FILM INSERT MOLDING BASED ON POLYOXYMETHYLENE AND POLY(LACTIC ACID): MORPHOLOGY AND MECHANISM OF INTERFACIAL ADHESION

摘要

The combination of polyoxymethylene (POM) and poly(lactic acid) (PLA) is possible due to their compatibility. Film insert moldings were fabricated by using PLA as the film and POM copolymers with various oxyethylene repeating units as the substrate resin. The interfacial adhesion properties between the film and substrate were determined by means of micro-cutting analyses. POM containing high oxyethylene content shows superior adhesive strength than those with low oxyethylene content. After removal of PLA film by solvent etching, the POM surface was observed by field-emission scanning electron microscopy. It was found that the PLA molecules have diffused in between the POM lamellar, which explains the spherulitic structures found on the surface of the etched POM substrate. To determine the depth of the PLA penetration, the film-substrate interface was observed through Laser Raman Spectrometer. The deepest PLA penetration was found in POM substrates with the highest oxyethylene content. This shows that there was optimum partial mixing between PLA and POM with high oxyethylene content at the film-substrate interface. The growth of the POM-PLA mix layer was explained by the mechanism of "negative pressure" in POM phase attributed by POM crystallization and partial miscibility between POM and PLA.