J. Cosmet. Sci., 60, 135–141 (March/April 2009) 135 The Aqualon SLT: A novel device for measuring hair stiffness and lubricity K. ABRAHAM VAYNBERG and M. NALL, Ashland Inc., 500 Hercules Road, Wilmington DE 19804. Synopsis The ability to quantify hair property changes in response to treatment is essential to the successful develop- ment of new formulations and benefi ting agents. In the attempt to expand the toolbox of hair tress testing tools, we developed a device that allows hair scientists to measure hair tress changes in stiffness and lubricity. The tool is based on a system of pins mounted on free rotating bearings and is operated in two modes: rotating and stationary. The hair attributes are measured by threading a hair tress through the pin assembly and measuring the total work of pulling through in rotational and stationary modes (the latter mode is obtained by immo- bilizing pins by a retaining plate). The data thus obtained is de-convoluted into the work of apparent stiffness (rotational mode) and the work of the friction-on-pins or lubricity (stationary mode minus the apparent stiff- ness). The data can be further reduced to produce an apparent friction coeffi cient defi ned as a ratio of the apparent lubricity to the apparent stiffness. This work demonstrates the utility of the parameters measured by the Aqualon SLT and illustrates how the device can be used to predict and understand the impacts of various hair treatments. INTRODUCTION Consumer panel studies are the ultimate in decision making when it comes to personal care products. These studies, however, are expensive and time consuming to be suitable for day-to-day R&D activity and thus, not surprisingly, every application lab contains devices intended to quantify hair attributes to help streamline the development process. The single most widely used test is based on measuring the combing forces in both the wet and dry state, fi rst described by Newman et al. (1) and further improved by Kamath et al. (2). The test captures the effect of conditioning treatments and generally refl ects the combined characteristics of comb-to-hair friction, hair-to-hair friction, hair entangle- ment, stiffness and volume (applicable in dry state). Hair stiffness is an attribute recognized to be important to hair styling and relates to the body and volume of a hair assembly (3). Several methods exist to measure hair fi ber stiff- ness. For example, hair fi ber stiffness can be deduced from fi ber bending characteristics (4) or through torsional rigidity (5). These methods provide fundamental mechanical infor- mation for individual hair fi bers but the information can not be readily extended to the hair assembly stiffness due to the hair fi ber variability and the fi ber to fi ber interaction. A three-point bending experiment had been recently described to measure “hair supple- ness.” In this experiment, a tool imposing the three-point bend was slid along the tress

JOURNAL OF COSMETIC SCIENCE 136 length and the force measured. “Suppleness” thus combines attributes of the hair friction on the tool, fi ber-fi ber friction and the fl exural stiffness of hair (6). Our own device, con- ceived and developed independently of this work, takes the approach a step further by allowing to separate the contributions of fi ber-fi ber friction and stiffness, referred to as apparent stiffness in this work, from the friction on the surface of the tool, defi ned as appar- ent lubricity. The design of the Aqualon SLT, measurement method, and the utility of stiffness and lubricity are described herein. AQUALON SLT DESIGN AND MATERIALS Figure 1 illustrates a prototype version of the Aqualon SLT* in the assembled state placed on a platform at the base of the Instron Tensile Tester. The plastic screw on the face of the device is used to switch between rotational (pins can freely rotate) and stationary (pins immobilized) modes of operation. The action of the screw is illustrated in Figure 2. The inside of the detached face plate shows attached rubber circles located, when assembled, opposite to the pins. When the face plate is engaged, the rubber circles push on the pins and immobilize them. Alternatively, when the screw is pulled out, the spring (also shown in the fi gure) acts to push the plate away from the pins thus allowing them to rotate freely. Pins are covered by tightly fi tting replaceable Tefl on sleeves. Figure 3 shows how the hair tress is threaded through the tool. Testing was carried out with Caucasian virgin and bleached hair tresses from International Hair Importers weigh- ing 3 grams and measuring 1 × 12 . The Aqualon SLT, however, can be readily adjusted *Patent pending. The Aqualon SLT device in its improved form can be obtained from Ashland Aqualon Performance Materials by contacting Abe Vaynberg at kvaynberg@herc.com Figure 1. The Aqualon SLT placed on platform mounted on Instron Tensile Tester.