Homogeneously Dispersed Carbon Nanofiber/High-Density Polyethylene Nanocomposite Compatibilized by Dilakylimidazolium Tetrafluoroborate

Hindawi Journal of Nanomaterials Volume 2019, Article ID 8125670, 16 pages https://doi.org/10.1155/2019/8125670 Research Article Homogeneously Dispersed Carbon Nanofiber/HighDensity Polyethylene Nanocomposite Compatibilized by Dilakylimidazolium Tetrafluoroborate J. Samuel , S. Al-Enezi , A. Al-Banna, and G. Abraham Polymeric Product Enhancement and Customization Program, Petroleum Research Center, Kuwait Institute for Scientific Research, P.O. Box 24885, Safat 13109, Kuwait Correspondence should be addressed to J. Samuel; Received 20 February 2019; Revised 13 May 2019; Accepted 5 August 2019; Published 15 September 2019 Academic Editor: Yasuhiko Hayashi Copyright © 2019 J. Samuel et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. High-density polyethylene (HDPE) was used in this study as a matrix for accommodating carbon nanofiber (CNF) along with ionic liquid, to investigate the effect of nanofibers loading on the morphological thermal and rheological properties of the composites. The nanocomposite materials were prepared via melt processing using dilakylimidazolium tetrafluoroborate (ionic liquid) as a compatibilizing agent. The samples blended with imidazolium ionic liquid exhibited higher thermal stability, while DSC analysis showed the clear miscibility of ionic liquid in the HDPE matrix with a single endothermic peak. The influence of CNF (ranging from 0, 0.5, 1, and 2 wt.%) and ionic liquid concentration on the viscoelastic parameters was investigated. The rheological analysis showed the shear-thinning behavior of the composites. An improvement in the viscoelastic properties was observed as the nanofiber concentration increased. Composites blended with ionic liquid (HDPE/CNF/IL) exhibited slightly lower values of complex viscosity and modulus over the corresponding HDPE/CNF nanocomposites. Therefore, it is also significant that the reduction in melt viscosity is an additional benefit for polymer composite processing as a result of the wetting effect by polymer-ionic liquid combinations. 1. Introduction The incorporation of a small amount of nanomaterials such as carbon nanotubes (CNTs) and carbon nanofibers (CNFs) into the polymer matrix significantly improves the electrical properties and mechanical performance of the polymeric materials [1–3] offering great openings for developing multifunctional polymer composite materials, for electromagnetic interference (EMI) shielding electrostatic dissipative (ESD) protection and electrochemical applications [4–6]. However, the overall performance of the polymer nanocomposite mainly depends on the effective dispersion in to the polymer matrix and nanoparticle polymer adhesion [7]. CNFs are different from CNTs in its preparation methods, its unique physical characteristics, and the prospect of low-cost fabrication [8]. CNF requires less purification and readily available with low cost while comparing CNT. The combination of architectural flexibility and high mechanical strength allows the nanofibers to be used in fabricating tough composites for vehicles and aerospace [9]. When combined with polymers, the CNFs can induce improvement in the mechanical properties of the neat polymer and improvement dependent upon the type of polymer matrix, the efficiency of dispersion, and processing history [10, 11]. Vapor-grown carbon fibers (VGCFs) are the class of CNFs prepared by the catalytic chemical vapor deposition method. The incorporation of high-aspect ratio VGCF in polymer matrix usually exhibits improved physical properties [12] with a conceding in the processing difficulty. Therefore, evaluating the thermal and rheological properties is considered to be an important tool to address these issues related to dispersion behavior. In a number publication, the dispersion and rheological properties of VGCF reinforced polyolefins have been described [13–16]. The dispersion study of VGCF in ionic liquid reported that the aggregated lump of VGCF completely disappeared in the ionic liquid with longer alkyl chain [17]. 2 The use of ionic compatibilizer has been reported to be a suitable method to improve CNT dispersion in polystyrene matrix [18, 19]. Therefore, more related research will be quite interesting to improve dispersions of VGCF with suitable cationic modifications using ionic liquid, a nonflammable, thermally, mechanically, and electrochemically stable salt. Additionally, the presence of long alky groups enables easy melt processing of polymer nanocomposites. The present research looked into dependence of both VGCF and modified VGCF content on physical properties in high-density polyethylene (HDPE), one of the polyolefins most widely used in structural, packaging applications. The objective is to explore the possibility of preparing VGCF/HDPE composites with improved processability. The mechanical behavior of the resultant thermoplastic composites will be further assessed with the help to rheological analysis. From a material design point, not only dispersion and compatibility but also other synergic properties will be addressed to develop polymer nanocomposites with balanced properties. 2. Materials Commercially available CNFs (>98% carbon basis, D × L 100 nm × 20‐200 μm; produced by a vapor-grown method) were obtained from Sigma-Aldrich, and ionic liquid (IL) and 1-hexadecyl-3-methylimidazolium tetrafluoroborate > 98% were supplied by IoLiTec. 2.1. Preparation of HDPE/CNF Composites. The overall physical properties of the CNF/HDPE composites are mainly influenced by the dispersion of the CNF in the polymer matrix. Therefore, the dispersion technique plays a key role in the preparation of CNF composites. The most widely used method is melt mixing, due to its easiness and cost effectiveness. In order to obtain a good distribution of CNF in the polymer matrix, a high shear melt mixing is usually essential, although this method will lead to a relatively good dispersion of the CNF. Therefore, the relatively low shear mixing method without sacrificing the dispersion is still a challenge for the preparation of CNF/polymer composites by the melt mixing approach. The use of IL along with CNFs is a promising method to support their dispersion in the polymer matrix. In this process, the compatibility between the IL and CNF is the key factor, which decides the CNF dispersion and the overall performances of the composites. In the first stage, the CNF powder and HDPE pellets with different filler ratios (0, 0.5, 1, and 2 wt.%) with and without IL (1 wt.%) were carefully mixed to ensure an adequate distribution of the particles at the macroscale level. The mixture was then melt-mixed in a laboratory scale twin screw extruder (HAAKE) at a rotor speed of 200 rpm followed by pelletization. Test specimens were prepared using a bench top HAAKE injection molding machine. The temperatures of different (...truncated)