3.1. FTIR analysis
The transmittance mode was used to record all FTIR spectra in the wave number range of 4000–500 cm− 1. The IR spectrum for graphite is included in Fig. 2. Graphite powder exhibits a peak at 1574 cm− 1 that shows C = C aromatic vibration. The lack of any major peak in graphite's FTIR spectra (Fig. 2) confirms mass graphite's chemical inertness. [16].
The cover of the FT-IR spectra of polymer nanocomposites is shown in Fig. 3 (a–d). At 914 cm− 1, the C–O expanding vibrations of the epoxide ring of the slick epoxy can be noticed. The shortfall of this top in cured epoxy and the nanocomposites shows that all the epoxide rings are opened during the curing reaction or the response between the epoxide ring and graphite. The broad peak because of the C–OH extending in unadulterated epoxy vanishes in the nanocomposites showing that the response happens between the functional groups of epoxy-UP and graphite. The band close to 1604 cm− 1 relates to the N–H bunches present in every one of the composites. The C–H out-of-plane deformity band around 827 cm− 1 is seen in nanocomposites adjusted with graphite filler.
3.2. X-ray diffraction
The XRD patten for graphite displayed a high crystalline degree with a solid and sharp diffraction line at 2θ = 26.24° which identified with diffraction peak at (0 0 2) plane with a d- spacing of 3.42 Å as demonstrated in Fig. 4 [17]. These qualities are practically identical to the acknowledged worth of 3.35 Å in graphite crystallography [18].
The XRD data indicates no diffraction peak (Fig. 5a, b) under 80° (2θ), even after relieving the different epoxy/graphite nanocomposites and epoxy/UP/graphite nanocomposites (1, 3, and 5 wt % graphite). Considering the unmistakable composition of graphite particles, it is commonly predicted that there will be a crystalline peak at 2θ = 26.24°. At 2θ = 26.24°, the low-stacking fillers (1 wt % graphite) have no discernible graphite peak. In the graphite merged polymer composite, it can be seen that the most densely stacked graphite filler has a crystalline peak. These findings show that fundamental graphite nanoplatelet exfoliation occurs in epoxy polymer nanocomposites for a wide range of graphite loadings, but with a decrease in the unnecessary part of graphite being in the exfoliated state as graphite concentration increases, as seen by XRD.
3.3. Thermal property
TGA curve of graphite displays a general weight reduction of almost 1% in the scope of (30–800°C) as portrayed in Fig. 6a [19]. Graphite is demonstrated to be amazingly thermally stable over a temperature range up to 800°C. Yet, there will be a nanocomposite arrangement tumble down with warm debasement bends that increment the graphite composition in the epoxy/UP hybrid materials.
The outcomes exhibit no critical weight reduction up to ∼350°C for all epoxy/UP/graphite composites. As the temperature was expanded (> 350°C), the weight reduction expanded altogether over a restricted temperature range, as seen by the lofty inclines (Fig. 6a, b). The degradation temperature (Td60) of graphite incorporated epoxy system (Fig. 6) increments (407, 409, 411°C), and a high char yield at 600°C (12.76, 13.99, and 15.19%) uncover a superior scattering of graphite prompting a more grounded interaction with the epoxy resin. A maximum Td60 value (526°C) is seen in (Fig. 5) the 5 wt% graphite filled 10%UP toughened epoxy matrix, uncovering better similarity of epoxy with graphite and a relating expansion in the char yield (32.49%) at 600°C (Table 1). The presentation of graphite upgrades the performance by going about as a better encasing and mass vehicle obstruction than the unpredictable items created during deterioration. Likewise, the measure of build-up increments with an expanding graphite content.
Table 1
TGA data of hybrid epoxy-UP nanocomposites (graphite filler).
