# Preparation and Lubricating Properties of Polystyrene Composite Microspheres
###### Abstract  
In order to improve the lubrication performance of polystyrene microspheres (PS) as solid lubricant in drilling fluids, elastic graphite-polystyrene composite microspheres (EGR/PS), montmorillonite-elastic graphite-polystyrene composite microspheres (OMMT/EGR/PS), and polytetrafluoroethylene-polystyrene composite microspheres (PTFE/PS) were prepared by suspension polymerization. OMMT/EGR/PS has a rough surface, while the surfaces of the other three composite microspheres are smooth. Among the four kinds of composite microspheres, the largest particle is OMMT/EGR/PS, and the average size is about 400 \(\upmu\)m. The smallest particle is PTFE/PS, and the average size is about 49 \(\upmu\)m. Compared with pure water, the friction coefficient of PS, EGR/PS, OMMT/EGR/PS and PTFE/PS reduced by 25%, 28%, 48%, and 62%, respectively. The wear tracks of EGR/PS, OMMT/EGR/PS and PTFE/PS are narrower and smoother than those of pure water. When the content of PTFE is 4.0 wt%, the friction coefficient and wear volume of PTFE/PS are 0.213 and 2.45 \(\times\) 10\({}^{-4}\) mm\({}^{3}\)--74% and 92.4% lower than that of pure water, respectively.  
composite microspheres; lubricating properties; polystyrene; PTFE +
Footnote †: journal: materials  
0000-0002-22001-1111  
material, good chemical stability and not reacting with other materials [7; 8]. However, PS bearing capacity and high-temperature resistance are poor, with easily softened deformation in the use process, thus affecting the lubrication effect. One of the effective ways to solve the above problems is preparing composite microspheres by polymerizing styrene and other materials.  
Montmorillonite (MMT) is a natural layered silicate commonly used in polymer modification, usually for the preparation of polymer-clay nanocomposites, because MMT can improve the thermal stability and mechanical properties of polymers. As such, the composite material has good heat-resistance stability and high strength and stiffness [9; 10]. It can also improve the load-bearing capacity of the composite microspheres. Elastic graphite (EGR) has the advantages of high purity, good flexibility, and high elasticity. It has stable performance and temperature resistance [11], and does not react chemically with other drilling fluid additives. EGR is also a good lubricant material [12].  
Polytetrafluoroethylene (PTFE) is a high-molecular-weight polymer obtained by polymerizing tetrafluoroethylene monomer. It has high-temperature resistance characteristics, so it can improve composite microspheres' high-temperature resistance. It has a very low friction coefficient, so it can be used as an additive with excellent self-lubricating properties and has been widely used in solid lubricating materials and greases [13; 14]. It is worth noting that substances like PTFE decompose extremely slowly under ambient conditions, so they will accumulate in organisms and the environment and cause harm [15], but considering the complete alternative will entail huge cost, we can ameliorate these problems through its production process [16] and recycling research. At the same time, the use of PTFE's excellent self-lubricating properties can also be maximized [17]. Therefore, PTFE still has important application value in lubricant additives.  
In this study, to further improve the lubricating performances of PS, organic montmorillonite (OMMT), elastic graphite (EGR) and PTFE were used as additives to be compounded with styrene by suspension polymerization methods to prepare three kinds of polystyrene composite microspheres. The composite microspheres were successfully tested as additives for high-performance lubricants [18]. The effects of additive components on the tribological properties of polystyrene microsphere lubricants were investigated, and the composite microspheres' lubrication mechanism is discussed and revealed.