**2.1 Density of the nanocomposites**

Density is an important property in several weight sensitive applications. In many applications, polymer composites are replacing traditional or conventional metals and metal based composites mainly for their low densities. Density of a composite depends on the relative proportion of matrix and the reinforcing filler. There is always a difference between the measured and the theoretical density values of a composite due to the presence of empty space and hole. These empty spaces or voids majorly affect the performance of the nanocomposites. A larger void content indicates lower value of fatigue resistance, greater susceptibility to water penetration and weathering [45]. The theoretical and measured densities of nanocomposites along with corresponding volume fraction of voids are presented in **Table 1**. The theoretical density was calculated for nanocomposite samples by weight additive principle, which states that:

$$\mathbf{d} = \mathbf{w}\_1 \mathbf{d}\_1 + \mathbf{w}\_2 \mathbf{d}\_2 \tag{1}$$

**201**

nanofiller content.

holes or pores.

**Figure 1.**

inclusions.

*Mechanical and Tribological Properties of Epoxy Nano Composites for High Voltage Applications*

may be noted from **Table 1** that density values of the nanocomposite calculated theoretically from weight fractions using Eq. (1) are not in agreement with the experimentally determined values. Theoretically calculated density values are larger when compared to equivalent experimental values due to empty space or voids and

*Variation of density as a function of filler content for epoxy and vinyl ester nanocomposites.*

The knowledge of void fraction is therefore essential for estimation of the quality of the composites. From the measured densities of Epoxy-oMMT, Epoxy-TiO2 and Vinyl ester-oMMT nanocomposites (**Figure 1**), it is clear that pure Epoxy

±0.0088 respectively. With the incorporation of oMMT and TiO2 nanofillers, an increase in the density of the nanocomposites is observed. This is observed to be true in both Epoxy and Vinyl ester matrix with nanosized oMMT and TiO2 filler

It is evident from **Figure 1** that the density values for Epoxy-oMMT nanocomposite increases with the nanofiller loading content. However, the increase in the density was small in Epoxy-oMMT nanocomposites. With the addition of 7 wt.% oMMT, the density of Epoxy increases by 1% but the density of Epoxy-TiO2 increases by 10%. This is due to higher density of TiO2 as compared to oMMT. The density of Vinyl ester is higher than that of Epoxy due to the presence of bromine. Bromine is a heavy atom and there are four bromine atoms bonded in one molecule, and this result in density being higher for brominated Vinyl ester. Similar trends are

Hardness is one of the significant factors that control the wear property of the composite samples. In this work, the data obtained for micro-hardness of the Epoxy and Vinyl ester composites with different types of weight percentage of fillers loading have been obtained. **Figure 2** shows the experimental results of measurements of micro-hardness of pure Epoxy and Epoxy-oMMT, Epoxy-TiO2, pure Vinyl ester and Vinyl ester-oMMT nanocomposite samples with different weight percentage of

**Figure 2** indicates that the addition of oMMT nanofiller into Epoxy, Vinyl ester

and TiO2 to Epoxy results in significant improvement in hardness of nanocomposites. In general, mechanical properties of nanocomposite depend primarily on following things namely filler content, filler size and shape, the degree of interfacial

with an error of

and Vinyl ester resin has an average density of 1.17 and 1.34 g/cm3

noticed for Vinyl ester-oMMT nanocomposites.

**2.2 Micro-hardness of the nanocomposites**

*DOI: http://dx.doi.org/10.5772/intechopen.88236*

where d is the density of the nanocomposite, w1 and w2 are the weight fractions of the fillers, epoxy and hardener, d1 and d2 are their corresponding densities. It


**Table 1.**

*Theoretical, experimental densities and void fractions in nanocomposites.*

*Mechanical and Tribological Properties of Epoxy Nano Composites for High Voltage Applications DOI: http://dx.doi.org/10.5772/intechopen.88236*

**Figure 1.** *Variation of density as a function of filler content for epoxy and vinyl ester nanocomposites.*

may be noted from **Table 1** that density values of the nanocomposite calculated theoretically from weight fractions using Eq. (1) are not in agreement with the experimentally determined values. Theoretically calculated density values are larger when compared to equivalent experimental values due to empty space or voids and holes or pores.

The knowledge of void fraction is therefore essential for estimation of the quality of the composites. From the measured densities of Epoxy-oMMT, Epoxy-TiO2 and Vinyl ester-oMMT nanocomposites (**Figure 1**), it is clear that pure Epoxy and Vinyl ester resin has an average density of 1.17 and 1.34 g/cm3 with an error of ±0.0088 respectively. With the incorporation of oMMT and TiO2 nanofillers, an increase in the density of the nanocomposites is observed. This is observed to be true in both Epoxy and Vinyl ester matrix with nanosized oMMT and TiO2 filler inclusions.

It is evident from **Figure 1** that the density values for Epoxy-oMMT nanocomposite increases with the nanofiller loading content. However, the increase in the density was small in Epoxy-oMMT nanocomposites. With the addition of 7 wt.% oMMT, the density of Epoxy increases by 1% but the density of Epoxy-TiO2 increases by 10%. This is due to higher density of TiO2 as compared to oMMT. The density of Vinyl ester is higher than that of Epoxy due to the presence of bromine. Bromine is a heavy atom and there are four bromine atoms bonded in one molecule, and this result in density being higher for brominated Vinyl ester. Similar trends are noticed for Vinyl ester-oMMT nanocomposites.

#### **2.2 Micro-hardness of the nanocomposites**

Hardness is one of the significant factors that control the wear property of the composite samples. In this work, the data obtained for micro-hardness of the Epoxy and Vinyl ester composites with different types of weight percentage of fillers loading have been obtained. **Figure 2** shows the experimental results of measurements of micro-hardness of pure Epoxy and Epoxy-oMMT, Epoxy-TiO2, pure Vinyl ester and Vinyl ester-oMMT nanocomposite samples with different weight percentage of nanofiller content.

