Processing And Characterization Of Damping And Acoustic Composites Based On Textile Waste Rubber

With the rapid development of the modern industry and traffic technology, noise pollution is becoming a more and more serious environmental issue that the human society faces in recent years due to its harmful effect on human health and ecological environment. Noise pollution control has become a hot topic. Vibration and noise pollution is becoming a more and more serious environmental issue so that the clamor for the vibration and noisy reduction is on the rise. As one of the key methods in noise and oscillatory control field, the viscoelastic damping technology is especially suitable for controlling of wide frequency and multi-peak resonant vibration, which is a critical problem in modern aircraft, ship, and automobile industry. As the key of the viscoelastic vibration damping technology, polymer damping material has got great development. Therefore, extensive studies have been carried out to develop new materials with improved damping properties.As a large producing country of rubber products which, at the same time, is in serious short of rubber resources China consumes most of the rubber materials, creating a large number of rubber wastes every year. Vulcanizing in the rubber production process causes the chain molecules being cross-linked into the threedimensional network structure, which improves the strength, hardness, elasticity and aging, in order to meet the needs of engineering application. The wastes may pose a serious threat to the environment as they have stable three-dimensional chemical network structure, which makes their meltdown and dissolution, almost impossible. Burning produces a great deal of exhaust fumes, arbitrarily discarded breeds mosquitoes. Traditional methods of waste disposal such as landfill, combustion heat utilization at the early stage have become irrelevant and unacceptable because of the associated environmental problems. It is therefore necessary to improve or to develop a certain process or applications for waste rubber. The ideal method is recycling which shall be both environmentally friendly and economically viable.Every year a large number of old roller and leather collars are to be scrapped in the textile factory. The main components of those raw materials are Nitrile Butadiene Rubber(NBR) and Polyvinyl Chloride(PVC). There are several ways to make use of recycling particles. The most familiar method is to introduce a small amount of recycling particles into the NBR and PVC before they are made into rollers. But even a tiny amount will affect the quality. Some people verified that the mixing of recycling particles with a certain ratio of concrete contributes to the improvement of the tenacity and impact resistance of concrete materials, as well as achievement of sound insulation properties.However it decreases the tensile strength yet and the viscoelastic properties of rubber are invalid just as the filler. In order to take full advantage of the reclaimed rubber and make full use of its characteristic, it is necessary to find a new way to treat and to reuse it. Turning waste into treasure while endowing the waste material with new features is a new highlight of the textile reclaimed rubber application. From the perspective of resource utilization, taking the directly crushed waste powder as the matrix to develop functional composites has potential innovation application value.In respect of the excellent damping properties of the waste rubber, it can be made full use of to prepare damping materials. This is not only a breakthrough for the source of damping material, but also in some cases can solve a series of problems, such as the environmental pollution caused by scrap rubber and waste of resources. Because of the low elastic modulus and the poor creep resistance of waste rubber, it can not be used directly as damping material, and it can be applied only in the composite formation with other materials. The research and development of waste rubber based high performance damping composites come into being under this background. A series of new composites such as organic hybrid composites, fiber reinforced composites, ternary composites and laminated gradient composites with the reclaimed rubber powder(R-Rubber) of the textile waste rubber from old rollers and leather collars as the matrix have been produced. This paper reported on their damping properties, effective sound absorbing characteristics as well as their strong mechanical properties, so as to illustrate the possibility of expanding the application of textile reclaimed rubber to other fields. It is the focus and the innovative point of this research. From the following areas for analysis:(1) High-performence damping organic hybrid materials based on textile waste rubberIn this paper, in order to prepare organic hybrid damping materials with high damping performance, hindered phenol compound 4,4’-Thio-bis(6-tert-butyl-m-methyl phenol)(AO-300) was screened out through some theoretical analysis and experimental tests. Then binary R-Rubber/AO-300 organic hybrid materials were thus obtained by adding them into R-Rubber matrix and heatpressure quench forming technology. The additive effects of AO-300 on the damping properties, infrared spectral properties and microstructure morphology of R-Rubber were investigated and the molecular mechanism of different systems was discussed so as to extend the application field of R-Rubber into organic hybrid systems. The results show that R-Rubber/AO-300 systems exhibited an exceptional damping performance in the wide range of temperature. DMA results