Mechanical Conditioning of Textile Fibers

Abstract

Mechanical conditioning denotes the alterations which remain temporarily or permanently in textile fibers after they have been deformed. These alterations are the result of changes in the structure of textile fibers. The altered tensile properties, including tensile recovery behavior, of mechanically conditioned fibers were investigated. Cotton, Fortisan, Ethocel, acetate, silk, viscose, Dacron polyester fiber, Orlon acrylic fiber, Vicara, Vinyon NORU, casein, Nylon Type 300, Saran, human hair, and wool were tested either as single fibers, as multifilaments, or as staple yarns. Mechanical conditioning was performed mostly by repeated extensions (cycling) to 80% of the extensibility. The response of fibers to this procedure varies widely. If a fiber is susceptible to mechanical conditioning due to its visco-elastic behavior, its morphology (length, cross section) and stress-strain properties are altered considerably. The new extensibility and the work of rupture decrease, and the elastic recovery increases. The initial modulus and the breaking tenacity can remain unchanged; they can increase or they can decrease. The yield point can become more or less pronounced, or it can increase or decrease; even new yield points can appear after mechanical conditioning. In connection with mechanical conditioning, the following topics were investigated : ( 1) altera tions occurring spontaneously or produced by heat and swelling after mechanical conditioning of cellulose acetate; (2) structural changes of cellulose fibers due to stretching (stress hardening and fatigue) ; (3) cold-drawing of a Dacron monofilament; and (4) behavior of a cotton thread after repeated extensions to different strain levels.