**Figure 2** indicates that the addition of oMMT nanofiller into Epoxy, Vinyl ester and TiO2 to Epoxy results in significant improvement in hardness of nanocomposites. In general, mechanical properties of nanocomposite depend primarily on following things namely filler content, filler size and shape, the degree of interfacial

*Nanorods and Nanocomposites*

**2. Results and discussion**

**2.1 Density of the nanocomposites**

weight additive principle, which states that:

**Samples (wt.%) Density (g/cm3**

*Theoretical, experimental densities and void fractions in nanocomposites.*

velocities.

Shao Rong and co-authors [43] have proved that the epoxy/SiO2-TiO2 nanocomposites are effective in lowering the frictional coefficient and wear rate. The results of these experiments [43] indicate that the wear mechanism of composites changed from adhesive wear to mild abrasive wear and fatigue wear with the increase of the SiO2-TiO2 content. Chang and co-authors [44] have proved that the addition of nanoTiO2 apparently reduced the frictional coefficient and significantly enhanced the wear resistance of the composites, especially at contact pressures and sliding

The present study incorporates different evaluation techniques to encompass

Density is an important property in several weight sensitive applications. In many applications, polymer composites are replacing traditional or conventional metals and metal based composites mainly for their low densities. Density of a composite depends on the relative proportion of matrix and the reinforcing filler. There is always a difference between the measured and the theoretical density values of a composite due to the presence of empty space and hole. These empty spaces or voids majorly affect the performance of the nanocomposites. A larger void content indicates lower value of fatigue resistance, greater susceptibility to water penetration and weathering [45]. The theoretical and measured densities of nanocomposites along with corresponding volume fraction of voids are presented in **Table 1**. The theoretical density was calculated for nanocomposite samples by

where d is the density of the nanocomposite, w1 and w2 are the weight fractions of the fillers, epoxy and hardener, d1 and d2 are their corresponding densities. It

Epoxy-oMMT 0 1.170 1.170 -

Epoxy-TiO2 2 1.231 1.222 0.73

Vinyl ester-oMMT 0 1.346 1.346 –

**Theoretical Experimental**

2 1.184 1.176 0.65 5 1.206 1.181 2.03 7 1.221 1.182 3.13

5 1.323 1.284 2.91 7 1.384 1.294 6.50

2 1.351 1.347 0.29 5 1.368 1.348 1.46 7 1.379 1.349 2.14

d = w1 d1 + w2 d2 (1)

**) Void fraction (%)**

properties of mechanical and wear characteristics.

**200**

**Table 1.**

**Figure 2.** *Micro-hardness of epoxy and vinyl ester nanocomposites.*

interaction or between the filler particles and polymer matrix and degree of dispersion of nanofiller within the polymer matrix. The improvement in the hardness property of the nanocomposites may be attributed to the intercalated and exfoliated clay platelets structure [46].

The intercalated/exfoliated clay platelets effectively restrict indentation and increase the hardness of the nanocomposites [46]. Similarly, incorporation of TiO2 into Epoxy increases the degree of dispersion, thereby increases the hardness of nanocomposite. Organomodified montmorillonite has a much greater surface hardness because of its ceramic nature. Therefore, the contribution of oMMT to the hardness is greater as compared to TiO2 filled nanocomposites. From the observed data it is clear that the increment in hardness is more significant up to 5 wt.% of filler loading. The increase in hardness for 5 wt.% filled polymer matrix may be partly attributed to the intrinsic hardness of nanofiller and the nanoparticles might be offering better resistance against Epoxy and Vinyl ester segmental motion under indentation.

On the other hand, increase in filler loading from 5 to 7 wt.% and the rise in value of the hardness is trivial implying that higher filler loading gives rise to undesired dispersion and agglomeration in the polymer matrix. When in comparison with the oMMT and TiO2 nanocomposites loading is concerned, the Epoxy-oMMT nanocomposite reveal greater hardness values for the different filler loadings are concerned. Among all the nanocomposites investigated maximum micro-hardness value is recorded for Epoxy nanocomposite filled with 7 wt.% oMMT.

#### **2.3 Mechanical properties**

The measured tensile properties of Epoxy-oMMT, Epoxy-TiO2 and Vinyl esteroMMT nanocomposites are shown in **Table 2**. It is noticed from the **Table 2** that, lower values of tensile strength and tensile elongation are obtained for nanocomposites than those of pure Epoxy and Vinyl ester. However, the Young's moduli are evidently enhanced by the addition of fillers. As seen in **Table 2**, the tensile strength of these nanocomposites invariably decreases with increase in filler loading irrespective of the type of filler. Similar observations have been reported by some investigators [47].

The tensile strength and fracture toughness of a nanocomposite samples depend upon the filler shape, size and amount which is mixed with the polymer matrix, the strong bond between the nanofiller and the polymer matrix, the robustness of the

**203**

Vinyl ester-oMMT

**Table 2.**

*Mechanical and Tribological Properties of Epoxy Nano Composites for High Voltage Applications*

polymer matrix and the filler. Nanofillers affect the mechanical properties in accordance with their packing characteristics, size and interfacial interaction. The highest three dimensional packing of filler reflects the size distribution and shapes of the particles. The space between the particles is implicit to be packed with polymer matrix and no empty spaces or air bubbles are expected. With this condition, for a given nanocomposite, the matrix amount is fewer and it acts as separate segment or compartment to hold up tensile load. Properties of nanocomposites are manipulated by the individual properties of the filler and the matrix and also the filler-matrix interface. Ability of the matrix to transfer the load to the filler particles, is its major purpose, and depends on the adhesion and compatibility between the filler and matrix. The tensile strengths of the nanoparticles filled Epoxy are less than that of pure Epoxy/Vinyl ester. The decreasing trend of adhesion with respect to relatively higher filler loading points towards the phenomenon of dewetting occurs at the interface. The figure shows a close up view of matrix region where more particles are concentrated. There can be two reasons for the decline in the strength properties of the filled nanocomposites as compared to the pure polymers which is evident

