The Research Of Mechanics, Tribology And Stability On PP/MMT And PMMA/MMT Nanocomposites

In recent years, the investigation of polymer/montmorillonite nanocomposites has become a very important field since such materials exhibit unexpected physical and chemical properties that differ significantly from that of their bulk counterparts.On the base of the calculation of cell of montmorillonite (MMT) structure with empirical electron theory of solids and molecules (EET), selecting polypropylene (PP, typical universal plastics) and poly (methyl methacrylate) (PMMA, typical engineering plastics) as matrix respectively, this dissertation studied mechanical properties, thermal properties, tribological behavior and sulfuric acid corrosion behavior of exfoliated PMMA/MMT and PP/MMT nanocomposites prepared through emulsion intercalation polymerization and melt intercalation in twin-screw extruder respectively.The valence electron structure of montmorillonite was calculatied by means of EET. The results show that, in the crystal structure of montmorillonite, Si of octahedron can't be replaced by Mg, but can be replaced by Al, and Al of tetrahedron can be replaced by Mg. EET calculation also explains the stability of three sub-layer of MMT layer, so the distance between layers of montmorillonite can be enlarged when in polar medium while that of three sub-layer is invariable.The addition of MMT (about 2 wt%) can improve the hardness and tensile strength of PP matrix, restrain abrasive wear under water lubrication condition (wear mass loss and friction coefficient of composites under 250 N load is reduced to 50 % and 88 % respectively, compared with that of bare PP), lessen adhesive wear and plastic zone formation of PP matrix under dry sliding condition (wear mass loss of composites, under 150 N load, is reduced to 30 %～40 %), but which phenomena becomes worse with the increase of load. Furthermore, the research of thermal properties shows that, the temperature of beginning lost weight of PP/MMT nanocomposites containing 1 wt%～2 wt% MMT is higher obviously than that of pure PP Compared with KH-V6 type MMT, TJ-2 type MMT can improve the tribology behavior under dry sliding condition and thermal properties of PPmatrix more obviously.The addition of MMT (about 5 wt%) can improve the hardness, reduce adhesive wear of PMMA matrix effectively (under dry sliding and water lubrication condition, wear mass loss of composites under 150 N load is reduced to 25 %～35 % and 55 % respectively, compared with that of pure PMMA under the same condition), and improve the thermal properties of PMMA. Compared with MMT of KH-γc and TJ-2 types, KH-V6 type MMT improves the thermal decomposition temperature of PMMA matrix more effectively.The effects of concentration and corrosion time of sulfuric acid and content of MMT on the corrosion rates of PMMA and PMMA/MMT nanocomposites in sulfuric acid were studied using weight loss testing method. The solution shows that, with the increase of MMT content, corrosion rate of PMMA/MMT nanocomposites in sulfuric acid decreases first, then increases. The corrosion rate of composites containing 2 %～3 % MMT is lowest for the barrier of MMT layer. The corrosion rates of both PMMA and its composites decrease with the increasing of corrosion time, while increase with the increasing of the concentration of sulfuric acid. Compared with MMT of TJ-2 type, MMT of KH-V6 has a better sulfuric acid corrosion resistance for PMMA.On the base of building percolation model of exfoliated polymer/montmorillonite nanocomposites, analyzed toughening and the improving of wear mass loss resistance mechanism, which were verified with scale law, of polymer/montmorillonite nanocomposites with percolation theory. The solution shows that exfoliative montmorillonite layers become cross-linking of nanocomposites and own toughening and reduce wear mass loss effection, which Corresponds With percolation theory.The thermal decomposition kinetics research shows that, the apparent activation energy of PP/2 wt% TJ-2 type MMT nanocomposites is higher than that of PMMA before 22 % mass loss. When mass loss is between 30 %～80 %, the most probable mechanism functions of PP and PP/2 wt% TJ-2 type MMT nanocomposites are Valensi equation (n=1/2) and Mampel Power theorem, corresponding mechanism is two-dimension diffusion and exponential function respectively. The apparent activation energy of PMMAis below that of PMMA/5 wt% KH-V6 type MMT nanocomposite before 37 % mass loss, and the former surpasses the latter after 44 % mass loss. When mass loss is between 20 %～80 %, the most probable mechanism functions of PMMA and PMMA/5 wt% KH-V6 type MMT nanocomposites are Jander equation (n=2) and G-B equation, corresponding mechanism is three-dimension diffusion. The addition of KH-V6 type MMT, prolongs, about double, the thermal decomposition time at a certain mass loss and temperature of PMMA/MMT nanocomposites, compared with pure PMMA, which shows the improvement of thermal stability of composites.