LOAD-ELONGATION OF HAIR COILS 229 •.• CAHN ELECTROBALANCE HAIR FIBER ALLIGATOR CLIP HELIPATH STAND Figure 1. Apparatus to measure force to elongate hair fiber coils. carefully attached to the tip end of fibers by means of the adhesive on the tape. Weights were checked before and after use, and no changes detected. All experiments were conducted at 40% RH over a saturated solution of zinc nitrate in a glove box. RESULTS AND DISCUSSION LOAD-ELONGATION BEHAVIOR OF SINGLE FIBER CURLS The initial curled or coiled length, when released from the rods, was 9.5 -+ 2.5 cm. The fibers were then extended at a constant rate (2.18 cm/min) recording the load- elongation curve on a strip chart recorder through a Cahn © electrobalance (the load cell). In one procedure, neither end of the fiber could rotate thus extension involved both bending and twisting, and the shearing action became greater as the fiber approached its "straight" length. Figure 2 illustrates the observed load-elongation behavior for extension of a typical fiber coil by this method, and reveals three distinct regions. Region I represents the initial curl or the fiber coil length under its own weight just after removal from the rod and its initial extension. Region II represents the major extension of the coil, and Region III the point where the load increases rapidly and the fiber approaches its "straight" length. By a second procedure, fibers are water set and their root end attached to the electrobalance as before however, the tip end is attached to a clip mounted on a small petri dish resting on light mineral oil in a container sitting on the Hellpath stand. By this method the fiber can uncoil as it elongates. Fiber coils are then extended at the

230 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS z uJ I II III 30 • • 20 15 INITIAL CURL = 7.7 cm I• TAUT LENGTH= 30 cm I0 = . 0 0 •,0 4o 6o so i00 I•,0 140 160 leo •,oo t. OAD [MASS (,.g)] Figure 2. Load-elongation curve of single fiber coil. 6O 55 5O 45 • 35 z 30 ß • 25 - 20 UNCURLING _ I_ STRETCHING -i (A) CURL HOOKEAN LIMIT (B) CURL TURNOVER POINT (C) TAUT LENGTH (D) HOOKEAN LII•IT (E) TURN OVER POINT (F) STRESS TO BREAK I i i i i m i i I I0 I0 2 I0 3 I0 4 I0 õ LOAD [MASS (m(])] Figure 3. Total load-elongation curve of single hair fiber coil. (E)I ..... (F)