Study Of The Preparation, Structure And Properties Of New Polyurethane Nanocomposites

The properties of polyurethane elastomer(PUE) are between rubber and plastics. PUE not only owns the property of high elasticity and high strength,but also its abradability,especially the biologic and blood compatibility.Meanwhile,PUE has other property such as oil resistivity,shockproof,low temperature resistance, resistance to ozon,radio-resistance,insulation,and so on.PUE has outstanding comprehensive properties,and has been widely used in civil,sports,aerospace, military affairs and other fields,and thus has become one kind of indispensable important materials.However,strength,biocompatibility,and thermal oxidation resistance properties of PUE greatly limit its wider applications.In order to widen its realm of applications,particular nanoparticles are usually added in PU system to improve its physical properties.In this thesis,poly(diethylene adipate)(PDA),isophorone diisocyanate(IPDI), isophorone diamine(IPDA) were used to prepared three different types of polyurethane nanocomposites.The main contents and the results obtained are as follows:(1) A series of polyurethane/carbon nanotube composites has been prepared through in-situ polymerization and solution casting.Homogeneous dispersion of multi-walled carbon nanotubes(MWNTs) throughout PU matrix is observed by scanning electron microscopy on the fracture surfaces of the composites.Strong interfacial adhesion between the MWNTs and the PU matrix,as evidenced by the presence of broken but strongly embedded MWNTs in the matrix,is favorable to stress transfer from polymer matrix to the nanotubes.The fine dispersion of carbon nanotubes(CNTs) and strong interfacial adhesion between the CNTs with the matrix are responsible for the simultaneous and significant enhancement in the strengthening and toughening of PU matrix.In addition,the thermal stability of PU was also improved after incorporating CNTs into the matrix.(2) A series of organic/inorganic hybrid materials have been prepared by copolymerizing polyurethane and 3-(trimethoxysilyl) propyl methacrylate(TPM) via addition fragmentation chain transfer(RAFT),at several feeding ratios.The copolymer precursors could self-assemble into spherical micelles in selective solvents and then be hydrolyzed and condensed to generate PU-SiO₂ hybrid sol-gel materials. The silica spheres undergo a change from less number with larger diameter to more number with smaller and homogeneous diameter with increasing the TPM content. The hybrid copolymers possess excellent thermal stability and mechanical property.(3) The interlayer surface of CoAl-layered double hydroxide(CoAl-LDH) was modified by exchanging the interlayer carbonate anions by dodecyl sulfate anions (DS).PU was then intercalated by in situ polymerization to get the PU/CoAl-LDH nanocomposites.By using XRD technique,the nanoscale exfoliated dispersion of CoAl-LDH layers in the PU matrix was verified by the disappearance of the(003) reflection of the organically modified CoAl-LDH when the LDH loading is less than 2.0 wt%.The strong interaction between the LDH nanolayers and polyurethane chains is responsible for the excellent mechanical properties of PU/LDH nanocomposites.The weak alkaline catalysis of DS to polyurethane chain,together with the degradation of LDH below 300℃,accounts for the faster degradation process shown in the TGA profiles.The real-time Fourier transform infrared reveals that these nanocomposites have a slower thermo-oxidative rate than neat PU between 160℃and 340℃,due to the barrier effect of CoAl-LDH nanolayers.The nanocomposites obtained are one kind of promising flame-retardant materials.