Abstract
Polystyrene-organo-montmorillonite (PS-OMMT) nanocomposite particles were prepared via emulsion polymerization of styrene in the presence of montmorillonite modified with an anionic surfactant, sodium lauryl sulfonate (SLS), and its tribological properties as an additive to polyalphaolefin (PAO) were tested. The results of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) showed that SLS molecules resided in the montmorillonite (MMT) interlayer space. The effects of OMMT on the morphology and properties of the nanocomposites were also investigated. Gel permeation chromatography (GPC) and dynamic light scattering (DLS) demonstrate that the presence of OMMT can effectively reduce the average molecular weight and average particle size of PS. XRD and transmission electron microscopy (TEM) of the PS-OMMT nanocomposites indicate that exfoliated and intercalated structures form and that the MMT layers either are partly embedded inside the PS particles or remain on their surface. Compared with pure PS, the PS-OMMT nanocomposites possessed higher stability to thermal decomposition and higher glass transition temperatures. Adding nanocomposite particles reduces the friction coefficient, and thus, the antiwear properties of the PAO are significantly improved. The PS-OMMT-3 (3 wt % of OMMT based on styrene) particles have the best tribological performance and maintained a stable, very low coefficient of friction of 0.09.
Highlights
Polymer-clay nanocomposites have attracted considerable interest from researchers due to their tremendous properties and broad applications [1,2,3,4,5]
The temperatures of the maximum decomposition rate (Tmax ), as revealed by the derivative thermogravimetry (DTG) curves, followed the same trend and increased by 6.7 ◦ C, 18.1 ◦ C and 13.0 ◦ C, respectively, compared with pure PS. These results suggested that the introduction of OMMT improved the thermal stability of the polystyrene, which may be attributed to a labyrinth or barrier effect originating from the high aspect ratio of the clay layers, which can prevent diffusion of the volatile decomposition products out of the polymer in the thermal degradation zone [39]
Fourier transform infrared (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) data confirmed the intercalation of sodium lauryl sulfonate (SLS) into the MMT interlayer spaces in acidic media
Summary
Polymer-clay nanocomposites have attracted considerable interest from researchers due to their tremendous properties and broad applications [1,2,3,4,5]. The factors impacting the efficiency of these nanocomposite materials include the aspect ratio of the clay layers, the dispersion quality and the interfacial adhesion between the polymer matrix and the clay layers [10,11]. Unique and improved properties are often observed when the dispersed clay layers were less than 100 nm thick. Many techniques have been evaluated to achieve homogeneous dispersions of ultrafine silicate clay layers inside polymer matrices. Layered silicates such as sodium-montmorillonite (MMT), which is an aluminosilicate mineral with sodium counterions between its layers, are one of the types of materials
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