Comparative effects of rocket-grade hydrogen peroxide solution on POM and UHMWPE: aging behaviors and tribological properties

Tribological properties of UHMWPE/PAANa/Ph4Sn composite materials in seawater lubrication

The blended composites with ultra-high molecular weight polyethylene (UHMWPE) as the matrix polymer, sodium polyacrylate (PAANa), and tetraphenyltin (Ph4Sn) as fillers were prepared by hot compression molding process. The friction and wear behavior of GCr15 balls with composites mating pairs under the seawater environment was explored, and the friction and wear mechanism was analyzed. The results show that adding PAANa, a polyelectrolyte material, can effectively reduce the friction coefficient of UHMWPE/PAANa/Ph4Sn composites. The wear resistance of composites increased significantly with increasing Ph4Sn content compared with pure UHMWPE, and the best wear resistance was observed at 1% content. The primary wear mechanism of UHMWPE/PAANa/Ph4Sn composites changed from adhesive wear of pure UHMWPE to plastic deformation at lower PAANa and Ph4Sn contents and finally to adhesive wear and spalling. This work provides a theoretical basis for preparing and applying other polymer blend composites.

Properties of compression molded ultra-high molecular weight polyethylene: effects of varying process conditions

Ultrahigh molecular weight polyethylene (UHMWPE) has been extensively used in various tribological systems because of its outstanding tribological properties and excellent overall performance. Compression molding is the main molding method for UHMWPE, and the process parameters of molding have a profound effect on its material properties. In this study, three groups of UHMWPE samples were prepared, and their physical, mechanical, and tribological properties under different molding process parameters were examined—with a particular focus on the frictional and wear behavior of the material under various heating-temperatures, pressing-temperatures and pressures—and the friction and wear mechanisms of UHMWPE were analysed. Studies have shown that the rise in heating-temperature promotes the diffusion of polymer chains, resulting in an increased friction coefficient and wear loss of UHMWPE. The main wear mechanism switches from plastic deformation to fatigue wear. With an increase in the pressuring-temperature, the friction coefficient first increases and then decreases, while the wear loss increases, and the dominant wear mechanism switches from fatigue wear and plastic flow to plastic flow. With an increase in pressure, the friction coefficient and wear loss first decrease and then increase, and the prime wear mechanism changes from plastic deformation and fatigue wear to fatigue wear.

Influence of early thermal-oxidative ageing on the structure and properties of polyoxymethylene copolymer

Thermal-oxidative ageing of polyoxymethylene (POM) copolymer in the oven at 100°C for 1, 2, 3, 5, 7, 10, 14 and 21 days and the influence of early thermal-oxidative ageing on POM structure and properties were studied by means of wide-angle X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry and tensile test. Based on the results, we found that the early thermal-oxidative ageing of POM copolymer can be divided into three regions. The region I is the initial 3 days. In this region, some molecular chains rearranged, resulting in internal stress relaxation, increase of crystallinity degree and grain size due to the perfection of crystal structure; both extended chain crystal (ECC) and folded chain crystal (FCC) increased and ECC grew faster than FCC. The region II is from 3 days to 10 days, and in this region, chain scission took place in amorphous region and led to chemi-crystallization. The region III is after 10 days. In this region, the structure and performance of POM copolymer reached a stable situation at this stage. In this work, the difference between skin and core were also analysed.

Influences of interface structure on tribological properties of engineering polymer blends: a review

Polymer blends have been widely used as tribological materials for replacements of traditional metals and ceramics. Polymer blends consist of the reinforced phase, the matrix phase and interfaces between reinforced and matrix phase. Although the interface structure of polymer blends is usually small in size, it is one of the key factors for deciding the physical and tribological properties of polymer blends. Thus, this review highlights the most recent trends in the field of influences of interface structure on tribological properties of engineering polymer blends. Emphasis is given to the improvement methods of interfacial compatibility of polymer blends and the behavior variation of interface structure during friction process.