In the present study, the tensile strength of all nanocomposites is much lower than that of pure Epoxy and Vinyl ester may be assumed to be closely related to processing method. The compounding of oMMT in an Epoxy matrix with high shear mixing produces a highly viscous and foamy material. A higher content of oMMT leads to higher viscosity. Furthermore, the diethyltoluenediamine used to functionalize Nanomer 1.30E can voluntarily contribute in the curing reaction and delamination of the clay platelets. This results in highly viscous fluid with time and hampers the complete removing of gas before the process of curing. The nanocomposites with 7 wt.% of oMMT, the removal of gas turn out to be more critical. The presence of small gas bubbles in 2, 5 and 7 wt.% oMMT nanocomposites confirms the same. The additional reason for voids can be air entered during transfer of the largely

gelatinous material into the mold. Furthermore, the tensile strength of all the samples in the range of 30–70 MPa indicates break initiation from analogous types of defects. Consequently, it might be understood that under loading condition, breaks may begin from these tiny spaces or voids and result in sample failure at

*DOI: http://dx.doi.org/10.5772/intechopen.88236*

from data shown in **Table 2** and discussed below;

**(MPa) ± 1.5%**

Epoxy-oMMT 0 47.50 1.44 10.39

Epoxy-TiO2 2 32.60 1.61 10.41

2 31.56 1.73 10.50 5 37.95 1.90 11.30 7 33.79 2.09 9.35

5 36.91 1.72 10.98 7 32.47 1.82 11.18

 71.10 3.49 2.54 69.40 3.55 2.38 66.21 3.74 2.22 64.10 3.91 2.08

**Tensile modulus (GPa) ± 1.5%**

**Elongation at break (%) ± 2%**

**Samples (wt.%) Tensile strength** 

*Mechanical properties of polymer nanocomposites.*

#### *Mechanical and Tribological Properties of Epoxy Nano Composites for High Voltage Applications DOI: http://dx.doi.org/10.5772/intechopen.88236*

polymer matrix and the filler. Nanofillers affect the mechanical properties in accordance with their packing characteristics, size and interfacial interaction. The highest three dimensional packing of filler reflects the size distribution and shapes of the particles. The space between the particles is implicit to be packed with polymer matrix and no empty spaces or air bubbles are expected. With this condition, for a given nanocomposite, the matrix amount is fewer and it acts as separate segment or compartment to hold up tensile load. Properties of nanocomposites are manipulated by the individual properties of the filler and the matrix and also the filler-matrix interface.

Ability of the matrix to transfer the load to the filler particles, is its major purpose, and depends on the adhesion and compatibility between the filler and matrix. The tensile strengths of the nanoparticles filled Epoxy are less than that of pure Epoxy/Vinyl ester. The decreasing trend of adhesion with respect to relatively higher filler loading points towards the phenomenon of dewetting occurs at the interface. The figure shows a close up view of matrix region where more particles are concentrated. There can be two reasons for the decline in the strength properties of the filled nanocomposites as compared to the pure polymers which is evident from data shown in **Table 2** and discussed below;


#### **Table 2.**

*Nanorods and Nanocomposites*

clay platelets structure [46].

*Micro-hardness of epoxy and vinyl ester nanocomposites.*

**Figure 2.**

**2.3 Mechanical properties**

investigators [47].

interaction or between the filler particles and polymer matrix and degree of dispersion of nanofiller within the polymer matrix. The improvement in the hardness property of the nanocomposites may be attributed to the intercalated and exfoliated

The intercalated/exfoliated clay platelets effectively restrict indentation and increase the hardness of the nanocomposites [46]. Similarly, incorporation of TiO2 into Epoxy increases the degree of dispersion, thereby increases the hardness of nanocomposite. Organomodified montmorillonite has a much greater surface hardness because of its ceramic nature. Therefore, the contribution of oMMT to the hardness is greater as compared to TiO2 filled nanocomposites. From the observed data it is clear that the increment in hardness is more significant up to 5 wt.% of filler loading. The increase in hardness for 5 wt.% filled polymer matrix may be partly attributed to the intrinsic hardness of nanofiller and the nanoparticles might be offering better resis-

tance against Epoxy and Vinyl ester segmental motion under indentation.

value is recorded for Epoxy nanocomposite filled with 7 wt.% oMMT.

On the other hand, increase in filler loading from 5 to 7 wt.% and the rise in value of the hardness is trivial implying that higher filler loading gives rise to undesired dispersion and agglomeration in the polymer matrix. When in comparison with the oMMT and TiO2 nanocomposites loading is concerned, the Epoxy-oMMT nanocomposite reveal greater hardness values for the different filler loadings are concerned. Among all the nanocomposites investigated maximum micro-hardness

The measured tensile properties of Epoxy-oMMT, Epoxy-TiO2 and Vinyl esteroMMT nanocomposites are shown in **Table 2**. It is noticed from the **Table 2** that, lower values of tensile strength and tensile elongation are obtained for nanocomposites than those of pure Epoxy and Vinyl ester. However, the Young's moduli are evidently enhanced by the addition of fillers. As seen in **Table 2**, the tensile strength of these nanocomposites invariably decreases with increase in filler loading irrespective of the type of filler. Similar observations have been reported by some

The tensile strength and fracture toughness of a nanocomposite samples depend upon the filler shape, size and amount which is mixed with the polymer matrix, the strong bond between the nanofiller and the polymer matrix, the robustness of the

**202**

*Mechanical properties of polymer nanocomposites.*

In the present study, the tensile strength of all nanocomposites is much lower than that of pure Epoxy and Vinyl ester may be assumed to be closely related to processing method. The compounding of oMMT in an Epoxy matrix with high shear mixing produces a highly viscous and foamy material. A higher content of oMMT leads to higher viscosity. Furthermore, the diethyltoluenediamine used to functionalize Nanomer 1.30E can voluntarily contribute in the curing reaction and delamination of the clay platelets. This results in highly viscous fluid with time and hampers the complete removing of gas before the process of curing. The nanocomposites with 7 wt.% of oMMT, the removal of gas turn out to be more critical. The presence of small gas bubbles in 2, 5 and 7 wt.% oMMT nanocomposites confirms the same.

