Development Of Hemp/polypropylene Textile Sound Absorbing Composites

Taking sound-absorbing requirement,manufacturability and environmental protection into account,hemp staple fibers and low melting point PP fibers are chosen as raw materials.The characteristic of low melting point is used to bond the web.By the combination of traditional opening and blending,carding technology and hot-pressing process,the composite materials with different hemp staple fibers content as well as the similar density are made.Using octave center frequency as the frequency of tested signal,the maximum and minimum sound pressure are decided by the data acquisition system(from Institute of Acoustic and Vibration,Beijing)and standing wave tube model SZZB,then absorption coefficient of the corresponding frequency is obtained.The thickness,surface density,porosity and tensile properties of the composite materials are tested.Analyzing the porosity change with adding hemp fibers,testing their mechanical properties and sound-absorbing performance can find out that the combined influence of the hemp staple fiber content on the material properties;The anisotropy of polypropylene composites caused by the content of hemp fiber and the carding technology affecting the properties of polypropylene composites,and the effect of water absorption on the impact properties of the composites were also discussed.This paper analyzes whether the radiation resistance of hemp content is up to the national standard,and calculates the influence of the porosity of the composite material on the sound absorption property under different cannabis content.The result shows the performance of the fiber is the basis of the composite performance.The physical and mechanical properties of the fiber determine the performance and processing technology of the final product.The hot press process is used to process the fiber web,and the temperature,pressure and time are conveniently controlled.Hot-pressed composite materials,good dimensional stability,good breaking strength;hot-pressing process equipment is simple,short molding cycle,temperature,pressure and time are relatively easy to grasp,the thickness of the thermocomposites can also be controlled,and its processing is intermittent Operational process.In addition,the sound absorption coefficient of hot-pressing composite materials is improved by the addition of hemp fibers.The sound absorption coefficient of composite material is improved greatly with increasing the thickness of materials in the same frequency.With the increase of the content of hemp,the sound absorption coefficient of the composite also increased correspondingly,Indicating that increasing the thickness can expand the sound absorption performance of the material in low frequency.For the same hot-pressed composite material,the sound-absorbing performance of the hot-pressed composite material is nonlinear with the increase of the frequency,but the overall upward trend;After 19 days of immersion,the material has obvious water absorption;the hemp content of 50%has the strongest effect on anisotropy;based on the impact property,the 40-50%content seems to be the most ideal;the wet state of the bending performance test decreases,close to or lower than the pure polypropylene fiber material,The impact strength is obviously increased;the transverse mechanical properties are weaker when there is the same water absorption in the longitudinal and horizontal direction;the carding twice shows that the anisotropy is not good,the water absorption effect is good,the flexural property is good,and the impact strength is decreased.The anti-ultraviolet radiation performance of different cannabis content is very good,all of them reach the national standard index,and the porosity is the largest and the sound absorption property is the best when the cannabis content reaches 40.This kind of composite materials are suitable for sound-absorbing material in high frequency used in automobile field.