showed that R-Rubber/AO-300 was compatible and only one damping peak appeared. With increasing AO-300 content, tan δ max increased remarkably up to 1.0 and its peak position shifted towards higher temperature from 6.19℃ to 34.42℃ approaching room temperature, due to the hybridization of the two components. As the AO-300 content in R-Rubber increases from 40 phr to 80 phr, the effect temperature range increases from 55.32 to 63.14℃. This value is markedly higher than that of common organic hybrids consisting of polar polymers and small organic molecules. FTIR analysis revealed that the hybridization effect was attributed to the formation of strong intermolecular hydrogen bonds between them. It can be concluded from the SEM results that R-Rubber was a typical complex matrix morphological structure. When a small amount of AO-300 was introduced to R-Rubber, the samples morphology presented the typical complex matrix morphological and hybrid state coexistence in composites. When the AO-300 content is larger than the critical value, more excess AO-300 molecules are crystallized. It is believed that R-Rubber/AO-300 composites can be developed as a kind of new high-performance damping materials, which can be suitable for a wide temperature range and applied to various damping applications.(2) Acoustic properties of R-Rubber/SHPF composite materialsA series of thin, low-cost and environment-friendly elastomeric composites consisting of reclaimed rubber(R-Rubber) was produced and evaluated in terms of their damping property, acoustic property, as well as mechanical property in this chapter. The results show that R-Rubber/SHPF elastomeric composites exhibited an exceptional damping performance with a broad temperature range. The addition of the SHPF fiber as a filling material diminishes the free volume of the polymer molecular chain. At the same time, the existence of the interface phase has a positive effect on the damping property. These two mechanisms interact with each other, which leads to the tan δmax of the composite first increased and then decreased. The effective damping area of the composite with 25 phr SHPF content was from 16.8℃ to 85.7℃. It is a kind of damping material with wide effective functional area. Meanwhile, the SHPF content, thickness and cavity of R-Rubber/SHPF composites had a significant influence on acoustic properties. The composite with 25 phr SHPF content and 1 mm thickness was noted, giving a sound absorption coefficient peak, 0.407 at 2500 Hz. When the thickness of the composite including 20 phr SHPF content was increased(0.5 mm to 2 mm), Rubber/SHPF presented better sound absorption performance at intermediate-low frequency. The rigidity and strength of the composites was significantly enhanced by adding SHPF into the matrix, which laid the foundation for the applications of R-Rubber/SHPF in engineering field.(3) R-Rubber/AO-300/SHPF ternary composites with high damping and acoustical propertiesThe researches toward two kinds of binary systems show that R-Rubber/AO-300 systems exhibited an exceptional damping performance in the wide range of temperature, while the introduction of SHPF into R-Rubber matrix can effectively improve the sound absorbing property, while lead to a decreasing of damping performance of R-Rubber matrix. As to the attenuation of damping performance of R-Rubber/AO-300 organic hybrids, combination of fiber reinforcement and organic hybridization was adopted in order to develop a high-performance damping material with good acoustic property. We selected SHPF as the reinforcement fiber and combined its reinforcement effect with the hybridization effect of AO-300. Thus, a series of ternary R-Rubber/AO-300(100/40)/SHPF samples were prepared and measurements were made on their dynamic mechanical properties and sound absorbing characteristics. Results showed that by the introduction of SHPF into R-Rubber/AO-300(100/40) hybrid systems, the air is introduced into the material by means of the hollow structure of fiber, and the crystal-fiber network structure is formed by the crystallization induced effect of fiber. It improved the poor mechanical properties of the ordinary sound absorption material, and that acoustical absorption property of materials increased significantly due to the crystal network structure.Overall, when mass radio of R-Rubber/AO-300(100/40)/SHPF blends is 100/40/15, acoustical absorption property of ternary systems have been improved largely. Waste rubber based ternary system composites possesses both damping and acoustic property, so as to illustrate the possibility of expanding the application of textile reclaimed rubber to other fields.(4) Laminated gradient hybrid composites based on textile waste rubberIn this section, a series of laminated gradient samples were prepared based on the R-Rubber/AO-300 hybrid materials with different AO-300 content by the melt hot pressing method. And from the view of the stress state of laminated gradient samples under the three point bending mode, structural loss factor theory model was established. Experiments and theoretical verification show that the laminated samples have a wider damping temperature range than the single layer samples. There is one damping peak in the tan δ versus temperature curve of two layers samples, and two peaks for three or four layers samples. With the increase of the number of layers, the two peaks of the material are all increased, and the area of the concave valley between two peaks is also rising. This method provides a new theoretical basis and design proposal for the utilization of waste rubber to preparing the laminated gradient damping material.