The additional reason for voids can be air entered during transfer of the largely gelatinous material into the mold. Furthermore, the tensile strength of all the samples in the range of 30–70 MPa indicates break initiation from analogous types of defects. Consequently, it might be understood that under loading condition, breaks may begin from these tiny spaces or voids and result in sample failure at

fairly low strains [48]. The other reason is that the corner points of the irregular shape of the spherical filler namely TiO2 particulate, may result in stress concentration in the Epoxy matrix. These two factors are perhaps responsible for significant reduction in tensile strengths of the nanocomposites. A comparison of the results reveals that the Vinyl ester-oMMT nanocomposites possess higher tensile strength confirming the effect of incorporation of oMMT filler which improves nanofillermatrix surface adhesion or interface in the composite.

The tensile modulus shows a marked increase with increasing oMMT, TiO2 content from 0 to 7 wt.% in Epoxy and Vinyl ester matrices. The improvement in the Young's modulus can be attributed to the exfoliation and good dispersion of nanosized filler particles that restricts the mobility of polymer chains under loading as well as good interfacial adhesion between the particles and the polymer matrix [49]. The orientation of clay platelets and polymer chains with respect to the direction of loading can also contribute to the reinforcement effects [49]. Unlike the Young's modulus, nanocomposites of any nanoclay content show a lower tensile strength than that of pure Epoxy. Similar results are reported by Zerda and co-authors [50] but in contrast, an increase in tensile strength values of nanocomposites are also reported [51, 52].

As reported in literature, the strain at break of nanocomposites usually declines with increasing filler content. Low filler loadings cause a significant drop in fracture strain. It may be recalled that the composite is made up of partly filler and partly matrix. Due to the rigid nature of the fillers, most of the deformation comes from the polymer. The actual deformation is experienced only by the polymer matrix which is much larger than the measured deformation of the sample. With the result, that the polymer failure reaches failure strain limit at lower level of total deformation. Hence, the total composite strain-to-break decreases. However, it is interesting to observe that nanocomposites of the present study show contrary results that is strain-to-break behavior as comparable to conventionally filled composites. It tends towards slightly higher values for filler content of less than 5 wt.% (**Table 2**).

This increase suggests that the nanoparticles are able to introduce additional mechanisms of failure and energy consumption without blocking matrix deformation. Particles may induce matrix yielding under certain conditions and may furthermore act as inhibitors to crack growth by pinning the cracks [15]. Nevertheless, if the fillers exceed 5 wt.%, the failure strain undergoes a slight decrease. Such a reduction leads to that the large proportion of fillers start dominating, and they reduce the matrix deformation by mechanical restraining.

The decrease in tensile strength and the upgrading of values of hardness with the filler addition is due to the following reasons: under the action of a mechanical (tensile) force, the interface between filler and polymer matrix will tend to debonding, depending on interfacial bond strength and this can direct to a break in the nanocomposite material. On the other hand, in case of hardness, pressing stress is in act. The matrix phase and the nanofiller phase would be hard-pressed together. Thus the interfacing bond can transfer pressure more effectively and thus there is an enhancement in the values of hardness.

#### **2.4 Flexural properties**

**Table 3** lists the average values of flexural modulus for different weight percentages of oMMT and TiO2 nanofillers. The flexural modulus of Epoxy resin is 2.30 GPa. The addition of oMMT and TiO2 to Epoxy resin is expected to reinforce the resin and increase its elastic modulus and the results are on expected lines. The flexural modulus of nanocomposites shows increase with oMMT and TiO2 concentrations. For 7 wt.% of oMMT and TiO2 loading, improvement in the flexural

**205**

*Mechanical and Tribological Properties of Epoxy Nano Composites for High Voltage Applications*

Epoxy-oMMT 0 2.30 — 89 —

Epoxy-TiO2 2 2.52 8.73 96 7.29

**% change**

2 2.34 1.70 91 2.20 5 2.57 10.50 95 6.31 7 2.69 14.49 100 11.0

5 2.85 24.12 102 12.74 7 3.07 33.77 105 15.23

 3.56 — 99 — 3.79 6.06 63 36.36 4.05 12.09 56 43.43 4.26 16.43 45 54.54

**Flexural strength (MPa) ± 1.5%**

**% change**

**(GPa) ± 1.5%**

modulus is 14 and 33% respectively. The addition of 7 wt.% oMMT into Vinyl ester increases the flexural modulus by 16% and the flexural strength of Epoxy resin and Vinyl ester resin are observed to be 89 and 99 MPa respectively. The maximum improvement in the flexural strength is observed with the addition of 7 wt.% oMMT and TiO2 and it is 11 and 15% as compared to pure polymer. Significant improvement in the flexural strength of around 54% is observed at 7 wt.% Vinyl

The gradual increase in flexural strength and modulus, of nanocomposites, reveals that mechanical stresses are efficiently transferred via the interface. The significant uniqueness of nanocomposites is considered to explain this phenomenon about quality of the interface in the nanocomposites, (static adhesion strength) usually take part in significant responsibility in the materials' capability to convey stresses and elastic deformation from the base polymer matrix to

This is correct for nanofillers filled composites, because they have high part of interfacing. If the interaction between filler and matrix is poor, then filler particles are not capable of carrying out any part of the outside weight. Further, the power of the nanocomposite will not be superior as compared to that of pure polymer matrix. Instead of this, if the fillers and matrix bond is strong, then the tensile strength of composite can be higher than that of polymer matrix [15, 16]. The comparison of the results reveals that Vinyl ester-oMMT nanocomposite shows higher flexural

In **Figure 3**, the variation of the coefficient of friction can be observed for the three nanocomposite materials, as a function of the sliding distance, for load of 30 N and sliding velocity of 1 m/s. Initially, an increase in friction coefficient is associated with the initial running-in period is observed. After the initial runningin period the friction coefficient stabilizes as a function of sliding distance. Epoxy-TiO2 shows lesser coefficient of friction, followed by Epoxy-oMMT. Among the three nanocomposite systems studied, pure Epoxy shows higher coefficient of

*DOI: http://dx.doi.org/10.5772/intechopen.88236*

**Samples (wt.%) Flexural modulus** 

ester-oMMT nanocomposite.

