| In this paper,hemp fiber,corncob particles and corncob powder with fineness of0.667tex and length of 3.2mm are used as raw materials,and PE particles with diameter of1mm are used as adhesive,hemp fiber web is obtained by loosening,carding,laying and other processes,and then the fiber web is sprinkled with PE particles and corncob particles or corncob powder to obtain particle fiber web or powder fiber web,after six layers of fiber web are laminated,hemp fiber web is obtained by hot melt bonding.The results show that at800-1000 Hz,the average sound absorption coefficient of the composite fabric material formed by the combination of hemp fiber and corncob particles is higher than that of the composite fabric material formed by the combination of hemp fiber and other particles(rubber particles,paper shell particles,coconut shell particles),this is because the corncob particles with a rougher surface cause more multiple scattering of incident sound waves and more attenuation of sound waves;When the amount of corncob particles increased from 2g,3g,4g,10g,20g,to 30g,the average sound absorption coefficient of the composite fabric material gradually increased by 99.5%,mainly due to the loose and porous surface of corncob particles,the surface is rough;when the amount of corncob powder increases from10g to 52g,the sound absorption of the material decreases,because the porosity of the material decreases,the pore connectivity decreases,the collision probability and the number of collisions between the sound wave and the inner hole are lower.When the particle size of corncob decreased from 4mm,3mm,2mm to 1mm,the average sound absorption coefficient increased from 0.156 to 0.336.When the particle size of corncob powder decreased from0.850mm,0.25mm,0.178mm to 0.150mm,the average sound absorption coefficient gradually increased by 38.4%,this is due to the smaller pore diameter inside the material,which increases the reflection of sound waves in the material and increases the attenuation of sound waves.Hemp fiber/corncob powder has longer pore channels,smaller pore diameter,higher porosity and uniformity than hemp fiber/corncob particle composite fabric material,so it has better sound absorption;When the volume density of the fiber web of the composite fabric material increases from 0.039 g/cm~3to 0.154 g/cm~3,the fiber surface area increases,the contact area between the sound wave and the fiber increases,and the reflection inside the material increases.The average sound absorption coefficient gradually increases from 0.168to 0.286.When the volume density of the fiber web of the composite fabric material continues to increase from 0.154 g/cm~3to 0.263 g/cm~3,the porosity decreases,the pore connectivity decreases,the collision probability and the number of collisions between the sound wave and the inner hole are lower,and the average sound absorption coefficient of the composite fabric material decreases from 0.286 to 0.152;The more the number of fiber web layers in the particle fiber web of the composite fabric material,the better the sound absorption performance,mainly because the interface between the fiber web layers increases the number of reflections of sound waves inside the material;when the powder dosage gradient increases or the thickness gradient of the fiber web decreases along the incident direction of the sound wave,the sound absorption of the composite fabric material gradually increases.The main reason is that when the acoustic resistance gradually increases,the surface layer exists less corncobs and the acoustic resistance is smaller.The sound wave is more likely to enter the interior of the material,and the internal resistance of the material is larger,the sound wave is more easily attenuated,and the resistance matching is more conducive to sound absorption.Hemp fiber/corncob powder composite fabric is easy to fall during testing and use,which reduces the sound absorption performance,to improve the performance and sound absorption performance of composite fabric materials,hemp fiber/corncob powder composite fabric and PE melt-blown nonwovens are ultrasonically bonded to obtain hemp fiber/corncob powder/PE melt-blown nonwovens laminated material.The effects of process parameters and structural parameters on the sound absorption performance of laminated materials were studied.The results show that the average sound absorption coefficient of the laminated material prepared by PE melt-blown nonwovens is 18.0%higher than that of hemp fiber/corncob powder/PE film composite fabric material,and 10.1%higher than that of hemp fiber/corncob powder/PP melt-blown nonwovens laminated material,it is mainly due to the low softness of PE melt-blown nonwovens,which stabilize material effectively,and the surface is loose and porous,and the sound wave is easier to enter the laminated material and be absorbed;The average sound absorption coefficient of the material on the front of the PE melt-blown nonwovens is 31.5%higher than that of the material on both sides of the PE melt-blown nonwovens,and 24.5%higher than that of the laminated material on the opposite side of the PE melt-blown nonwovens,the main reason is that the film resistance of the surface layer is small,so that the sound wave can enter the material easily.The resistance of the composite fabric material in the inner layer is larger,so that the sound wave is better absorbed,forming an acoustic resistance matching,and the PE melt-blown nonwovens reduces the reflection of the sound wave outside the material;The sound absorption of laminated materials bonded by ultrasonic bonding is better than that by white glue bonding,because ultrasonic bonding has greater porosity and fiber integrity.When the number of cells increases from 2,4,6,8 to 12,the average sound absorption coefficient of the laminated material increases from 0.339 to 0.423,which is because the material is more stable and compact.The research of this topic lays a foundation for the research and application of broadband sound absorption materials,and provides guidance for the design of fabric-type broadband sound absorption materials and the research of sound absorption performance. |
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