Synergic Effect of Nanolignin and Metal Oxide Nanoparticles into Poly(l-lactide) Bionanocomposites: Material Properties, Antioxidant Activity, and Antibacterial Performance.

Erlantz Lizundia,Debora Puglia,Livia Visai,Luigi Torre,Ilaria Armentano,Francesca Luzi,Federico Bertoglio,Elisa Restivo

doi:10.1021/acsabm.0c00637

Abstract

Binary and ternary poly(l-lactide) (PLLA)-based nanocomposites, containing nanolignin (1 wt %) and different metal oxide nanoparticles (0.5 wt %, Ag2O, TiO2, WO3, Fe2O3, and ZnFe2O4), were realized by solvent casting, and their morphological, thermal, surface, optical, antioxidant, and antimicrobial characterizations were performed. The presence of metal oxide nanoparticles at the selected weight concentration affects the surface microstructure of the PLLA polymer, and this outcome is particle-type dependent, according to the shape, morphology, and chemical properties of the selected nanoparticles (NPs). Analogously, wettability of PLLA-based nanocomposites was slightly modified by the presence of hydrophobic lignin nanoparticles and different shaped metal oxides. Results of differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD) tests confirmed that nanoparticle addition confined the mobility of the amorphous phase, increasing at the same time the formation of more numerous but less perfect PLLA crystals. Interestingly, antioxidant activity was also obtained in ternary-based nanocomposites, where a synergic effect of lignin and metal oxide nanoparticles was obtained. Antibacterial tests showed manifest activity of TiO2 and Ag2O nanoparticles containing PLLA films, and the time dependence was more evident for Staphylococcus aureus than for Escherichia coli. Lignin nanoparticles are able to provide protection against UV light while still allowing visible light to pass and even surpass the UV-protection capacity provided by many inorganic nanoparticles. This makes them an attractive renewable additive for the realization of PLLA/metal oxide nanocomposites in the fields of food, drug packaging, and biomedical industry, where antibacterial and antioxidant properties are required.

Highlights

Polylactic acid (PLA) is a highly potential polymeric material, owing to its exceptional mechanical, transparency, biocompatibility, and biodegradability properties
The presence of lignin nanoparticles affected the morphologies of the produced ternary films, as confirmed by the smoother and more hydrophobic surfaces, with the exception of PLLA/1LNP/ 0.5Ag2O, where the roughness effect was predominant on chemical nanoparticle reactivity
The combined use of metal oxides and lignin proved effective in UV-protection capacity, surpassing the results obtainable with inorganic nanoparticles

Summary

Introduction

Polylactic acid (PLA) is a highly potential polymeric material, owing to its exceptional mechanical, transparency, biocompatibility, and biodegradability properties. Some limitations, such as the narrow processing window due to the high melting temperature and poor thermal stability and limited protection toward many biological, chemical, and physical environmental conditions (physical stress, light, microorganisms, oxygen, and moisture), restrict its complete use in some industrial applications, as in the case of the food packaging sector.[1] In recent times, lignin, as the most abundant natural material after cellulose, has received much interest, due to its multifunctionalities: reinforcement effect, UV protection, and antimicrobial and antioxidation properties.[2] In addition, its use in polylactic acid is considered attractive, being both materials biobased and biodegradable. Different facile and practical routes have been proposed, such as reactive compatibilization,[4] copolymer addition,[5] and filler acetylation.[6]

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