*Flexural properties of the polymer nanocomposites.*

nanofillers [15, 16].

Vinyl ester-oMMT

**Table 3.**

strength and modulus.

**2.5 Friction and dry sliding wear behavior**

friction for all the sliding distances.


*Mechanical and Tribological Properties of Epoxy Nano Composites for High Voltage Applications DOI: http://dx.doi.org/10.5772/intechopen.88236*

#### **Table 3.**

*Nanorods and Nanocomposites*

reported [51, 52].

fairly low strains [48]. The other reason is that the corner points of the irregular shape of the spherical filler namely TiO2 particulate, may result in stress concentration in the Epoxy matrix. These two factors are perhaps responsible for significant reduction in tensile strengths of the nanocomposites. A comparison of the results reveals that the Vinyl ester-oMMT nanocomposites possess higher tensile strength confirming the effect of incorporation of oMMT filler which improves nanofiller-

The tensile modulus shows a marked increase with increasing oMMT, TiO2 content from 0 to 7 wt.% in Epoxy and Vinyl ester matrices. The improvement in the Young's modulus can be attributed to the exfoliation and good dispersion of nanosized filler particles that restricts the mobility of polymer chains under loading as well as good interfacial adhesion between the particles and the polymer matrix [49]. The orientation of clay platelets and polymer chains with respect to the direction of loading can also contribute to the reinforcement effects [49]. Unlike the Young's modulus, nanocomposites of any nanoclay content show a lower tensile strength than that of pure Epoxy. Similar results are reported by Zerda and co-authors [50] but in contrast, an increase in tensile strength values of nanocomposites are also

As reported in literature, the strain at break of nanocomposites usually declines with increasing filler content. Low filler loadings cause a significant drop in fracture strain. It may be recalled that the composite is made up of partly filler and partly matrix. Due to the rigid nature of the fillers, most of the deformation comes from the polymer. The actual deformation is experienced only by the polymer matrix which is much larger than the measured deformation of the sample. With the result, that the polymer failure reaches failure strain limit at lower level of total deformation. Hence, the total composite strain-to-break decreases. However, it is interesting to observe that nanocomposites of the present study show contrary results that is strain-to-break behavior as comparable to conventionally filled composites. It tends towards slightly higher values for filler content of less than 5 wt.% (**Table 2**). This increase suggests that the nanoparticles are able to introduce additional mechanisms of failure and energy consumption without blocking matrix deformation. Particles may induce matrix yielding under certain conditions and may furthermore act as inhibitors to crack growth by pinning the cracks [15]. Nevertheless, if the fillers exceed 5 wt.%, the failure strain undergoes a slight decrease. Such a reduction leads to that the large proportion of fillers start dominating, and they

The decrease in tensile strength and the upgrading of values of hardness with the filler addition is due to the following reasons: under the action of a mechanical (tensile) force, the interface between filler and polymer matrix will tend to debonding, depending on interfacial bond strength and this can direct to a break in the nanocomposite material. On the other hand, in case of hardness, pressing stress is in act. The matrix phase and the nanofiller phase would be hard-pressed together. Thus the interfacing bond can transfer pressure more effectively and thus there is

**Table 3** lists the average values of flexural modulus for different weight percentages of oMMT and TiO2 nanofillers. The flexural modulus of Epoxy resin is 2.30 GPa. The addition of oMMT and TiO2 to Epoxy resin is expected to reinforce the resin and increase its elastic modulus and the results are on expected lines. The flexural modulus of nanocomposites shows increase with oMMT and TiO2 concentrations. For 7 wt.% of oMMT and TiO2 loading, improvement in the flexural

matrix surface adhesion or interface in the composite.

reduce the matrix deformation by mechanical restraining.

an enhancement in the values of hardness.

**2.4 Flexural properties**

**204**

*Flexural properties of the polymer nanocomposites.*

modulus is 14 and 33% respectively. The addition of 7 wt.% oMMT into Vinyl ester increases the flexural modulus by 16% and the flexural strength of Epoxy resin and Vinyl ester resin are observed to be 89 and 99 MPa respectively. The maximum improvement in the flexural strength is observed with the addition of 7 wt.% oMMT and TiO2 and it is 11 and 15% as compared to pure polymer. Significant improvement in the flexural strength of around 54% is observed at 7 wt.% Vinyl ester-oMMT nanocomposite.

The gradual increase in flexural strength and modulus, of nanocomposites, reveals that mechanical stresses are efficiently transferred via the interface. The significant uniqueness of nanocomposites is considered to explain this phenomenon about quality of the interface in the nanocomposites, (static adhesion strength) usually take part in significant responsibility in the materials' capability to convey stresses and elastic deformation from the base polymer matrix to nanofillers [15, 16].

This is correct for nanofillers filled composites, because they have high part of interfacing. If the interaction between filler and matrix is poor, then filler particles are not capable of carrying out any part of the outside weight. Further, the power of the nanocomposite will not be superior as compared to that of pure polymer matrix. Instead of this, if the fillers and matrix bond is strong, then the tensile strength of composite can be higher than that of polymer matrix [15, 16]. The comparison of the results reveals that Vinyl ester-oMMT nanocomposite shows higher flexural strength and modulus.

