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.

An innovative headspace sampling and injection system for gas chromatography was designed using a longitudinally modulating cryogenic system mounted around the sampling loop of a two-position loop injector. The setup was hyphenated to a fast low thermal mass gas chromatograph, allowing transient concentrations of semivolatile analytes to be monitored in real time with a time resolution of 4.5 min. The performance of the instrument, and in particular its cryotrapping efficiency, was characterized using a mixture of long-chain alkanes, methyl esters, ethyl esters, and alcohols of different volatilities. The device was found to be ideally suited to the analysis of semivolatile compounds with boiling points ranging between 190 and 320 degrees C, which are typical for a majority of perfumery raw materials. The new instrument was successfully used to monitor the release of eight odorant compounds from cotton towels to which fabric softener had been applied that alternatively contained the fragrance in free form or in microencapsulated form. The analytical results, unprecedented in their level of precision and time resolution for such an application, evidenced the major impact of microencapsulation technology on the kinetics of fragrance release during the drying of the towels and on the triggering of additional fragrance release by applying mechanical stress to the fabric to rupture the microcapsule walls.

The release of volatile bioactive molecules, such as fragrances, can be controlled by microencapsulation in core-shell polymeric delivery systems. Currently, most of the available polymers are based on melamineformaldehyde materials, and the release is generally triggered by the rupture of the brittle and stiff shell.However, formaldehyde-based chemistry may often be undesirable in applications for consumer goods such as personal care products or detergents for fabrics, and there is a strong need for formaldehydefree microcapsules in these applications. In this article, formaldehyde is successfully substituted by glyoxal and its derivatives to allow the polymerization of melamine and other amines to prepare oligomers as starting point for core/shell polymerization. The oligomer synthesis is optimized via the reactant composition and towards an enhanced potential cross-linking density. The formulations with the most branched oligomers are applied at the interface of oil-in-water emulsions to prepare microcapsules. Their capacity to retain volatile molecules is measured by thermogravimetry and their mechanical properties are measured by micromechanical testing using compression-retraction cycles on multiple individual microcapsules. The results reveal an excellent retention capacity for volatile molecules and tunable mechanical properties that make these capsules highly suitable as a formaldehyde-free alternative to conventional aminoplast microcapsules.

The evaporation kinetics of pure Romascone 1 (methyl 2,2-dimethyl-6-methylene-1-cyclohexanecarboxylate) and Romascone 1 when mixed with vinyl acetate (VAc) nanoparticles have been determined by using thermogravimetric analysis. For pure Romascone 1 , the evaporation rate follows an Arrhenius dependence with temperature. When Romascone 1 is mixed with VAc nanoparticles, two evaporation mechanisms are identified depending on the presence of comonomer and crosslinking degree. (a) Evaporation limited by the presence of non-interactive nanoparticles. The evaporation rate is governed by the evolution of the equilibrium vapor pressure that depends on the volume fraction of volatile molecules. (b) Evaporation limited by the diffusion of volatile molecules through a polymeric particle wall.Since the diffusion depends on the physical state or structure of the polymeric nanoparticle phase, the volume fraction of volatile molecules is a determinant parameter. Furthermore, a sudden modification in the evolution of the diffusion coefficient with volatile volume fraction gives rise to discussion on phase transition.