**2. Experiment Details**

Mechanical blending of PP and NR with the addition of LNR as a compatibiliser has been reported to be optimal at a temperature of 175-185°C and a rotor speed of 30-60rpm. The percentage of LNR used depends on the ratio of NR to PP. For a NR:PP ratio of 30:70 the best physical properties are obtained at 10% LNR [27]. The compatibiliser helps to induce the interaction between the rubber and plastic interphase and thereby increases the homoge‐

MWCNTs/TPNR composites with different amounts of MWCNT were prepared and their thermal properties have been investigated by [28]. The higher thermal conductivity was ach‐ ieved in the samples with 1 and 3wt% of MWCNTs compared to the pristine TPNR. Any sample with MWCNTs content higher than 3wt% caused the conductivity to decrease. In addition, the improvement of thermal diffusivity and specific heat was also achieved at the same percentage. DMA confirmed that the glass transition temperature (Tg) increased with

The tensile strength, tensile modulus, and also the impact strength of TPNR/MWCNTs are improved significantly while sacrificing high elongation at break by incorporating MWCNTs. The reinforcing effect of MWCNTs was also confirmed by DMA where the addi‐ tion of nanotubes has increased the storage modulus, the loss modulus, and also the glass transition temperature (Tg). Homogeneous dispersion of MWCNTs throughout the TPNR matrix and strong interfacial adhesion between MWCNTs and matrix as confirmed by SEM images are proposed to be responsible for the significant mechanical enhancement [29].

The reinforcing effect of two types of MWCNTs has also confirmed by dynamic mechanical analysis where the addition of nanotubes have increased in the storage modulus E', and the loss modulus E'', in the addition the glass transition temperature (Tg) increased with an in‐ crease in the amount of MWCNTs. The addition of MWCNTs in the TPNR matrix improved the mechanical properties. The tensile strength and elongation at break of MWCNTs 1 in‐ creased by 23%, and 29%, respectively. The Young's modulus had increased by increasing the content of MWCNTs. For MWCNTs 2 the optimum result of tensile strength and Young's modulus was recorded at 3% which increased 39%, and 30%, respectively. The laser flash technique was used to measure the thermal conductivity, thermal diffusivity and spe‐ cific heat, from the results obtained. The high thermal conductivity was achieved at 1 wt% and 3 wt% of MWCNTs compared with TPNR after 3 wt% it decreased, also the improve‐ ment of thermal diffusivity and specific heat was achieved at the same percentage. The MWCNTs 1 and 2/TPNR nanocomposites were fabricated and the tensile and properties

In this chapter, the effect of multi-walled carbon nanotubes with and without acid treatment on the properties of thermoplastic natural rubber (TPNR) was investigated. Two types of MWCNTs were introduced into TPNR, which are untreated multi-walled carbon nanotubes (UTMWCNTs) (without acid treatment) and treated multi-walled carbon nanotubes (TMWCNTs) (with acid treatment). Using this method, MWCNTs are dispersed homogene‐ ously in the TPNR matrix in an attempt to increase the properties of these nanocomposites. The effect of MWCNTs on the mechanical and thermal properties of TPNR nanocomposites

neity of the blend.

were measured [30].

is reported in this chapter.

the increase in the amount of MWCNTs.

122 Syntheses and Applications of Carbon Nanotubes and Their Composites

Polypropylene, with a density of 0.905 g cm-3, was supplied by Propilinas (M) Sdn. Bhd, natural rubber was supplied by Guthrie (M) Sdn. Bhd, and polypropylene (PP) with a densi‐ ty of 0.905 g/cm3 was supplied by Polipropilinas (M) Sdn. Bhd were used in this research. Maleic anhydride–grafted–polypropylene (MAPP) with a density of 0.95 g/cm3 was sup‐ plied from Aldrich Chemical Co., USA. Liquid natural rubber (LNR) was prepared by the photochemical degradation technique.

A Multi-walled carbon nanotubes (MWCNTs) were provided by Arkema (Graphis‐ trengthTM C100). Table 1 shows the properties of multi-walled carbon nanotubes (MWCNTs).


**Table 1.** Properties of multi-walled carbon nanotubes (MWCNTs).

#### **2.1. Preparation of TPNR-Multi-Walled Carbon Nanotubes (MWCNTs) Composite**

Mixing was performed by an internal mixer (Haake Rheomix 600P). The mixing tempera‐ ture was 180°C, with a rotor speed of 100 rpm and 13 min mixing time. The indirect techni‐ que (IDT) was used to prepare nanocomposites, this involved mixing the MWCNTs with LNR separately, before it was melt blended with PP and NR in the internal mixer. TPNR nanocomposits were prepared by melt blending of PP, NR and LNR with MWCNTs in a ra‐ tio of 70 wt% PP, 20 wt% NR and 10wt% LNR as a compatibiliser and 1,3,5 and 7% MWCNTs.

#### **2.2. Acid Treatment of MWCNTs**

Two types of MWCNTs were introduced to the TPNR which is untreated MWCNTs (MWCNTs 1) and treated MWCNTs (MWCNTs 2), MWCNTs 2 were treated by immersing neat MWCNTs in a mixture of nitric and sulfuric acid with a molar ratio of 1:3, respectively. In a typical experiment, 1g of raw MWCNTs was added to 40ml of the acid mixture. Then, the oxidation reaction was carried out in a two-necked, round-bottomed glass flask equip‐ ped with reflux condenser, magnetic stirrer and thermometer. The reaction was carried out for 3 hours at 140°C. After that, this mixture was washed with distilled water on a sintered glass filter until the pH value was around 7, and was dried in a vacuum oven at 70°C for 24hours [31].

#### **2.3. Characterizations**

Fourier transform infrared (FTIR) spectroscopy analysis was carried out on the Perkin Elmer spectrum V-2000 spectrometer by the potassium bromide (KBr) method for MWCNTs. The samples were scanned between 700 to 4000 cm-1 wave number. Differences in the peaks as well as the new peaks of MWCNTs and MWCNTs after acid treatment were observed to identify any functional groups on the MWCNTs tubes surface.

The tensile properties were tested using a Testometric universal testing machine model M350-10CT with 5 kN load cell according to ASTM 412 standard procedure using test speci‐ mens of 1 mm thickness and a crosshead speed 50 mm min-1. At least five samples were tested for each composition, and the average value was reported.

The impact test was carried out using a Ray Ran Pendulum Impact System according to ASTM D 256-90b. The velocity and weight of the hammer were 3.5m/s and 0.898kg, respectively.