#### **2.5 Friction and dry sliding wear behavior**

In **Figure 3**, the variation of the coefficient of friction can be observed for the three nanocomposite materials, as a function of the sliding distance, for load of 30 N and sliding velocity of 1 m/s. Initially, an increase in friction coefficient is associated with the initial running-in period is observed. After the initial runningin period the friction coefficient stabilizes as a function of sliding distance. Epoxy-TiO2 shows lesser coefficient of friction, followed by Epoxy-oMMT. Among the three nanocomposite systems studied, pure Epoxy shows higher coefficient of friction for all the sliding distances.

**Figure 3.** *Coefficient of friction of 5 wt.% filler filled polymer nanocomposites.*

**Figure 4.**

*Wear volume as a function of sliding distance of 5 wt.% filler filled polymer nanocomposites.*

The variation of wear volume as a function of sliding distance is shown in **Figure 4**, for the three nanocomposites, for load of 30 N and sliding velocity of 1 m/s. As seen in the **Figure 4**, a linear increase of the wear volume loss as a function of the sliding distance is observed. This increase is more significant for the pure Epoxy. Nanoparticles filled polymer composites such as Epoxy-oMMT, Epoxy-TiO2 and Vinyl ester-oMMT have shown a lesser wear volume loss during the sliding processes.

The wear volume and specific wear rate (Ks) as a function of sliding distance for pure Epoxy and oMMT filled Epoxy nanocomposites are shown in **Figures 5** and **6** respectively. From **Figure 5**, it is observed that the wear volume loss increases with increase in sliding distance for all the nanocomposites. Wear volume loss showed an upward trend in the gradient, as the sliding distances were increased in case of pure Epoxy (**Figure 5**). The sliding over a pure epoxy surface with a flat steel, the counter surface of which is ground to a roughness of 0.25–0.30 μm (arithmetic mean) under a load of 30 N and at a velocity of 1 m/s, resulted in a specific wear rate of 10.54 × 10<sup>−</sup><sup>5</sup> mm3 /Nm for 1000 m sliding distance (**Figure 6**).

The result obtained possibly may be due to enhanced temperature occurs for the duration of the process of wear. The wear resistance varies in the order of weight percentages as follows; 5 > 2 > 7 > 0% by weight of oMMT filler in polymer matrix. It is clear from the data in the **Figure 6** that the specific wear rate value of pristine

**207**

7 wt.% filler content.

**Figure 5.**

**Figure 6.**

*Mechanical and Tribological Properties of Epoxy Nano Composites for High Voltage Applications*

*Wear volume as a function of sliding distance of pure epoxy and oMMT filled epoxy nanocomposites.*

Epoxy be linear up to 2000 m and rises nonlinearly up to 4000 m. The specific wear rate of oMMT nanofillers filled Epoxy nanocomposites decreases linearly with increase in sliding distances except in the case of 7 wt.%. Epoxy resin with 5 wt.% of nanofillers (oMMT) has the smallest specific wear rate, whereas specific wear rate of pristine Epoxy rises above 5 wt.%. This is due to the poor interaction or adhesion Epoxy matrix nano-particles and the accumulation of the nanoparticles at

*Specific wear rate as a function of sliding distance of pure epoxy and oMMT filled epoxy nanocomposites.*

The incorporation of 5 wt.% of oMMT in Epoxy, results in decrease in specific wear rate by 70–80%. The tendency is in agreement with that of the tensile strength and hardness results and is listed in **Table 2** and **Figure 2** respectively. It is well known that majority of micro-fillers used are generally very successful in the reduction the wear property of different polymers. In the pristine Epoxy, wear trash consists of deformed polymer matrix containing broken down and powdered matrix particles and wear powder of the metallic opposite surface. The constituent parts can either be lost from the contact region or stay there for unchanging time as a

*DOI: http://dx.doi.org/10.5772/intechopen.88236*

*Mechanical and Tribological Properties of Epoxy Nano Composites for High Voltage Applications DOI: http://dx.doi.org/10.5772/intechopen.88236*

#### **Figure 5.**

*Nanorods and Nanocomposites*

**206**

10.54 × 10<sup>−</sup><sup>5</sup>

mm3

**Figure 4.**

**Figure 3.**

*Wear volume as a function of sliding distance of 5 wt.% filler filled polymer nanocomposites.*

*Coefficient of friction of 5 wt.% filler filled polymer nanocomposites.*

The variation of wear volume as a function of sliding distance is shown in **Figure 4**, for the three nanocomposites, for load of 30 N and sliding velocity of 1 m/s. As seen in the **Figure 4**, a linear increase of the wear volume loss as a function of the sliding distance is observed. This increase is more significant for the pure Epoxy. Nanoparticles filled polymer composites such as Epoxy-oMMT, Epoxy-TiO2 and Vinyl ester-oMMT have shown a lesser wear volume loss during the sliding processes.

/Nm for 1000 m sliding distance (**Figure 6**).

The result obtained possibly may be due to enhanced temperature occurs for the duration of the process of wear. The wear resistance varies in the order of weight percentages as follows; 5 > 2 > 7 > 0% by weight of oMMT filler in polymer matrix. It is clear from the data in the **Figure 6** that the specific wear rate value of pristine

The wear volume and specific wear rate (Ks) as a function of sliding distance for pure Epoxy and oMMT filled Epoxy nanocomposites are shown in **Figures 5** and **6** respectively. From **Figure 5**, it is observed that the wear volume loss increases with increase in sliding distance for all the nanocomposites. Wear volume loss showed an upward trend in the gradient, as the sliding distances were increased in case of pure Epoxy (**Figure 5**). The sliding over a pure epoxy surface with a flat steel, the counter surface of which is ground to a roughness of 0.25–0.30 μm (arithmetic mean) under a load of 30 N and at a velocity of 1 m/s, resulted in a specific wear rate of

*Wear volume as a function of sliding distance of pure epoxy and oMMT filled epoxy nanocomposites.*

#### **Figure 6.**

*Specific wear rate as a function of sliding distance of pure epoxy and oMMT filled epoxy nanocomposites.*

Epoxy be linear up to 2000 m and rises nonlinearly up to 4000 m. The specific wear rate of oMMT nanofillers filled Epoxy nanocomposites decreases linearly with increase in sliding distances except in the case of 7 wt.%. Epoxy resin with 5 wt.% of nanofillers (oMMT) has the smallest specific wear rate, whereas specific wear rate of pristine Epoxy rises above 5 wt.%. This is due to the poor interaction or adhesion Epoxy matrix nano-particles and the accumulation of the nanoparticles at 7 wt.% filler content.

