Enhanced tribological performance of the multi-layer graphene filled poly(vinyl chloride) composites

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Abstract

Multi-layer graphene (MLG) filled poly(vinyl chloride) (PVC) composites were prepared by using conventional melt-mixing methods in order to improve tribological performance of rigid PVC. We investigated microstructure, microhardness, friction coefficient, and wear resistance of the MLG/PVC composites in details. We found that the presence of MLG could greatly decrease friction coefficient and wear rate of the MLG/PVC composites, implying higher wear resistance and tribological performance of the nanocomposites compared with neat PVC. Moreover, the wear mechanism of the MLG/PVC composites was also presented. Such high tribological performance of the MLG/PVC composites is mainly attributed to enhanced toughness of the MLG/PVC composites and high self-lubricant performance of the MLG. In light of its high tribological performance, the MLG/PVC composites have great potential to be used as wear-resistant materials in many fields.

Introduction

Poly(vinyl chloride) (PVC) is one of the most widely used polymeric materials in the world due to its low cost, high mechanical strength, good fire-retardance, and good chemical resistance, and it has been applied as cable conduits, stair armrests, and flooring materials in many fields [1]. In some circumstances, wear resistance of materials is an extremely important evaluation index which directly determines service life of products [2], [3]. However, rigid PVC materials without plasticizers are typically brittle, and some microcracks are easily generated and propagated under friction stress [4], which greatly hinders practical application of rigid PVC as wear-resistant materials in many fields. In that case, developing high wear-resistant PVC materials has attracted considerable attention from industrial and academic fields.

Some methods for improving wear-resistance of PVC have been developed for several decades. Coating protective layers of diamond and amorphous carbon onto PVC surface can greatly increase wear resistance [5], [6], but these layers are so brittle that they can be easily peeled off. Some elastomers such as polyurethane and modified rubber have been used to increase toughness and wear resistance of PVC materials [7], but there still exist some disadvantages of complex process and high cost. Some inorganic fillers such as glass fibers and silicon carbide particles have also been added into PVC materials to increase wear resistance of composites [2], [7], [8], [9], [10], [11], but these high-density inorganic fillers cannot be well dispersed due to their high density and poor compatibility with polymeric matrix, and consequently a large amount of filler loading is generally needed for obtaining acceptable wear resistance of composites [12], [13], [14].

Recently, some nanocarbon materials, especially carbon nanotubes (CNTs) and graphene, have attracted great interest from academic and industrial fields due to their light-weight, small size, and large specific surface areas, and good compatibility with polymer [15], [16], [17]. It has been reported that the presence of carbon nanomaterials can greatly enhance strength and toughness of polymeric matrix and effectively hinder propagation of microcracks, consequently resulting in high wear resistance of the nanocomposites [18], [19], [20], [21], [22], [23]. Especially, graphene materials exhibit extraordinary self-lubricant characteristics due to its unique flexible graphitic layers, extremely high strength, and easy shear capability on its densely packed and atomically smooth surface [24], [25], [26], [27], [28], [29], showing great potential for graphene to be used as high performance lubricant in many fields. Tai et al. reported that the presence of graphene oxide (GO) could greatly increase tribological performance of ultra-high-molecular-weight polyethylene (UHMWPE) [21]. Shen et al. found that wear resistance of epoxy could be remarkably improved by adding only a small amount of GO [22]. Most of these researches focused on improvement of tribological performance of traditional engineering plastics such as epoxy, nylon, polyimide, and UHMWPE [23], but enhanced tribological performance of graphene filled PVC composites has not been reported so far.

The purpose of this paper is to obtain graphene/PVC composites with high tribological performance by taking full advantages of high self-lubricant properties of graphene. The graphene/PVC composites were prepared by adding commercial multi-layer graphene (MLG) into PVC matrix by means of conventional melt-mixing and hot-pressing technique. Microstructure and microhardness of the MLG/PVC composites were characterized, and tribological performance such as friction coefficient and wear rate was also investigated in details. We found that the MLG/PVC composites exhibited higher wear resistance than the neat PVC, which is mainly attributed to the enhanced toughness of the MLG/PVC composites and high self-lubricant performance of the MLG.

Section snippets

Materials

Multi-layer graphene (MLG) powders, which were produced by using interlayer catalytic exfoliation (ICE) technique, were supplied by Sichuan Jinlu Group Co., Ltd. China. Layer number of the used MLG is less than 10, and its thickness and lateral size is 1–5 nm and 10–15 μm, respectively. The MLG has a high purity of over 97% (its C/O ratio is more than 20), and its electrical conductivity is over 700 S/cm. Poly(vinyl chloride) (PVC) resin powders (general type of SG-5), rear-earth stabilizer, and

Microstructure of the MLG/PVC composites

Fig. 1 shows SEM images of the MLG and fracture surface of the MLG/PVC composites with various MLG loadings. It can be seen from Fig. 1a that the MLG shows large size, thin thickness, and typical crumpled morphology due to its large aspect ratio of over 1000, showing high flexibility of the used MLG. Fig. 1b is the SEM image of smooth fracture surface of rigid PVC, showing typical brittle fracture due to high sensitivity of the rigid PVC to microcracks [4]. Fracture morphology of the MLG/PVC

Conclusions

The MLG/PVC composites were prepared by using conventional melt-mixing and hot-pressing methods, and its microstructure, microhardness, tribological performance were investigated in details. We found that the presence of MLG caused decrease in microhardness of the MLG/PVC composites due to high flexibility of the crumpled MLG. Furthermore, the MLG/PVC composites exhibit much lower friction coefficient and wear rate than the neat PVC, indicating that the presence of MLG can greatly improve the

Acknowledgements

We acknowledge financial supports from the Hi-Tech Research and Development Program of China (No. 2012AA030303), the Hundred Talents Program of Chinese Academy of Sciences, and the Fund for Creative Research Groups of China (No. 51221264).

References (37)

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