**6. Results and discussion**

#### **6.1. Thermal analysis by DSC**

Heating the polymers results in a number of phase changes such as the glass transition (*T<sup>g</sup>* ), crystallization transition (*T<sup>c</sup>* ), and melting point (*Tm*). DSC analysis is a useful technique to identify the location of these thermal parameters. In the DSC curves, the sharp peaks are related to the polymer melting and the areas under these peaks provide the heat of fusion (∆*H*). Furthermore, the smaller inconsistencies at the lower temperature are most likely related to the glass transition.

In this research, DSC technique is used to investigate the transition temperatures and the crystallization degree of different polymers. Accordingly, the DSC curves were examined to evaluate the physical characteristics of individual materials. It should be noted that for DSC runs, the complete set of heating-cooling process were repeated three times for each polymer, where the first run is usually carried out to remove any impurities and moisture from the sample. In addition, in order to evaluate the transitions accurately, a temperature scan over a wide range temperature is considered for DSC analysis.

In DSC analysis, the thermal parameters for bitumen depend on the refined petroleum source as well as the petroleum refining process. **Figure 6** shows the DSC thermograph of neat bitumen and its corresponding first-derivative curve. The effects detected in the thermograph, as assigned previously (for example, see [28–30]), are described below.

An increase in the heat capacity for neat bitumen can be observed in the DSC curve by an abrupt change in the slope of the curve placed in the low-temperature region (around −30°C) corresponding to the glass transition temperature (*T<sup>g</sup>* ) of the bitumen. The glass transition temperature (*T<sup>g</sup>* ) is a material's temperature at which all molecular transitional motion is frozen; therefore, the material becomes rigid and brittle at or below this temperature. The glass transition temperature of polymers is one of the most important parameters as it is related to the average molecular weight of polymers and hence provides information about their composition. Moreover, it demonstrates the viscoelastic behavior of polymers at low temperatures [31]. Therefore, the glass transition temperature of neat bitumen is believed to be closely related to the low-temperature performance of asphalts. As shown in **Figure 6**, the middle point of the temperature range where the transition occurs is considered as the

To achieve DSC curve for rubber, similar to bitumen, three cycles of cooling and heating were considered as the method of the experiment with the same heating rate of 10°C/min, cooling

Evaluation of Structural and Thermal Properties of Rubber and HDPE for Utilization as Binder Modifier

The DSC thermograph of rubber (**Figure 7**) presented a glass transition temperature (*T<sup>g</sup>*

−55° C. However, due to amorphous nature of rubber, DSC curve does not present a well-

For HDPE DSC analysis, as shown in **Figure 8**, it can be observed that HDPE started to lose its solid form at around −100°C corresponding to the glass transition temperature (*<sup>T</sup> <sup>g</sup>*

HDPE. As the temperature increases, a strong endothermic peak average value at 134°C can be observed, which is most likely related to the melting of crystalline domains of HDPE.

The DSC curve of HDPE in second heating cycle is illustrated in **Figure 9**. As can be observed, the energy consumption for melting of crystalline domain of HDPE was 221.1 J/g that occurred

The cooling cycle involves the rate of cooling temperature of 10°C /min. As shown in **Figure 10**, the peak point for HDPE becomes totally solid at around 115°C, which means that the crystal-

been found from literature for HDPE (for example, see [34, 35]). The calculation of the crystal-

It should be noted that fully crystalline polymers do not exhibit glass transition temperature, and their structure will not change until the melting point. However, according to DSC ther-

) at

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) of

of 287.3 J/g has

rate of −10°C/min, and temperature range of −100–200°C.

between the beginning and end of melting point.

lization temperature (Tc) of HDPE, an exothermic peak, is 115°C.

lizable fraction content for HDPE shows a value of about 76%.

mographs, HDPE is considered as semicrystalline polymer.

**Figure 7.** DSC and DDSC thermograms of rubber.

To estimate the amount of crystallized fraction of HDPE, the values of ∆Ho

defined melting temperature.

**Figure 6.** DSC and DDSC thermograms of bitumen.

glass transition temperature. In addition, as shown in **Figure 6**, *Tgonset* of bitumen is at about −40°C. Referring to [32], the *Tgonset* temperature is more closely related to the glass transition temperature of the saturate fraction that has the lowest *T<sup>g</sup>* . The main *T<sup>g</sup>* reflects the characteristics of the glass transition temperature of the majority of components.

At temperature above *T<sup>g</sup>* , an exothermal peak and a broad endothermal peak from about −20 to 85°C is observed. The big exothermal peak next to the glass transition is most likely the result of crystallization of small paraffin molecules, and melting of the crystallites formed during heating or cooling is known as the main reason to produce endothermal peaks in this region [32].