The incorporation of 5 wt.% of oMMT in Epoxy, results in decrease in specific wear rate by 70–80%. The tendency is in agreement with that of the tensile strength and hardness results and is listed in **Table 2** and **Figure 2** respectively. It is well known that majority of micro-fillers used are generally very successful in the reduction the wear property of different polymers. In the pristine Epoxy, wear trash consists of deformed polymer matrix containing broken down and powdered matrix particles and wear powder of the metallic opposite surface. The constituent parts can either be lost from the contact region or stay there for unchanging time as a

"transport layer." In such cases, the polymer constituent can cushion the opposite surface and reduces the toughness, but the broken matrix particles and wear powder of the metallic opposite surface will take steps as a third body abrasive guiding to increase the abrade of the opposite surface. Thus, specific wear rate of the pristine Epoxy depend on presence of various elements in the wear trash. During the process of wear, no film was formed on the opposite surface and thus maximum specific wear rate was observed in pristine Epoxy.

The wear volume loss is low for oMMT filled Epoxy nanocomposites as compared to pure Epoxy. At the beginning of sliding, the two surfaces of all the asperities are in contact with each other. When shear forces are applied, the asperities get deformed. The oMMT particles protrude out from the surface of the sample and initially, the Epoxy matrix wears out and only oMMT nanoparticles remain in contact with the countersurface. As sliding distance increases, the wear rate starts decreasing and the oMMT nanoparticles wear out the steel countersurface. Due to extreme hardness of the countersurface, oMMT nanoparticles adhere to the matrix and excess filler concentration is observed on the exposed composite surface after prolonged sliding. During sliding, a rolling effect of nanoparticles may reduce the shear stress, the frictional coefficient, and the contact temperature.

For the oMMT filled Epoxy nanocomposites, a three-body contact condition is induced by the addition of nanoparticles between the contact surfaces, which is evidenced by presence of the grooves on the worn surfaces (**Figure 8a** and **b**). Hence, it is proposed that during the sliding process, many of the hard particles are embedded in the soft polymeric transfer film on the counter surface which creates grooves on the sample surface. In this way, the distance between the countersurface and the sample gets enhanced, i.e., the particle act like as spacers. This in turn, can cause reduction in the adhesion between the contacting surfaces. Therefore, the coefficient of friction of oMMT filled Epoxy is always less than that of pure Epoxy. Moreover, as the nanoparticles are free to move and they tend to be dispersed uniformly over the transfer film during the wear process. This can result in a more uniform contact stress between the contact surfaces and in turn minimizes the stress concentration [53–55].

In the present work, the wear-resistant of Epoxy nanocomposite filled with small size oMMT particles (<40 nm) transfers well to the counterface and its transfer film is thin, uniform and adheres strongly to the countersurface. Thus, the improvement in the tribological behavior of Epoxy-oMMT nanocomposite is related to the improved characteristics of the transfer film.

#### **2.6 Morphology of wear affected surface**

SEM assessment of worn surfaces of pure base resin and organically modified montmorillonite nanoclay (oMMT) added nanocomposites against metal counter surface with a load of 30 N and sliding velocity of 1 m/s are given in **Figures 7a**, **b** and **8a, b** respectively. **Figure 7a** and **b** represents the features worn surfaces of base resin. Projectile marked depicts the direction of sliding. At lesser enlargement, the worn surface is moderately rough and allied with micro-cracks in the epoxy (**Figure 7a**). The advanced microscopy image indicates (**Figure 7b**), break to the epoxy matrix is elevated ensuing in extra base material elimination from the nanocomposite surface. The loss and contact temperature are significantly enlarged, leading to increase in fracture of the base epoxy near the region of interface.

The interface surface break extremely increases with channel by the Epoxy removed (**Figure 7b**). A comparison of results of **Figure 7a** and **b**, indicates that the damaged outside surfaces are highly smoother at the mentioned sliding conditions and separation of matrix is very much limited with the content of organically modified montmorillonite nanoclay particles. **Figure 8** indicates shape and size of the wear debris

**209**

**Figure 8.**

**Figure 7.**

*magnification.*

*(b) higher magnification.*

*Mechanical and Tribological Properties of Epoxy Nano Composites for High Voltage Applications*

and debris shape changes for organically modified nanoclay composite. The shape of the debris changes to spherical and finer in comparison to that seen in **Figure 7** when the nanofillers were not present. These small or fine particles build up marks of dense material as seen in **Figure 8a** and **b**. Enlarged magnification (**Figure 8b**) shows the

*Scanning electron micrograph of 5 wt.% oMMT filled epoxy at 30 N, 1 m/s. (a) Lower magnification and* 

*Scanning electron micrograph of pure epoxy at 30 N, 1 m/s. (a) Lower magnification and (b) higher* 

The surface worn is comparatively soft and illustrated by surface damage due to fatigue, usually taken places at elevated temperatures and eliminates the surface deposit by microcracks. A space consists of worn out particle are held jointly by thermal and mechanical processes implicated in sliding, particularly roughing due to frictional heat, and compression due to the load applied. Consequently, due to the adding up of Organically Modified Montmorillonite nanoclay (oMMT) nanoparticles, outside surface reliability is preserved in the polymer matrix with a steady process of wear is taking place even at elevated load and velocity situations and thus guide to an increased load bearing capability of the nanocomposite. In addition, for nanocomposite samples, the width of traces of the wear for the nanocomposites throughout the

makeup of the packed material formed by addition of the wear debris.

process of sliding was considered using scanning electron microscope.

