Effect of Graphene Nanoplatelets (GNPs) on Tribological and Mechanical Behaviors of Polyamide 6 (PA6)

Vol. 39, No. 3 (2017) 277-282, DOI: 10.24874/ti.2017.39.03.01 RESEARCH Tribology in Industry www.tribology.fink.rs Effect of Graphene Nanoplatelets (GNPs) on Tribological and Mechanical Behaviors of Polyamide 6 (PA6) F. Mindivan a a Bilecik Seyh Edebali University, Bozuyuk Vocational College, Department of Technical Programs, Bilecik, Turkey. Keywords: Graphene Composite Polyamide 6 Scratch hardness Tribology Corresponding author: Ferda Mindivan Bilecik Seyh Edebali University, Bozuyuk Vocational College, Department of Technical Programs, Bilecik, Turkey. E-mail: ABSTRACT The effects of Graphene Nanoplatelet (GNP) on mechanical and tribological properties of Polyamide 6 (PA6) were studied. The composites were blended using twin-screw extruder and subsequently injection molded for test samples. Mechanical properties were investigated in terms of microhardness, scratch hardness and Young’s modulus measurements and tensile test. The tribological behavior of composites was studied by using ball-on-disc reciprocating tribometer. Recent studies showed that the addition of GNP in PA6 matrix resulted in enhancement of mechanical and tribological properties. 1. INTRODUCTION ) – ALIGN LEFT Strong composite materials based on polymeric matrices are increasingly used in wide range of engineering applications, due to their higher stiffness-to-weight ratio in comparison with metallic materials as well as their enhanced corrosion-resistance. In order to improve their poor surface characteristics, various particles such as carbon nanotubes and boron carbide have been used especially in the recent decade [1,2]. Due to its extraordinary mechanical properties with a reported Young’s modulus of 1 TPa and a tensile strength of 130 GPa [3,4], graphene nanoplatelets (GNPs) are an ideal reinforcement for strengthening polymer matrices. In order to improve the properties of GNP-polymer © 2017 Published by Faculty of Engineering composite, the surface of GNPs is modified either physically or chemically [5]. It is generally considered that the surface modification of GNPs is beneficial to improve the dispersal property of GNPs in polymer matrix. However, the modifying process is usually complicated and damages the structure of the GNPs and thereby greatly reduces their mechanical properties [6]. Thus, the enhancement effect of the GNPs will be weakened. The objective of this paper is to fabricate PA6/GNP composites and investigate the effects of GNP loading content on the mechanical and tribological properties of the PA6/GNP composites without using any surface modification process. 277 F. Mindivan, Tribology in Industry Vol. 39, No. 3 (2017) 277-282 2. EXPERIMENTAL METHODS GNPs in this study were GRAFEN-IGP2 nanoplatelets (Grafen Chemical Industries, Turkey). These nanoparticles consist of short stacks of graphene layers having a lateral dimension of 5 nm and a thickness of 5–8 nm. SEM observation (Fig. 1) of GNPs shows that the GNPs superimpose together and look like wrinkled or crumpled thin paper. Melt blending of PA6 and GNP was carried out in a co-rotating twin screw extruder (Thermoprism TSE 16 TC, L/D 24) at a screw speed of 100 rpm and barrel temperature profile of 230-230-230-230-230 °C, followed by granulation (3–5 mm long and 3 mm in diameter) in a pelletiser and drying. Prior to extrusion, the PA6 polymer and GNP were dehumidified in a vacuum oven at 90 °C for a period of 24 h. The GNP content in the PA6/GNP composites was varied from 1 – 4 wt.% (Table 1). The composite mixture was molded using a laboratory scale plunger type injection-molding machine (Micro injector, Daca Instruments) at a barrel temperature of 200 °C and mold temperature of 30 °C, for preparation of microhardness, scratch hardness, Young’s modulus, tensile and tribological test samples. Fig. 1. The SEM image of GNPs. Table 1. Ratios and codes of GNP in the composites. Samples PA6/GNP-1 PA6/GNP-2 PA6/GNP-4 GN Content (in weight %) 1 2 4 Room temperature mechanical properties of the unfilled PA6 and PA6/GNP composites were determined according to microhardness and Young’s modulus measurements, scrathch hardness and tensile tests. Microhardness measurement was carried out on metallographic samples under the load of 50 g with a Vickers indenter. At least ten successive measurements 278 were performed for each condition. The Impulse Excitation Technique (IET) was used to measure the Young’s modulus of the sample series in accordance with the ASTM E 1876 standard [7]. Briefly, IET utilises the phenomenon of free mechanical resonance of flexural vibrations when these vibrations are excited by tapping the test sample. Analysis of the fundamental frequency of a specific vibration mode, which depends on sample mass, stiffness, and geometry, allows determining the Young’s modulus by measuring the resonance frequency. The tensile test samples with a gage length of 80 mm were also tested according to the ASTM D 3822 standard [8] on Lloyd LR 5K tensile testing machine with a load cell of 10 N and the deformation rate was 20 mm/min. All the results represented an average value of five tests with standard deviations. The scratch tester, designed and built in our laboratory, was used to carry out scratch tests equipped with a Rockwell C-type conical indenter under laboratory environment condition (the temperature was 25 °C and the humidity was 30-35 % RH). The tests were conducted at four different loads (5, 10, 15 and 20 N) with a constant tip velocity of 0,007 m/s. The length of the scratch was kept constant as 10 mm. In order to assess tribological properties of the unfilled PA6 and PA6/GNP composites, the friction and wear tests were conducted on a reciprocating wear tester under dry sliding conditions. The ambient temperature was approximately 25 °C and the relative humidity was nearly 40 ±5 %. The wear tests on all samples were performed under a constant load of 10 N using a 10 mm diameter 304 steel ball at a sliding velocity of 1.7 cm s-1. In all tests, the total sliding distance was kept constant at 50 m. The wear was calculated by analysing width and depth of wear scars developing on sample surfaces with the help of a contact stylus profilometer (SJ400). Following the wear tests, the steel counterface surfaces were examined under an Optical Microscope (OM) in order to investigate the wear mechanisms. Then, scratch and wear scars on the surfaces of the unfilled PP and PA6/GNP composites were examined using a Scanning Electron Microscope (SEM- Carl Zeiss AG - SUPRA 40). 3. RESULTS AND DISCUSSION Figure 2 showed XRD patterns of the unfilled PA6 and PA6/GNP composites. PA6 exhibited F. Mindivan, Tribology in Industry Vol. 39, No. 3 (2017) 277-282 polymorphic structures containing two types of crystal form: monoclinic (α) and pseudohexagonal (γ). The representative diffraction peaks observed at 2θ=20.4° and 21.8° corresponded to α and γ crystalline phases of the unfilled PA6 [9,10], respectively. As sho (...truncated)