Referring to [31], the exothermic effect just above the *T<sup>g</sup>* in DSC thermographs is negligible, as it has been associated in previous studies (for example, see [28, 30]) with the crystallization of certain molecules, which are not crystallized during cooling.

In addition, referring to the literature (for example, see [25, 28–30, 33]), the dissolution of the crystallized fractions (CF) is the main reason of the enthalpy changes and can be calculated from the area under the peak to a reference enthalpy of dissolution. As shown in **Figure 6**, in order to calculate this parameter, a straight baseline between the end of the glass transition and the end of the endothermic effects is drawn. In this research, the reference enthalpy value of 180 J/g is used for the estimation of the amount of crystallized fraction of bitumen based on previous investigations [1, 4, 15, 25, 26, 33]. The calculation of the crystallizable fraction content shows a value of about 4%, which is considered small. The presence of wax content in bitumen is commonly responsible for the extent of crystallizable fractions, which is the main reason for the problem of pavement exudation and inappropriate thermal susceptibility [15].

To achieve DSC curve for rubber, similar to bitumen, three cycles of cooling and heating were considered as the method of the experiment with the same heating rate of 10°C/min, cooling rate of −10°C/min, and temperature range of −100–200°C.

The DSC thermograph of rubber (**Figure 7**) presented a glass transition temperature (*T<sup>g</sup>* ) at −55° C. However, due to amorphous nature of rubber, DSC curve does not present a welldefined melting temperature.

For HDPE DSC analysis, as shown in **Figure 8**, it can be observed that HDPE started to lose its solid form at around −100°C corresponding to the glass transition temperature (*<sup>T</sup> <sup>g</sup>* ) of HDPE. As the temperature increases, a strong endothermic peak average value at 134°C can be observed, which is most likely related to the melting of crystalline domains of HDPE.

The DSC curve of HDPE in second heating cycle is illustrated in **Figure 9**. As can be observed, the energy consumption for melting of crystalline domain of HDPE was 221.1 J/g that occurred between the beginning and end of melting point.

The cooling cycle involves the rate of cooling temperature of 10°C /min. As shown in **Figure 10**, the peak point for HDPE becomes totally solid at around 115°C, which means that the crystallization temperature (Tc) of HDPE, an exothermic peak, is 115°C.

To estimate the amount of crystallized fraction of HDPE, the values of ∆Ho of 287.3 J/g has been found from literature for HDPE (for example, see [34, 35]). The calculation of the crystallizable fraction content for HDPE shows a value of about 76%.

It should be noted that fully crystalline polymers do not exhibit glass transition temperature, and their structure will not change until the melting point. However, according to DSC thermographs, HDPE is considered as semicrystalline polymer.

**Figure 7.** DSC and DDSC thermograms of rubber.

glass transition temperature. In addition, as shown in **Figure 6**, *Tgonset* of bitumen is at about −40°C. Referring to [32], the *Tgonset* temperature is more closely related to the glass transition

to 85°C is observed. The big exothermal peak next to the glass transition is most likely the result of crystallization of small paraffin molecules, and melting of the crystallites formed during heating or cooling is known as the main reason to produce endothermal peaks in this

it has been associated in previous studies (for example, see [28, 30]) with the crystallization of

In addition, referring to the literature (for example, see [25, 28–30, 33]), the dissolution of the crystallized fractions (CF) is the main reason of the enthalpy changes and can be calculated from the area under the peak to a reference enthalpy of dissolution. As shown in **Figure 6**, in order to calculate this parameter, a straight baseline between the end of the glass transition and the end of the endothermic effects is drawn. In this research, the reference enthalpy value of 180 J/g is used for the estimation of the amount of crystallized fraction of bitumen based on previous investigations [1, 4, 15, 25, 26, 33]. The calculation of the crystallizable fraction content shows a value of about 4%, which is considered small. The presence of wax content in bitumen is commonly responsible for the extent of crystallizable fractions, which is the main reason for the problem of pavement exudation and inappropriate thermal

. The main *T<sup>g</sup>*

, an exothermal peak and a broad endothermal peak from about −20

reflects the characteris-

in DSC thermographs is negligible, as

temperature of the saturate fraction that has the lowest *T<sup>g</sup>*

**Figure 6.** DSC and DDSC thermograms of bitumen.

Referring to [31], the exothermic effect just above the *T<sup>g</sup>*

certain molecules, which are not crystallized during cooling.

At temperature above *T<sup>g</sup>*

region [32].

