| Damping materials are very important in the field of vibration and noise control.Homopolymers, which possess narrow effective damping temperature range and poormechanical properties, can’t fulfill practical application. Application of piezoelectricdamping material can provide a promise way to solve these problems. In this study,the multi-walled carbon nanotubes (MWCNTs), and three VER-EP IPNs, PMMA-EPIPNs and PU-EP IPNs, were chosen as conductive filler and resin matrix for thepreparation of piezoelectric damping composite materials. The conductive property,mechanical properties, damping properties, thermal stability, dielectric properties andpiezoelectric property were systematically studied, which will give a new insight intothe design of novel damping materials with high strength and broaden dampingtemperature range.MWCNTs were treated by concentrated H2SO4/HNO3. After the treatment, thecarboxyl group was introduced, and the amorphous carbon was removed. Result oftransmission electron microscopy found the ends of nanotubes were cut and theentanglement and agglomeration was decreased. X ray photoelectron spectroscopyanalysis showed that the surface oxygen content of MWCNTs was increased from3.7%to18.9%, which can be helpful for the smooth formation of conductivepathways.VER-EP IPNs matrix was prepared by simultaneous method. The heterogeneousplastic structure, which creates from dismatch of curing speed between VER and EP,could contribute to the improvement of toughness. Compared with pristine epoxy, thetensile and impact strength of VER-EP IPNs could be increased by14.1%and96.1%respectively. The thermal stability of VER-EP IPNs increased with VER content,which can be attributed to the higher content of rigid benzene rings in vinyl ester resin.When the VER content is50%of the epoxy, the maximum loss factor could beincreased to0.805, while the effective damping temperature range could be broadenedto38.6℃.PMMA-EP IPNs matrix was prepared by sequential method. The hole at the endof crack prevents the crack extension, which results in the toughness improvement ofepoxy. The addition of PMMA could increase the impact strength by17.6%, while thetensile strength was impaired by the increasing content of PMMA. The thermalstability of PMMA-EP IPNs decreased with PMMA content, which can be attributed to the weak intermolecular force between PMMA and EP. When the PMMA content is20%of the epoxy, the maximum loss factor could be increased to0.484, while theeffective damping temperature range could be broadened to32.2℃.PU-EP IPNs matrix was prepared by sequential method. The tensile and tear ofPU and hole shear yield mechanism have a synergistic toughening effect for epoxy,which makes the tensile and impact strength of PU-EP IPNs increased by24.0%and52.3%, respectively. The thermal stability of PU-EP IPNs increased with increasingcontent of PU, which can be attributed to the grafting reaction between PU and EP.When the PU content is50%of the epoxy, the maximum loss factor could beincreased to0.816, while the effective damping temperature range could be broadenedto50.7℃.The influence of MWCNTs content on the electric conductivity was studied. Theresult showed that the electric conductivity increased with increasing content ofMWCNTs, the percolation threshold value appeared in these three IPNs piezoelectricdamping materials. When the conductive materials lie in the insulator-semiconductortransition, the electric charge can be transformed to thermal energy efficiently. Theoptimum electric conductivity of these three piezoelectric damping materials are10-6s/m,10-10～10-8s/m and10-8s/m. Moreover, the surface treatment of nanotubescould improve the dispersion of MWCNTs in VER-EP IPNs piezoelectric dampingmaterials, and thus decrease the percolation threshold value. However, the percolationthreshold value increased with the addition of treated MWCNTs into the PMMA-EPIPNs and PU-EP IPNs piezoelectric damping materials.The piezoelectric ceramic and conductive filler content take great effect on themechanical properties of these three composite materials. The tensile strengthincreased, while the impact strength decreased with the incorporation of piezoelectricceramic into the VER-EP IPNs and PU-EP IPNs piezoelectric damping materials. Thetensile strength increased from29.9MPa to38.4MPa, and the impact strengthincreased from5.1kJ/m2to11.5kJ/m2with the incorporation of PVDF intoPMMA-EP IPNs piezoelectric damping materials. The mechanical properties ofVER-EP IPNs and PMMA-EP IPNs piezoelectric damping materials decreased withthe increasing content of treated MWCNTs due to the restricted mobility of polymerchains. However, the mechanical properties of PU-EP IPNs piezoelectric dampingmaterials could be enhanced by the addition of treated MWCNTs.The piezoelectric ceramic, conductive filler, IPNs matrix formation and surface treatment of MWCNTs greatly affects the damping properties of IPNs piezoelectricdamping materials. With the increasing content of piezoelectric ceramic in these threecomposite materials, the damping temperature range was broadened while the lossfactor peak decreased. The excellent damping properties can be achieved when theconductive filler content at the percolation threshold value. The loss factor curvesshifted to a lower temperature with the increasing content of VER, PMMA and PU inIPNs piezoelectric damping materials. The damping properties was improved by thesurface treatment of MWCNTs in VER-EP IPNs piezoelectric damping materials,while a opposite phenomenon could be observed in PMMA-EP IPNs and PU-EP IPNspiezoelectric damping materials.The piezoelectric ceramic content also greatly affects the dielectric properties ofthese three IPNs piezoelectric damping materials. The dielectric constant anddielectric loss increased with the increasing piezoelectric ceramic content in VER-EPIPNs and PU-EP IPNs piezoelectric damping materials, while the minimum dielectricproperties of PMMA-EP IPNs piezoelectric damping materials was obtained at thePVDF content of40%. |
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