Mechanical characterization of the HDPE / CNFs nanocomposites

Abstract

Numerous researchers have demonstrated a keen interest in polymer-based nanocomposite materials because of their notable and desirable characteristics. Nanocomposites are types of materials whereby the matrix is reinforced with nanomaterials to improve their properties. Nanocomposite materials have dimensions less than 100 nm. These materials are created by mixing two main components, which is a polymer and a nanofiller to produce a nanocomposite. This combination yields a new material that has special properties, and researchers are interested in studying the changes in the mechanical behaviour of these materials as a result of added nanomaterials. Despite a large volume of investigations on nanocomposites at normal laboratory temperatures (room air temperature), studies are scare for elevated temperatures. Therefore, this current work aims to characterize the mechanical and thermal behaviour of polymer-based nanocomposites. Special focus was given to high-density polyethylene (HDPE) because of their potential for application to many aspects of engineering. Although they have displayed attractive properties under room air temperature, their behaviour under elevated temperature remains largely unclear. In this study, varying weight fractions of carbon nanofibers (CNFs), specifically 0 wt%, 1 wt%, and 2 wt% were integrated to polyethylene with high density (HDPE). To achieve this, the nanocomposites were prepared using melt blending through a twin-screw extrusion process, followed by injection moulding process to produce standardised test specimens. Furthermore, surface modification techniques such as the usage of grafted maleic anhydride HDPE (HDPE-g-MA) and a liquid polyester bonding agent were applied to strengthen the interfacial adhesion between the carbon nanofibers (CNFs) and the HDPE base. It is found that the incorporation of carbon nanofibers to the base material strengthens the properties of the HDPE/CNF nanocomposites. In this study, the mechanical characteristics of HDPE/ CNFs materials were investigated by preparing samples through an extrusion process. An extrusion process is a manufacturing technique used to create a nanocomposite material by combining a polyethylene with high density (HDPE) with carbon nanofibers. Carbon nanofibers were mixed into the HDPE base by means of utilizing a co-rotating twin-screw extruder, during extrusion the temperature profile was controlled across different zones of the barrel, ranging from 100 0C at the feed zone to 210 0C at the die zone and the rotational speed of the screw was kept constant at 100 rev per minutes to ensure homogenous blending of the nanocomposites. High-density polyethylen coupons that were reinforced with different percentages (0-2) wt% of carbon nanofibers, were prepared in dog bone shape. To investigate mechanical and thermal properties, a reference material containing neat HDPE and HDPE reinforced with CNFs (hereafter codenamed as HDPE/CNFs) blends were studied. Thermogravimetric (TGA) method was used to examine the degradation of the specimens and their decomposition at different temperatures. Differential scanning calorimetry was used to assess the thermal behavior of the material. The results showed significant improvement in the strength of a material when carbon nanofibers (CNFs) were added to HDPE. The findings indicated notable enhancement in the thermal stability with the incorporation of CNFs, ensuring efficient stress transfer from the nanofiber to the base. Furthermore, thermal properties demonstrated improvement, suggesting increased thermal stability. These findings align with previous studies which have reported that incorporating carbon nanofibers into polymer matrices leads to improved thermal stability due to their ability to mix well with polymers.