| Damping materials are extensively used in various fields such as vehicles, industrial machine, construct and building, home appliances, precise instruments, military equipments and so on. Typical candidate damping materials for the application of passive damping are viscoelastic polymers. Since the mechanical or acoustic vibrating energy is partly converted into Joule's heat through the viscoelastic damping effect in the vicinity of its glass transition temperature (Tg), and in turn reduce the vibration and noise. The damping properties of polymers depend on its Tg, but homopolymers usually havenarrow glass transition region. Their applications are limited to some extent. In order to obtain good damping materials with both a high damping peak and a broad temperature range, and reduce the dependence of its Tg, four sections are mainly included in this dissertation as follows:1. High-performance Organic Hybrid Damping MaterialsIn order to further understand the damping mechanism of an organic hybrid of polymer and a small molecule, the Chlorinated Polyethylene (CPE) is used as the matrix, and two kinds of organic small molecules with similar chemical structure 2, 2'-methylene-bis-(6-tert-butyl-4-ethyl-phenol)(EBP),2'-methylene-bis-(4-methyl-6-cyclohexyl--phenol) (ZKF) are chosen as the organic additives. Then, two kinds of hybrid materials CPE/EBP and CPE/ZKF are made by hot-pressing and quenching.For CPE/EBP hybrids, differential scanning calorimetry (DSC) shows that, the EBP is incompatible with the CPE matrix, and a novel glass-transition range arises within the temperature range from 20 to 40℃on DSC scanning curves. However, none of glass-transition range of EBP is found on the DSC curves except within that from -10 to 0℃. Therefore, the interactional mechanism between CPE and EBP are different from the conventional polymer blend systems with two or mutli-component. The FT1R results show that, Due to the intermolecular hydrogen bonding interaction between Cl of CPE and the hydroxyl groups of EBP, most of EBP form EBP-rich domains frozen by quenching process, and cause the phase separation. The CPE/EBP hybrids show two loss peaks on tanδ- T curve, which broaden the efficient damping temperature range. For CPE/ZKF hybrids, the DSC and DMA show that, the ZKF is compatible with the CPE matrix, and there is only one loss peak on the tanδ-T curve for all the samples. With increasing the ZKF weight content, the loss peak of the CPE/ZKF hybrids increases dramatically and the loss peak position shifts to higher temperature. The FTIR results show that, a small molecule ZKF formed two hydrogen bonds with two CPE chains at the same time, acted as a bridge. The energy dissipation due to dissociation of the intermolecular hydrogen-bond network is larger than that of due to general friction between polymer chains. Therefore, CPE/ZKF hybrids is a good damping material with a high loss peak near its Tg.2. The Aging Phenomena and the Damping Stability of Organic HybridsWhen the CPE/EBP and CPE/ZKF organic hybrids are aged under the room temperature for twelve months, there is some white powder on the surface of the hybrids. The aging mechanism and the effect of aging phenomena on the damping properties of CPE/ZKF hybrids have been investigated in this section. The DSC results show that, the white powder is caused due to the crystal of EBP. For the aged CPE/ZKF hybrids, the FTIR spectra shows that, there is a evident change of the hydrogen bonding in the region ranging from 3000 to 3500 cm-1, and the bridge-like hydrogen bond disappeared that is centered at 3208 cm-1, which results in the loss of the higher damping peak of the CPE/ZKF hybrids. The results show that the stability of the damping properties of the CPE/ZKF hybrids is not well.For further studying the stability of the damping properties of CPE/ZKF hybrids, consequently, the CPE/ZKF/EBP three-component hybrids are investigated, and it is found that there is a synergistic effect between ZKF and EBP on the damping properties of the three-component hybrids. When adding a small quantity of EBP into CPE/ZKF systems, not only the loss peak intensity of the CPE/ZKF/EBP hybrids can be further improved, but also its loss peak position can be lowered to a required temperature region. It is further found that, both the physical bulk side group and hydrogen-bond network should cause the synergistic interaction between EBP and ZKF. On the other hand, the damping stability of the CPE/ZKF hybrids can be improved excellently by adding a small amount of EBP.3. Piezoelectric Composites with a Broad Efficient Damping Temperature Range Due to that, piezoelectric ceramic damping materials are brittle, fragile, and hard, with the result that not only have some difficulty in proceeding technology, but also the electro-mechanical coupling factor is not very good. As a way of improving these inferior properties, the piezoelectric ceramic powder is substituted by the organic small molecule ZKF with strong dielectric behavior, for further studying the piezo-damping properties of CPE/ZKF/VGCF composites by DMA.At the vitrification point, the piezo-damping effect is not obvious, as the mechanical vibration energy converts into thermal energy is higher due to the friction between molecules of CPE matrix. Within the temperature range of 60～80℃, at a low content of VGCF, there are no conductive paths throughout the composites and the piezo-damping effect is not obvious. As the VGCF content exceeds the percolation threshold, a continuous conductive network begin to be formed, the loss factor is increased dramatically, present a peak at 16vol% VGCF content, and finally decreases again. This indicates that the piezo-damping effect really functions in the systems and that the efficient damping temperature region, which reduce the dependence of its Tg.In comparison with CPE/ZPT/VGCF systems, the CPE/ZKF/VGCF composites not only have a high loss peak, but also have an obvious piezo-damping effect. On the other hand, the storage modulus also is great improved due to the present of the VGCF and ZKF.4. Multi-layered Hybrid Composites with a Broad and High Damping RangeFor CPE/ZKF hybrids, with increasing the ZKF content, not only the loss peak height of the hybrids increase dramatically, but also the loss peak position can be adjusted. However, the width of loss peak is narrow for practical applications. Therefore, to obtain good damping materials with a broad and high damping range, we design a novel multi-layered organic hybrid material, which overlap several organic hybrid layers with different ZKF content and corresponding loss peak position by hot-pressing process.In this section, we analyze and discuss the possibility of using the multi-layered hybrid materials to broaden the efficient damping range, and prediction of the damping properties of multi-layered hybrid materials is also studied. The predicted and experimental results show that, it is possible to obtain damping material with broad efficient damping range by two-layered hybrid materials, the value in the middle of two peaks can be improved by increasing the number of layers of the multi-layered hybrids and there is a higher minimum value. Thus, it is feasible in theory and experiment to broaden the efficient damping range by multi-layered hybrid materials, which provides a new approach and solid basis for developing high performance damping materials with a broad and high damping range.
|
PDF Full Text Request