Effect of Lignin Incorporation on Properties of Polyester Films of Lignin-Grafted-PCL/PLGA/PLA Polymers as Packaging...

This article reports on the effect of lignin on the properties of films made from lignin (LN) grafted to either PCL, PLGA, or PLA. LN-PCL/PLGA/PLA polymers were synthesized by an acylation reaction, and lignin grafting was confirmed using FTIR and H NMR spectroscopy. Films were made from the grafted polymers with a solvent-casting technique. The thermal, mechanical, and functional properties of the films were measured using standard methods and compared against the properties of the polyester films without lignin. Thermal analysis of the films showed glass transition temperatures of 55.9, 46.2, and 56 °C for LN-PCL, LN-PLGA, and LN-PLA, similar to those of the free polyesters. LN grafting reduced strain at break and yield strength, particularly when grafted to PLA, while having minimal impacts on PCL and PLGA. All LN-PCL/PLGA/PLA films presented an UV transmittance below 15%, an improvement over those of the polyesters measuring 60% and up, showing a high potential as a UV-shielding material. Contact angle analysis indicated no effect on the wettability of the films from incorporating lignin, with an average water contact angle of 82.71 ± 8.42°. While permeability was similar across polymers, ranging from 3.6 × 10¹² to 8.5 × 10^-12 g/Pa*s*m for PLGA and PCL films, that of LN-PLA was significantly higher (1.5 × 10¹¹ ± 1.9 × 10^-12g/Pa*s*m), but in the same range. In summary, the lignin films had comparable properties to those of the neat polyesters while having higher UV-shielding properties, indicating the potential of lignin-grafted materials as biodegradable alternatives for packaging UV-sensitive products.