A STUDY OF THE SWELLING OF HAIR IN MIXED AQUEOUS SOLVENTS (1) By E. I. VA•,•co, Ph.D. Polytechnic Institute of Brooklyn, N.Y. AND GAuu•t, •BAR•ETT Warner-Hudnut, Inc., New York, N.Y. THE SWELLING of fibers and other polymers is the process where- by fibers in contact with vapors or liquids incrbase their volume. No doubt the swelling is caused by the up-take of vapor or liquid by the fiber. The importance of the swelling phenomenon is common- place. The theoretical significance of swelling lies in its relation to the chemical structure and the organization of the polymers. With the possible exception of x-ray investigations, no other method has shed more light on the sub- microscopic structure of fibers than the study of swelling. The practi- cal significance of swelling is due to the fact that it forms the basis for such processes as dyeing and plasticizing. Most of the finishing processes of textile fibers are based on swelling. Cosmetic processing of human hair, such as setting, either temporarily or"permanen tly," as well as shampooing and dyeing, involves swelling. It is therefore not surprising that the swelling of keratin fibers has been made the subject of numerous investigations. However, due to the diversity of methods employed, available data on human hair is lacking coherence, and it shows many voids. The purpose of our study is to fill in some of the voids and to collect extensive data by using a uniform and convenient method. In the following we present some of our results and attempt their interpre- tation. DESCRIPTION OF THE METHOD Swelling can be determined by measuring the change which occurs either in the volume or in the weight of the polymer when brought into contact with a vapor or a liquid. In the case of fibers, the volume change can be directly observed only with the aid of a microscope. Due to the variation of the fiber diameter, a number of individual measurements are required in order 108

SWELLING OF HAIR IN MIXED AQUEOUS SOLVENTS 109 to determine one significant value. This makes the method somewhat tedious. The observation of the change in weight is more convenient, but it poses the problem of how to remove the excess liquid clinging to the surface of the fiber and in the capillaries between the indi- vidual fibers. Blotting is probably the simplest means to accomplish this, but hard to define for sufficient reproducibility. Centrifugal drain- ing is the alternate method occasion- ally used with fibers. Preston, Nimkar, and Gundavda (2) of Manchester University, England have recently shown that the centrif- ugal treatment leaves considerable amounts of external liqui. ds in the capillary pockets formed by the assembly of fibers. If such is the case, this method is not capable of giving true values of imbibed liquid. However, we found that with human hair the centrifuge apparently re- moves practically all of the external liquid..The reason for this is that human hair is much thicker than the usual textile fibers, certainly thicker than the fibers used by Preston and his co-workers. The centrifugal method was our choice as the most convenient means to determine well-defined and repro- ducible values of swelling of human hair. The hair used was blended Euro- pean, dark brown, female hair, about 20 cm. in length, previously soaped and rinsed (supplied by J. Fleischer Co., New York, N.Y.) For easy handling the bundle of hair was separated into swatches approximately 400 to 800 mg. in weight. Each sample was tied to- gether with a double knot and condi- tioned for several weeks in a desicca- tor containing saturated potassium acetate, corresponding to approxi- mately 20 per cent relative humidity. We determined the regain of the hair conditioned in the desiccator by drying to constant weight in vacuum over phosphorus pentoxide at 100øC., and found a moisture content of 7.6 per cent. This value is in good agreement with the values of Chamberlain and Speak- man (3), which show for female hair a regain of 6.5 per cent on adsorp- tion and 8.0 per cent on desorption at 20 per cent relative humidity. In calculating the weight increase of the hair by swelling, the regain of the sample has been taken into account. Notwithstanding the fact that all samples as introduced in the swelling bath contained 7.6 per cent moisture, the values given in this paper refer to the bone- dry state of the hair. The swelling experiments were carried out at room temperature No special precautions were taken to maintain constant temperature but in the air-conditioned labora- tory the temperature remained be- tween 25 and 30øC. The swelling bath consisted of $0 ml. of liquid kept in ground-glass-stoppered Pyrex bottles. Concentrations for solids are expressed as weight of solute in grams per 100 ml. of total solution (wt./vol.) and for liquids, as weight of liquid solute in grams per