Dynamic mechanical analysis for determining the glass transition temperature, storage and loss modulus was carried out using DMA 8000 (PerkinElmer Instrument), operating in sin‐ gle cantilever mode from -100 to 150°C at a constant frequency of 1 Hz, with a heating rate of 5°C/min. The dimensions of the samples were 30 x 12.5 x 3 mm.

The thermal conductivity was measured by a laser flash method. Disk-type samples (12.7 mm in diameter and 1mm in thickness) were set in an electric furnace. Specific heat capaci‐ ties were measured with a differential scanning calorimeter DSC. Thermal diffusivity (λ, Wm\_1 K\_1) was calculated from thermal diffusivity (α, m2 s\_1), density (ρ, g cm\_3) and spe‐ cific heat capacity (Cp, J g\_1 K\_1) at each temperature using the following:

$$
\lambda \models \alpha . \rho . \mathsf{C} . \tag{1}
$$

The generation of chemical functional groups on MWCNTs was confirmed using Fourier transform infrared spectroscopy (FT-IR) spectra which were recorded between 400 cm\_1

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The FT-IR spectra of pure MWCNTs and the surface treated MWCNTs are shown in Figure. 2 and Figure 3. The characteristic bands due to generated functional groups are observed in the spectrum of each chemically treated MWCNTs. In figure 2 we could not see any band compared with the treated MWCNTs. The acid treated MWCNTs shows new peaks in com‐ parison with the FT-IR spectrum of the untreated MWCNTs, which lack the hydroxyl and carbonyl groups. The peaks around 1580 cm\_1 are assigned to the O–H band in C-OH, and the peaks at 674 cm-1 are assigned to COOH, as shown in Figure 3. This demonstrates that

hydroxyl and carbonyl groups have been introduced on the nanotube surface [33].

**Figure 1.** Example of chemical functionalization of carbon nanotubes.

**Figure 2.** FTIR spectra of MWCNTs (before acid treatment).

and 4000 cm\_1.

The reference used for the heat capacity calculation was a 12.7mm thick specimen of pyro‐ ceram. The reference sample was coated with a thin layer of graphite before the measure‐ ment was performed. The thermal conductivity of MWCNTs reinforced TPNR matrix composites of all volume fractions was studied from 30°C to 150°C. The morphology of the MWCNTs and the composite were examined using a scanning electron microscope (Philips XL 30). The samples were coated with a thin layer of gold to avoid electrostatic charging during examination.

### **3. Results and Discussion**

#### **3.1. Fourier-Transform Infrared Spectroscopy**

The method used to functionalize the pristine MWCNTs in this study was the acid treatment method, which is described in section 2.2. Through this process, MWCNTs were oxidized and purified by eliminating impurities such as amorphous carbons, graphite particles, and metal catalysts [32]; the functional group of the surface of the CNTs are as shown in Figure 1.

The generation of chemical functional groups on MWCNTs was confirmed using Fourier transform infrared spectroscopy (FT-IR) spectra which were recorded between 400 cm\_1 and 4000 cm\_1.

The FT-IR spectra of pure MWCNTs and the surface treated MWCNTs are shown in Figure. 2 and Figure 3. The characteristic bands due to generated functional groups are observed in the spectrum of each chemically treated MWCNTs. In figure 2 we could not see any band compared with the treated MWCNTs. The acid treated MWCNTs shows new peaks in com‐ parison with the FT-IR spectrum of the untreated MWCNTs, which lack the hydroxyl and carbonyl groups. The peaks around 1580 cm\_1 are assigned to the O–H band in C-OH, and the peaks at 674 cm-1 are assigned to COOH, as shown in Figure 3. This demonstrates that hydroxyl and carbonyl groups have been introduced on the nanotube surface [33].

**Figure 1.** Example of chemical functionalization of carbon nanotubes.

**2.3. Characterizations**

during examination.

**3. Results and Discussion**

**3.1. Fourier-Transform Infrared Spectroscopy**

Fourier transform infrared (FTIR) spectroscopy analysis was carried out on the Perkin Elmer spectrum V-2000 spectrometer by the potassium bromide (KBr) method for MWCNTs. The samples were scanned between 700 to 4000 cm-1 wave number. Differences in the peaks as well as the new peaks of MWCNTs and MWCNTs after acid treatment were observed to

The tensile properties were tested using a Testometric universal testing machine model M350-10CT with 5 kN load cell according to ASTM 412 standard procedure using test speci‐ mens of 1 mm thickness and a crosshead speed 50 mm min-1. At least five samples were

The impact test was carried out using a Ray Ran Pendulum Impact System according to ASTM D 256-90b. The velocity and weight of the hammer were 3.5m/s and 0.898kg, respectively.

Dynamic mechanical analysis for determining the glass transition temperature, storage and loss modulus was carried out using DMA 8000 (PerkinElmer Instrument), operating in sin‐ gle cantilever mode from -100 to 150°C at a constant frequency of 1 Hz, with a heating rate

The thermal conductivity was measured by a laser flash method. Disk-type samples (12.7 mm in diameter and 1mm in thickness) were set in an electric furnace. Specific heat capaci‐ ties were measured with a differential scanning calorimeter DSC. Thermal diffusivity (λ, Wm\_1 K\_1) was calculated from thermal diffusivity (α, m2 s\_1), density (ρ, g cm\_3) and spe‐

The reference used for the heat capacity calculation was a 12.7mm thick specimen of pyro‐ ceram. The reference sample was coated with a thin layer of graphite before the measure‐ ment was performed. The thermal conductivity of MWCNTs reinforced TPNR matrix composites of all volume fractions was studied from 30°C to 150°C. The morphology of the MWCNTs and the composite were examined using a scanning electron microscope (Philips XL 30). The samples were coated with a thin layer of gold to avoid electrostatic charging

The method used to functionalize the pristine MWCNTs in this study was the acid treatment method, which is described in section 2.2. Through this process, MWCNTs were oxidized and purified by eliminating impurities such as amorphous carbons, graphite particles, and metal catalysts [32]; the functional group of the surface of the CNTs are as shown in Figure 1.

*λ* =*α*. *ρ*. C. (1)

identify any functional groups on the MWCNTs tubes surface.

