The application of polymers to wool is considered from the point of view of the surface free energies of wool and the polymers. A theory is developed explaining the effectiveness of different polymers in reducing felting shrinkage as heing due to the ease with which spreading can occur over the surface of the wool fibers. It is shown that a useful criterion for spreading is that γ, (the critical surface tension) of wool must be greater than γe of the applied polymer. Spreading coefficients are calculated for various polymers on normal wool and on wool pretreated with chemical reagents. The spreading coefficients agree with the relatiye effects of chemical pretreatments, which can improve the efficiency of polymer treatments. The best pretreatments are those which increase the critical surface tension of wool from 45 dyne cm (normal wool) to 65-70 dyne cm.

The critical surface tension of wool fibers was measured using the sink-float technique with various classes of test liquids. Nonpolar organic liquids and aqueous surfactants gave similar values of γ, but much lower values were obtained with butanol/water mixtures. Adsorption of butanol on the surface of the fibers is thought to be responsible for the low values of γ in the latter case. Removal of lipid material from the surface of fibers by extraction increases γ from 30 mN/m to 37 mN/m, similar to that obtained for horn keratin or polypeptide material. Exposure of fibers to a corona discharge in air at atmospheric pressure also increases γ.

The durability of wool/polymer adhesive Joints in wash liquors of different surface tension was determined by measuring the rate of felting shrinkage of polymer-treated wool sliver and fabric in each liquor. The rate of felting shrinkage increased as the surface tension of the liquor decreased. This trend in the rate of felting shrinkage of polymer-treated wool agreed well with the trend in the magnitude of the thermodynamic work of adhesion of a wool/polymer “adhint” in different liquids, calculated assuming only secondary bonding forces across the wool/polymer interface. Limitations of the theory are discussed

A study of the treatment of wool with a series of self-cross-linking polyacrylates has shown a wide range of possible uses in wool finishing. The softer polyacrylates give better resistance to felting and a higher increase in abrasion resistance than the harder polymers, and are more generally useful since reductions in felting, tumble drying shrinkage, and pilling, and increases in tensile strength and abrasion resistance are obtained with no significant changes in stiffness, tear strength, or wrinkle recovery. However, the harder polymers can be used to obtain improved washability and durability of wool fabrics, together with increased stiffness and fullness if desired.Reduced felting is probably due to partial covering of fiber surfaces by polymer. rather than to fiber bonding, but some bonding can occur and this may produce such properties of polymer-treated wool such as reduced pilling and resistance to tumble drying shrinkage. , ~

The rate of felting of an untreated wool fabric in buffer solutions (in the presence or absence of nonionic detergent) increases with increasing temperature of the felting solu tion until a maximum rate is reached at 40-70° C. This rate then remains constant with further increase in temperature up to 90° C. The exact temperature at which the maximum is reached depends on the pH of the solution and on the action of the machine used for felting. Behavior is different in soap solutions, the maximum rate, reached at 40-50° C. being followed by a rapid decrease in rate with further increase in tempera ture up to 90°C. With wool made shrink-resistant by industrrally used oxidation procedures, the rate reaches a maximum at 30-40° C. depending on the pH of the felting solution. The rate decreases rapidly with further increase in temperature. Relative to untreated wool, there is a contmual decrease in felting rate of the shrink-resistant wool with increasing temperature. This is due to changes in the inherent felting property of the shrink- resistant wool with temperature of the felting solution, and not to irreversible changes in wool structure brought about by chemical attack of the solutions on the treated wool. The results emphasize the need for accurate temperature control in all felting tests and also show that best results would be obtained with shrink-resistant wool if solutions used for laundering were of high pH and at high temperatures. However, the use of such solutions at present is hunted by questions of dyefastness and possible damage to the wool.