Preparation And Properties Study Of Damping And Acoustical Composites Based On Chlorinated Polyethylene

Materials are the bases of the advance of engineering and technology. Polymer marix composites as up-rising star are bringing significant changes in material and engineering. fields. With the progress of industrialization, as well as the construction of railway, highway and other infrastructures, vibration and noise, just like air pollution, water pollution, become a major threat of modern society. In order to reduce the vibration and noise, researchers are working on developing effective damping vibration and noise reduction materials. Traditionally, polymer works as damping material by consuming the energy at the glass transition temperature with its elasticity, or say, transferring vibration energy or sound energy into heat. However, currently, most polymer matrix composites with vibration damping and noise reduction have several draw backs. Firstly, due to the narrow glass transition temperature, most materials are temperature (frequency)dependent, making a very narrow damping functional zone. Secondly, most available damping materials have no space for air, and the hollows to let the air go through, making its low performance in sound absorption and poor physical and mechanical properties. So, to develop a new polymer composites with vibration damping, noise reduction and the mechanical properties has significance in both scientific research and engineering application.Based on such circumstances, preparation, properties study of damping, acoustical and mechanical and mechanism analysis of vibration damping and sound absorption for composites based on chlorinated polyethylene are innovative thinkings refering to devolopment of organic hybrid high damping composites, fiber reinforced sound absorption composites and multilayered sound-absorbing structures concluding perforated plates in the dissertation.We are trying to link sound absorption and damping vibration reduction when sound wave is to regarded as the vibration of particles, and systemically researched the relationship between the micro-structure of the composites and its damping and sound absorption properties, and finally successfully developed a new high-performance sound absorbing materials. Our research can be divided into the following aspects:(1) CPE/AO2246hybrid composites with high damping performancewe choose Chlorinated Polyethylene (CPE) as matrix and2,2’-methylene-bis -(6-tert-butyl-4-methyl-phenol)(AO2246), a domestic chemical of small functional molecules as filling materials in the chapter.Add AO2246into CPE in the mixing mill, and then mix them completely, then after heat-pressure quench forming, the new hybrid composites of CPE/AO2246can be prepared. After preparation, we tested the co-relation between the content of AO2246and the damping properties of the hybrid composites, as well as investigated the linking between the micro structure of hybrid composites and their damping properties.The results of DMA show that there is only one damping peak on the Tan8-T curve of composites, which indicates that CPE and AO2246form a compatible system. When the content of AO2246is less than50%, the damping peak rises with the increase of the content of AO2246, meanwhile, the glass transition temperature moves towards the high end. When the content of AO2246reaches50%, damping peak begins to decline, demonstrating a critical point of the content of AO2246on the improvement of the damping property of hybrid composite. Also, photo of SEM shows that there exists a small amount of crystal structures of AO2246when the content of AO2246is very low. While, at the high content of AO2246, flocculent aggregation structures are common in the composites On the edge of the aggregation structure, micro-crystals of AO2246can be found. The aggregation structure is advantageous for the improvement of damping property while the contributions of micro-crystal of AO2246is positive and negative aspects of the improvement of the damping property:First, the micro-crystals fill the space among CPE molecules, reducing the free volume, making a negative contribution to the damping. Second, at the glass-transition temperature, the friction between the CPE molecules and the micro-crystal and the micro-crystal themselves increase when the movement of the molecules are intensified, then improving the damping property. After the content of AO2246reaches the point where the perfect aggregation structure forms, the improvement of damping property depends on the contribution of the micro-crystal of AO2246.To explore the effect of preparation method on the property of CPE/AO2246hybrid composites, we employed different process methods. The results show that there are vast of three-dimensioned grain-formed crystals in the composite without heat-pressure process, which function as a inorganic filling materials and finally weakens the damping property. The hybrid composites with hot-pressure process contains large number of aggregation structures and the quantity of crystal declined dramatically, and the quantity of crystal of composite with high-temperature hot-pressure is more than its with low-temperature hot-pressure, damping property of composites with hot-pressure process obtains obvious improvement,Glass transition temperature of composites with hot-pressure process shift to high temperature while glass transition temperature of composites with different temperature hot pressure is almost same. However, due to the hydrogen bond between the a-H of CPE and the hydroxy of AO2246in high temperature hot-process, the damping property of composites with high temperature hot-pressure process is better than that of the composites without low temperature hot--pressure process.