Synthesis of D-Limonene Loaded Polymeric Nanoparticles with Enhanced Antimicrobial Properties for Potential Application in Food Packaging

Abstract

Mini-emulsion polymerization was applied for the synthesis of cross-linked polymeric nanoparticles comprised of methyl methacrylate (MMA) and Triethylene Glycol Dimethacrylate (TEGDMA) copolymers, used as matrix-carriers for hosting D-limonene. D-limonene was selected as a model essential oil, well known for its pleasant odor and its enhanced antimicrobial properties. The synthesized particles were assessed for their morphology and geometric characteristics by Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM), which revealed the formation of particles with mean diameters at the nanoscale (D[3,2] = 0.135 μm), with a spherical shape, while the dried particles formed larger clusters of several microns (D[3,2] = 80.69 μm). The percentage of the loaded D-limonene was quantified by Thermogravimetric Analysis (TGA), complemented by Gas Chromatography-Mass Spectrometry analysis coupled with a pyrolysis unit (Py/GC-MS). The results showed that the volatiles emitted by the nanoparticles were composed mainly of D-limonene (10% w/w of dry particles). Particles subjected to higher temperatures tended to decompose. The mechanism that governs the release of D-limonene from the as-synthesized particles was studied by fitting mathematical models to the release data obtained by isothermal TGA analysis of the dry particles subjected to accelerated conditions. The analysis revealed a two-stage release of the volatiles, one governed by D-limonene release and the other governed by TEGDMA release. Finally, the antimicrobial potency of the D-limonene-loaded particles was demonstrated, indicating the successful synthesis of polymeric nanoparticles loaded with D-limonene, owing to enhanced antimicrobial properties. The overall performance of these nanoparticles renders them a promising candidate material for the formation of self-sterilized surfaces with enhanced antimicrobial activity and potential application in food packaging.

Keywords: D-limonene; antimicrobial properties; cross-linking; essential oils; mini-emulsion polymerization; nanoparticles; volatile release.

Figure 1

Schematic representation of the mini-emulsion polymerization process, and the possible structure of the synthesized nanoparticles.

Figure 2

The main effect plots for the responses of interest: (A) Loading and (B) D[3,2], respectively.

Figure 2

The main effect plots for the responses of interest: (A) Loading and (B) D[3,2], respectively.

Figure 3

Monomer (MMA) conversion versus time, for P(MMA-TEGDMA) nanoparticles (●) and D-limonene, loaded P(MMA-TEGDMA) nanoparticles (◦) synthesis.

Figure 4

Sample temperature scan thermograph (continuous line) and derivative plot (dotted line).

Figure 5

Gaussian peak fitting of mass loss first derivative plot.

Figure 6

Release products chromatographs for three different temperatures. Decomposition products are present for 250 °C.

Figure 7

Particle size distribution for the synthesized (A) latex particles, (B) the dried particles, and (C) the re-dispersed particles in water.

Figure 8

SEM micrographs of the dry particles, taken for different angles and magnification. (A) Representative spherical nanoparticles and small particle clusters, (B) Large-sized spherical particles cluster, and (C) particle cluster of different sizes.

Figure 9

Isothermal TGA thermographs for different temperatures.

Figure 10

Normalized isothermal TGA data obtained for different temperatures, fitted by a first-order and a diffusion-based mathematical model.

Figure 11

Plots of the natural logarithm of k and D values (lnk and lnD, respectively) against 1/T, used for the activation energies calculation for the case of 1st order and the diffusion from sphere model, respectively.

Figure 12

Antimicrobial activity assessment of the synthesized nanoparticles, against four microorganisms of interest. The test was performed in the presence of 50, 75, 100, 200, and 250 µL of 10% w/v nanoparticle suspension in ddH₂O (total D-limonene content: 0.51, 0.76, 1.01, 2.02, and 2,53 μg, respectively, as-determined by TGA analysis).