Study on characteristics of paper laminated with biodegradable plastics, 3. Elemental and morphological analyses of polylactide deterioration

Elemental and morphological analyses were applied to investigate the degradation behavior of commercial polylactide (PLA) film, poly (L-lactide) (PLLA) and poly (DL-lactide) (PDLLA) by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The PLLA and PDLLA samples consisted of three types of carbon: C-C (C-H), C-O and O=C-O, which corresponded to their theoretical composition. However, the XPS analysis revealed that the surfaces of the PLA film highly resistant to acid hydrolysis were overspread with unknown constituents consisting of nitrogen and unoxidized carbon, not being announced officially. The AFM analysis offered a clear distinction in the surface deterioration of the PLA samples; and the alkaline treatment excavated numerous holes on the PLA surfaces. These results indicated that the commercial plastics are chemically modified on their surfaces to improve the physical properties for practical use, resulting in being deprived of biodegradability and eco-compatibility. It was also suggested that the enlargement in the specific surface area, which may occur at the early stage on PLA degradation, possibly accelerated the PLA decomposition rate. A new conception in the material design for paper-based composites was proposed; a local alkaline circumstance expected by alkaline fillers, e.g., CaO available in papermaking processes would effectively promote the PLA decomposition.