120 Modified Asphalt

susceptibility [15].

tics of the glass transition temperature of the majority of components.

**Figure 8.** DSC and DDSC thermograms of HDPE for heating cycles.

to evaluate the thermal stability of materials. Hence, in this research, the thermal stability of three polymers was studied by TGA in air and the main features of the curves including the

Evaluation of Structural and Thermal Properties of Rubber and HDPE for Utilization as Binder Modifier

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123

For bitumen, the thermogravimetric experiment results for 5 mg samples under air atmosphere over the temperature range of 30–590°C using a total purge gas flow of 100 mL/min and a heating rate of 10°C·min−1 show that the onset temperature of the main mass loss effect

) were calculated

onset temperatures of the mass loss effects (*TO*) and the peak temperatures (*Tp*

**Figure 10.** DSC and DDSC thermograms of HDPE for cooling cycles.

from the TGA and DTG curves.

(TO) is 370°C, as shown in **Figure 11**.

**Figure 11.** TGA, DTG, and D2TG thermograms of neat bitumen.

**Figure 9.** DSC and DDSC thermograms of HDPE for second heating cycle.

In addition, as HDPE has higher molecular weight than bitumen, the melting and crystallization temperature of HDPE is higher to provide more energy for reaching to these points. In addition, the melting and crystallization temperature of HDPE are close to each other, which can be confirmed from literature survey [36].

#### **6.2. Thermal analysis by TGA**

The thermal stability of polymers is an important property to be considered for fitting their performance to the proper final application. Thermogravimetric analysis is a good technique Evaluation of Structural and Thermal Properties of Rubber and HDPE for Utilization as Binder Modifier http://dx.doi.org/10.5772/intechopen.75535 123

**Figure 10.** DSC and DDSC thermograms of HDPE for cooling cycles.

to evaluate the thermal stability of materials. Hence, in this research, the thermal stability of three polymers was studied by TGA in air and the main features of the curves including the onset temperatures of the mass loss effects (*TO*) and the peak temperatures (*Tp* ) were calculated from the TGA and DTG curves.

For bitumen, the thermogravimetric experiment results for 5 mg samples under air atmosphere over the temperature range of 30–590°C using a total purge gas flow of 100 mL/min and a heating rate of 10°C·min−1 show that the onset temperature of the main mass loss effect (TO) is 370°C, as shown in **Figure 11**.

**Figure 11.** TGA, DTG, and D2TG thermograms of neat bitumen.

**Figure 9.** DSC and DDSC thermograms of HDPE for second heating cycle.

**Figure 8.** DSC and DDSC thermograms of HDPE for heating cycles.

122 Modified Asphalt

can be confirmed from literature survey [36].

**6.2. Thermal analysis by TGA**

In addition, as HDPE has higher molecular weight than bitumen, the melting and crystallization temperature of HDPE is higher to provide more energy for reaching to these points. In addition, the melting and crystallization temperature of HDPE are close to each other, which

The thermal stability of polymers is an important property to be considered for fitting their performance to the proper final application. Thermogravimetric analysis is a good technique

**Figure 12.** TGA, DTG, and D2TG thermograms of rubber.

Referring to [31], the decomposition of bitumen occurs in at least three steps, considering three temperature ranges, as shown in **Figure 11**. In the temperature range of T < 350°C, the decomposition of saturates and aromatics results in mass loss of bitumen. Over the temperature range of 350 < T < 500°C, resins and aromatics as well as asphaltenes are the main decomposed fractions, and at high temperatures of T > 500°C, the substantial mass change in bitumen occurs as a result of decomposition of asphaltenes. However, resins and aromatics are still decomposed in this range of temperature.

462°C in the DTG curve. This degradation involves a mass loss of about 91% in HDPE due to the thermal cracking of hydrocarbon chains and the production of oxygenated hydrocarbons

The analysis of the microstructure of polymers was performed using scanning electron microscope (SEM). The results of the microscopy of as well as the energy dispersive spectroscopy

As can be observed in **Figure 14**, the surface of bitumen appears as networks of highly entan-

(EDS) analysis on the individual polymers are given in **Figures 14**–**16**.

**Figure 14.** EDS analysis and SEM image of bitumen at 400 magnification.

O [37]. The degradation ends approximately around 490°C.

Evaluation of Structural and Thermal Properties of Rubber and HDPE for Utilization as Binder Modifier

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125

including CO, CO<sup>2</sup>

gled strings.

