Highly Photostable Optical Grade Polylactide Compounds for Compact LED Luminaires

In polymer optics for LED luminaires, materials are lacking which combine properties needed for a modern, circular, and biobased economy and the high technological demands. With respect to this the photostability of optical-grade polylactide (PLA) compounds with fatty acid amides as clarifiers was evaluated. Clouding of the PLA is avoided by the incorporation of two fatty acid amides with favorable performance, namely N, N '-ethylenebis(stearamide) and N, N '-ethylenebis(12-hydroxystearamide). To enable the application of such novel PLA compounds in compact LED luminaires, high photostability at elevated temperatures is essential. The compounds were irradiated with high radiant fluxes at 450 nm for a total of 5000 h. Earlier studies have already attributed high photostability to neat PLA under those conditions, whereas optical-grade polycarbonate showed signs of aging after a few hundred hours. The present study demonstrates identical photostability for the PLA compounds containing fatty acid amides. During the first thousand hours, the UV-Vis transmission of all tested PLA samples increased, while haze levels remained unchanged. Furthermore, thermal and infrared spectroscopic analyses reveal no signs of incipient photodegradation. Although a decrease in the molecular weight of the samples was identified by size exclusion chromatography, fatty acid amides are proven to have no adverse effects on the photothermal aging of PLA. These findings confirm the high photostability of optical-grade PLA compounds, making them viable eco-friendly alternatives for the replacement of fossil-based polymers in optics.