS? on PET substrate. The pristine PET substrate displays an oxygen transmission rate ?OTR? of ?8.431 cm³ m^-2 day^-1 atm^-1, while the ?H-LDH/CTS?_n films display a superior oxygen barrier property in comparison with pure PET and ?P-LDH/CTS?_n films. The OTR of ?H-LDH/CTS?10 film decreases dramatically with a value below the detection limit of commercial instrumentation (< 0.005 cm³ m^-2 day^-1 atm^-1). The improved oxygen barrier property is mainly attributed to the following two factors:firstly, H-LDH is capable of restraining the migration of oxygen both in vertical and parallel direction owing to its unique hierarchical structure; secondly, the oxygen vacancies on H-LDH surface serve as capture traps to absorb permeating oxygen, which results in a decreased free volume and further enhancement of the barrier property.?2? The hydrophobic LDHs sample was prepared by a combined two-step process, including the synthesis of Mg₂Al-LDH colloid and following modification by nonionic surfactant Tween 80. Subsequently, the multilayer films were fabricated by an alternate spin-coating technique by using modified LDH and polymer polydimethylsiloxane ?PDMS? as building blocks. The composite films with two-dimensional structure are hydrophobic with water contact angle of ?110°. Meanwhile, the films show excellent barrier properties both to oxygen and water molecule. The OTR and water molecule transmission rate ?H2OTR? is ?48.213 and ?10.824 cm³ m^-2 day^-1 atm^-1, respectively. Furthermore, the films display metal anti-corrosion property, verified by means of electrochemical impedance spectroscopy and polarization curve measurement. Therefore, this work provides a facile and cost-effective strategy to fabricate oxygen/water barrier materials, which can serve as a promising candidate for food/pharmaceutical packaging and metal protection.