124 Syntheses and Applications of Carbon Nanotubes and Their Composites

tested for each composition, and the average value was reported.

of 5°C/min. The dimensions of the samples were 30 x 12.5 x 3 mm.

cific heat capacity (Cp, J g\_1 K\_1) at each temperature using the following:

**Figure 2.** FTIR spectra of MWCNTs (before acid treatment).

Figure 5 (A and B) displayed no nanoparticles in the acid-modified MWCNTs. The particles might have been removed during acid modification. This reveals that the acid-modified MWCNTs were straight and that some of them aggregated in bundles, which were dis‐ persed well in the matrix. The length of the MWCNTs were reduced during acid modifica‐ tion, since the mixed acid corroded the MWCNTs. TEM microphotographs of the unmodified and acid-modified, curled and entangled MWCNTs demonstrate that the

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**Figure 5.** TEM micrograph of MWCNTs after acid treatment with different magnifications (A) 45000 (B) 100000.

The tensile strengths of TPNR reinforced with MWCNTs (with and without treatment) of different percentages (1%, 3%, 5% and 7%) are shown in Figure 6. Generally, both MWCNTs exhibited an increasing trend up to 3wt% content. Further increments in MWCNTs content

From Figure 6, TPNR with UTMWCNTs and TMWCNTs have optimum results at 3 wt%, which, compared with TPNR, increased by 23% and 39%, respectively. The tensile strength increased radically as the amount of MWCNTs concentration increased. The mechanical performance, such as tensile properties, strongly depends on several factors such as the properties of the filler reinforcement and matrix, filler content, filler length, filler orientation,

decreased the tensile strength compared to the optimum filler loading.

MWCNTs are straight.

**3.3. Mechanical Properties**

*3.3.1. Tensile strength*

**Figure 3.** FTIR spectra of MWCNTs (after acid treatment).

#### **3.2. Transmission Electron Microscopy (TEM)**

TEM microphotographs of pure MWCNTs are shown in Figure 4 (A and B). The figure presents unmodified MWCNTs containing particles with diameters of 5–12 nm. The nano‐ particles may be impurities from amorphous carbon and can be removed by acid treatment. According to the supplier, the unmodified MWCNT contains approximately 5% amorphous carbon. Figure 4 B demonstrates that most of the nanoparticles were deposited on the sur‐ face of the carbon nanotubes and some of them were dispersed throughout the solution used to view the MWCNTs by TEM.

**Figure 4.** TEM micrograph of Pure MWCNTs before acid treatment with different magnifications (A) 45000 (B) 100000.

Figure 5 (A and B) displayed no nanoparticles in the acid-modified MWCNTs. The particles might have been removed during acid modification. This reveals that the acid-modified MWCNTs were straight and that some of them aggregated in bundles, which were dis‐ persed well in the matrix. The length of the MWCNTs were reduced during acid modifica‐ tion, since the mixed acid corroded the MWCNTs. TEM microphotographs of the unmodified and acid-modified, curled and entangled MWCNTs demonstrate that the MWCNTs are straight.

**Figure 5.** TEM micrograph of MWCNTs after acid treatment with different magnifications (A) 45000 (B) 100000.

#### **3.3. Mechanical Properties**

#### *3.3.1. Tensile strength*

**Figure 3.** FTIR spectra of MWCNTs (after acid treatment).

126 Syntheses and Applications of Carbon Nanotubes and Their Composites

**3.2. Transmission Electron Microscopy (TEM)**

used to view the MWCNTs by TEM.

100000.

TEM microphotographs of pure MWCNTs are shown in Figure 4 (A and B). The figure presents unmodified MWCNTs containing particles with diameters of 5–12 nm. The nano‐ particles may be impurities from amorphous carbon and can be removed by acid treatment. According to the supplier, the unmodified MWCNT contains approximately 5% amorphous carbon. Figure 4 B demonstrates that most of the nanoparticles were deposited on the sur‐ face of the carbon nanotubes and some of them were dispersed throughout the solution

**Figure 4.** TEM micrograph of Pure MWCNTs before acid treatment with different magnifications (A) 45000 (B)

The tensile strengths of TPNR reinforced with MWCNTs (with and without treatment) of different percentages (1%, 3%, 5% and 7%) are shown in Figure 6. Generally, both MWCNTs exhibited an increasing trend up to 3wt% content. Further increments in MWCNTs content decreased the tensile strength compared to the optimum filler loading.

From Figure 6, TPNR with UTMWCNTs and TMWCNTs have optimum results at 3 wt%, which, compared with TPNR, increased by 23% and 39%, respectively. The tensile strength increased radically as the amount of MWCNTs concentration increased. The mechanical performance, such as tensile properties, strongly depends on several factors such as the properties of the filler reinforcement and matrix, filler content, filler length, filler orientation, and processing method and condition. The improvement in the tensile strength may be caused by the good dispersion of MWCNTs in the TPNR matrix, which leads to a strong in‐ teraction between the TPNR matrix and MWCNTs. These well-dispersed MWCNTs may have the effect of physically crosslinking points, thus, increasing the tensile strength.

*3.3.2. Young's Modulus*

Figure 7 shows the effect of filler content on the tensile modulus of TPNR reinforced by TMWNTs and UTMWCNTs. The same trend as for the tensile strength in Figure 6 was ob‐ served for the tensile modulus of TMWCNTs. Figure 6 clearly shows that the presence of

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The remarkable increase of Young's modulus with TMWCNTs content shows a greater im‐ provement than that seen in the tensile strength at high content, which indicates that the Young's modulus increases with an increase in the amount of the TMWCNTs. At 3 wt% of TMWCNTs the Young's modulus is increased by 34 % compared to TPNR. The Young's modulus of UTMWCNTs increased with the increase in the amount of UTMWCNTs. The maximum result was achieved at 3wt%, with an increase of about 22%, which was due to the good dispersion of nanotubes displaying perfect stress transfer [36].The improvement of modulus is due to the high modulus of MWCNTs [37]. The further addition of TMWCNTs and UTMWCNTs from 5 to 7 wt% increased the Young modulus dropped respectively.

As explained before, a reduction in performance occurred at higher filler contents for both types of MWCNTs, as depicted in Figure 7. Initially it increases with filler content and then decreases when exceeding the filler loading limit due to the diminishing interfacial fillerpolymer adhesion. It is assumed that aggregates of nanotube ropes effectively reduce the as‐

> 0% 1% 3% 5% 7% **wt % of MWCNTs**

**Figure 7.** Young's Modulus of TPNR reinforced with MWCNTs (with and without treatment).

TPNR TPNR+UTMWCNTs TPNR+TMWNTs

MWCNTs has significantly improved the tensile modulus of the TPNR.

pect/ratio (length/diameter) of the reinforcement.

