Abstract
Polymer-based nanocomposites (PNC) are plastic-based composite materials produced through the combination of a polymer matrix and nanofillers of less than 100 nm in length. PNCs have recently attracted attention in the automotive, aerospace, pipeline, biomedical, and other industries where lightweight, high-strength, easy-to-shape, corrosion-resistant, low-density, and long-life span materials are required. However, producing such materials is challenging since it requires the best combination of polymer matrices and nanofillers, the optimal weight fraction of nanofillers within the polymer matrix, the finest mixing of the polymer matrix and the nanofillers, and the best processing method with well-regulated processing parameters. This work focused on the investigation of the effect of 2 % weight fractions of titanium carbide (TiC), carbon nanofiber (CNF), calcium carbonate (CaCO3), and nano-clay on the thermal stability, rheological behaviour, tensile properties, and the specific strengths of pure low-density polyethylene (LDPE), pure high-density polyethylene (HDPE), and pure polyamide 6/nylon 6 (PA6). The 2 % weight fraction was selected as optimal for the improvement of the mechanical, thermal and other properties of polymers, this is supported by the studies conducted in the past. It was highlighted that an increase in the weight fraction of nanofillers from 0 wt% to roughly between 2 wt% and 3 wt% improves mechanical properties of polymers; however, the weight fraction above 3.5 Wt% results in agglomerations of nanofillers within polymer matrix that compromise the output quality of the polymer-based nanocomposites in terms of mechanical, thermal and other properties. The goal of the study was to examine the influence of the stated nanofillers on the thermal and mechanical properties of the mentioned polymers, respectively. To achieve the goal of this investigation, clear objectives were set, a robust literature review was conducted, a relevant research methodology was adopted, and the specimens were produced and characterised according to the relevant standards. The results were analysed and discussed, with the major findings outlined together with the further recommendations.
The conducted literature highlighted the following: (1) PNCs are engineering materials fabricated by reinforcing/enhancing polymer matrices with nanofillers of different sizes and geometries, (2) parameters influencing the performance of the PNC include the type of polymer matrix, nanofiller types and sizes, nanofiller weight/volume fraction within the polymer matrix, the mixing procedure of polymer matrix and the nanofibers, processing techniques and their operating parameters, (3) different nanofillers have different influences on thermal degradation, rheological behaviour, viscosity, morphology, and mechanical properties of
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different polymer matrices, (4) the engineering properties and the performance of PNC materials can be predicted using theoretical models, and numerical models and, they are not accurate when compared to the experimental results since they do not consider the influence of the mixing procedure and the processing parameters, (5) the experimental method is highlighted as the best method to analyse the performance and the engineering properties of PNC because it considers various factors, and the output products can be tested and applied to industries.
The obtained TGA results showed that the thermal stability of the pure LDPE and its corresponding nanofillers was established between 26 oC and 190 oC, that of pure HDPE and its respective nanocomposites was achieved between 26 oC and 220 oC, whereby pure PA6 and its corresponding nanocomposites achieved the thermal stability between 26 oC and 270 oC. The results also showed that the 2% weight fraction of TiC, CNF, CaCO3, and Nano-Clay did not enhance the thermal stability of pure LDPE, HDPE, and PA6. However, the TGA results provided the crucial information required for the processing temperatures of the LDPE, HDPE, PA6, and their corresponding nanocomposites. The results illustrated that the acceptable processing temperature for extrusion melting and mixing as well as for the compression moulding for pure LDPE and its corresponding nanocomposites is between 110 oC and 190 oC or below, for pure HDPE and its corresponding nanocomposites is between 130 oC and 220 oC or below, and for pure PA6 and its corresponding nanocomposites is between 200 oC and 270 oC or below. In this case, 110 oC, 130 oC, and 200 oC are the melting point temperatures for pure LDPE, HDPE, and PA6 and their corresponding nanocomposites, and 190 oC, 220 oC, and 270 oC are the respective maximum temperatures they can reach before degradation. The same temperature ranges were used respectively for processing the rheology, DMA, and tensile test specimens.
The rheology results showed that the addition of a 2 % weight fraction of TiC, CNF, CaCO3, and Nano-Clay improved the complex viscosity of pure LDPE by 10 %, 20 %, 9 %, and 7 % at an angular frequency of 0.1 rad/s and 08 %, 14 %, 7 %, and 3 % at the angular frequency of 100 rad/s, respectively. The same weight fraction of TiC, CNF, CaCO3, and Nano-Clay improved the complex viscosity of pure HDPE by 0.2 %, 12 %, 15 %, and 15 % at 0.1 rad/s, respectively. However, at the angular frequency of 100 rad/s, the 2 wt% of TiC decreased the complex viscosity of pure HDPE by 4 %, whereas the 2 wt% of CNF, CaCO3, and Nano-Clay improved its complex viscosity by 0.7 %, 9 %, and 9 %, respectively. Furthermore, the addition of 2 weight fractions of TiC and CaCO3 improved the complex viscosity of pure PA6 by 81 %
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and 41 % at the angular frequency of 0.1 rad/s, whereas the 2 wt% of CNF and Nano-Clay decreased its complex viscosity by 34 % and 3 % at the same frequency, respectively. At the frequency of 100 rad/s, the addition of 2 % weight fraction of TiC, CNF, CaCO3, and Nano-Clay decreased the complex viscosity of pure PA6 by 7 %, 29 %, 8 %, and 9 %, respectively. The overall rheology results showed that different combinations of nanofillers and polymer matrices result in different rheological behaviour.