Relative percentage of Epoxy/UP/Graphite materials | Material code | Temperature at characteristic weight loss, ˚C | Residue at 600 ˚C, % |
10% | 20% | 40% | 60% |
100/00/00 | E | 347 | 366 | 389 | 413 | 12.05 |
99/00/01 | E1G | 341 | 362 | 382 | 407 | 12.76 |
97/00/03 | E3G | 343 | 363 | 385 | 409 | 13.99 |
95/00/05 | E5G | 344 | 364 | 386 | 411 | 15.19 |
94/05/01 | E5P1G | 352 | 369 | 389 | 413 | 11.85 |
92/05/03 | E5P3G | 343 | 364 | 385 | 407 | 14.05 |
90/05/05 | E5P5G | 340 | 362 | 384 | 410 | 18.68 |
89/10/01 | E10P1G | 335 | 359 | 381 | 403 | 10.69 |
87/10/03 | E10P3G | 341 | 361 | 383 | 406 | 18.11 |
85/10/05 | E10P5G | 321 | 344 | 387 | 526 | 32.49 |
84/15/01 | E15P1G | 337 | 360 | 384 | 405 | 13.98 |
82/15/03 | E15P3G | 339 | 359 | 382 | 406 | 16.34 |
80/15/05 | E15P5G | 340 | 361 | 385 | 408 | 17.67 |
A critical improvement in the Tg of the epoxy matrix (332, 334, and 335°C) by the incorporation of 1, 3 and 5 wt% graphite (Fig. 7) likewise uncovers the unbending nature acquired by the epoxy lattice by very much scattered fillers because of the arrangement of substance connections between the amine gathering of graphite and epoxy cluster [20]. A huge improvement in Tg of the UP (5,10,15 wt%) hardened epoxy matrix is seen when fused with 1, 3, and 5 wt% of graphite (Fig. 7a, b) separately. An abatement in Tg of epoxy when hardened with UP has been totally balanced by the expansion of graphite into a similar framework as uncovered by the huge addition in Tg value [Table 2]. Such expansions in Tg are because of the obliged chain versatility and expansion in thickness by very much scattered fillers by the interaction of graphite and epoxy group [21].
Table 2
Thermal behaviour of hybrid epoxy-UP nanocomposites (graphite filler)
Relative percentage of Epoxy/UP/Graphite materials | Glass Transition temperature (Tg), °C |
100/00/00 | 325 |
95/05/00 | 308 |
90/10/00 | 306 |
85/15/00 | 322 |
99/00/01 | 332 |
97/00/03 | 334 |
95/00/05 | 335 |
94/05/01 | 337 |
92/05/03 | 329 |
90/05/05 | 326 |
89/10/01 | 321 |
87/10/03 | 321 |
85/10/05 | 299 |
84/15/01 | 306 |
82/15/03 | 309 |
80/15/05 | 305 |
3.4. Tensile Property
The addition of 1, 3, and 5% (by wt.%) graphite into the epoxy matrix dramatically boosted tensile strength (8.9, 16.2, and 61.2%), with higher concentrations scarcely causing nanocomposites to form. With the addition of 1, 3, and 5 wt% graphite to the epoxy matrix, the tensile modulus increased by 10.3, 21.5, and 31.9%, respectively [22]. This could be due to the development of an exfoliated structure during nanocomposite preparation, because no agglomeration but only conceivable clay reinforcement takes place.
Table 3
Tensile properties of epoxy-UP nanocomposites (graphite filler)
Relative percentage of Epoxy/UP/Graphite materials | Tensile strength MPa | Tensile Modulus MPa | Elongation at Break % |
99/00/01 | 37.7 | 1685 | 2.13 |
97/00/03 | 40.2 | 1856 | 2.66 |
95/00/05 | 55.8 | 2015 | 4.72 |
94/05/01 | 35.6 | 1705 | 2.25 |
92/05/03 | 38.9 | 1985 | 2.43 |
90/05/05 | 44.5 | 2247 | 2.75 |
89/10/01 | 38.1 | 1695 | 2.26 |
87/10/03 | 45.3 | 1829 | 3.27 |
85/10/05 | 52.7 | 2154 | 4.65 |
84/15/01 | 35.4 | 1754 | 2.07 |
82/15/03 | 37.1 | 1945 | 2.41 |
80/15/05 | 43.6 | 2165 | 3.25 |
The addition of 1, 3, and 5 wt% graphite to a 5 wt% (2.9, 12.4, and 28.6%), 10 wt% (10.1, 30.1, and 52.3%), and 15 wt% (2.3, 7.2, and 26%), UP toughened epoxy matrix led to a significant in a dramatic rise in tensile strength as the clay content increased, probably due to the enhancement in the load transfer capacity of the polymer matrix by adding graphite. The tensile strength of unmodified epoxy, clay filled epoxy, and UP-epoxy containing nanoclay is compared in Fig. 8. The tensile strength of the clay-filled UP-epoxy was higher than that of pure epoxy. As a result of the polymer intercalating between them, the interfacial interactions between matrix and reinforcements are improved.