250

300

350

**Young's modulus (MPa)** 

400

450

500

**Figure 6.** Tensile strength of TPNR reinforced with MWCNTs (with and without treatment).

A good interface between the CNTs and the TPNR is very important for a material to stand the stress. Under load, the matrix distributes the force to the CNTs, which carry most of the applied load. The order of these value is TPNR/TMWCNTs > TPNR/UTMWCNTs > TPNR. The better properties in tensile strength for the TPNR/TMWCNTs nanocomposites could be due to the improved dispersion of the MWCNTs, as well as the response to the opportuni‐ ties offered by the acid treated MWCNTs. Furthermore, the MWCNTs after acid treatment contain many defects as well as acidic sites on CNTs, such as carboxylic acid, carbonyl and hydroxyl groups. These will greatly enhance the combination of CNTs in a polymer matrix, thus improving the mechanical strength of the nanocomposites [34]. When the content of MWCNTs is higher, the MWCNTs cannot disperse adequately in the TPNR matrix and ag‐ glomerate to form a big cluster. This is because of the huge surface energy of MWCNTs as well as the weak interfacial interaction between MWCNTs and TPNR, which leads to inho‐ mogeneous dispersion in the polymer matrix and negative effects on the properties of the resulting composites that cause a decrease in the tensile strength [35].

#### *3.3.2. Young's Modulus*

and processing method and condition. The improvement in the tensile strength may be caused by the good dispersion of MWCNTs in the TPNR matrix, which leads to a strong in‐ teraction between the TPNR matrix and MWCNTs. These well-dispersed MWCNTs may

> 0% 1% 3% 5% 7% **wt % of MWCNTs**

A good interface between the CNTs and the TPNR is very important for a material to stand the stress. Under load, the matrix distributes the force to the CNTs, which carry most of the applied load. The order of these value is TPNR/TMWCNTs > TPNR/UTMWCNTs > TPNR. The better properties in tensile strength for the TPNR/TMWCNTs nanocomposites could be due to the improved dispersion of the MWCNTs, as well as the response to the opportuni‐ ties offered by the acid treated MWCNTs. Furthermore, the MWCNTs after acid treatment contain many defects as well as acidic sites on CNTs, such as carboxylic acid, carbonyl and hydroxyl groups. These will greatly enhance the combination of CNTs in a polymer matrix, thus improving the mechanical strength of the nanocomposites [34]. When the content of MWCNTs is higher, the MWCNTs cannot disperse adequately in the TPNR matrix and ag‐ glomerate to form a big cluster. This is because of the huge surface energy of MWCNTs as well as the weak interfacial interaction between MWCNTs and TPNR, which leads to inho‐ mogeneous dispersion in the polymer matrix and negative effects on the properties of the

**Figure 6.** Tensile strength of TPNR reinforced with MWCNTs (with and without treatment).

resulting composites that cause a decrease in the tensile strength [35].

TPNR TPNR+UTMWCNTs TPNR+TMWCNTs

have the effect of physically crosslinking points, thus, increasing the tensile strength.

128 Syntheses and Applications of Carbon Nanotubes and Their Composites

10

12

14

16

**Tensile strength (MPa)**

18

20

Figure 7 shows the effect of filler content on the tensile modulus of TPNR reinforced by TMWNTs and UTMWCNTs. The same trend as for the tensile strength in Figure 6 was ob‐ served for the tensile modulus of TMWCNTs. Figure 6 clearly shows that the presence of MWCNTs has significantly improved the tensile modulus of the TPNR.

The remarkable increase of Young's modulus with TMWCNTs content shows a greater im‐ provement than that seen in the tensile strength at high content, which indicates that the Young's modulus increases with an increase in the amount of the TMWCNTs. At 3 wt% of TMWCNTs the Young's modulus is increased by 34 % compared to TPNR. The Young's modulus of UTMWCNTs increased with the increase in the amount of UTMWCNTs. The maximum result was achieved at 3wt%, with an increase of about 22%, which was due to the good dispersion of nanotubes displaying perfect stress transfer [36].The improvement of modulus is due to the high modulus of MWCNTs [37]. The further addition of TMWCNTs and UTMWCNTs from 5 to 7 wt% increased the Young modulus dropped respectively.

As explained before, a reduction in performance occurred at higher filler contents for both types of MWCNTs, as depicted in Figure 7. Initially it increases with filler content and then decreases when exceeding the filler loading limit due to the diminishing interfacial fillerpolymer adhesion. It is assumed that aggregates of nanotube ropes effectively reduce the as‐ pect/ratio (length/diameter) of the reinforcement.

**Figure 7.** Young's Modulus of TPNR reinforced with MWCNTs (with and without treatment).

#### **3.3.3 Elongation at Break**

The elongation at the break of TPNR with TMWCNTs and UTMWCNTs is shown in Figure 8. For TMWCNTs and UTMWCNTs, the elongation at break decreased with the increase in the amount of MWCNTs, compared with TPNR.

**3.3.4 Impact Strength**

5

0% 1% 3% 5% 7% **wt % of MWCNTs**

The effect of filler loading on the impact strength of TPNR/TMWCNTs and TPNR/ UTMWCNTs nanocomposites is given in Figure 9. It shows that incorporation of MWCNTs

The results exhibited better impact strength for TMWCNTs and UTMWCNTs at 3 wt% with an increase of about 82% and 46%, respectively. This is due to the better dispersion of car‐ bon nanotubes in the matrix, which generated a significant toughening effect on the TPNR/ TMCWNTs nanocomposite compared with TPNR/UTMWCNTs nanocomposites. However, when the load is transferred to the physical network between the matrix and the filler, the debonding of the chain segments from the filler surface facilitates the relaxation of the ma‐

The low impact energy was attributed to the filler content being more than 3wt%. This will reduce the ability of reinforced composites to absorb energy during fracture propagation. However, in the case of elastomer-toughened polymer, the presence of the elastomer basi‐ cally produces stress redistribution in the composite, which causes micro cracking or craz‐ ing at many sites, thereby resulting in a more efficient energy dissipation mechanism [38].

Consequently, because of their higher surface energy and large aspect ratio, it will be diffi‐ cult for the nanotubes to disperse in the TPNR when the TMWCNTs and UTMWCNTs con‐ tent are higher. This will lead to less energy dissipating in the system due to the poor interfacial bonding and induces micro spaces between the filler and polymer matrix. This causes micro-cracks when impact occurs, which induces easy crack propagation. Therefore,

**Figure 9.** Impact Strength of TPNR reinforced with MWCNTs (with and without treatment).

trix entanglement structure, leading to higher impact toughness.

into TPNR considerably affects the impact strength of TPNR nanocomposites.