(2) CPE/SHPF composites with high damping and sound absorption propertyThe research chooses seven-hole hollow polyester fibers with three dimensional crimp (SHPF) as the air-carrier and enhancer of the composites on the basis of mechanism analysis of sound-absorbing materials and repeated experiments in the chapter.The CPE/SHPF composites can be obtained by adding SHPF into CPE, mixing them completely and then performing a heat-quench process. We also investigated the effect of the content of fiber on the elasticity, sound absorption property and mechanical property, as well as the effect of the thickness of the composites and the deepness of back cavity.The SEM and3D video microscope research indicates that the fibers exist in an irregular form in the composite when few fiber is added. With the introduction of more fiber, the fiber networks form in the composite. The more fibers are introduced, the more complete the network structures are. The hollows inside the fiber bring air into the composite. Air can transfer the sound energy to heat by its viscous effect and the friction between air and the hollow wall. However, due to the low efficiency of heat transportation in the state of unformed fiber networks, the sound absorption property is very poor. When the network structures have formed, effective pathway of energy consumption and transfer are then established, thus, this composite becomes a novel sound absorption material.Sound absorption property of this composite is a much better than that of most currently available materials when the content of fiber reaches20%. In this circumstance, as the thickness of the composites increases, the materials show an excellent sound absorption property in low and middle frequency, which turns out to be sound absorbing materials with relative low thickness in a broad frequency range. Furthermore, it is possible to be a sound absorbent with specific frequency range by constructing a complex sound absorbing structure with rear air layer, which can generate cavity resonance in certain frequency.The SHPF function as inorganic filling in the composite. They can fill the space between the macro-molecules, limiting the free space of macro-molecules and hindering the movement of them, which makes negative contribution to the damping property. On the other hand, in the glass transition region, the frictions between fibers and CPE and among fibers themselves increase with the intensification of the molecular movement, which turns out to improve the damping property. Overall the former plays a major role. Therefore, the decline of the damping peak is very significant with the addition of more fibers. Meanwhile, the glass transition temperature exhibits a shift toward the high temperature direction. The positive co-relation between the content of the fiber and the decline of the damping peak indicates that the sound absorption property of the composite is simple the contribution of the air layer of the fiber network, and the damping property makes no contribution to the sound absorption property.Our research also show that the elongation rate of the compound sharply decreases and the breaking strength increases with the introduction of SHPF. When the content of the fiber reach the point where the fiber network structure totally inhibits the elasticity of CPE, the the breaking strength exhibits a linear increase with the increase of the content of the fiber. The introduction of the fiber give the composite a relative high obdurability, which is important for the application in engineering.(3) CPE/AO2246/SHPFcomposites with high damping and acoustical propertiesThe researches toward two kind of bi-component composites show that the CPE/AO2246composite has a good damping property, while the CPE/SHPF only has a poor damping property but good sound absorbing property. Preliminary studies have proved the positive co-relation between the damping property and sound absorbing property. Based on this reason, we try to add SHPF into the CPE/AO2246, making the CPE/AO2246/SHPF composite and investigste the distribution of AO2246and fibers in the compound, the damping property, the sound absorption property and the mechanical performances.The results show that Fiber can act as a crystallization-inducer of AO2246, and then AO2246exists as a crystal covering the fiber’s surface in the composite with adding fibers. AO2246that are not crystallized forms "semi hybrid" with the CPE molecules. The AO2246covered fiber fill the space among macro-molecules, reducing the loss factor. However, there are strong hydrogen bonds between Cl and-OH and the friction between matrix and AO2246and that among AO2246themselves increases. Because of the existence of hydrogen bonds, the storage modulus ascends significantly, thus the loss factor has a trend of declining. However, we found that that energy consuming index (LA) increases with the addition of fiber, which shows that the damping property has been improved.The coverage of crystal enlarges the surface area of fiber, and can help the formation of crystal-fiber network structure. Thus, the heat produced by the sound absorption can easily diffused through the network, which greatly improved the sound absorbing property of the tri-components composite. When fiber content is as few as4.76%, tri-component comcomposite can form certain network structure, which equals to the bi-component composite containing20%fibers with the same thickness.The addition of SHPF dramatically reduces the elongation rate of CPE/AO2246/SHPF and greatly increases the breaking strength. Compared with CPE/SHPF composite, the tri-component composite has a much better obdurability, and can be used as a high performance sound absorbing material with good mechanical property.(4)Acoustic absorbing property of multilayered structures containing perforated platesBoth the bi-component and the tri-component composites mention in this research can be classified as porous material. When material is thin, this kind of material has a common sound absorption curve:good at middle to high frequency but poor at low frequency at low thickness. In order to improve sound absorption property of material at low frequency, materials must make very thick. While sound absorption material is headed in lightweight direction. Based on these, we make a series of multilayered structure containing perforation plates and CPE/SHPF, to perform a acoustic property study of structure materials.The research results show that two sound absorption peaks can be observed when the structure contains more than two perforation plates. Furthermore, the frequency of the first sound absorption peak is related with the thickness of perforation plate of rearest end. The higher the thickness is, the lower the frequency is. The peak value of the sound absorption is related to the perforation rate of the plates:higher perforation rate leads to higher sound absorption coefficient. The second sound absorbing peak demonstrates a slight shift with the shift of the first peak. We can see that the structure material exhibits a great sound absorbing property from the contribution of sound absorption composite film when the frequency of second sound-absorbing peak approaches2500Hz. In a summer, this kind of multilayered structure can fully utilize the mechanism of porous sound-absorbing material and cavity resonance, and can be a high performance sound absorbing material in wide range. They have a great prospect in engineering application.