PHYSICOCHEMICAL PROPERTIES OF DELIPIDIZED HAIR 359 array of mercury-cadmium-telluride detector and an automated high precision XY sample stage. Images were acquired with 6.25 μm step size, 8 scans for each spectrum and 8 cm-1 spectral resolution. IR spectra were analyzed using ISys 3.1 software (6). DIFFERENTIAL SCANNING CALORIMETRY A Q2000 differential scanning calorimeter (TA Instruments, New Castle, DE) was used with pressure resistant, high-volume stainless steel pans. Samples consisted of 8 to 12 mg of cut (2–5 mm) hair fi bers, along with roughly 55 (±1.5) mg of deionized water. Each pan was sealed and allowed to sit for at least 6 h at room temperature to insure equi- librium water content and distribution within the hair fi bers. Heating at a rate of 2°C was performed from 22 to 190°C in standard mode. Three repetitions per lot were con- ducted. TA Universal Analysis 2000 for Windows software, version 4.7A, was used to determine the denaturation temperature (Td) and the enthalpy of denaturation (ΔH). Peak integrations were performed using the sigmoidal horizontal method, with the left marker staked at 110°C and the right positioned in the middle of the post-transition fl at baseline section (typically just below 150°C). TENSILE STRENGTH An Instron (model 3345) universal testing system for compression and tension, manufac- tured by Instron (Norwood, MA), was used for tensile strength measurements. The in- strument was equipped with a 100 N capacity force transducer (model 2519-103) and pneumatic grips (250 N capacity) with rubber-coated jaws capable of holding single hair fi bers. Each fi ber was mounted with metal and the samples were extended at a rate of 25 mm/min with data acquisition set at 100 Hz. Before tensile strength measurements, fi ber diameters were determined with a laser micrometer (Mitutoyo, model LSM-5000) purchased from Dia-Stron, Ltd. DYNAMIC VAPOR SORPTION ANALYSIS A DVS Advantage-1 gravimetric vapor sorption analyzer from Surface Measurement Sys- tems (Alperton, Middlesex, United Kingdom) was used. Hair samples consisted of ap- proximately 25 fi bers tied into a small loop weighing approximately 5 mg. The average diameter of the fi bers of each sample was determined using a Mitutoyo laser micrometer (Dia-Stron, Ltd.). Samples were subjected to 0–90% RH at 25°C in steps of 10% RH followed by 90–0% RH in steps of 10% RH. Each sorption/desorption step was 8 h in duration. Data were analyzed using DVS Standard Analysis Suite V6.1.1, DVS Advanced Analysis Suite V6.1.1, and Isotherm Analysis Suite V2.1.1. MECHANICAL ANALYSIS OF HAIR-SHAPED OMEGA LOOPS The instrumentation and experimental procedures were similar to those used in previous work (7). In brief, omega loop hair tresses were constructed by gluing both ends of the hair
JOURNAL OF COSMETIC SCIENCE 360 (approximately 0.3 g of 3.5-in. long hair) to square Plexiglas plates using Duco cement, leaving 1.5 in. of fi bers between the tabs. The hair was wetted, then shaped into an omega loop using a Tefl on rod, and allowed to dry at 50% RH for 12 h. Mechanical measure- ments were carried out with a Texture Analyzer (Stable Micro Systems, Godalming, United Kingdom). We fi rst examine untreated hair, then we reinsert a Tefl on rod in the omega loop so that treatment with styling resins may be administered. Polymer-treated omega loops are allowed to dry for 12 h at 50% RH followed by measurements. STREAMING POTENTIAL ANALYSIS In this study, we used streaming potential instrumentation, referred to as a dynamic elec- trokinetic and permeability analyzer, manufactured by Better Cosmetics, LLC (Bethel, CT) (8). This custom-built device allows for the collection of electrokinetic parameters (streaming potential and conductivity) as well as permeability of fi ber plugs. The dy- namic electrokinetic and permeability analyzer consists of a streaming potential cell, valve assembly controlling the fl ow of liquids, conductivity meter, pH and temperature meter, pressure controller, test and treatment solution reservoirs, and electronic balance fl ow meter. INVERSE GAS CHROMATOGRAPHY SURFACE ENERGY ANALYSIS All analyses were carried out using an inverse gas chromatography surface energy analyzer and the data were analyzed using both standard and advanced SEA Analysis Software. For all experiments, between 1.5 and 2.0 g of hair samples (entire strands) were packed into an individual silanized glass column (300 mm long by 4 mm inner diameter). The sam- ples were run at a series of surface coverages with both alkanes (undecane, decane, nonane, octane and heptanes only four alkanes were used for calculations) and polar probe mole- cules (ethanol, acetone, ethyl acetate, dichloromethane, and acetonitrile) to determine the dispersive surface energy as well as the acid–base free energy of desorption. In this study, each column was preconditioned for 1 h at 25°C and 30% RH with helium carrier gas to normalize all samples at a humidity representative of ambient conditions. At no time were the samples exposed to dry helium conditions, as not to induce irreversible changes to the hair fi bers. All experiments were carried out at 25°C and 30% RH with a 10 sccm total fl ow rate of helium, and using methane for dead volume corrections. MATERIALS The majority of the experiments were performed on Asian hair purchased from Interna- tional Hair Importers and Products, Inc., Glendale, NY. Hair tresses were prepared by gluing 2 g of fi bers to a 1.5-in × 1.5-in Plexiglas tab with Duco Cement. The resulting dimensions of the hair tresses were 6.4 inch in length and 1.25 inch in width. Hair tresses were precleaned with a 3% ammonium lauryl sulfate solution and rinsed thoroughly before use in the experiments. Rinse-off treatments were administered with polyquaternium-55 and quaternium-26, which are commercial products by Ashland, Inc. (Covington, KY)
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