J. Soc. Cosmet. Chem. 25 297-306 (1974) ¸ 1974 Society of Cosmetic Chemists of Great Britain Studies of the factors controlling the action of hair sprays II. The adhesion of hair spray resins to hair fibres R. W. RANCE* Synopsis--Measurements have been made of the ADHESION of HAIR SPRAY RESINS to HAIR FIBRES and the importance of adhesion in determining hair spray properties is discussed. The similarities between the technology in the bonded fabric field and in the hair spray field are considered and useful extrapolations concerning adhesion and other resin properties may be made. For good adhesion at least two rextuircmcnts arc apparently necessary. The viscosity of the resin solution must be low so that the resin remains in close interfacial contact with the fibre throughout the large dimensional changes occurring as the solvent evaporates. Also the resin itself must be sufficiently deformable to allow any stresses due to these dimensional changes to be dissipated and to enable the dried joint to withstand impact and bending. These factors, which emerge from earlier studies of adhesion, are found to be applicable in the present study. INTRODUCTION Polymer adhesion to wool fibres is known to be an important factor in the production of anti-felting properties on wool fabrics (1), and in the manufacture of non-woven textiles (2-4). Tikhomirov and Gusev have reported an investigation of the structural bonds and the properties * Unilever Research, Isleworth, Laboratory, 455 London Road, Isleworth, Middlesex. 297

298 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS of bonded fabrics, and consider that the strength of the bond between the binder and the fibre is one of the principal factors in the tensile strength of such fabrics (4). The strength of this bond depends mainly on the forces of adhesion which characterize the efficiency of the binder. These authors give results of measurements of the adhesion of polymeric binders to wool fibres and those results are among the first attempts at an experimental determination of the adhesion of polymers to natural fibres. Similar measure- ments on hair fibres do not seem to have been reported. The requirements of a good adhesive have been defined (5, 6) as the ability to wet the adherend, to be solid at the temperature of usage, and to be sufficiently deformable to minimize stress concentrations during solidi- fication. This latter requirement is also advantageous in the hairspray field since the resin bridges will be less liable to fracture during flexing of the hair fibres. Good adhesion of a hairspray resin to hair combined with good tensile properties of the resin will promote strong and lasting hold, while poor adhesion will give poorer hold but easy elimination on brushing or combing. The adhesive power of polymeric materials is normally assessed from tests on large specimens where the surface area of contact of the adhesive joint can be measured easily. Determination of adhesive strength becomes considerably more difficult when the adherend is a natural or synthetic fibre since the adhesive strength of a large specimen would be greater than the tensile strength of the fibre. The area of contact of the adhesive and the fibre surface must be kept small, therefore, but at the same time must be capable of accurate measurement. Thus in measuring the adhesion of hairspray resins to hair fibres a technique must be used in which the fibres are introduced into a resin block so that the fibre is bonded along a given, measurable length. Such a tech- nique has been developed by Shiryaeva, Gorbatkina and Andreevskaya (7) for the measurement of adhesive strength to glass fibres. This technique was adapted for use in the present study. EXPERIMENTAL A 10•o w/w solution of hairspray resin was allowed to evaporate in a flat circular silicone rubber mould to yield a resin film about 300 [tm thick. The dried film was cut into strips about 1 mm wide and 10 mm long while the film was still soft and flexible, and a small amount of the polymer