Effects of heat treatment on the mechanical properties of hair.
Synopsis A previous study having shown that there was no modification in superficial or deeper hair structure at temperatures below 100 degrees C, the influence of hair-drying conditions on mechanical properties has been examined. The hair speed and hair temperature given by different types of hair-drying equipment were considered and a novel method used each hair as its own control. Stress/strain curves were followed using an electrodynamometer and a range of hair types was considered: normal, grey, denatured, and bleached, the definitions being given by both appearance and the stress/strain curve. In comparison with ultimate structure, mechanical properties were modified at a lower temperature. The stiffness of the hair starts to increase markedly already at 40 degrees C for a drying time of 2 to 3 minutes and this appears.
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Centre de Recherche Appliquée en Dermobiochemie (C.E.R.A.D.), 51 rue Clement Marot, 69007 Lyon, France et Laboratoire de Pharmacie Industrielle et Technologie Parapharmaceutique, Faculté de Pharmacie, 8 avenue Rockefeller, 69008 Lyon, France.
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