The Critical Surface Tension of Wool

Abstract

A rapid method for the measurement of the critical surface tension γ c values of individual wool fibers is described. Using this method, a comprehensive study of the wettability of untreated wool fibers has been carried out, and subsequent changes in γ c after various chemical treatments have been monitored. It is shown that the value of γ c obtained depends on the liquid series used for the measurement; the use of aqueous alkanol solutions for such measurements is criticized. The value of γ c for Hcrcosset-57 has been measured, and the spreading coefficient S and work of adhesion WA for this polymer on wool have been re-evaluated.

Surface Energy of Wool

“…When the liquids cover a range of polarities, the CST obtained may be either higher or lower than the surface energy of the solid. This was the case when a value of 37 mN/m was obtained for a Southdown wool fiber [7]; additionally, only receding angles were measured, which would tend to give a high CST. For a range of liquids all of the same polarity, the resulting CST will be lower than the surface energy, unless the polarity of the liquids equals that of the solid, when the two quantities will coincide [8].…”

“…The contact angle may be calculated from the dimensions of a single droplet on a fiber [ 10], but the scale structure would still be a problem with wool, while evaporation and sorption of the liquid would lead to receding angles. The microscopic method of Grindstaff [ 16] offers the possibility of avoiding the scale edges, but when this method was applied to wool, only receding angles were measured because it proved difficult to measure advancing ones [7]. Furthermore, the Grindstaff apparatus requires constant manipulation during a number of measurements on each fiber.…”

“…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].…”

“…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].…”

“…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].…”