Figure.2 dedicates the XRD diffraction pattern of HDPE, MWCNT and HDPE/MWCNT hybrid composite. HDPE presented with two characteristic peaks at 21.4° and 23.2°. These peaks were also detected in hybrid composite, but the intensity was greater, hence, more crystalline. This could happen as a result of the interaction and crystallization behavior of MWCNT with HDPE during the blending process. The X-ray diffraction (XRD) pattern of MWCNTs is shown as well in Fig.2. MWCNT exhibits 2 peaks at around 2θ = 26˚ and other broad peak centered at 2θ = 43˚ corresponding to the (002) and (100) Bragg reflection planes having the interlayer spacing of 3.213 and 2.012A respectively [59].
Microscopy images have been collected with its two types the scanning and transmitting to further investigate the nanocomposite structure and the matrix distribution as shown in Fig. 3. Scanning electron images of the nanocomposite samples shows clearly the MWCNT among the polymer matrix. In the processing of HDPE and MWCNT blends by the melt blinder, the polymer chains of HDPE are overlapped with each other as shown in SEM figures. Also, HETEM confirms the MWCNT structure very well and nano-scaled design of the other material which composes the material. The homogenous distribution of the MWCNT over the whole matrix can be also observed.
3.2 Mechanical properties
Figure 4. (a) exploits the stress-strain curve for AL2O3/MWCNT@ HDPE Nanocomposite. It can be seen clearly that the composite specimens tend to reach the highest point around 0.3. It also shows the strain of samples with a higher concentration of MWCNT more than others with lower concentrations. Table.1 illustrates the overall view of different parameters that control the mechanical direction, i.e. elastic modulus, tensile strength, and ductile. The maximum value of young's modulus reaches up to 6.25% when MWCNT with 5% applied compared with 7 % compared with pure HDPE. The percentage of ductility reaches its max value at 5 wt.%CNT. Furthermore, toughness has been calculated from the area under the load versus stroke curve, the toughness of the pure polymer was about 160 MJm-3 which is less than in the case of (1%) MWCNT impeded into the polymer. The 1 wt.% CNT loaded sample reached the max value of about 610 MJm-3. the toughness decreased sharply with the increase of CNTs in the HDPE matrix as a result of the CNT agglomeration is low with increasing condensation of filler content.
Good dispersion between polymer and CNT particles could be another reason for the mechanical performance improvement as illustrated in Table. 1. The significant increase of tensile strength has been observed mainly between MWCNTs ratio 3 wt. (%) - 5 wt. (%). According to recent research work, MWCNTs reinforcement mostly provides also strength refinement, furthermore, it can also transfer their strength to composite materials by taking over the load applied to the matrix material. It has been confirmed that MWCNTs prohibit the propagation of cracks in the matrix during erosion situations through their foaming motion. This case is also confirmed by the literature. However, the minimum strengthening amount can vary due to acquire strength improvement according to the reinforcement material. But the MWCNTs used in the existing study generally give better results at 5% wt. [60-61].
Table 1. Mechanical Properties of Nano Composite.
|
Elastic modulus E (Gpa)
|
Ultimate Tensile strength
(Mpa)
|
Max force
(N)
|
Ductile
%EL
|
Toughness×106
J/m-3
|
Hardness
(Mpa)
|
(HDPE-0wt.%)
|
0.96±0.04
|
27.2
|
126.3±7.6
|
7.40
|
160
|
56.2±1.1
|
(HDPE-1wt.%)
|
0.72±0.03
|
24.2
|
112.7±3.5
|
11.48
|
610
|
62.08±1.8
|
(HDPE-2wt.%)
|
0.75±0.02
|
25.5
|
118±0
|
8.70
|
400
|
64.5±1.5
|
(HDPE-3wt.%)
|
0.74±0.01
|
26.1
|
121.7±2.5
|
9.54
|
210
|
66.2±1.07
|
(HDPE-5wt.%)
|
1.02±0.02
|
29.0
|
134.3±1.5
|
11.29
|
250
|
77.4±1.5
|
As shown in Fig. 4 (b) and (c) that the value of Vickers hardness increases with increasing the addition of MWCNTs. MWCNTs hardness increased up to 37% compared to pure HDPE. Furthermore, it shows also the increase of the viscoelastic moduli and Young’s modulus. This could be attributed to the narrowing of the interspaces between molecules and reduced mobility. One of the best ways to reinforce mechanisms in polymer matrices is to transfer shear stresses in the nanoparticle-matrix interface and to nucleate a 3D nanostructured network. It reduces the mobility of the polymer bonds, thus leading to changes in a glass transition and elastic modulus of the nanocomposite, and yielding focus at very low strains[62-63].