, and H2

**Figure 13.** TGA, DTG, and D2TG thermograms of HDPE.

**6.3. Microstructure analysis by SEM**

When selecting materials for modifying the binder, it is important that the modifier begins to degrade at a temperature above the bitumen modification temperature or the asphalt production temperature. Otherwise, it will lose its initial properties by the time the modification process is finished. In this research, TGA is used for determination of the degradation temperature of the waste materials, which are used for modifying the binder (i.e., rubber and HDPE). **Figure 12** shows the result of TGA on rubber.

As can be seen, the onset temperature of degradation for rubber is 238°C and the peak temperature of mass loss is 378°C, which can be observed as a peak in the first-derivative curve.

Similar to other polymers, TGA of the HDPE samples was done on approximately 5 mg samples over the range of room temperature to 590°C under air with 100 mL/min flow rate at a heating rate of 10°C·min−1.

The onset degradation temperature and peak temperature are determined from the derivative TGA curves for HDPE, as shown in **Figure 13**. In this figure, it can be observed that HDPE remains thermally stable up to a temperature of 430°C. After this temperature, HDPE starts to degrade dramatically followed by a substantial step with maximum mass loss rates placing at Evaluation of Structural and Thermal Properties of Rubber and HDPE for Utilization as Binder Modifier http://dx.doi.org/10.5772/intechopen.75535 125

**Figure 13.** TGA, DTG, and D2TG thermograms of HDPE.

462°C in the DTG curve. This degradation involves a mass loss of about 91% in HDPE due to the thermal cracking of hydrocarbon chains and the production of oxygenated hydrocarbons including CO, CO<sup>2</sup> , and H2 O [37]. The degradation ends approximately around 490°C.

#### **6.3. Microstructure analysis by SEM**

**Figure 12.** TGA, DTG, and D2TG thermograms of rubber.

124 Modified Asphalt

are still decomposed in this range of temperature.

HDPE). **Figure 12** shows the result of TGA on rubber.

a heating rate of 10°C·min−1.

Referring to [31], the decomposition of bitumen occurs in at least three steps, considering three temperature ranges, as shown in **Figure 11**. In the temperature range of T < 350°C, the decomposition of saturates and aromatics results in mass loss of bitumen. Over the temperature range of 350 < T < 500°C, resins and aromatics as well as asphaltenes are the main decomposed fractions, and at high temperatures of T > 500°C, the substantial mass change in bitumen occurs as a result of decomposition of asphaltenes. However, resins and aromatics

When selecting materials for modifying the binder, it is important that the modifier begins to degrade at a temperature above the bitumen modification temperature or the asphalt production temperature. Otherwise, it will lose its initial properties by the time the modification process is finished. In this research, TGA is used for determination of the degradation temperature of the waste materials, which are used for modifying the binder (i.e., rubber and

As can be seen, the onset temperature of degradation for rubber is 238°C and the peak temperature of mass loss is 378°C, which can be observed as a peak in the first-derivative curve. Similar to other polymers, TGA of the HDPE samples was done on approximately 5 mg samples over the range of room temperature to 590°C under air with 100 mL/min flow rate at

The onset degradation temperature and peak temperature are determined from the derivative TGA curves for HDPE, as shown in **Figure 13**. In this figure, it can be observed that HDPE remains thermally stable up to a temperature of 430°C. After this temperature, HDPE starts to degrade dramatically followed by a substantial step with maximum mass loss rates placing at The analysis of the microstructure of polymers was performed using scanning electron microscope (SEM). The results of the microscopy of as well as the energy dispersive spectroscopy (EDS) analysis on the individual polymers are given in **Figures 14**–**16**.

As can be observed in **Figure 14**, the surface of bitumen appears as networks of highly entangled strings.

**Figure 14.** EDS analysis and SEM image of bitumen at 400 magnification.

due to poor performance of asphalt binders, as well as to increase the PG grade of the asphalt binder [38]. Based on these research studies, the utilization of polymers as modifier improves some of the bitumen's properties such as elasticity, cohesion, and temperature susceptibility, which they all subsequently lead to the improvement of asphalt mixture performance.

Evaluation of Structural and Thermal Properties of Rubber and HDPE for Utilization as Binder Modifier

For these reasons, and as a quite effective way of disposing of the increasing volume of nonbiodegradable wastes, which are increasingly generated in societies, plastic wastes and rub-

In modification of bitumen with additives, having knowledge about the effects of modifiers on thermal stability is of high importance resulting in manufacturing more thermally stable binders. Accordingly, in this research, the thermal behavior of modifiers and bitumen was

fusion, <sup>∆</sup> *Hm*, and the percentage of crystallinity, CF (%) of samples can be easily determined from the DSC curves. This information can be useful in understanding the characteristics and the composition of polymers. In addition, many researchers have proposed different equations for estimation of the glass transition temperature of mixture based on the composition and the glass transition of the components of the mixture. All these equations are basically representing the relation between the glass transition temperature of a mixture and those of its components using a basic mathematical form but with minor variations. The glass transition calculated using these equations for the blend of bitumen with 2% HDPE and 8% rubber

which could be attributed to several effects including certain level of miscibility between the additives (i.e., HDPE and rubber) and bitumen. Thus, using these equations, it may be possible to achieve the formulation of the desired modified binder considering the composition

