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When choosing a hair spray, consumers are often guided by the degree of hold the product offers. However, surveys and market studies show that most respondents consider a pleasant touch to be just as important as good hold.
These contradictory goals present formulators with a challenge: a hair spray that gives a very firm hold has poor tactile properties—the hair feels unnaturally stiff, hard, inflexible and rough. Conversely, if a hair spray is to impart a pleasant, soft and natural feel, the hold will inevitably be reduced.
Other requirements, too, are contradictory. For example, the polymer film that forms on the hair must be readily soluble or dispersible in water so it can be washed out with water and shampoo, but it must not be hygroscopic or the hair will become tacky in humid air and lose its hold. Various desirable mechanical properties—failure stress and shear strength; elasticity and hardness—are likewise contradictory, as are the polymer film’s cohesive and adhesive properties.
For environmental reasons, hair spray manufacturers also seek significant reductions in the content of volatile organic compounds (VOC). If this involves substituting water for a considerable proportion of the ethanol, a highly volatile solvent, and if conventional polymer systems are used, both the formulations’ technical quality and the useful properties of hair spray products will be degraded. One of the consequences is an increase in the polymer solution’s viscosity and surface tension, which leads to the formation of large aerosol particles and prevents uniform distribution of the solution on the hair. In addition, a higher water content in organic polymers typically results in longer drying times and a more tacky film.
This is only an excerpt of the full article that appeared in Cosmetics & Toiletries, but you can purchase the full-text version.