Table 2. Mechanical Properties of Hybrid Al2O3/HDPE/MWCNT Nano Composite.
|
Elastic modulus E (GPa)
|
Ultimate Tensile strength
(MPa)
|
Max force
(N)
|
Ductile
%EL
|
Toughness
MJ/m-3
|
Hardness
(HV0.03)
|
(0wt%CNT, 3wt%AL2O3)
|
0.97±0.013
|
24.6
|
125.7±1.53
|
23.2
|
569
|
64.58±1.2
|
(0.6wt%CNT, 2.4wt%AL2O3)
|
1.00±0.073
|
28.01
|
130.7±9.61
|
25.5
|
705
|
64.58±1.2
|
(1.2wt%CNT, 1.8wt%AL2O3)
|
0.97±0.008
|
27.3
|
127±1.00
|
19.79
|
399
|
70.20±1.3
|
(1.8wt%CNT, 1.2wt%AL2O3)
|
0.95±0.053
|
26.5
|
123.3±6.81
|
27.7
|
604
|
56.62±1.5
|
(2.4wt%CNT, 0.6wt%AL2O3)
|
0.97±0.002
|
27.1
|
126.8±0.29
|
17.9
|
369
|
62.25±1.6
|
According to the results also it has been found that addition of alumina linearly increases the hardness and elastic modulus as shown in Table 2. Hardness and Elastic modulus have been figured out against MWCNTs and alumina content. The maximum level of hardness can be seen at (HCNTAL3) was 70.20±1.3 MPa with an increase in hardness by 6% comparing to 3wt%MWCNT and Elastic modulus values and 1±0.073 GPa at (HCNTAL2). Toughness and ultimate tensile for composites containing (HCNTAL2) increased by 75% and 7.6% compared to (3wt%CNT). Moreover, ductility also increased by adding aluminum oxide into the polymer matrix as illustrated in Table. 2. For composites containing (HCNTAL4) and (HCNTAL2) the ductility has been increased with adding aluminum oxide to the matrix showing an improvement ~145%, 200 % in comparison with 3wt% MWCNTs and 5wt%MWCNT polymer matrix respectively. It has been found that adding aluminum oxide to MWCNTs content caused marked improvements in mechanical properties of the resultant 3%wt MWCNTs / HDPE composites and equal to 5wt%MWCNTs/ HDPE. The possible idea behind that is the homogenous dispersion of nanotubes into the polymer matrix as confirmed using TEM images.
3.3 TGA analysis of HDPE/MWCNT composites.
TGA curves shows that onset temperature dwindling with the addition of chemically treated MWCNT due to amorphous carbon present in the CNTs, Mass loss degradation temperature of the composite increases as the MWCNTs ratio increases according to the TGA data as shown in Fig. 5 (a).
The lowest mass loss rate value is obtained for 3% and 5% MWCNTs. This exploits that mass loss melting speed rate decreases with increasing MWCNTs weight ratio and melting point temperature increases as shown in Fig.5 (b).
3.4. Moisture absorption
One of the most important parameters which considered a key factor that has been identified for polymer nanocomposite was water absorption because it usually affects their operating time[64-65]. The idea that cellulosic fibers easily absorb water is one of the reasons for fiber surface treatments. The particles treated by graphite fibers and its derivatives may absorb less amount of moisture, and thus support adhesion to the polymer matrix, which results in better execution in a humid environment. The high-water absorption of the polymer nanocomposite may cause difficulties during processing. This can be due to partial curing of the thermosetting matrices, the presence of gaps or cracks, or even poor matrix–fiber adhesion [66]. It was observed that HDPE/MWCNT nanocomposites express less water absorption compared to that of pure HDPE alone as shown in Fig. 6. The inclusion of MWCNTs facilitated the crystallization of HDPE and therefore led to higher crystallinity in HDPE Nanocomposites. This made it more difficult for water to diffuse into the HDPE matrix.
3.5 Cytotoxic activity of AL2O3/HDPE/MWCNT composites
The in vitro cytotoxicity tests of AL2O3/HDPE/MWCNT composites over human normal epithelial cell line 1- BJ1 (normal Skin fibroblast).The sample prepared by using the composite with concentrations between (100 to 0.78 µg/ml) and 100-75 PPM MTT with a different activity. It can be considered that MTT assay probing system for the study of the toxicity particularly because of normal cells very sensitive against this material. According to the results, the majority of cells remains safe and viable under all concentration which is in strong agreement with the literature as shown in Fig.7.