3.5 Morphology of graphite
The as-gotten graphite was inspected utilizing the SEM to examine their morphology before fuse into the epoxy/UP matrix. The graphite displays enormous platelets of the size of ∼20–100 µm as shown in Fig. 9.
Figure 10 shows the SEM micrographs for the freeze-break surface of epoxy/UP-based composites with graphite nanosheets. The graphite flakes seem white in the pictures and the epoxy/UP lattice is viewed as grey. The rich qualities of a skimming cracked surface are appeared, which demonstrate the hardening impact of the graphite nanosheets. It very well may be unmistakably found in Fig. 10a that there is a significant distance between two nanosheets. Nonetheless, at a higher convergence of filler, the nanosheets become either exceptionally close or in direct contact with one another, as is found in Fig. 10b. The SEM pictures show the development of an almost directing organization with a uniform scattering of graphite nanosheets into the epoxy/UP matrix. The 1 wt% graphite-filled hybrid epoxy and epoxy/UP nanocomposites additionally show a homogeneous morphology demonstrating the synthetic connection of polymer particles with nanoparticles (Fig. 10c, d). The productive collaboration emerges because of the impact of intermolecular bonding among graphite and polymer lattice frameworks, prompting the development of nanocomposites. In 5 wt% graphite filled composites, graphite is evenly dispersed in the substrate of epoxy and UP hardened epoxy resin which ensures stronger interfacial connection valuable to the mechanical properties of that same polymer composites. (Fig. 10e, f).
3.6. Dielectric property
Figure 11 shows the frequency dependence conductivity spectrum for sample Epoxy + 1% graphite (E1G); epoxy + 3% graphite (E3G); epoxy + 5% graphite (E5G); epoxy + 5% polyester + 1% graphite (E5P1G); epoxy + 5% polyester + 3% graphite (E5P3G); epoxy + 5% polyester + 5% graphite (E5P5G); epoxy + 10% polyester + 1% graphite (E10P1G); epoxy + 10% polyester + 3% graphite (E10P3G); epoxy + 10% polyester + 5% graphite (E10P5G); epoxy + 15% polyester + 1% graphite (E15P1G); epoxy + 15% polyester + 3% graphite (E15P3G); epoxy + 15% polyester + 5% graphite (E15P5G) respectively.
The conductivity increases almost straightly with the applied frequency, as seen by the characteristic curves for all of the samples. This indicates the presence of an ohmic relationship in the frequency range under consideration [23–26]. This is owing to the vibration-dominated polymer base, which is overlaid by stretching. The conductivity increases with increasing frequency, as shown by the entire plot.
Also, the graph shows that the conductivity increments with increases graphite and UP weight percentage (wt%). Both CE-graphite and CE-UP polymer blends showed a diminishing in electrical conductance with expanding filler focus to a specific level; after which, the electrical conductance started to increment with a further expansion in graphite wt% as displayed in Fig. 11. The range, low frequency is the normal future of CE, UP, graphite. Yet, for expanded wt% of graphite, UP, and frequency, the power of the multitude of peaks have been tremendously improved; these upgrades demonstrate that both hydrogen and oxygen atoms of the CE, graphite, and UP composite are unable to form hydrogen security either with water particles or with other O–H gatherings of CE. Thusly, the intramolecular, intermolecular, and hydration hydrogen bond are being influenced, which prompts a diminishing in qualities of hydrogen bonds. Since the previously mentioned changes have been experienced in the vibrational mode, in this manner, the powers of a peak at high frequency are sustained to narrow peaks [27]. This can be further proved by FTIR and XRD.
