Caffeine Encapsulation in Metal Organic Framework MIL-53(Al) at Pilot Plant Scale for Preparation of Polyamide Textile Fibers with Cosmetic Properties

Abstract

Currently in the marketplace, we can find clothing items able to release skin-friendly ingredients while wearing them. These innovative products with high-added value are based on microencapsulation technology. In this work, due to its lightness, flexibility, porosity, chemical affinity and adsorption capacity, metal-organic framework (MOF) MIL-53(Al) was the selected microcapsule to be synthesized at a large scale and subsequent caffeine encapsulation. The synthesis conditions (molar ratio of reactants, solvents used, reaction time, temperature, pressure reached in the reactor and activation treatment to enhance the encapsulation capacity) were optimized by screening various scaling-up reactor volumes (from lab-scale of 40 mL to pilot plant production of 3.75 L). Two types of Al salts (Al(NO₃)₃·9H₂O from the original recipe and Al₂(SO₄)₃ as commercial SUFAL 8.2) were employed. The liporeductor cosmetic caffeine was selected as the active molecule for encapsulation. Caffeine (38 wt %) was incorporated in CAF@MIL-53(Al) microcapsules, as analyzed by TGA and corroborated by GC/MS and UV-vis after additive extraction. CAF@MIL-53(Al) microcapsules showed a controlled release of caffeine during 6 days at 25 °C (up to 22% of the initial caffeine). These capsules were incorporated through an industrial spinning process (with temperatures up to 260 °C) to manufacture PA-6 fibers with cosmetic properties. Up to 0.7 wt % of capsules were successfully incorporated into the fibers hosting 1700 ppm of caffeine. Fabrics were submitted to scouring, staining, and washing processes, detecting the presence of caffeine in the cosmetic fiber.

Keywords: MIL-53(Al); Metal organic framework; caffeine; carboxylate ligand; microencapsulation; polyamide; scaled-up synthesis; textile fiber.

Figure 1

CAF@MIL-53(Al) sample (encapsulation MOF/caffeine weight ratio of 1:2), together with as-synthesized in water MIL-53(Al)as, activated MIL-53(Al), and pure caffeine recrystallized under the conditions of synthesis of MIL-53(Al) for comparison. (a) XRD patterns, (b) FTIR analysis.

Figure 2

MIL-53(Al) synthesis with a water/methanol mixture solvent at pilot plant scale: (a) TGA, (b) SEM. TGA of CAF@MIL-53(Al) is included inferring 35 wt % of caffeine encapsulation.

Figure 3

MIL-53(Al) synthesized with SUFAL® 8.2 at the lab and large scales. Synthesis at different conditions of temperature and times specified in Table 2: (a) TGA curves, (b) XRD patterns.

Figure 4

MIL-53(Al) synthesized with SUFAL 8.2 with water/methanol solvent mixture at pilot plant scale. (a) TGA. (b) SEM. TGA of CAF@MIL-53(Al) SUFAL® 8.2 is included inferring 31 wt % of caffeine encapsulation.

Figure 5

Percentages by weight of caffeine encapsulated in the different capsules synthesized at large scale.

Figure 6

Caffeine delivery of CAF@MIL-53(Al) over time at 25 °C tested by UV–vis.

Figure 7

(a,b) SEM images of two different sections corresponding to 0.70 wt % CAF@MIL-53 PA-6 fibers.

Figure 8

SEM-EDX study of a PA-6 fiber section containing 0.70 wt % CAF@MIL-53. (a) SEM image. (b) Elemental analysis of five points. (c) EDX mapping of the selected area. Al from MIL-53(Al) is depicted in red and Ti from TiO₂ particles in green.