Lahoussine Ouali

Formation and Mechanical Characterization of Aminoplast Core/Shell Microcapsules

This work aims at establishing a link between process conditions and resulting micromechanical properties for aminoplast core/shell microcapsules. The investigated capsules were produced by the in situ polymerization of melamine formaldehyde resins, which represents a widely used and industrially relevant approach in the field of microencapsulation. Within our study, we present a quantitative morphological analysis of the capsules size and shell thickness. The diameter of the investigated capsules ranged from 10 to 50 μm and the shell thickness was found in a range between 50 and 200 nm. As key parameter for the control of the shell thickness, we identified the amount of amino resin per total surface area of the dispersed phase. Mechanical properties were investigated using small deformations on the order of the shell thickness by atomic force microscopy with a colloidal probe setup. The obtained capsule stiffness increased with an increasing shell thickness from 2 to 30 N/m and thus showed the same trend on the process parameters as the shell thickness. A simple analytical model was adopted to explain the relation between capsules geometry and mechanics and to estimate the elastic modulus of the shell about 1.7 GPa. Thus, this work provides strategies for a rational design of microcapsule mechanics.

Synthesis of hydroxypropyl cellulose derivatives modified with amphiphilic diblock copolymer side-chains for the slow release of volatile molecules

Hydroxypropyl cellulose (HPC) was used as carrier material to prepare comb-like grafted block copolymers having an amphiphilic core–shell structure. The hydroxyl groups of HPC were partially protected with trimethylsilyl groups and the free OH groups used to initiate the ring opening polymerisation (ROP) of L-lactide. The end-chain of the grafted hydrophobic poly(L-lactide) (PLLA) chain was then functionalised with 2-bromopropionyl bromide which was used to polymerise the tert-butyl acrylate (tBA) monomer by atom transfer radical polymerisation (ATRP). The hydrophobic PtBA block was then hydrolysed to a hydrophilic poly(acrylic acid) (PAA) block. The resulting amphiphilic grafted copolymer HPC-g-(PLLA-b-PAA) was dissolved in an ethanol/water mixture (9u2006:u20061), such as a typical Eau de Toilette (EdT) formulation. Atomic force microscopy (AFM) and size measurements confirmed the presence of core–shell structures in solution. A significant swelling of HPC-g-(PLLA-b-PAA) in the presence of a volatile bioactive molecule, methyl 2,2-dimethyl-6-methylene-1-cyclohexanecarboxylate (Romascone®), was observed by dynamic light scattering (DLS). Furthermore, the presence of HPC-g-(PLLA-b-PAA) significantly decreased the evaporation rate of Romascone®, thus serving as an efficient fragrance delivery system in formulations with high ethanol content.