The general pattern seen in the conductivity spectra over time shows that the CEUP-graphite composite structural components are collapsing. While for the increasing concentration, the response is increasing and, in the order, (i) E1G < E3G > E5G, (ii) E1G < E5P1G < E5P3G < E5P5G, (iii) E1G < E3G < E5P1G < E10P1G < E10P3G > E10P5G, (iv) E1G < E3G < E5P1G < E5P3G < E10P1G < E15P1G < E15P3G > E15P5G. Increased graphite incorporation in CE improves the uniformity of the composite, which increases the discomfort that prompts aggregate arrangement. The results of SEM were used to confirm the aggregates. The separation distance of free mobile ions will be reduced by these aggregates, and neutral ion pairs will form. As a result, there was a comparable drop in conductivity. The conductance of the composite samples E10P5G and E15P5G decreased as a result of this. When CE-graphite and CE-UP blends were compared, the composites CE/UP/graphite had the highest conductivity. The epoxy-graphite polymer composite has a lower minimum electrical conductivity than the epoxy–polyester polymer composite. This indicates that the epoxy polymer is graphite-reinforced. Furthermore, higher concentrations of polyester and graphite have more linkages, which means that bonds will develop faster than with a lesser concentration of epoxy. As a result, the conductivity of the specific sample E5G E3G, E10P5G E10P3G, and E15P5G E15P3G is decreased.
3.7. Anti-biofouling properties
Bacterial density of the deployed panel is analysed and the count has been displayed in the Table 4.
The bacterial density appeared to be greatest in the plate E10P3G with 61x105 CFU and lowest in the glass plate (40 x104), followed by the fibre plate (17 x105 CFU) which was proven to be efficient against early colonisation of biofilm bacteria after 24 hours (Fig. 12). The graphite composite plates E10P3G and E15P3G demonstrated significant resistance to biofilm formation after 48 hours, with bacterial loads of 42 x105 and 45 x 105 CFU, respectively. Biofilm production was shown to be more prevalent in the wooden sample (24 x106 CFU). Surprisingly, when compared to the fibre sample, almost all of the polymer composites are resistant to bacterial activity after 96 hours and have a substantially lower CFU value. When compared to other composites, E15P1G (60 x 105 CFU) and E10P5G (10 x 106 CFU) have low bacterial density. In comparison to the remainder of the materials, the adherence of microbiological activity in 1 and 5 percent filler mixed with 10 and 15 percent UP blend epoxy is reduced (Fig. 13). When compared to the other material utilised, the adhesion of macro-fouling organisms such barnacles and mussels also degreased during the second and third months (Fig. 14). This demonstrates that the epoxy/UP blend with included clay is more resistant to fouling communities.
Table 4
Biofilm bacteria population for hybrid epoxy composites (graphite filler)
Relative percentage of Epoxy/UP/Graphite materials | Material code | Biofilm bacteria population |
24 hrs. | 48 hrs. | 96 hrs. |
CFU | CFU | CFU |
100/00/00 | E | 13x105 | 3x106 | 49x106 |
95/05/00 | E5P | 11.5x105 | 10x106 | 59x106 |
90/10/00 | E10P | 33.2x105 | 59x105 | 52x106 |
85/15/00 | E15P | 32x105 | 46x105 | 18x105 |
99/00/01 | E1G | num | 63x105 | 48x105 |
97/00/03 | E3G | 58.8x105 | 11x106 | 3x106 |
95/00/05 | E5G | 28x105 | 19.8x106 | 6x106 |
94/05/01 | E5P1G | num | 13.4x106 | 12x106 |
92/05/03 | E5P3G | 50.2x105 | 13.1x106 | 33x106 |
90/05/05 | E5P5G | 43x105 | 68x105 | 22x106 |
89/10/01 | E10P1G | num | 51x105 | 15.2x106 |
87/10/03 | E10P3G | 61.6x105 | 42x105 | 18x106 |
85/10/05 | E10P5G | num | 12x106 | 10x106 |
84/15/01 | E15P1G | 48x105 | 74x105 | 6x106 |
82/15/03 | E15P3G | 23.2x105 | 45x105 | 19x106 |
80/15/05 | E15P5G | 23.8x105 | 75x105 | 0 |
-- | Plastic | 10x105 | 69x105 | 59x106 |
-- | Glass | 40x104 | Tnc | 52x106 |
-- | Fibre | 17x105 | 18x106 | 14.6x107 |
-- | Wood | 23x105 | 24x106 | 68x106 |