Can Fabric Release a Floral Fragrance Little by Little?

There are ways to make a fabric-softener fragrance linger on cloth other than simply adding more perfume. One approach is to attach the part that will become a fragrance to another molecule, then release it little by little on the fabric.

A study published by Serge Lamboley and colleagues in 2023 investigated “profragrances” that release floral and fruity odorants. Which molecular structures make it easier to sustain fragrance release from cotton after a fabric-softener treatment? The study connected molecular reactions with the amount of fragrance that actually moves from cloth into the air.

A different mechanism from breaking a capsule

A profragrance is a precursor that generates an odorant through a reaction. Unlike microcapsules, which enclose fragrance in tiny containers that break under friction, it releases fragrance when chemical bonds within a molecule are cleaved.

The structures used here were imidazolidin-4-ones, which release fragrance through a decomposition reaction involving water. The researchers synthesized several precursors by reacting three floral or fruity cyclopentanone fragrance materials with materials derived from amino acids and other starting materials.

The aim was not simply to make something that decomposes quickly. It had to remain stable in a bottle of fabric softener yet release fragrance at an appropriate rate after dilution and deposition on cloth. Reconciling those requirements is the challenge of this technology.

The same connectivity, but different reactions in three dimensions

The synthesized precursors included stereoisomers: molecules with the same atomic connectivity but different arrangements in space. The researchers separated these where possible and characterized them using methods including NMR, which probes molecular structure.

When some precursors were kept in methanol and examined over several weeks, separately isolated isomers interconverted and approached a particular mixture ratio. Whichever form was present initially, the composition tended to settle toward a similar mixture with time.

A state in which forward and reverse reactions balance and the overall proportions remain constant is called equilibrium. The speed of reaching it, however, was not the same in every case. Among precursors derived from the amino acid proline, some decomposed or changed form relatively quickly, while others did so more slowly.

Recreating a fabric-softener treatment on a small scale

For the fabric tests, the team added precursors to an unperfumed fabric-softener formulation. They diluted it approximately 330-fold with water in a small vial and added a 15 cm square of cotton. After shaking for 3 minutes and leaving it for 2 minutes, they wrung out the cloth and hung it up to dry.

The control was a softener containing the same fragrance that the precursor would release, added directly as the free odorant. The amounts were matched by the number of fragrance molecules potentially released from the precursor, not simply by using equal weights of precursor and fragrance.

This was a laboratory simulation of a fabric-softener treatment, not a consumer trial using household washing machines. The researchers measured fragrance release after the cotton had dried for either 1 day or 3 days.

Measuring fragrance in the air around the cloth

The dried cloth was placed in a small sampling chamber, and air at 25°C and 75% relative humidity passed through it at a constant rate. The fragrance carried out by the air was trapped and quantified by gas chromatography. This recorded the headspace concentration around the cloth over time.

Cloth treated with precursors produced higher headspace concentrations than controls receiving fragrance directly. The extent depended on precursor structure: when the authors summed concentrations across the sampling points, the comparison gave factors of approximately 2–100.

Precursors made with proline-derived materials released particularly large amounts in this comparison. Values near the maximum reached approximately 80 ng per liter of air. A nanogram, abbreviated ng, is one-billionth of a gram.

The figure of 100-fold, however, compares measured headspace concentrations. It does not mean that people perceived the fragrance as 100 times stronger, that it lasted 100 times as many days, or that 100 times as much fragrance remained on the fabric. The study did not assess perceived intensity or preference in people.

Structures that release early and structures that release later

Release after 1 day and after 3 days also differed between precursors. Those derived from glycine and some other materials tended to release more at the 3-day measurement than at the 1-day measurement. Proline-derived precursors, by contrast, generally released more after 1 day, indicating relatively rapid fragrance delivery.

Even within one type of precursor, stereochemistry could reverse the ranking. In one pair of isomers, the form that released more after 1 day released less after 3 days, when the other form overtook it. Early release alone therefore does not determine the later pattern.

Stereochemistry did not make a large difference for every precursor. Glycine-derived compounds gave similar headspace concentrations even when their isomers were separated. Both the molecular framework and its spatial arrangement need to be considered when selecting a release rate for an intended use.

A closed solution is not the same as cloth in flowing air

An important feature of the study was its distinction between equilibrium in solution and continued evaporation from cloth. When the fragrance remains within a system, the formation and decomposition of the precursor can be considered as opposing reactions in balance.

When fragrance evaporates from fabric and is carried away by air, however, its local amount decreases. This favors further reaction toward fragrance release from the precursor. The authors suggest that this difference helps explain sustained release from dry cloth.

If isomers also move toward the same mixture over time, costly separation may not always be necessary for product use. Experiments with separated isomers help reveal the mechanism, while the practical prospect may be to use mixtures. The authors regarded this as another important implication.

What still needs checking before product use

Measurements were performed at least twice, but temperature and humidity during fabric drying varied, and the results showed variability. The findings compare the particular softener formulation, cotton, drying times, and measurement conditions used here. They need not be identical with other fibers, formulations, or real wearing conditions.

The authors present bio-based amino-acid materials as a direction toward environmentally considerate release technology. The study did not, however, comprehensively establish long-term product storage stability, biodegradability, or skin compatibility. Controlling fragrance delivery and establishing a whole product’s safety and environmental performance are separate tasks.

All four authors conducted the research as employees of Firmenich SA. The work received no external funding, and some of its results are covered by patent application WO 2021/209396.

Summary

Delivering fragrance as molecules that decompose to release an odorant, rather than adding the odorant directly to cloth, increased headspace concentrations after 1 and 3 days. Changing the precursor framework and stereochemistry also changed its release rate.

The key is to design the mechanism that retains fragrance together with the process by which it escapes into the air. This study offers molecular-level clues for connecting stability in a closed container, deposition on fabric, and release after drying.

References

Lamboley, S., Vuichoud, B., de Saint Laumer, J.-Y., & Herrmann, A. (2023). Release of Volatile Cyclopentanone Derivatives from Imidazolidin-4-One Profragrances in a Fabric Softener Application. Molecules, 28(1), 382. DOI: 10.3390/molecules28010382 / Full original article. Original article license: CC BY 4.0.