*DOI: http://dx.doi.org/10.5772/intechopen.88236*

*Mechanical and Tribological Properties of Epoxy Nano Composites for High Voltage Applications DOI: http://dx.doi.org/10.5772/intechopen.88236*

**Figure 7.**

*Nanorods and Nanocomposites*

wear rate was observed in pristine Epoxy.

"transport layer." In such cases, the polymer constituent can cushion the opposite surface and reduces the toughness, but the broken matrix particles and wear powder of the metallic opposite surface will take steps as a third body abrasive guiding to increase the abrade of the opposite surface. Thus, specific wear rate of the pristine Epoxy depend on presence of various elements in the wear trash. During the process of wear, no film was formed on the opposite surface and thus maximum specific

The wear volume loss is low for oMMT filled Epoxy nanocomposites as compared to pure Epoxy. At the beginning of sliding, the two surfaces of all the asperities are in contact with each other. When shear forces are applied, the asperities get deformed. The oMMT particles protrude out from the surface of the sample and initially, the Epoxy matrix wears out and only oMMT nanoparticles remain in contact with the countersurface. As sliding distance increases, the wear rate starts decreasing and the oMMT nanoparticles wear out the steel countersurface. Due to extreme hardness of the countersurface, oMMT nanoparticles adhere to the matrix and excess filler concentration is observed on the exposed composite surface after prolonged sliding. During sliding, a rolling effect of nanoparticles may reduce the

For the oMMT filled Epoxy nanocomposites, a three-body contact condition is induced by the addition of nanoparticles between the contact surfaces, which is evidenced by presence of the grooves on the worn surfaces (**Figure 8a** and **b**). Hence, it is proposed that during the sliding process, many of the hard particles are embedded in the soft polymeric transfer film on the counter surface which creates grooves on the sample surface. In this way, the distance between the countersurface and the sample gets enhanced, i.e., the particle act like as spacers. This in turn, can cause reduction in the adhesion between the contacting surfaces. Therefore, the coefficient of friction of oMMT filled Epoxy is always less than that of pure Epoxy. Moreover, as the nanoparticles are free to move and they tend to be dispersed uniformly over the transfer film during the wear process. This can result in a more uniform contact stress between the

shear stress, the frictional coefficient, and the contact temperature.

contact surfaces and in turn minimizes the stress concentration [53–55].

to the improved characteristics of the transfer film.

**2.6 Morphology of wear affected surface**

In the present work, the wear-resistant of Epoxy nanocomposite filled with small size oMMT particles (<40 nm) transfers well to the counterface and its transfer film is thin, uniform and adheres strongly to the countersurface. Thus, the improvement in the tribological behavior of Epoxy-oMMT nanocomposite is related

SEM assessment of worn surfaces of pure base resin and organically modified montmorillonite nanoclay (oMMT) added nanocomposites against metal counter surface with a load of 30 N and sliding velocity of 1 m/s are given in **Figures 7a**, **b** and **8a, b** respectively. **Figure 7a** and **b** represents the features worn surfaces of base resin. Projectile marked depicts the direction of sliding. At lesser enlargement, the worn surface is moderately rough and allied with micro-cracks in the epoxy (**Figure 7a**). The advanced microscopy image indicates (**Figure 7b**), break to the epoxy matrix is elevated ensuing in extra base material elimination from the nanocomposite surface. The loss and contact temperature are significantly enlarged, leading to increase in fracture of the base epoxy near the region of interface.

The interface surface break extremely increases with channel by the Epoxy removed (**Figure 7b**). A comparison of results of **Figure 7a** and **b**, indicates that the damaged outside surfaces are highly smoother at the mentioned sliding conditions and separation of matrix is very much limited with the content of organically modified montmorillonite nanoclay particles. **Figure 8** indicates shape and size of the wear debris

**208**

*Scanning electron micrograph of pure epoxy at 30 N, 1 m/s. (a) Lower magnification and (b) higher magnification.*

#### **Figure 8.**

and debris shape changes for organically modified nanoclay composite. The shape of the debris changes to spherical and finer in comparison to that seen in **Figure 7** when the nanofillers were not present. These small or fine particles build up marks of dense material as seen in **Figure 8a** and **b**. Enlarged magnification (**Figure 8b**) shows the makeup of the packed material formed by addition of the wear debris.

The surface worn is comparatively soft and illustrated by surface damage due to fatigue, usually taken places at elevated temperatures and eliminates the surface deposit by microcracks. A space consists of worn out particle are held jointly by thermal and mechanical processes implicated in sliding, particularly roughing due to frictional heat, and compression due to the load applied. Consequently, due to the adding up of Organically Modified Montmorillonite nanoclay (oMMT) nanoparticles, outside surface reliability is preserved in the polymer matrix with a steady process of wear is taking place even at elevated load and velocity situations and thus guide to an increased load bearing capability of the nanocomposite. In addition, for nanocomposite samples, the width of traces of the wear for the nanocomposites throughout the process of sliding was considered using scanning electron microscope.

#### *Nanorods and Nanocomposites*

The highest and lowest trace width for the pristine Epoxy resin is 50 and 25.35 μm correspondingly. In the case of, 5 wt.% of organically modified Monmorillonite nanoclay (oMMT) filled Epoxy nanocomposite, the width of the trace is 27.69–18.46 μm respectively. It was accomplished from the width of the trace that organically modified Monmorillonite nanoclay (oMMT) filled Epoxy nanocomposite has the smallest width of trace and consequently observed that improved resistance to wear.