TPNR TPNR+UTMWCNTs TPNR+TMWCNTs

(TPNR) Composite

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Characterization and Morphology of Modified Multi-Walled Carbon Nanotubes Filled Thermoplastic Natural Rubber

10

15

**Impact strength (KJ/m^ 2)**

20

It can be deduced that the reinforcing effect of MWCNTs is very marked. As the MWCNTs content in the TPNR increases, the stress level gradually increases, however, the strain of the nanocomposites decreased at the same time. This is because the MWCNTs included in the TPNR matrix behave like physical crosslinking points and restrict the movement of polymer chains. This indicates that, when the amount of CNTs incorporated into the rubber increase it tends to decrease the ductility and the material become stronger and tougher, however, at the same time, it is also

**Figure 8.** Elongation at Break of TPNR reinforced with MWCNTs (with and without treatment).

#### **3.3.4 Impact Strength**

**3.3.3 Elongation at Break**

the same time, it is also

20

120

220

**Elongation at break (%)**

320

420

the amount of MWCNTs, compared with TPNR.

130 Syntheses and Applications of Carbon Nanotubes and Their Composites

The elongation at the break of TPNR with TMWCNTs and UTMWCNTs is shown in Figure

8. For TMWCNTs and UTMWCNTs, the elongation at break decreased with the increase in

It can be deduced that the reinforcing effect of MWCNTs is very marked. As the MWCNTs

content in the TPNR increases, the stress level gradually increases, however, the strain of the

nanocomposites decreased at the same time. This is because the MWCNTs included in the

TPNR matrix behave like physical crosslinking points and restrict the movement of polymer

chains. This indicates that, when the amount of CNTs incorporated into the rubber increase

it tends to decrease the ductility and the material become stronger and tougher, however, at

0% 1% 3% 5% 7% **wt % of MWCNTs**

**Figure 8.** Elongation at Break of TPNR reinforced with MWCNTs (with and without treatment).

TPNR TPNR+MWNTs 1 TPNR+MWNTs 2

**Figure 9.** Impact Strength of TPNR reinforced with MWCNTs (with and without treatment).

The effect of filler loading on the impact strength of TPNR/TMWCNTs and TPNR/ UTMWCNTs nanocomposites is given in Figure 9. It shows that incorporation of MWCNTs into TPNR considerably affects the impact strength of TPNR nanocomposites.

The results exhibited better impact strength for TMWCNTs and UTMWCNTs at 3 wt% with an increase of about 82% and 46%, respectively. This is due to the better dispersion of car‐ bon nanotubes in the matrix, which generated a significant toughening effect on the TPNR/ TMCWNTs nanocomposite compared with TPNR/UTMWCNTs nanocomposites. However, when the load is transferred to the physical network between the matrix and the filler, the debonding of the chain segments from the filler surface facilitates the relaxation of the ma‐ trix entanglement structure, leading to higher impact toughness.

The low impact energy was attributed to the filler content being more than 3wt%. This will reduce the ability of reinforced composites to absorb energy during fracture propagation. However, in the case of elastomer-toughened polymer, the presence of the elastomer basi‐ cally produces stress redistribution in the composite, which causes micro cracking or craz‐ ing at many sites, thereby resulting in a more efficient energy dissipation mechanism [38].

Consequently, because of their higher surface energy and large aspect ratio, it will be diffi‐ cult for the nanotubes to disperse in the TPNR when the TMWCNTs and UTMWCNTs con‐ tent are higher. This will lead to less energy dissipating in the system due to the poor interfacial bonding and induces micro spaces between the filler and polymer matrix. This causes micro-cracks when impact occurs, which induces easy crack propagation. Therefore, the higher agglomeration of MWCNTs can cause the mechanical properties of the compo‐ sites to deteriorate [39].

#### **3.4. Thermal Properties**

#### *3.4.1. Glass Transition Temperature*

The dynamic mechanical data shows that the glass transition temperature of the TPNR/ UTMWCNTs and TPNR/TMWCNTs is affected by the addition of the different amounts of MWCNTs, as depicted in Figure 10.


*3.4.2. Thermal Conductivity*

TPNR 1wt% 3wt% 5wt% 7wt% **wt% of MWCNTs**

**Figure 10.** Glass Transition Temperature of TPNR reinforced with MWCNTs (with and without treatment).

To study the effect of MWCNTs filler on thermal conductivity, the temperature was varied

from (30 – 150) °C. The carbon filler loading was from 1wt% to 7wt% for two types of carbon

nanotubes (UTMWCNTs and TMWCNTs). Introducing MWCNTs to TPNR can significantly

enhance the thermal conductivity of the TPNR matrix, as shown in Figure 11 and Figure 12.

As shown in figure 11 at 30°C the thermal conductivity of TPNR/TMWCNTs composites,

Thermal conductivity increased at 3wt% compared to 1wt%, 5wt% and 7wt%, respectively,

and for TPNR/UTMWCNTs, the thermal conductivity increased at 3wt%, as compared to

TPNR at the same temperature as shown in figure 12. Thermal transport in the CNT compo‐

sites includes phonon diffusion in the matrix and ballistic transportation in the filler.

UTMWCNTs TMWCNTs

(TPNR) Composite

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**Tg** 



0

From the figures, the Tg for the TPNR/TMWCNTs nanocomposites is higher than the corre‐ sponding temperature for the TPNR and TPNR/UTMWCNTs nanocomposites, usually the Tg of a polymeric matrix tends to increase with the addition of carbon nanotubes. The rise in Tg in any polymeric system is associated with a restriction in molecular motion, reduction in free volume and/or a higher degree of crosslinking (TPNR/TMWCNTs > TPNR/ UTMWCNTs) due to the interactions between the polymer chains and the nanoparticles, and the reduction of macromolecular chain mobility.

With the high amount of MWCNTs (after 3wt %) of TMWCNTs and UTMWCNTs the Tg drops. This might be due to the phase separation/agglomeration of MWCNTs, this allows the macromolecules to move easily. When the content of MWCNTs is higher, the MWCNTs congregate, possibly because the intrinsic van der Waals forces occurs, which leads to bub‐ bles and small aggregates. The conglomerations and matrix holes existing in the network of MWCNTs may perform as defects, which make the macromolecules move easily, and the Tg of the matrix is decreased.

