Лако-красочные материалы — производство

KEITH D. PERRING

PERFUME CREATION AND PHYSICAL CHEMISTRY

The perception of a perfume depends, in the first place, upon the presence of odorant molecules in the air, and upon their nature and concentration. Most perfume starts off life as a liquid comprising a wide variety of molecules and of a known composition. In general, perfumers do not have a corresponding knowledge of the composition of volatiles in the air above such a mixture, except on those occasions where headspace analysis has provided hard analytical data (see Chapter 12). Perfumers therefore have to build up knowledge bases that summarize the olfactory behaviour of hundreds of ingredients under many different circumstances:

—in admixture with diverse permutations of other perfume materials (commonly 20-100 different feedstocks, any of which may them­selves be complex oils);

—in product forms ranging from aqueous liquids to powders, creams, solids, etc.;

—on substrates such as hair, skin, cotton, etc.

Gaining this sort of experience is a lifetime’s work for a perfumer, but it is possible to help the process by understanding the factors that govern the physical performance of perfume. One of the challenges for the physical chemist is to be able to predict what happens when a perfume is incorporated into different products; in particular, how does the composition of the perfume headspace alter, and what will be the ‘in­use’ perfume behaviour (for example, how to maximize a perfume’s

useful lifetime on skin, or ensure that a laundry perfume not only supplies a pleasant smell in the detergent, but also on the fabric after drying).

It is known that as soon as a perfume is incorporated into a product matrix, pronounced effects occur on some ingredients, those for which the ‘microenvironmental’ interactions have changed significantly. Phy­sicochemical interaction is a consideration no matter what the base, whereas chemical interactions only become really important in con­sumer products possessing a reactive challenge for fragrance, for example products with low or high pH (e. g. below 4, above 9), or redox power (e. g. cold wave hair products or laundry bleaches). (Chemical stability issues are elaborated in Chapter 9.)

Physical fragrance-base interactions, which are very different to those experienced by fragrance ingredients when in the ‘bottle’, affect the profile of odorants in the headspace, and probably also have consequences for the evaporation characteristics. It is easy to see how complex this situation is, particularly in view of the ever-changing composition of the perfume as it evolves during evaporation. Never­theless, a number of broad generalizations based on physical properties can aid the perfumer in the selection of ingredients for any particular product and desired performance criteria. Some of the physicochemical properties that underlie ingredient behaviour are highlighted below, and are part of the knowledge base the perfumer brings to bear. In the particular case of the Business Scents Ltd brief, this knowledge here can be added to by studying the fragranced products analytically to quantify actual perfume headspace, and by studying the delivery profiles of the various perfume components to the target substrates, skin and hair. In this way, a broader range of perfume ingredients may be identified that will perform better from the point of view of transport and distribution — after that, it’s back to the perfumer.