Migration of nanosized layered double hydroxide platelets from polylactide nanocomposite films

Abstract

Melt-extruded L-polylactide (PLA) nanocomposite films were prepared from commercially available PLA and laurate-modified Mg–Al layered double hydroxide (LDH-C₁₂). Three films were tested for total migration as well as specific migration of LDH, tin, laurate and low molecular weight PLA oligomers (OLLA). This is the first reported investigation on the migration properties of PLA-LDH nanocomposite films. The tests were carried out as part of an overall assessment of the suitability of such films for use as food contact materials (FCM). Total migration was determined according to a European standard method. All three films showed migration of nanosized LDH, which was quantified using acid digestion followed by inductively coupled plasma mass spectrometric (ICP–MS) detection of ²⁶Mg. Migration of LDH from the films was also confirmed by examining migrates using transmission electron microscopy (TEM) and was attributed indirectly to the significant PLA molecular weight reduction observed in extruded PLA-LDH-C₁₂ films. Migration of tin was detected in two of the film samples prepared by dispersion of LDH-C₁₂ using a masterbatch technique and migration of the laurate organomodifier took place from all three film types. The results indicate that the material properties are in compliance with the migration limits for total migration and specific lauric acid migration as set down by the EU legislation for FCM, at least if a reduction factor for fresh meat is taken into consideration. The tin detected arises from the use of organotin catalysts in the manufacture of PLA.

Keywords:

• ICP-MS
• chromatography, GC
• metals analysis
• food contact materials
• food simulants
• migration

Acknowledgements

The authors thank The Danish Strategic Research Council for supporting the NanoPack (Biopolymer Nanocomposite Films for use in Food Packaging Applications) project (File No. 2106-06-0061).