Furthermore, in this research, TGA is used in determining the degradation temperature of the waste materials. A modifier that begins to degrade at a temperature below the bitumen modification temperature or the asphalt production temperature is not adequate since it will have lost its initial properties by the time the modification process is finished. In the case of analyzed waste materials, all degrade at temperatures above 200°C and therefore should be adequate for bitumen modification. The main features of TGA curves for individual polymers were discussed in previous sections. From these results, it was observed clearly that HDPE

The authors would like to acknowledge the Advanced Materials Characterization Facility

value for blend is lower than those obtained for neat bitumen,

and T m, enthalpy of

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bers can be a reasonable potential materials for consideration as binder modifier.

studied using TGA, DSC, and SEM facilities. The thermal parameters of Tg

of components and the results of DSC analysis on each component.

followed by bitumen have higher thermal stability than crumb rubber.

(AMCF) at Western Sydney University for their expert technical assistance.

is −28.8°C. The calculated *T<sup>g</sup>*

**Acknowledgements**

**Conflict of interest**

The authors declare no conflict of interest.

**Figure 15.** EDS analysis and SEM image of rubber at 400 magnification.

**Figure 16.** EDS analysis and SEM image of HDPE at 400 magnification.

**Figure 15** shows the coarse texture of rubber. The irregular shape and rough texture of rubber can be attributed to its processing method, which is the ambient procedure.

Furthermore, the microstructure of HDPE is shown in **Figure 16**. It should be noted that HDPE has a higher viscosity compared to bitumen. The materials with high viscosity do not separate easily, and therefore, they present in the form of dispersed phase, as can be clearly observed in **Figure 16**.

### **7. Summary and conclusion**

Today, pure bitumen no longer provides suitable performance for pavements due to the current traffic. Therefore, attempts have been made to maximize the effectiveness of asphalt binders selected for construction projects based on a standard asphalt binder classification system. Binder modification technique is used as an alternative to minimize the pavement failures due to poor performance of asphalt binders, as well as to increase the PG grade of the asphalt binder [38]. Based on these research studies, the utilization of polymers as modifier improves some of the bitumen's properties such as elasticity, cohesion, and temperature susceptibility, which they all subsequently lead to the improvement of asphalt mixture performance.

For these reasons, and as a quite effective way of disposing of the increasing volume of nonbiodegradable wastes, which are increasingly generated in societies, plastic wastes and rubbers can be a reasonable potential materials for consideration as binder modifier.

In modification of bitumen with additives, having knowledge about the effects of modifiers on thermal stability is of high importance resulting in manufacturing more thermally stable binders. Accordingly, in this research, the thermal behavior of modifiers and bitumen was studied using TGA, DSC, and SEM facilities. The thermal parameters of Tg and T m, enthalpy of fusion, <sup>∆</sup> *Hm*, and the percentage of crystallinity, CF (%) of samples can be easily determined from the DSC curves. This information can be useful in understanding the characteristics and the composition of polymers. In addition, many researchers have proposed different equations for estimation of the glass transition temperature of mixture based on the composition and the glass transition of the components of the mixture. All these equations are basically representing the relation between the glass transition temperature of a mixture and those of its components using a basic mathematical form but with minor variations. The glass transition calculated using these equations for the blend of bitumen with 2% HDPE and 8% rubber is −28.8°C. The calculated *T<sup>g</sup>* value for blend is lower than those obtained for neat bitumen, which could be attributed to several effects including certain level of miscibility between the additives (i.e., HDPE and rubber) and bitumen. Thus, using these equations, it may be possible to achieve the formulation of the desired modified binder considering the composition of components and the results of DSC analysis on each component.

Furthermore, in this research, TGA is used in determining the degradation temperature of the waste materials. A modifier that begins to degrade at a temperature below the bitumen modification temperature or the asphalt production temperature is not adequate since it will have lost its initial properties by the time the modification process is finished. In the case of analyzed waste materials, all degrade at temperatures above 200°C and therefore should be adequate for bitumen modification. The main features of TGA curves for individual polymers were discussed in previous sections. From these results, it was observed clearly that HDPE followed by bitumen have higher thermal stability than crumb rubber.
