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. 2024 Feb 27;16(5):637.
doi: 10.3390/polym16050637.

Mechanochemical Encapsulation of Caffeine in UiO-66 and UiO-66-NH2 to Obtain Polymeric Composites by Extrusion with Recycled Polyamide 6 or Polylactic Acid Biopolymer

Cristina Pina-Vidal  1   2 , Víctor Berned-Samatán  1   2 , Elena Piera  3 , Miguel Ángel Caballero  3 , Carlos Téllez  1   2
Affiliations

Mechanochemical Encapsulation of Caffeine in UiO-66 and UiO-66-NH2 to Obtain Polymeric Composites by Extrusion with Recycled Polyamide 6 or Polylactic Acid Biopolymer

Cristina Pina-Vidal et al. Polymers (Basel). .

Abstract

The development of capsules with additives that can be added to polymers during extrusion processing can lead to advances in the manufacturing of textile fabrics with improved and durable properties. In this work, caffeine (CAF), which has anti-cellulite properties, has been encapsulated by liquid-assisted milling in zirconium-based metal-organic frameworks (MOFs) with different textural properties and chemical functionalization: commercial UiO-66, UiO-66 synthesized without solvents, and UiO-66-NH2 synthesized in ethanol. The CAF@MOF capsules obtained through the grinding procedure have been added during the extrusion process to recycled polyamide 6 (PA6) and to a biopolymer based on polylactic acid (PLA) to obtain a load of approximately 2.5 wt% of caffeine. The materials have been characterized by various techniques (XRD, NMR, TGA, FTIR, nitrogen sorption, UV-vis, SEM, and TEM) that confirm the caffeine encapsulation, the preservation of caffeine during the extrusion process, and the good contact between the polymer and the MOF. Studies of the capsules and PA6 polymer+capsules composites have shown that release is slower when caffeine is encapsulated than when it is free, and the textural properties of UiO-66 influence the release more prominently than the NH2 group. However, an interaction is established between the biopolymer PLA and caffeine that delays the release of the additive.

Keywords: UiO-66; UiO-66-NH2; caffeine; metal organic framework; microencapsulation; polyamide; polylactic; textile composite.

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Conflict of interest statement

The authors declare that this research work has been carried out within the LMP53_21 project that was funded by the Government of Aragon in collaboration with the company Nurel S.A. Elena Piera and Miguel Ángel Caballero were employed by the company Nurel. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure A1
Figure A1
Images of (a) UiO-66c, (b) UiO-66s, and (c) UiO-66-NH2, before and after caffeine encapsulation.
Figure A2
Figure A2
Particle size distribution of UiO-66c, UiO-66s, and UiO-66-NH2.
Figure A3
Figure A3
TEM images of (a) UiO-66c, (b) UiO-66s, and (c) UiO-66-NH2.
Figure A4
Figure A4
SEM images of caffeine crystals.
Figure A5
Figure A5
13C NMR spectra of PA6 composites compared with the solid sample’s spectra.
Figure A6
Figure A6
Normalized values of caffeine release in PA6 and PLA composites showing the evolution with time and temperature. The amount of composites introduced was 7.956 g, 8.414 g, 7.398 g, and 7.981 g for PA6 composites (UiO-66c, UiO-66s, caffeine, and UiO-66-NH2) and 9.380 g and 9.4261 g for PLA composites (UiO-66c and caffeine).
Figure A7
Figure A7
1H NMR spectra of liquids obtained after liquid–solid extraction at different temperatures (25–50–80 °C) at 12 days (80 °C): (a) PA6 composites. (b) PLA composites.
Figure 1
Figure 1
Photographs of the prepared polymer composites: (a) PA6 + CAF@UiO-66c, (b) PA6 + CAF@UiO-66s, (c) PA6 + UiO-66-NH2, (d) PA6 + caffeine, (e) PLA + CAF@UiO-66c, (f) PLA + CAF@UiO-66s, (g) PLA + CAF@UiO-66-NH2, (h) PLA + caffeine.
Figure 2
Figure 2
Nitrogen adsorption–desorption (Ads-Des) isotherms of UiO-66c, UiO-66s, and UiO-66-NH2 before (a) and after (b) caffeine encapsulation.
Figure 3
Figure 3
XRD spectra of UiO-66s, UiO-66c, UiO-66-NH2, and simulated UiO-66 using Mercury 3.8 software [54] and CCDC 1018045 [55] from Cambridge Crystallographic Data Centre. The XRD of the samples after the caffeine encapsulation process are also shown.
Figure 4
Figure 4
FTIR spectra of UiO-66c, UiO-66s, and UiO-66-NH2 before and after caffeine encapsulation.
Figure 5
Figure 5
SEM images of (a) UiO-66c, (b) UiO-66s, and (c) UiO-66-NH2. SEM images of UiO-66 with encapsulated caffeine (d) CAF@UiO-66c, (e) CAF@UiO-66s, and (f) CAF@UiO-66-NH2.
Figure 6
Figure 6
TGA (a) and DTG (b) analysis of UiO-66c, UiO-66s, and UiO-66-NH2 samples before and after caffeine encapsulation. TGA was carried out under nitrogen flow.
Figure 7
Figure 7
13C CP MAS NMR spectra of caffeine, UiO-66c, UiO-66s, and UiO-66-NH2, and the corresponding encapsulated samples (CAF@UiO-66c, CAF@UiO-66s, and CAF@UiO-66-NH2).
Figure 8
Figure 8
XRD of PA6 and PLA composites of UiO-66 encapsulated samples and pure caffeine.
Figure 9
Figure 9
FTIR spectra of polymer composites of UiO-66 encapsulated samples and pure caffeine: (a) PA6. (b) PLA.
Figure 10
Figure 10
TGA (a) and DTG (b) characterization of PA6 composites. TGA (c) and DTG (d) characterization of PLA composites. TGA was carried out under air flow.
Figure 11
Figure 11
SEM images of PA6 composites (a) pure PA6, (b) PA6 + CAF@UiO-66c, (c) PA6 + CAF@UiO-66s, (d) PA6 + CAF@UiO-66-NH2, (e) PA6 + caffeine, (f) Atomic percentages of Zr in cross-section SEM images obtained from EDX analysis.
Figure 12
Figure 12
SEM images of PLA composites (a) pure PLA, (b) PLA + CAF@UiO-66c, (c) PLA + CAF@UiO-66s, (d) PLA + CAF@UiO-66-NH2, (e) PLA + caffeine, (f) atomic percentages of Zr in cross-section SEM images obtained from EDX analysis.
Figure 13
Figure 13
Release experiments of solid samples, CAF@UiO-66c, CAF@UiO-66s, CAF@UiO-66-NH2, and a physical mixture of both MOF with caffeine, determined by UV–Vis absorption. The error bars come from the measurement of two samples prepared in different batches.
Figure 14
Figure 14
Normalized values of caffeine release in PA6 and PLA composites showing the evolution with time and temperature. The amount of polymer composites introduced was 0.5 g for all samples.
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