Characterization and Morphology of Modified Multi-Walled Carbon Nanotubes Filled Thermoplastic Natural Rubber (TPNR) Composite http://dx.doi.org/10.5772/50726 133

**Figure 10.** Glass Transition Temperature of TPNR reinforced with MWCNTs (with and without treatment).

#### *3.4.2. Thermal Conductivity*

the higher agglomeration of MWCNTs can cause the mechanical properties of the compo‐

The dynamic mechanical data shows that the glass transition temperature of the TPNR/

UTMWCNTs and TPNR/TMWCNTs is affected by the addition of the different amounts of

From the figures, the Tg for the TPNR/TMWCNTs nanocomposites is higher than the corre‐

sponding temperature for the TPNR and TPNR/UTMWCNTs nanocomposites, usually the

Tg of a polymeric matrix tends to increase with the addition of carbon nanotubes. The rise in

Tg in any polymeric system is associated with a restriction in molecular motion, reduction in

free volume and/or a higher degree of crosslinking (TPNR/TMWCNTs > TPNR/

UTMWCNTs) due to the interactions between the polymer chains and the nanoparticles,

With the high amount of MWCNTs (after 3wt %) of TMWCNTs and UTMWCNTs the Tg

drops. This might be due to the phase separation/agglomeration of MWCNTs, this allows

the macromolecules to move easily. When the content of MWCNTs is higher, the MWCNTs

congregate, possibly because the intrinsic van der Waals forces occurs, which leads to bub‐

bles and small aggregates. The conglomerations and matrix holes existing in the network of

MWCNTs may perform as defects, which make the macromolecules move easily, and the Tg

sites to deteriorate [39].

**3.4. Thermal Properties**

*3.4.1. Glass Transition Temperature*

132 Syntheses and Applications of Carbon Nanotubes and Their Composites

MWCNTs, as depicted in Figure 10.

and the reduction of macromolecular chain mobility.

of the matrix is decreased.

To study the effect of MWCNTs filler on thermal conductivity, the temperature was varied from (30 – 150) °C. The carbon filler loading was from 1wt% to 7wt% for two types of carbon nanotubes (UTMWCNTs and TMWCNTs). Introducing MWCNTs to TPNR can significantly enhance the thermal conductivity of the TPNR matrix, as shown in Figure 11 and Figure 12.

As shown in figure 11 at 30°C the thermal conductivity of TPNR/TMWCNTs composites, Thermal conductivity increased at 3wt% compared to 1wt%, 5wt% and 7wt%, respectively, and for TPNR/UTMWCNTs, the thermal conductivity increased at 3wt%, as compared to TPNR at the same temperature as shown in figure 12. Thermal transport in the CNT compo‐ sites includes phonon diffusion in the matrix and ballistic transportation in the filler.

The improvement in thermal conductivity in TMWCNTs/TPNR may stem from the im‐ proved percolation because of the better dispersion and formation of a network [40]. The dispersion of 1wt% and 3wt% TMWCNTs is better than 5wt% and 7wt% in TPNR, at 5% and 7% the TMWCNTs agglomerated inside TPNR. Therefore, the large amounts of junc‐ tions among the carbon nanotubes form a single conducting path, which is believed to be the reason why the measured thermal conductivity is low. For the UTMWCNTs the conduc‐

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The significant enhancement in the thermal conductivity of CNT nanocomposites is possi‐ bly attributed to the kinks or twists of UTMWCNTs. When the phonon travels along the nanotubes, if it meets the kinks or twists it would be blocked at those sites. The existence of such kinks or twists in CNTs would lead to a decrease in the effective aspect ratio of the nanotubes [41] when the amount of UTMWCNTs increases, and, thus, the thermal conduc‐ tivity of UTMWCNTs-TPNR nanocomposites would be reduced. Therefore, the acid treat‐ ment of MWCNTs in TPNR could reduce these kinks or twists of TMWCNTs due to the good dispersion of MWCNTs in TPNR, causing the thermal conductivity of the nanocom‐

Two factors have been proposed to explain the significant enhancement of thermal conduc‐ tivity with TMWCNTs (1) the rigid linkage between TMWCNTs and TPNR matrix with pro‐ vides good interface compatibility which may reduce interface thermal resistance; (2) the good interface compatibility allows TMWCNTs to disperse well in the matrix, consequently, the results of the TEM indicate that TMWCNTs possess good dispersion and good compati‐

The formation of the UTMWCNTs bundles restrict the phonon transport in composites, which maybe be attributed to two reasons (1) the UTMWCNTs aggregation reduces the as‐ pect ratio, consequently, decreasing the contact area between the UTMWCNTs and the TPNR matrix; (2) the UTMWCNTs bundles cause the phenomenon of reciprocal phonon

The resistance to phonon movement from one nanotube to another through the junction will hinder phonon movement and, hence, limit the thermal conductivity. The low ther‐ mal conductivity could be partly due to the non-uniform diameter and size, as well as, the defects in and the nano-scale dimension of UTMWNTs. However, the numerous junctions between carbon nanotubes involved in forming a conductive path and the exceptionally low thermal conductance at the interface [42] are believed to be the main reason for the

The effect of reducing the thermal conductivity is the transfer of phonons from nanotube to nanotube. This transition occurs by direct coupling between CNTs, in the case of the im‐ proper impregnated ropes, CNT-junctions and agglomerates, or via the matrix. In all these cases, the transition occurs via an interface and, thus, the coupling losses can be attributed to an intense phonon boundary scattering. At the same time the thermal conductivity decreas‐ es with the increase in temperature (if the temperature is near the melting point of the ma‐ trix). This indicates that the thermal conductivity of the composites is dominated by the

vector, which acts like a heat reservoir and restricts heat flow diffusion.

tivity at 3wt% and 1wt% is better than 5wt% and 7wt%, respectively.

posites to increase.

bility in the TPNR matrix.

low thermal conductivity.

**Figure 11.** Thermal Conductivity of TPNR reinforced with UTMWCNTs.

**Figure 12.** Thermal Conductivity of TPNR reinforced with TMWCNTs.

The improvement in thermal conductivity in TMWCNTs/TPNR may stem from the im‐ proved percolation because of the better dispersion and formation of a network [40]. The dispersion of 1wt% and 3wt% TMWCNTs is better than 5wt% and 7wt% in TPNR, at 5% and 7% the TMWCNTs agglomerated inside TPNR. Therefore, the large amounts of junc‐ tions among the carbon nanotubes form a single conducting path, which is believed to be the reason why the measured thermal conductivity is low. For the UTMWCNTs the conduc‐ tivity at 3wt% and 1wt% is better than 5wt% and 7wt%, respectively.

