The Study Of Tribological Properties Of Sulfur-Containing Special Engineering Plastics

The special sulfur-containing engineering plastics and their composites have excellent tribological properties and have been extensively applied in tribological field. The opinion from literatures that the excellent tribological properties of polyphenylene sulfide (PPS) and its composites probably have a relationship with the tribochemical reaction has not been confirmed yet.To clarify the above point, the influence of internal and external factors on the tribological properties of three special sulfur-containing engineering plastics, PPS, polyethersulfone (PES) and polysulfone (PSU) which have the similar structure was investigated systematically. The tribological properties were tested by an end-face contact mode and a pin-on-disc contact configuration wear testers. The pattern of worn surface and debris was observed with the aid of Scanning Electron Microscopy (SEM), Dynamic Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC), Thermo Gravimetric Analysis (TGA), Fourier Transform Infrared Spectrometry (FT-IR), X-Ray Diffraction (XRD), and X-Ray Photoelectron Spectroscopy (XPS). The friction and wear mechanism of sulfur-containing polymers was discussed on that basis.The conclusions of this dissertation were drawn as follows:1 In dry sliding, the friction coefficient of PPS fluctuated between 0.4 and 0.96 with the PV value increasing. However, that of PES and PSU kept stable at about 0.48, afterwards declined to 0.3 as the velocity increased. The wear rate of PPS declined first, and then rose up, while that of PES and PSU kept increasing. At 0.2m/s, 100N, the wear rate of PPS was 2.1×10^-5 mm³ /N·m which is the 1/10 of PES and PSU.2 Various external factors such as load and velocity influenced the tribological properties of PPS, PES and PSU by affecting the temperature of the worn interface. With the interfacial temperature increasing, the wear mechanism transited from abrasive wear to adhesion and melt wear. When it arrived at the glass transition temperature, the mechanical properties of PES and PSU sharply decreased and resulted in the high wear rate. But the mechanical properties of PPS decreased slowly because of its inherent semi-crystalline structure, so the wear rate changed slightly.3 The tribochemical reactions and reaction products between metal couple and sulfur-containing polymers were related to the valence state of sulfur, metal activity and interfacial temperature. The tribochemical reactions were difficult to happen for PES and PSU due to the low activity of high valence state sulfur in them. The lower valence state sulfur in PPS has higher activity which leads to the tribochemical reaction between PPS and metal couple by forming a firm transfer film.4 The transfer film plays a main role in the wear properties of the three polymers at lower PV value. The lower wear rate of PPS was associated with the firm transfer film formed between PPS and the metal couple. The aggregation structure is the major factor affecting the wear properties of these polymers at higher PV value. The semi-crystalline structure and its inherent thermosetting characteristics mainly caused the excellent wear properties of PPS.The above results are important to understanding the tribological law of sulfur-containing polymers and developing new friction materials, furthermore enrich the theoretical study of polymer tribochemistry.