Fabrication of UV- and Heat-Resistant PDLA/PLLA-g-Nanolignin Composite Films by Constructing Interfacial Stereocomplex Crystallites

In the present work, a lignin nanoparticle grafted on a PLLA copolymer (LNP-g-PLLA) was prepared via ring-open polymerization with L-lactide as the raw material and -OH of lignin as the initiator. Then, PDLA/PLLA-g-nanolignin composite films with various quantities of LNP-g-PLLA were fabricated by a solvent casting method. Results from differential scanning calorimetry and wide-angle X-ray diffraction evidenced the formation of SC at the interface between PDLA and the LNP-g-PLLA copolymer, which was helpful to improve the heat resistance. Dynamic mechanical analysis showed that the storage moduli of the PDLA/15g-LNP composite sample are 547 and 264 MPa at 80 and 140 degrees C, respectively, while they are only 12 and 4 MPa for pure PDLA. The tensile test results illustrated a significant improvement in the mechanical performance, which was supposed to be attributed to the interfacial compatibility between PDLA and the LNP-g-PLLA copolymer, resulting in the enhancement of the HC crystallization of PDLA. Furthermore, PDLA/PLLA-g-nanolignin composite films were found to have excellent UV resistance due to the inherent UV shielding property of lignin nanoparticles. When the LNP-g-PLLA amount was 9.0 wt %, the PDLA/9g-LNP film shielded nearly 100 wt % of UV-B irradiation, while only quite limited UV-A irradiation was transmitted. The excellent heat resistance and UV shielding properties endow the composite films with great potential application in some heatable and UV shielding packaging.

Automated summary

By grafting lignin nanoparticles onto PLLA, composite films with excellent thermal resistance and UV shielding properties were prepared, showing great potential in applications such as heatable and UV shielding packaging.