The significant enhancement in the thermal conductivity of CNT nanocomposites is possi‐ bly attributed to the kinks or twists of UTMWCNTs. When the phonon travels along the nanotubes, if it meets the kinks or twists it would be blocked at those sites. The existence of such kinks or twists in CNTs would lead to a decrease in the effective aspect ratio of the nanotubes [41] when the amount of UTMWCNTs increases, and, thus, the thermal conduc‐ tivity of UTMWCNTs-TPNR nanocomposites would be reduced. Therefore, the acid treat‐ ment of MWCNTs in TPNR could reduce these kinks or twists of TMWCNTs due to the good dispersion of MWCNTs in TPNR, causing the thermal conductivity of the nanocom‐ posites to increase.

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

**Figure 11.** Thermal Conductivity of TPNR reinforced with UTMWCNTs.

134 Syntheses and Applications of Carbon Nanotubes and Their Composites

**Figure 12.** Thermal Conductivity of TPNR reinforced with TMWCNTs.

Thermal conductivity (W/mk)

**0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45**

Thermal conductivity (W/mK)

30 60 90 120 150 TemperatureOC

TPNR TPNR+1%TMWCNTs TPNR+3%TMWCNTs

TPMR+5%TMWCNTs TPNR+7%TMWCNTs

**30 60 90 120 150** Temperature °C

TPNR TPNR+ 1% UTMWCNTs TPNR+ 3% UTMWCNTs TPNR+ 5% UTMWCNTs

TPNR+ 7% UTMWCNTs

Two factors have been proposed to explain the significant enhancement of thermal conduc‐ tivity with TMWCNTs (1) the rigid linkage between TMWCNTs and TPNR matrix with pro‐ vides good interface compatibility which may reduce interface thermal resistance; (2) the good interface compatibility allows TMWCNTs to disperse well in the matrix, consequently, the results of the TEM indicate that TMWCNTs possess good dispersion and good compati‐ bility in the TPNR matrix.

The formation of the UTMWCNTs bundles restrict the phonon transport in composites, which maybe be attributed to two reasons (1) the UTMWCNTs aggregation reduces the as‐ pect ratio, consequently, decreasing the contact area between the UTMWCNTs and the TPNR matrix; (2) the UTMWCNTs bundles cause the phenomenon of reciprocal phonon vector, which acts like a heat reservoir and restricts heat flow diffusion.

The resistance to phonon movement from one nanotube to another through the junction will hinder phonon movement and, hence, limit the thermal conductivity. The low ther‐ mal conductivity could be partly due to the non-uniform diameter and size, as well as, the defects in and the nano-scale dimension of UTMWNTs. However, the numerous junctions between carbon nanotubes involved in forming a conductive path and the exceptionally low thermal conductance at the interface [42] are believed to be the main reason for the low thermal conductivity.

The effect of reducing the thermal conductivity is the transfer of phonons from nanotube to nanotube. This transition occurs by direct coupling between CNTs, in the case of the im‐ proper impregnated ropes, CNT-junctions and agglomerates, or via the matrix. In all these cases, the transition occurs via an interface and, thus, the coupling losses can be attributed to an intense phonon boundary scattering. At the same time the thermal conductivity decreas‐ es with the increase in temperature (if the temperature is near the melting point of the ma‐ trix). This indicates that the thermal conductivity of the composites is dominated by the interface thermal transport between the nanotube/matrix or nanotube/nanotube interface. Thus, it is believed that the decreased effective thermal conductivity of the studied compo‐ sites could be due to the high interface thermal resistance across the nanotube/matrix or nanotube/nanotube interfaces.

As shown in Figure 11 and Figure 12, the thermal conductivity of TMWCNTs reinforced TPNR matrix composites for all volume fractions studied from 30°C to 150°C is better than UTMWCNTs. The effect of temperature on the thermal conductivity is clear from 30°C to 90°C, as shown in the figures. This is because of the opposing effect of temperature on the specific heat and thermal diffusivity. Eventually, at high temperatures, as the phonon mean free path is lowered, the thermal conductivity of the matrix approaches the lowest limit and the corresponding thermal resistivity approaches the highest limit.

**Figure 13.** TPNR with 1wt% UTMWCNTs.

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**Figure 14.** TPNR with 3wt% UTMWCNTs.

**Figure 15.** TPNR with 7wt% UTMWCNTs.

#### *3.4.3. Morphological Examination*

The TEM can observe the morphology of UTMWCNTs/TPNR and TPNR/TMWCNTs nano‐ composites, which indicates the dispersion abilities of MWCNTs in TPNR matrix before and after treatment of MWCNTs, which summarizes the TEM images of TPNR with 1wt%, 3wt% and 7wt% UTMWCNTs as shown in figure 12-14. Figure 13 shows the good dispersion of 3wt% of UTMWCNTs inside TPNR, and exhibits the better interfacial adhesion of UTMWCNTs and TPNR, Figure 14, 7wt% of UTMWCNTs, shows the poor dispersion and the large UTMWCNTs agglomerates of UTMWCNTs. This is because of the huge surface en‐ ergy of MWCNTs, as well as, the weak interfacial interaction between UTMWCNTs and TPNR, which leads to inhomogeneous dispersion in the polymer matrix and negative effects on the properties of the resulting composites that causes a decrease in the tensile strength. This supports our results for thermal behavior, which due to the kinks or twists of CNTs can affect the thermal conductivity. Therefore, so when the phonon travels along the nanotube and the phonon meets the kinks or twists, it could be blocked at those sites. The existence of those kinks or twists in CNTs would result in a decrease in the effective aspect ratio of nano‐ tubes at 7wt% UTMWCNTs because of agglomeration compared with 3wt% of MWCNTs due to the good dispersion. The homogenous dispersion of TMWCNTs in the composites is confirmed by TEM after acid treatment. Figure 15 shows the 3% TMCWNTs, which are very well dispersed in the matrix, there by suggesting a strong polymer nanotubes interfacial. Strong interfacial adhesion is essential for efficient stress transfer from the matrix to the nanotubes; this supports our observation that the higher efficiency of carbon nanotubes as‐ sists in enhancing the properties of TPNR. Low magnification was necessary to observe the poor dispersion of 7wt% of TMWCNTs in TPNR as depicted in Figure 17. The figure clearly shows a large number of unbroken carbon nanotubes but less than Figure 14, indicating a poor polymer/nanotube adhesion which is attributed to the reduction in the properties of TPNR/MWCNTs nanocompsites.

