Development of Poly(lactic acid)-Based Biocomposites with Silver Nanoparticles and Investigation of Their Characteristics

Abstract

Nowadays, the demand for food packaging that maintains the safety and quality of products has become one of the leading challenges. It can be solved by developing functional materials based on biodegradable polymers, such as poly(lactic acid) (PLA). In order to develop PLA-based functional materials with antibacterial activity, silver nanoparticles (AgNPs) were introduced. In the present study, AgNPs stabilized by a copolymer of ethylene and maleic acid were used. Under the joint action of shear deformations and high temperature, the biocomposites of PLA with poly(ethylene glycol) and AgNPs were produced. Their mechanical and thermal characteristics, water absorption, and structure were investigated using modern methods (DSC, FTIR, Raman spectroscopy, SEM). The effect of AgNP concentration on the characteristics of PLA-based biocomposites was detected. Based on the results of antibacterial activity tests (against Gram-positive and Gram-negative bacteria, along with yeast) it is assumed that these systems have potential as materials for extending the storage of food products. At the same time, PLA-PEG biocomposites with AgNPs possess biodegradability.

Keywords: antibacterial activity; poly(lactic acid) (PLA); silver nanoparticles (AgNPs); structure; thermal properties.

Figure 1

SEM micrograph of AgNP powder.

Figure 2

Stress–strain diagrams of PLA–PEG₄₀₀₀ biocomposites with AgNPs (wt%): 0.01 (1), 0.03 (2), 0.5 (3).

Figure 3

Water absorption curves for PLA-based biocomposites (wt%): PLA–PEG₁₀₀₀ (90:10) (1), PLA–PEG₁₀₀₀ (80:20) (2), PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.01) (3), PLA–PEG₁₀₀₀ + AgNPs (90:10 + 0.1) (4), PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.2) (5).

Figure 4

SEM micrographs of the sample surface (a,b) and cross-sections (c,d) after tests of water absorption at different concentrations of AgNPs (×5000): PLA–PEG₁₀₀₀ + AgNPs (90:10 + 0.1 wt%) (a,c); PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.2 wt%) (b,d). Images are presented at different magnification: 5000 (a,b); 2500 (c,d).

Figure 4

SEM micrographs of the sample surface (a,b) and cross-sections (c,d) after tests of water absorption at different concentrations of AgNPs (×5000): PLA–PEG₁₀₀₀ + AgNPs (90:10 + 0.1 wt%) (a,c); PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.2 wt%) (b,d). Images are presented at different magnification: 5000 (a,b); 2500 (c,d).

Figure 5

SEM micrographs of the sample surface at different AgNP concentrations (×350): PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.2 wt%) (a); PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.5 wt%) (b).

Figure 6

Absorption of AgNPs. Photo: colloid.

Figure 7

Raman spectra: PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.02 wt%) (1); PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.2 wt%) (2).

Figure 8

FTIR spectra: PLA–PEG₁₀₀₀ + AgNPs (90:10 + 0.1 wt%) (1); PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.02 wt%) (2); PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.2 wt%) (3).

Figure 9

DSC heat flow curves of heating (a) and cooling (b) for PEG₄₀₀₀ (1), PLA (2), PLA–PEG₄₀₀₀ (90:10 wt%) (3), PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.2 wt%) (4).

Figure 10

Photos of PLA–PEG + AgNPs films in media with different bacteria. PEG₁₀₀₀ (a–d); PEG₄₀₀₀ (e–h). AgNP concentration (wt%): 0.1 (a,b,e,f); 0.5 (c,d,g,h). E. coli (a,g), B. subtilis (b,c,f), M. luteus (d,h), C. sporogenes (e).

Figure 11

Mass loss curves of biocomposites after exposure in soil: PLA–PEG₄₀₀₀ (90:10 wt%) (1); PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.1 wt%) (2); PLA–PEG₄₀₀₀ + AgNPs (90:10 + 0.5 wt%) (3). Photos of films before (left column) and after (right column) test in the same order as curves.