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. 2020 Dec 29;26(1):126.
doi: 10.3390/molecules26010126.

UV Protective, Antioxidant, Antibacterial and Compostable Polylactic Acid Composites Containing Pristine and Chemically Modified Lignin Nanoparticles

Ema Cavallo  1   2   3 , Xiaoyan He  4   5 , Francesca Luzi  4 , Franco Dominici  4 , Patricia Cerrutti  1   2 , Celina Bernal  2   3   6 , Maria Laura Foresti  1   2   3 , Luigi Torre  4 , Debora Puglia  4
Affiliations

UV Protective, Antioxidant, Antibacterial and Compostable Polylactic Acid Composites Containing Pristine and Chemically Modified Lignin Nanoparticles

Ema Cavallo et al. Molecules. .

Abstract

Polylactic acid (PLA) films containing 1 wt % and 3 wt % of lignin nanoparticles (pristine (LNP), chemically modified with citric acid (caLNP) and acetylated (aLNP)) were prepared by extrusion and characterized in terms of their overall performance as food packaging materials. Morphological, mechanical, thermal, UV-Vis barrier, antioxidant and antibacterial properties were assayed; appropriate migration values in food simulants and disintegration in simulated composting conditions were also verified. The results obtained indicated that all lignin nanoparticles succeeded in conferring UV-blocking, antioxidant and antibacterial properties to the PLA films, especially at the higher filler loadings assayed. Chemical modification of the fillers partially reduced the UV protection and the antioxidant properties of the resulting composites, but it induced better nanoparticles dispersion, reduced aggregates size, enhanced ductility and improved aesthetic quality of the films through reduction of the characteristic dark color of lignin. Migration tests and disintegration assays of the nanocomposites in simulated composting conditions indicated that, irrespectively of their formulation, the multifunctional nanocomposite films prepared behaved similarly to neat PLA.

Keywords: chemical modification; food packaging; lignin nanoparticles; nanocomposite films; polylactic acid.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) FE-SEM micrographs of lignin nanoparticle (LNP), treated with citric acid lignin nanoparticle (caLNP) and acetylated lignin nanoparticle (aLNP) and (b) changes in LNP’s polarity resulting from chemical modification: (left) LNP, caLNP and aLNP (5 mg) in chloroform (10 mL); (right) LNP, caLNP and aLNP (5 mg) in 50/50% v/v water (upper phase)/chloroform (lower phase) system.
Figure 2
Figure 2
(a) Optical micrographs of PLA nanocomposite films and (b) FE-SEM micrographs of PLA nanocomposite films with 1 wt % of LNP, caLNP and aLNP.
Figure 3
Figure 3
Tensile properties of PLA and PLA nanocomposite films: (a) Young’s modulus; (b) tensile strength and (c) strain at break.
Figure 4
Figure 4
Thermal properties of PLA and PLA nanocomposite films (differential scanning calorimetry (DSC) and derivative thermogravimetric (DTG)): (a) first heating; (b) cooling; (c) second heating and (d) DTG data.
Figure 5
Figure 5
UV–Vis transmittance spectra of PLA and PLA nanocomposites films.
Figure 6
Figure 6
Antioxidant activity evaluated by absorbance of DPPH at 517 nm: (a) lignin nanoparticles; (b) PLA and PLA nanocomposite films and (c) adical scavenging activity (RSA) values of PLA and PLA nanocomposite films.
Figure 7
Figure 7
Disintegration of PLA and PLA nanocomposite films in simulated composting conditions (58 °C): (a) visual observation and (b) disintegration values (wt %).
Figure 7
Figure 7
Disintegration of PLA and PLA nanocomposite films in simulated composting conditions (58 °C): (a) visual observation and (b) disintegration values (wt %).
Figure 8
Figure 8
Antibacterial activity tests for PLA and PLA nanocomposite films containing 3 wt % of fillers: (a) against Escherichia coli and (b) against Micrococcus luteus.
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