Лако-красочные материалы — производство

Discoloration and performance issues are important. For example, will the perfume diffuse from the shampoo pack and then again as the hair is being washed in warm water? Will it be substantive on the dry hair? Will it be soluble in the shampoo base? In Chapter 11, the issues relevant to predicting the performance of fragrance chemicals in certain situations are discussed. Molecules with a low relative molecular mass (RMM), for example ethyl hexanoate and limonene, diffuse most speedily on opening the cap of the shampoo bottle. Furthermore, depending upon their log P value, they are more or less ‘happy’ in the mainly aqueous environment of the shampoo: the higher the logP value, the more hydrophobic the molecules and vice versa. Hence, molecules such as limonene with relatively high logP (4.46) diffuse more readily than more polar molecules of similar RMM, such as 2-phenylethanol (phenyl ethyl alcohol or PEA) whose log P is 1.52.

Other factors complicate the situation and must be taken into consideration. An important one is the odour intensity of the molecule. A few very potent molecules in the headspace can give a greater odour appreciation than a large number of low intensity molecules. Another consideration is the active detergent level of the shampoo, which affects both the appreciation of the fragrance in the headspace above the shampoo and the solubility of the perfume oil in the detergent system. A system with a low concentration of active detergent has a smaller reservoir of micelles in which to solubilize the perfume mixture. Thus, more perfume is available for the headspace because less can be ‘dissolved’ in the shampoo base.

Substantivity on the hair is another important consideration when creating shampoo fragrances. The consumer expects his or her hair to be perceived as clean and fresh. This impression is closely linked to the longevity of the perfume ingredients on the hair. In this case, the molecules with high RMM values tend to be the ones that remain on the hair after rinsing and drying. Again, the odour intensity must be sufficiently high for detection by the nose as the number of molecules laid down on the hair surface is relatively small. Chapter 12 gives clues as to which fragrance molecules are most likely to be retained by hair protein, rather than disappear down the plughole along with the foam! Low logP value molecules tend to stay with the water. In fact, the perfumer also relies on substantivity data obtained by painstaking, empirical, ingredient studies. Dozens of hair switches are washed, rinsed, and dried following a protocol developed to distinguish between the good, poor or indifferent ingredients when assessed by a panel of perfumers. This information is then added to the perfumer’s knowledge base for future use.

So, for the shampoo version, the same changes to avoid discolora­tion are made as for the soap version. However, the percentage weight of citrus oils is increased to boost the limonene content. The fruity notes are also made more dominant, as these are favoured by many shampoo consumers. It is necessary to check that the watery, floral and tropical fruity notes are detectable on the hair after the shampooing process.