Oxygen Permeability of Novel Organic-Inorganic Hybrid Coatings

The oxygen barrier properties of composite materials, consisting of a 45 μm thick LDPE substrate coated by a thin layer (0.7-1 μm) of nanostructured hybrid organic/inorganic materials based on SiO2 and polyethylene-polyethylene glycol (PE-PEG) block copolymers, obtained via a sol-gel technique have been characterized at 35°C and 50°C. A significant decrease (25-40%) of the oxygen transfer rate has been observed for coated samples with respect to bare substrate both at 35°C and 50°C.

The barrier effect was further improved by adding of a second organic component capable of forming hydrogen bonds, namely poly(4-hydroxy styrene) (PHS): use of PHS leads to a remarkable decrease (50 - 70 %) of the oxygen transfer rate both at 35°C and 50°C. It has been determined that the optimal formulation is the one containing 22% of PHS and 33% of silica; the thickness required for the multilayer sample to have the same barrier properties as a 45 μm thick, homogenous film composed of HDPE, oPP and PLA is equal to 2.5, 0.2 and 0.1 μm respectively.