Crimp is the feature that illustrates the wavy form of wool fibers. Considering the very low moisture absorption as well as low heat insulation power of synthetic fibers, inserting crimp along the man-made fibers, improves the the transfer properties and hence renders man-made fibers more suitable for applications like apparel floor covering and home textiles. In this context, crimp frequency carries a great deal of importance and greatly affects the properties of the final product. Crimping the man-made fiber lies in the field of texturizing and is employed for almost all of man made fibers by stuffer box technique. Crimped staole fibers are converted to fibrous web using conventional carding process.The aim of this project was to investigate the effect of crimp frequency of polypropylene staple fibers on the sound and heat insulating properties of their non woven webs. To carry out this research, 3 lots of polypropylene fibers with linear densities of 9, 14, and18 denier was produced on an industrial scale melt spinning line equipped with sutffer box crimping unit. Low, medium and high levels of crimp frequency were chosen for each lot subjected to crimping unit limitations. The textured tows were then cut and then the non woven webs (10x10 cm 2 , 5 g/cm 2 ) were produced on a laboratory scale carding machine. The sound and heat insulating properties of the non-woven webs were measured by impedance tube and hot plate instrument, respectively. The results revealed that the sound absorption properties of non woven webs are not only affected by the crimp frequency of the fibers, but also factors such as fiber fineness, the thickness of webs as well as compression determine sound absorption. Higher levels of crimp frequency led to higher sound absorption by the carded webs, in other words the sound wave friction loss increases. The highest sound absorption coefficient was recorded for the sample with lowest fiber fineness and highest crimp frequency. As far as heat insulating properties are concerned, like sound absorption, apart from crimp frequency, other factors like fiber fineness and web porosity affected sound absorption. In this context, the air trapped between fibers plays an important role. The highest heat insulating property was also recorded for the web with lowest fineness and highest crimp frequency which were 9 denier and 1.9 crimp per cm, respectively. Keywords Crimp, sound absorption, heat insulation, nonwoven, polypropylene web
