Study On Tribological Modification Of Polyimide

Polyimide (PI) resins have excellent mechanical properties, resistance to extremely high and low temperature, and good dimension stability. However, there are still some problems to be further solved if neat PI resins were used as high-performance slef-lubricating and anti-wear materials.For current study on tribological modification of PI resins, there are still some shortcomings, such as single means, limited modified effect and so on. To overcome these points, tribological modification of PI was carried out comprehensively and in-depth by chain design, interface design and functionalization of filler in light of structure and compounding modification in this dissertation. As a result, excellent modified effect on tribological properties of PI was achieved.The main contents of this dissertation include:Firstly, in light of chain design, phenylacetylene terminated agent was incorporated into condensation polymerization to prepare oligomers with different calculated molecular weight, and then prepared modified PI resin matrix by thermal addition reaction. Secondly, in light of interface design, facing to modified and unmodified PI resin matrices, proposed different strategies for surface modification of filler, and prepared two kinds of PI composites with high wear resistance based on two different surface-modified graphene, respectively. Thirdly, in light of multi-functionalization of filler, prepared graphene oxide/nano-polytetrafluoroethylene composite filler by chemical compounding, and then prepared PI composites with low friction coefficient and high wear resistance via in-situ polymerization.Filler modification and dispersion, structure of PI resin and composites, worn surface and wear debris were analyzed and observed by X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance spectroscopy (NMR), fourier transform infrared spectroscopy (FTIR), raman spectroscopy (Raman), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Mechanical, thermodynamic, thermostability and tribological properties were evaluated by nanoindentation, universal mechanical testing machine, dynamic mechanical analyzer (DMA), thermogravimetric analysis (TGA) and reciprocating friction and wear tester. Based on these above characterizations, the relationship between structure and properties of PI materials and related mechanisms were discussed and analyzed in-depth.The main results of this dissertation are summarized, as follows:1. Chain structure of PI were controlled and optimized by different calculated molecular weight of crosslinkable oligomers. This significantly improved mechanical properties, glass transition temperature and anti-wear property of modified PI resin matrix. When calculated molecular weight of oligomer is 5000 g/mol, the performance of the modified PI matrix is the best.2. Surface modification of filler contributes to strengthen modified effect for PI composites. Both graphene oxide functionalized with phenylacetylene group (phenylacetylene-modified graphene oxide) and reduced graphene functionalized with small molecular segment with amino group (amino-modified graphene) can be dispersed homogeneously in the matrix, and form strong covalent bond with the matrix. This can contribute to effective stress transfer in the resulting PI composites and utilize tribological effect of graphene, yielding PI composites with high wear resistance.3. The incorporation of graphene oxide/nano-polytetrafluoroethylene composite filler can significantly reduce friction coefficient of PI composites, and further improve anti-wear property, yielding PI composites with low friction coefficient and high wear resistance. Graphene oxide and nano-polytetrafluoroethylene have synergy effect. When 1 wt%composite filler was added, a 60% decrease in friction coefficient and a more than 2-order of magnitude decrease in wear rate (from 156 × 10-6 mm3/Nm to 1.09×10-6 mm3/Nm) were achieved.4. The significant improvement in anti-wear property is ascribed the following aspects:homogeneous and oriented filler dispersion, strong interface, the increase in mechanical properties, the formation of transfer film and tribological effect of modified filler. The incorporation of nano-polytetrafluoroethylene by chemical compounding can remarkably reduce friction coefficient of the resulting PI composites.In the aspects of structure and compounding modification, studies were conducted in light of chain design, interface design and multi-functionalization of filler, and prepared modified PI resin matrix and composites with excellent comprehensive performance, especially for tribological properties. The research results can provide theoretical significance and practical value to deepen the relationship between polymer structure and tribological properties. In the meantime, the study also can richen modification methods of graphene/polymer composites, and verify that graphene can improve tribological properties of polymer.