Study On The Sound Absorption Properties Of Needle-Punched Nonwoven

With the development of science and technology, there are both advantages and disadvantages come along with it. The most important problem is envirenment pollution which has become the restriction on our social development. One of the three major sources of pollutin is noise pollution that has become more and more serious every day together with the development of manufacture and transportation industry. People's living condition has been seriously affected by noise pollution. The two main development directions of noise control technology are sound insulation and sound absorption. Sound insulation technology will cause secondary pollution or multiple pollution. Sound absorption technology is by means of energy dissipation. Then we can truly and effectively reduce noise. Mainly used for noise elimination is porous material which is used to be made by fibrous material. Textile materials processing technology is making products with fibrous material. And those products are all mostly with various shape of voids. But using defferent processing technology will make their voids much more defferent with each other. And this defference grows out much more deffernt sound absorption abilities of materials. That needle-punched nonwoven material prossess better sound absorption ability has been vertified. And the processing is low cost, high yield and environmentally friendly,etc. Needle-punched nonwoven is a kind of ideal material used for sound absorption, and recently has been widespread concern.This paper mainly contain two details:the structure and the fibre contentFor the structure part, several needle-punched nonwoven samples with defferent thickness, defferent bulk density and defferent combination structure were manufactured from polyester. Their noise absorption coefficient were measured using impedance tube instrument. The results show that in the low-mid frequency the sound absorption coefficient increase with the increase of thickness, and that in the high frequency the sound absorption coefficient increase in the beginning and then become lower. When we count out the average value of sound absorption coefficient, we discover that the value is linear corelation with the thickness of the material. The bulk density has the similarity with the thickness to the sound absorption coefficient. Several cobination structures of the solid core polyester needle-punched nonwoven and the hollow polyester needle-punch nonwoven were measured by the impedance tube. The results show that the combined structure with low density hollow material under high density solid core material has the better ability of sound absorption compared with others. More study on the sample with better sound absorption property, samples combined with different thickness of the two diffrent density parts were fabricated. The result show that different thickness combinations present opposite sound absorption performance in high and low frequencies. That is to say when the sample show better of sound absorption property in high frequencies, it will show a poorer performance in the low frequencies. An innovation study on the surface film show that surface film attached with higher density materials with hole on it has better sound absorption property, and especially good in the low frequencies.For the fibre part, we developed two denier levels and three different fibre shapes. Those fibre yield more surface area in the materials. We found that the material's sound absorption property increased with the surface area. We use cotton and flax fibers made into needle-punched non-woven materials and test the sound absorption property of those materials. The results show that there is no obvious difference between blended material sound-absorbing properties and pure stacking materials. Contrasted materials of defferent modulus, the sound absorption performance of materials is better than the materials which is not treated by alkali.