Xianqiang Pei

Shape memory polyurethanes containing azo exhibiting photoisomerization function

A series of azobenzene-containing polyurethanes (azoPU) was synthesized. The structure of the azoPU and the synthesis process were detected by FTIR and nuclear magnetic resonance (NMR), and the transition temperature was determined by differential scanning calorimetry (DSC). Tensile and cyclic thermomechanical experiment results revealed that excellent mechanical properties, shape fixity (Rf), and shape recovery (Rr) were obtained by the addition of azo to the chain of PU. Rr and Rf of azoPU increased with the increase of hard segment (HS) content. The higher HS content enhanced interaction among polymer chains as the chances of induced dipole–dipole interaction between aromatic rings increased in the presence of azo in the main chain. The materials presented trans-cis isomerization under UV irradiation in addition to the shape memory effect. The UV-vis spectrum indicated that photoisomerization occurred both in solution and solid state. It is expected that the work may be helpful in expanding the application of shape memory PU in areas of drug release and optical data storage.

A Synergistic Effect of Graphite and Nano-CuO on the Tribological Behavior of Polyimide Composites

Polyimide (PI) composites modified with nano-CuO and graphite were prepared by means of a hot press molding technique. The effects of nano-CuO and graphite on the tribological properties of the composites were studied using a block-on-ring arrangement. The results revealed that the incorporation of graphite alone improved the friction-reducing and anti-wear abilities of the PI composites, whereas incorporation of nano-CuO alone deteriorated the wear resistance of the PI composite owing to its abrasive effect. A synergistic effect was found for the combination of nano-CuO and graphite, which leads to the best tribological properties. The results showed that the filled PI composites exhibited worse tribological properties under higher load and sliding speed, and showed better friction and wear behavior under oil lubrication and worse tribological properties under water lubrication.

Friction and Wear of Potassium Titanate Whisker Filled Carbon Fabric/Phenolic Polymer Composites

Carbon fabric/phenolic composites modified with potassium titanate whisker (PTW) were prepared by a dip-coating and hot-press molding technique, and the tribological properties of the resulting composites were investigated systematically using a ring-on-block arrangement under different sliding conditions. Experimental results showed that the optimal PTW significantly decreased the wear-rate. The worn surfaces of the composites and the transfer film formed on the counterpart steel ring were examined by scanning electron microscopy (SEM) to reveal the wear mechanisms. The transfer films formed on the counterpart surfaces made contributions to the improvement of the tribological behavior of the carbon fabric composites. The friction and wear of the filled carbon fabric composites was significantly dependent on the sliding conditions. It is observed that the wear-rate increased with increasing applied load and sliding speeds.

Structural and Tribological Properties of Polyimide/Al2O3/SiO2 Composites in Atomic Oxygen Environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polyimide/Al2O3/SiO2 composites were investigated in a ground-based simulation facility, in which the energy of AO was about 5 eV and the flux was 7.2 × 1015 cm−2.s−1. The structural changes were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total-reflection FTIR (FTIR-ATR), while the tribological changes were evaluated by friction and wear tests as well as scanning electron microscopy (SEM) analysis of the worn surfaces. It was found that AO irradiation induced the oxidation and degradation of polyimide (PI) molecular chains. The destructive action of AO changed the surface chemical structure, which resulted in changes of the surface morphology and chemical composition of the samples. Friction and wear tests indicated that AO irradiation decreased the friction coefficient but increased the wear rate of both pure and Al2O3/SiO2 filled PIs.

Preparation, Characterization, and Properties of Polyamide 66/Maleic Anhydride -grafted-polypropylene/Clay Ternary Nanocomposites

Polyamide (PA) 66/PP-g-MA/Organic-modified MMT (OMMT) ternary composites were prepared by direct melt compounding. The FESEM results showed that the PP-g-MA phase dispersed homogeneously in the PA matrix due to the interfacial chemical reactions between the two phases. The mechanical properties of the composites were evaluated. The tensile and bending properties decreased and the notched impact strength increased with the increase of PP-g-MA. The tribological behaviors of the ternary composites were studied by means of a ball-on-disk apparatus. The ternary composites exhibited better tribological properties compared with the PA/OMMT system. This was probably due to the fact that the PP has good flexibility and a transferring film could be formed easily on the counterpart. Combining the results of the mechanical and tribological properties, the optimal mass fraction of PP-g-MA was 10 wt. %.

Damping Properties of Polyurethane/Epoxy Graft Interpenetrating Polymer Network Composites Filled with Short Carbon Fiber and Nano-SiO2

A series of short carbon fiber (CF) and nano-SiO2 filled polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites were prepared. The damping properties as well as tensile and impact strength of the IPN composites were studied systematically in terms of composition. Results revealed that the addition of short CF and nano-SiO2 can significantly improve the damping properties of pure PU/EP IPN, particularly at higher frequencies. Mechanical tests showed that the tensile strength of the IPN composites was improved after the incorporation of short CF and nano-SiO2, while the impact resistance of the composites was impaired after the addition of CF and higher content (beyond 1 wt%) of nano-SiO2. It is proposed that the CF and nano-SiO2 filled IPN composites would be useful as structural damping materials.

Reversible Emission Color Change of Eu-Polymer Complex Induced by Acetone

A Eu-polymer complex containing Eu(BA)3phen (BA stands for benzoic acid and phen is 1,10-phenanthroline) and epoxy resin was synthesized in. It was found that the emission light color under 254 nm UV light could change reversibly between red and blue with addition and evaporation of acetone in the Eu-polymer complex. To explain the reversibility of the emission color, the chemical structure and fluorescence property of the complexes were investigated using FTIR, UV-vis, and photoluminescence (PL) spectra. It is proposed that the competitive coordination between Eu/epoxy and Eu/acetone was responsible for the reversible emission color change.

Structural and Tribological Properties of Polytetrafluoroethylene Composites Filled with Glass Fiber and Al2O3 in Atomic Oxygen Environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polytetrafluoroethylene (PTFE) composites filled with both glass fibers and Al2O3 were investigated in a ground-based simulation facility, in which the average energy of AO was about 5 eV and the flux was 5.0 × 1015/cm2 s. It was found that AO irradiation first induced the degradation of PTFE molecular chains on the sample surface, and then resulted in a change of surface morphology. The addition of Al2O3 filler significantly increased the AO resistance property of PTFE composites. Friction and wear tests indicated that AO irradiation affected the wear rate and increased the friction coefficient of specimens. The PTFE composite containing 10% Al2O3 exhibit the best AO resistance and lower wear rate after long time AO irradiation.

A Comparative Investigation of Thermal and Tribological Properties of Thermoplastic and Thermosetting Polyimides with Similar Structural Formulae

Polymerization of monomer reactants (PMR)-type polyimide was synthesized and the homogeneous matrix resin solution (30–40% solid) was used to prepare film blocks for tribological tests. Compared with a thermoplastic polyimide with similar molecular formula and similar behavior of weight loss under heating, the high glass transition (Tg) and char yield of the PMR polyimide can be attributed to the self-reaction of phenylethynyl groups to result in a cross-linked structure. Tribological studies on both PMR type thermosetting polyimide and thermoplastic one showed that the friction coefficient and wear rate of the former polyimide were lower than that of the latter one under both similar and even more critical conditions. Scanning electron microscope examinations of worn surfaces and wear debris show that the wear type of the thermoplastic polyimide was adhesive wear and that of the thermosetting one was fatigue wear. In terms of all good tribological properties, this PMR-type thermosetting polyimide, due to its high PV limit, could be a potential candidate for tribo-material in dry sliding against steel under high speed and large load.