An Investigation On The Tribological Properties Of PBO And Chopped PBO Fiber Reinforced Polymer Composites

Poly (p-phenylene benzobisoxazole) (PBO) is a rigid-rod polymer with phenyl rings and heterocyclic groups in the backbone. It exhibits outstanding mechanical properties, as well as high thermal and chemical resistance. As a very promising high performance material, this rod-like aromatic heterocyclic polymer has attracted intensive attention during the past few decades, and already found a variety of applications, including aerospace, industrial materials and sports etc. However, its tribological properties are little to know until now. To handle the materials properly and explore their applications in tribological field, an investigation on the tribological properties of PBO and PBO reinforced polymer composites is very meaningful and necessary.In this paper, the friction and wear properties of the PBO were investigated under various loads, sliding speeds and ambient temperatures. Chopped PBO fiber reinforced Phenol Formaldehyde resin (PF) and Polytetrafluoroethylene (PTFE) composites were prepared, and effect of PBO's reinforcement on the tribological properties were evaluated. The means of Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectrometry (FT-IR), Thermo Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) were employed to elucidate the friction and wear mechanisms. Some innovative results showed as follows:1) Because of liquid crystal property, PBO forms a layered structure during the fabrication process. Because of this unique structural characteristics along with excellent heat and chemical resistance, PBO exhibits a relatively low friction coefficient (about 0.2) when sliding against steel, which is hardly affected by load, sliding speed and ambient temperature. Besides the low and steady friction, PBO also shows a good anti-wear property, it has a specific wear rate one fourteenth that of polyimide, a famous anti-wear polymer material. In a word, PBO exhibits excellent tribological properties, making it a promising material for application in tribological fields.2) When reinforced with chopped PBO fiber, PF and PTFE both show markedly improved anti-wear properties, while the friction coefficient varies within a small range. PBO's impacts on tribological properties are comparable with those of aramid fiber.3) As PBO fibers are soft and very wear resistant, they don't destroy the integrity of transfer film and wear surface during the sliding process, the fibers can undertake some stress and protect the matrix, thus reduce the wear.4) Compared with using PBO separately, when applied load is not harsh, filling PTFE and chopped PBO fiber simultaneously into PF matrix results in better tribological properties as PTFE can form an uniform lubricating layer on sliding surface.