Study On Structure Design And Properties For Polyurethane Damping Materials

Structure is the fundamental factor to determine the property of materials. Modification of the molecular structure of polyurethane(PU) damping materials is an effective way to improve its performance. In this study, PU damping materials of polyether, polyester and poly(ether-ester) types are designed according to group contribution analysis and polymer damping performance theory. Series of PU damping materials were prepared through adjusting the type and content of soft and hard segments and their performance were evaluated.Polyether PU were prepared by the reaction of tetrahydrofuran polyether(PTMG), polypropylene glycol polyether(PPG) with 2,4-tolulene diisocyanate(TDI100) and diphenyl methane diisocyanate(MDI50) using diol chain extenders and diamine chain extenders containing different side methyl groups. The maximum loss factor(tan δmax) of PPG-PU was higher than PTMG-PU significantly and the mechanical property was poor. The tan δmax of PPG2000-PU was slightly higher than PPG1000-PU and the temperature range with tan δ>0.3 shifted to the low temperature zone. Ether bond and side methyl group in diol chain extenders promoted increase in tan δmax and wider damping temperature range for tan δ>0.3. Phenyl in diamine chain extender reduced the damping temperature range of tan δ>0.3 and shifted to higher temperatures. Compared to the MDI50/BDO system, hard segment system of PU for TDI100/MOCA improved mechanical properties, the peak shape of DMA charts were flat and wide, and the damping temperature range of tan δ>0.3 shifted to higher temperatures.Polyester PU were prepared with poly(neopentyl glycol succinic acid)(PNS), poly(neopentyl glycol adipic acid)(PNA) and TDI100, isophorone diisocyanate(IPDI) using diamine chain extenders with different structures. The tan δmax of PNA-PU was higher than PNS-PU, glass transition temperature(Tg) was lower and the temperature range with tan δ>0.3 shifted to lower temperature zone. With increased molecular weight of PNS, the mechanical properties decreased, tan δmax of PU raised from 0.73 to 1.10, and the temperature range for tan δ>0.3 shifted to lower temperatures. The tan δmax of TDI100-PU was higher than IPDI-PU and the damping zone was narrow. The damping properties with diamine chain extenders of PU were at the order of MOCA>L-MOCA>M-CDEA. Lowering chain extension coefficient resulted in an increase in tan δmax and a noticeable decrease in the mechanical properties.Poly(ether-ester) PU was prepared with TDI100, MOCA and poly(neopentyl glycol propoxylated succinicacid)(PNPS) or poly(neopentyl glycol propoxylatedadipic acid)(PNPA) which were synthesized from neopentyl glycol propoxylated(PNP) and succinic acid(SA) or adipic acid(AA) through condensation polymerization. The damping properties of PNPS-PU were superior to PNPA-PU. With increased molecular weight of PNPS, the mechanical properties of PU decreased, the tan δmax slightly improved and the Tg significantly reduced.The structures of different soft segments or the raw materials were characterized by Fourier Transform Infrared Spectroscopy(FTIR) and Proton Nuclear Magnetic Resonance(1H-NMR). The molecular weights determined by Gel Permeation Chromatography(GPC) were similar to the theoretical molecular weights. The Atomic Force Microscope(AFM) images displayed the dark and concave domain showing that continuous phase distribution was the soft segment in PU. The bright domain was the hard component. The phase separation was evident with the increased molecular weight for soft segments. The Scanning Electron Microscopy(SEM) images further verified the apparent phase separation of PU damping materials. The results of Thermogravimetric Analysis(TGA) and Differential Scanning Calorimetry(DSC) indicated improved thermal properties of PU. The polyether PU had two Tgs corresponding to soft and hard segments, whereas polyester PU had only one Tg for soft segment. X-ray Diffraction(XRD) pattern showed small amounts of crystallization in polyester PU damping materials.The results of testing PNS-PU damping structure showed that excitation amplitude and load frequency had significant impact on equivalent horizontal stiffness, equivalent damping ratio, post-yield stiffness, and yield force, all indicating that in actual damping structural design, one should consider the relationship between various parameters.