## 4 Results and Discussion
### DSC Results  
The glass transition temperature (T\({}_{\mathrm{g}}\)) and crystallinity are two (2) important parameters that can be determined from differential scanning calorimetry (DSC) test results of bitumen samples. T\({}_{\mathrm{g}}\) is the temperature at which the bitumen transitions from a glassy state to a rubbery state, and it can be determined from the onset of the slope change in the heat flow curve that occurs during heating. Crystallinity, on the other hand, is the measure of the degree of crystalline fraction in bitumen, and it can be determined by comparing the measured heat of fusion to the theoretical heat of fusion. These parameters are crucial for understanding the thermal properties of bitumen, which in turn can affect the performance of asphalt pavement. The effects of Kraft lignin modification and blending conditions on the thermal properties of bitumen are discussed by comparing the T\({}_{\mathrm{g}}\) and crystallinity values of all samples (Figure 16). Figure 15: (a) TG and (b) DTG thermograms of VB, VB-HSM, 5L-HSM, 10L-HSM, and 20L-HSM samples on the operational temperature of the asphalt mix. As shown in Figure 17, the T\({}_{\rm g}\) values of the bitumen samples are obtained from the DSC analysis. In terms of blending conditions, it is observed that the T\({}_{\rm g}\) of the VB-HSM and VB-MM samples is \(-29.3\), and \(-29.9\)\({}^{\circ}\)C, respectively, which is lower than the VB sample (\(-29.2\)\({}^{\circ}\)C). This suggests that the blending conditions have a small impact on the physical properties of bitumen. In terms of the Kraft lignin effect, it is observed that the T\({}_{\rm g}\) of the HSM samples decreases as the Kraft lignin percentage increases, whereas the T\({}_{\rm g}\) of the MM samples remains relatively constant with increasing Kraft lignin content. This suggests that the effect of Kraft lignin on the T\({}_{\rm g}\) of bitumen is dependent on the blending conditions. The decrease in T\({}_{\rm g}\) with increasing Kraft lignin content in the HSM samples can be attributed to the increased interaction between the Kraft lignin and bitumen molecules due to the high shear rate. It is important to note that from the FTIR test results (Section 4.3), even if there is no chemical reaction between Kraft lignin and bitumen in HSM samples, the two components may still exhibit some degree of miscibility or compatibility with each other, which can also affect the T\({}_{\rm g}\) of the modified bitumen. It is important to acknowledge that the observed differences in T\({}_{\rm g}\) values among the samples are relatively small, within 1 \({}^{\circ}\)C. While these differences may not be as pronounced as in other studies [66; 67], they still provide valuable insights into the low-temperature behavior of modified bitumen. In conclusion, the DSC analysis of the bitumen samples shows that the blending conditions and Kraft lignin content have a small, but positive impact on the glass transition temperature (T\({}_{\rm g}\)) of bitumen (lower values than VB). These results suggest that the incorporation of Kraft lignin in bitumen can be an effective method to modify the physical properties of bitumen, but the blending conditions must be carefully controlled to achieve the desired effect. Figure 16: Glass transition temperature (T\({}_{\rm g}\)) and crystallization fraction of virgin bitumen using TM-DSC technique (T\({}_{\rm i}\) and T\({}_{\rm f}\) represent the initial and final temperatures, respectively, used to calculate the crystalline fraction). The calculation of the crystallizable fraction (%) is performed to determine the content of the crystalline fraction in the VB and lignin-modified bitumen samples. Table 5 shows that there is not a significant change in the crystallizable fraction with the addition of Kraft lignin and blending conditions. A higher crystallizable fraction (yellow zone in Figure 16) indicates a greater degree of crystalline structure within the bitumen.