Biodegradable Microcapsules of Poly(Butylene Adipate-co-Terephthalate) (PBAT) as Isocyanate Carriers and the Effect of the Process Parameters

Microcapsules of Poly(butylene adipate-co-terephthalate) (PBAT) Loaded with Aliphatic Isocyanates for Adhesive Applications

This work introduces the encapsulation of hexamethylene diisocyanate derivatives (HDI, TriHDI, and PHDI) with the biodegradable polymer poly(butylene adipate-co-terephthalate) (PBAT) through a solvent evaporation method. These microcapsules (MCs) were then employed in adhesive formulations for footwear. Moreover, MCs containing PHDI were produced in a closed vessel, demonstrating the potential for recovering and reusing organic solvents for the first time. The MCs were achieved with an isocyanate payload reaching up to 68 wt %, displaying a spherical shape, a core-shell structure, and thin walls without holes or cracks. The application of MCs as cross-linking agents for adhesives was evaluated following industry standards. The adhesives' strength surpassed the minimum requirement by a significant margin. Creep tests demonstrated that the formulation with MCs exhibits superior thermostability. Furthermore, the formulation with MCs-PHDI presented the best results reported to date for this type of system, as no displacement was observed in the bonded substrates. Environmental assessment indicates that adhesives with MCs have higher global warming potential (+16.2%) and energy consumption (+10.8%) than the standard commercial adhesives, but under alternative realistic scenarios, the differences can be insignificant. Therefore, adhesive formulations incorporating MCs promise to be on par with traditional adhesive systems regarding environmental impacts while providing benefits such as improved and safe handling of isocyanates and excellent bonding effectiveness.

One Factor at a Time and factorial experimental design for formulation of l-carnitine microcapsules to improve its manufacturability

l-carnitine is an essential dietary supplement of physiological importance. Handling and manufacture of l-carnitine is difficult due to its hygroscopic nature, resulting in impairing its flow properties, as well as solid dosage form stability. The study aimed at reducing l-carnitine hygroscopicity through its encapsulation within a hydrophobic, pH-insensitive polymer. A solid in oil in oil (s/o/o) emulsion solvent evaporation technique for microencapsulation was adopted to exclude the possibility of water uptake. The polymers used were two ethyl cellulose (EC) grades with different viscosities. The chosen solvent for the polymer was acetone, and liquid paraffin was the dispersion medium in which both the drug and polymer were insoluble. Sixteen formulations were developed, and evaluated to study the formulation parameters as anti-coalescent type, mixing speed, surfactant type and polymer ratio, and viscosity grade. A "One Factor at A Time" (OFAT) design of experiment, and a factorial design were utilized. Study results revealed that successful microencapsulation occurred by using Aerosil 200 (0.1 %) as anti-coalescent, a mixing speed of 1000 rpm, and Ethocel Std 20 at a 3:1 drug-to-polymer ratio. Microcapsule formulation containing l-carnitine base, successfully compressed into tablets, showed acceptable water content, disintegration time, hardness, and dissolution. Moreover, it showed acceptable stability upon storage at 40 °C at 75 % RH for six months compared to l-carnitine tablets prepared by wet granulation.