Surface Energy of Wool

Abstract

The dispersion and polar components of the surface free energy of untreated and chlorinated Lincoln wool fibers have been determined from the wetting forces of water and methylene iodide. The values obtained for the untreated wool fibers were close to those previously reported for human hair. Chlorination increased only the polar component. The three-phase boundary moved in steps corresponding to the scale spacing of the fiber surface. Procedures for determining relevant wetting forces were developed. The surface energy of wool is an important factor in the wet processing of wool and in the performance of the finished garment. In shrinkproofing wool by polymer deposition, surface thermodynamics may control the spreading of the polymer on the fiber surface and affect the subsequent adhesion of the polymer to the fiber [ 14]. Previous workers [2,7,14,26,30] have characterized the surface of the wool fiber by determining the critical surface tension (CST): this is the value of the surface tension of a wetting liquid at which the contact angle becomes zero [33].Certain chemical treatments of wool, such as chlorination, have been found to increase the CST.Feldtman and McPhee [ 14] proposed that the condition for spontaneous spreading of a liquid polymer on a fiber was that the fiber must have a higher CST than the polymer. Such treatments as chlorination did indeed increase the CST of the fiber and also resulted in a dramatic improvement in the shrinkproofing efficacy of the subsequent polymer application [ 14]. Although this effect was consistent with the theory, there are alternative mechanisms by which such treatments may improve the distribution and adhesion of a polymer. These mechanisms include the increased probability of chemical interactions between the polymer and the treated wool [ 13], the generation of anionic groups in the wool [ 13], and increased diffusion of polymer into the fiber [6,29]. At present, it is not clear to what extent changes in the surface energy of the wool affect the application of various polymers. The CST is not normally equal to the surface energy of the solid; if it were, the interfacial energy between the solid and the wetting liquids used in the test would have to be zero. In general, this condition is not met, and equations have been proposed expressing the interfacial energy in terms of the dispersion (ysj and polar (-ysP) components of the surface energies (ys) of the two phases [ 17, 24, 31 ]. Owens and Wendt developed a method to determine these components for any solid from measurements of the contact angles of a pair of pure liquids on the solid [24]. At present there are two alternative equations that can be used: the extended Fowkes' equation and Wu's equation. The form and use of these equations has been adequately presented in the literature [27, 32]. The optimum condition for spreading and adhesion is when the values of 'Y? and ys for the adhesive are equal to the values for the adherend [32]. In our laboratory, contact angles for each fiber were calculated from meas...

Chemical Modifications on Human Hair Studied by Means of Contact Angle Determination

“…As it is well known, the scale direction of fiber immersion plays an important role in adhesion tension hysteresis (30). It can be observed for UT fibers (Fig.…”

Reactive Plasma Species in the Modification of Wool Fibre

“…Hsieh and Yu (1992) demonstrated that this method of measuring contact angles 0 gives the same values as single fibre methods, for a range of materials including cotton. Single fibre measurements for wool were obtained by Brooks and Rahman (1986).…”

Effect of Shrinkproofing Pretreatments with Solvents and Polyamines on the Surface Energy of Wool

“…Our previous work on the application to wool of a method for determining the dispersion ('Y /) and polar ('Yl') components of the surface energy [2] has led to this investigation of those solvent and polyamine treatments, previously characterized only by CST measurements. Briefly, the method involves measuring the wetting forces as fibers are immersed in water and in methylene iodide.…”

“…We expected that a knowledge of the effect of these pretreatments on both components of the surface energy would point the way to improved shrinkproofing treatments. ' Experimental Raw Lincoln wool, cleaned successively with petroleum ether, water, methylene chloride, methanol and water, as described previously (sample UT 1 ) [2], was soxhlet extracted with a benzene/ethanol/water azeotrope for 6 hours. Raw wool from the same lot was soxhlet extracted with petroleum ether for 8 hours and with diethyl ether for 4 hours, then exhaustively washed in water (sample UT2).…”

“…The apparatus and procedure for determining ysd and 'Y l were basically as we described previously [2]. In this work, only advancing, dynamic wetting forces were used, so as to obtain surface energy values relating to the unwetted wool fibers.…”