Synthesis and characterization of silica hybrid coating materials for poly (lactic acid) film

Abstract

Silica/poly(lactic acid) hybrid materials were synthesized by sol-gel method and used as coating materials in order to improve the oxygen and water vapor barrier property of, poly(lactic acid), PLA films. The mixtures of Tetraethoxysilane (TEOS) and Triethoxyvinylsilane (VTES), containing a reactive double bond, were used as the inorganic silicate precursors to construct the siloxane network structure by co-hydrolysis and polycondensation reaction. Polymerization of the unsaturated bonds occurred by UV irradiation, as evidenced by sharp decrease of FTIR band at 1600 cm1, corresponding to terminal C-C stretching bond. PLA and 3-Isocyanatopropyl- triethoxysilane (ICPTES) were used as an organic polymer and a silane coupling agent, respectively. FTIR absorption band at 1550 cm1 was specified to the formation of amine groups (-NH), due to isocyanate groups in ICPTES reacting with hydroxyl groups in PLA chains. SEM was indicated that there were big cracks on the surface of coating materials without ICPTES. The water vapor barrier property of coated film showed a great improvement by 24.6% at the VTES/ TEOS ratio of 1: 1 (VT11), and the oxygen permeation coefficient (OPC) of VT11-coated film was decreased 24.8%, as compared to PLA neat film. The water contact angle of VT11-coated film decreased by 6.6%. XRD showed that the crystallinity of VT11-coated film was decreased after UV-irradiation for 1h. AFM also indicated that surface roughness of VT11-coated film decreased by 31.2% after UV-irradiation for 1h. Moreover, the water vapor barrier property was improved with the aging time increasing, because dense network structures were continuously generated after drying. In addition, UV- irradiated VT11-coated PLA film could retard the lipid oxidation more effective than PLA neat film and LDPE film. The film could be an alternative to maintain the quality and extend the shelf-life of shrimp crackers.