The DMA results showed that the 2 wt% of TiC, CNF, and Nano-Clay improved the storage modulus of pure LDPE by 64 %, 68%, and 95 % at 26 oC, respectively, whereas the 2 wt% of CaCO3 showed no influence. At the same temperature, 2 wt% of TiC, CNF, and Nano-Clay improved the loss modulus of pure LDPE by 70 %, 76 %, and 77 %, respectively, while the 2 wt% CaCO3 displayed no influence. The 2 wt% of CaCO3 and Nano-Clay improved the storage modulus of pure HDPE by 78 % and 74 %, respectively, whereby the 2 wt% of TiC, and CNF decreased its storage modulus by 94 % and 24 %, respectively. The loss modulus of pure HDPE reinforced with 2 wt% of CNF, CaCO3, and Nano-Clay improved by 21 %, 78 %, and 81 % at 26 oC correspondingly, whereas the 2 wt% of TiC decreased its loss modulus by 30 %. Moreover, the produced LDPE, HDPE and their corresponding nanocomposites showed both elastic and viscous properties, with elastic properties dominating the viscous properties at 26 oC, meaning they are ductile. The addition of 2 wt% of Nano-Clay improved the storage modulus of pure PA6 by 5 % at 26 oC, whereas the 2 wt% of TiC, and CaCO3 decreased it by 100 % and 6 % at 26 oC, respectively, and the 2 wt% of CNF did not show any influence. The 2 wt% of CaCO3 and Nano-Clay improved the loss modulus of pure PA6 by 41 % and 54 % at the same temperature. However, the addition of 2 wt% of TiC decreased the loss modulus of pure PA6 by 95 % at 26 oC, whereas 2 wt% of CNF showed no influence. The produced PA6-based nanocomposite samples were shown to have more elastic properties than viscous properties at 26 oC. This illustrates that the produced samples are brittle.
The tensile test results showed that the addition of 2 wt% of TiC, and CNF improved the elastic modulus of pure LDPE by 30 %, and 34 %, its yield strength by 40 %, and 44 %, its tensile strength by 9 % and 36 %, and its specific strength by 5 % and 34 %, respectively. However, adding 2 wt% of CaCO3, and Nano-Clay into the pure LDPE decreased its elastic modulus by 15 %, and 30 %, its yield strength by 15 %, and 27 %, its tensile strength by 17 %, and 18 %, and its specific strength by 22 % and 25 %, respectively. The 2 wt% of TiC and CNF improved the elastic modulus of pure HDPE by 10 % and 11 % whereas the 2 wt% of CaCO3, and Nano-Clay decreased it by 3 % and 10 %, respectively. The yield strength of pure HDPE was
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improved by 5 % and 2 % with the addition of 2 wt% of TiC, and Nano-Clay yet, reduced by 22 % and 15 % with the addition of 2 wt% of CNF and CaCO3, respectively. However, the addition of the 2 wt% of TiC, CNF, CaCO3, and Nano-Clay improved the tensile strength of the pure HDPE by 15 %, 18 %, 5 %, and 5 %, respectively. Moreover, the 2 wt% of TiC, and CNF improved the specific strength of the pure HDPE by 11 % and 15 %, whereby the 2 wt% of CaCO3, and Nano-Clay decreased it by 5 % and 6 %, respectively. The addition of the 2 % weight fraction of TiC, and CNF improved the elastic modulus of pure PA6 by 11 % and 18 % whereas the 2 wt% of CaCO3, and Nano-Clay decreased it by 6 % and 21 %, respectively. However, the 2 wt% of TiC, CNF, CaCO3, and Nano-Clay decreased the yield strength of the pure PA6 by 16 %, 14 %, 17 %, and 63 %, respectively. Moreover, the addition of the 2 wt% of TiC, CNF, CaCO3, and Nano-Clay improved the tensile strength of the pure PA6 by 29 %, 34 %, 17 %, and 22 %, respectively. Furthermore, the 2 wt% of TiC, CNF, CaCO3, and Nano-Clay improved the specific strength of pure PA6 by 22 %, 31 %, 12 %, and 17 %, respectively.
The overall results showed that 2 % weight fractions of TiC, CNF, CaCO3, and Nano-Clay do not improve the thermal stability and thermal degradation of pure LDPE, HDPE, and PA6. However, they do improve the loss modulus, storage modulus, and complex viscosity of pure LDPE, HDPE, and PA6. The general results showed that TiC and CNF are acceptable reinforcing agents for the improvement of the tensile strength and the specific strength of the pure LDPE, pure HDPE, and PA6.