Characterization and Morphology of Modified Multi-Walled Carbon Nanotubes Filled Thermoplastic Natural Rubber (TPNR) Composite http://dx.doi.org/10.5772/50726 137

**Figure 13.** TPNR with 1wt% UTMWCNTs.

interface thermal transport between the nanotube/matrix or nanotube/nanotube interface. Thus, it is believed that the decreased effective thermal conductivity of the studied compo‐ sites could be due to the high interface thermal resistance across the nanotube/matrix or

As shown in Figure 11 and Figure 12, the thermal conductivity of TMWCNTs reinforced TPNR matrix composites for all volume fractions studied from 30°C to 150°C is better than UTMWCNTs. The effect of temperature on the thermal conductivity is clear from 30°C to 90°C, as shown in the figures. This is because of the opposing effect of temperature on the specific heat and thermal diffusivity. Eventually, at high temperatures, as the phonon mean free path is lowered, the thermal conductivity of the matrix approaches the lowest limit and

The TEM can observe the morphology of UTMWCNTs/TPNR and TPNR/TMWCNTs nano‐ composites, which indicates the dispersion abilities of MWCNTs in TPNR matrix before and after treatment of MWCNTs, which summarizes the TEM images of TPNR with 1wt%, 3wt% and 7wt% UTMWCNTs as shown in figure 12-14. Figure 13 shows the good dispersion of 3wt% of UTMWCNTs inside TPNR, and exhibits the better interfacial adhesion of UTMWCNTs and TPNR, Figure 14, 7wt% of UTMWCNTs, shows the poor dispersion and the large UTMWCNTs agglomerates of UTMWCNTs. This is because of the huge surface en‐ ergy of MWCNTs, as well as, the weak interfacial interaction between UTMWCNTs and TPNR, which leads to inhomogeneous dispersion in the polymer matrix and negative effects on the properties of the resulting composites that causes a decrease in the tensile strength. This supports our results for thermal behavior, which due to the kinks or twists of CNTs can affect the thermal conductivity. Therefore, so when the phonon travels along the nanotube and the phonon meets the kinks or twists, it could be blocked at those sites. The existence of those kinks or twists in CNTs would result in a decrease in the effective aspect ratio of nano‐ tubes at 7wt% UTMWCNTs because of agglomeration compared with 3wt% of MWCNTs due to the good dispersion. The homogenous dispersion of TMWCNTs in the composites is confirmed by TEM after acid treatment. Figure 15 shows the 3% TMCWNTs, which are very well dispersed in the matrix, there by suggesting a strong polymer nanotubes interfacial. Strong interfacial adhesion is essential for efficient stress transfer from the matrix to the nanotubes; this supports our observation that the higher efficiency of carbon nanotubes as‐ sists in enhancing the properties of TPNR. Low magnification was necessary to observe the poor dispersion of 7wt% of TMWCNTs in TPNR as depicted in Figure 17. The figure clearly shows a large number of unbroken carbon nanotubes but less than Figure 14, indicating a poor polymer/nanotube adhesion which is attributed to the reduction in the properties of

the corresponding thermal resistivity approaches the highest limit.

nanotube/nanotube interfaces.

136 Syntheses and Applications of Carbon Nanotubes and Their Composites

*3.4.3. Morphological Examination*

TPNR/MWCNTs nanocompsites.

**Figure 14.** TPNR with 3wt% UTMWCNTs.

**Figure 15.** TPNR with 7wt% UTMWCNTs.

**4. Conclusion**

carbonyl and mainly carboxylic acid.

the amount of both types of MWCNTs.

enhancement.

Recently, it is believed that single-wall carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), coiled nanotubes and carbon nanofibers (CNFs) can be used as filler in the polymer matrix leading to composites with many enhanced properties, especially in mechanical properties. Furthermore, the inclusion of CNTs in a polymer holds the potential to improve the mechanical, electrical or thermal properties by orders of magnitude well above the performance possible with traditional fillers. In addition many researchers re‐ vealed that using functionalized MWCNTs or surface modification of MWCNTs as filler en‐ hanced the properties of nanocomposites. This enhancement was probably suggested because of the homogenous dispersion and stronger interaction between the MWCNTs and the polymer matrix. After being treated with an acid, some functional groups were intro‐ duced onto the MWCNTs surface, which can form a physical interaction with the polymer chain. In this chapter, the effect of multi-walled carbon nanotubes with and without acid treatment on the properties of thermoplastic natural rubber (TPNR) was investigated. Two types of MWCNTs were introduced into TPNR, which are untreated UTMWCNTs (without acid treatment) and treated TMWCNTs (with acid treated MWCNTs). The acid treatment of MWCNTs removed catalytic impurities and generated functional groups such as hydroxyl,

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The results in this chapter show that the properties of MWCNTs can be improved by using this method. The TEM micrograph has shown that the effect of acid treatment has rough‐ ened the MWCNTs surface and also reduced the agglomeration. Various functional groups have been confirmed using FTIR. The TPNR nanocomposite was prepared using the melt blending method. MWCNTs are incorporated in the TPNR nanocomposite at different com‐ positions which is 1, 3, 5 and 7 wt%. The addition of MWCNTs in the TPNR matrix im‐ proved the mechanical properties. At 3wt%, the tensile strength and Young's modulus of TPNR/UTMWCNTs increased 23% and 22%, respectively. For TPNR/TMWCNTs the opti‐ mum result of tensile strength and Young's modulus was recorded at 3% which increased 39% and 34%, respectively. In the addition the elongation of break decreased by increasing

The results exhibited better impact strength for UTMWCNT and TMWCNT at 3 wt% with an increase of almost 46 % and 82%, respectively. The reinforcing effect of two types of MWCNTs was also confirmed by dynamic mechanical analysis where the addition of MWCNTs have increased in the glass transition temperature (Tg) with an increase in the amount of MWCNTs (optimum at 3wt %) and it increased with the TMWCNTs more than the UTMWCNTs. Thermal conductivity improved with TMWCNTs compared to the UTMWCNTs. The homogeneous dispersion of two types of the MWNTs throughout the TPNR matrix and strong interfacial adhesion between the MWCNTs and the matrix as con‐ firmed by the TEM images are proposed to be responsible for the significant mechanical

**Figure 16.** TPNR with 1wt% TMWCNTs.

**Figure 17.** TPNR with 3wt% TMWCNTs.

**Figure 18.** TPNR with 7wt% TMWCNTs.
