## 5 Conclusions  
In this study, the chemo-thermal characteristics of lignin-modified bitumen were investigated with different percentages (5, 10, and 20%) of Kraft lignin under 2 blending protocols, including mechanical mixer (MM) and high-shear mixer (HSM). The results obtained from various tests, including Brookfield Rotational Viscosity (BRV), Dynamic Shear Rheometer (DSR), Fourier-Transform Infrared Spectroscopy (FTIR), Environmental Scanning Electron Microscopy (ESEM), Thermogravimetric Analysis (TGA), and Differential Scanning Calorimetry (DSC), provided valuable insights into the effect of blending conditions and properties of lignin-modified bitumen. The findings of the study are as follows. In terms of the influence of blending conditions:  
* The MM-produced samples result in higher viscosity and \(\mid\!\! * The addition of Kraft lignin increases the viscosity, stiffness, high-temperature stability, and \(\mid\)G*\(\mid\)/sin(6) value of bitumen (Sections 4.1 and 4.2);
* The addition of Kraft lignin alters the chemical structure of the modified bitumen without causing chemical reactions (Section 4.3). Moreover, increasing the amount of Kraft lignin in the samples leads to a more widespread distribution of Kraft lignin particles within the fibril structure, with no aggregation of Kraft lignin particles, here, for mass contents up to 20% (Section 4.4);
* The addition of Kraft lignin to bitumen decreases the thermal stability. A thermal event observed at 131 \({}^{\circ}\)C in the 20L-HSM sample suggests a possible interaction between Kraft lignin and bitumen at higher Kraft lignin content (20%), leading to the formation of a new phase (Section 4.5);
* The miscibility or compatibility between Kraft lignin and bitumen, even without chemical reaction, may slightly influence the Tg of modified bitumen, whereas the crystallizable fraction remains relatively constant across the lignin-modified bitumen samples (Section 4.6). Finally, this study highlights the potential of Kraft lignin as a bitumen modifier and emphasizes the influence of blending protocols and Kraft lignin content on the performance and properties of lignin-modified bitumen. The choice of the mixer can have a significant impact on the quality and characteristics of the lignin-modified bitumen in terms of blending Kraft lignin with bitumen. While a mechanical mixer may be sufficient for some additives, a high-shear mixer can provide more consistent and higher-quality results for Kraft lignin. The findings contribute to the development of environmentally friendly approaches in the asphalt industry by utilizing waste materials as modifiers. Further research is required to optimize the blending process. Further improvements can be made in the study of lignin-modified bitumen. It is essential to investigate TGA-FTIR, which provides a more comprehensive understanding of the chemical changes occurring during the thermal degradation process. To enhance future research in this area, considering additional analytical techniques are recommended, such as the determination of carbonyl and sulfoxide indices using FTIR, and the kinematic effect of lignin-modified bitumen through TGA. The results of this study are part of an ongoing effort and larger project to investigate the feasibility and performance of incorporating lignin into modified and unmodified bitumens, and cold, warm, and hot mix asphalts, and future publications will cover these aspects. Conceptualization, A.R.G. and A.C.; methodology, A.R.G., A.C. and A.M.; software, A.R.G. ; validation, A.R.G., A.C., J.-P.B., S.L. and A.M.; formal analysis, A.R.G. ; investigation, A.R.G. ; resources, A.R.G. ; data curation, A.R.G. ; writing--original draft preparation, A.R.G. ; writing--review and editing, S.L., A.C., J.-P.B. and A.M.; visualization, A.R.G. ; supervision, A.C. and J.-P.B. ; project administration, A.C., S.L. and J.-P.B. ; funding acquisition, J.-P.B. and A.C. All authors have read and agreed to the published version of the manuscript.