ANNALS OF THE UNIVERSITY OF ORADEA FASCICLE OF TEXTILES, LEATHERWORK 67 THE INFLUENCE OF THE NUMBER OF RIPPLE OF POLYACRYLONITRILIC FIBERS COTTON TYPE ON YARN PROPERTIES HRISTIAN Liliana 1 , BORDEIANU Demetra Lacramioara 1 , BŐHM-RÉVÉSZ Gabriella 2 1 "Gheorghe Asachi" Technical University of Iasi, Faculty of Textile, Leather & Industrial Management, Department of Engineering and Design of Textile Products, Blvd. Mangeron, No.28, Iasi, Romania 2 University of Oradea, Department of textiles-Leather and Industrial Management, B.St.Selavrancea Str. No. 4, 410058, Oradea, Romania, Corresponding author: Hristian Liliana, e-mail: hristian@tex.tuiasi.ro Abstract: In this study we aimed the influence of the number of undulations of polyacrylonitrile fibers, cotton type, on the properties of yarns with Nm50/1 fineness, made on BD 200 the rotor spinning machine. Rotor spinning of the synthetic fibers is largely influenced by some characteristics of the fibers as being: the quality and quantity of the avivage, frequency of undulations and the number of defects fiber. Tensile properties and structural characteristics aspect of the yarns carried on BD 200 rotor spinning machine are determined, at the fiber content, the structural model and the technological parameters of processing, by the result of the transfer of fibers proprieties, into the meaning fiber-yarn. The yarns structural compactness, determined by the degree of twisting and tensional properties are defining for the quality of yarns and warrants the corresponding to their destination. Structural characteristics of the yarns which are characterized by complexity and diversity of their actions were studied by determining the linear irregularity (U%) , standard deviatin (CV%) and the imperfections in the form of thinnin (S), thickening (G), neppines (N), relative to 1000 m yarn. Key words: fibers undulations fibers, linear irregularity, breaking length, rotor spinning machine, yarns resistance. 1. INTRODUCTION The rotor yarns are characterised by significant quality parameters, such as unevenness of linear density, the number of faults, and hairiness, which are better than those of ring yarns, and can be accepted as yarns of high quality [1]. The quality of the spun yarn can be significantly improved, while using equally raw material, by a suitable selection of the spinning system and the type of the spinning machine used [2]. Open-end (OE) rotor spun yarns have certain characteristics which differentiate them from conventional ring-spun yarns. This is because of differences which can be noted between their production method and structure [3]. In contrast to ring spinning, twisting during rotor spinning takes place from the inside onwards. Yarn elongation at break generally decreases as the rotor speed increases. This variation may be attributed to the increase in yarn tension at higher speeds and with