## 4 Qualitative Discussion
### Knowledge Gaps and Considerations for Further Research  
Using residual lignins to develop more eco-efficient products is a relevant strategy for emerging economies, especially those with large biomass availability, such as Brazil and India, which have great potential for producing LBAs. The LBAs manufacture contributes to recovering residual lignins from different industrial processes. In addition, the use of LBAs aids in mitigating greenhouse gas emissions, especially because these compounds replace commercial admixtures produced with raw materials from the petrochemical sector. Figure 8 shows a comparative profile of the content of the 37 articles selected for the qualitative discussion. The authors separate the information related to the type and source of the technical lignins used to produce the LBAs (raw material and industrial sector) and the characteristics of the experimental procedures performed (cement matrix and analyzes). Results show that at least 65% of the studies on new LBAs used lignins generated in pulp and paper mills. Biorefineries lignins, in turn, need higher valorization in this research area. Previous studies demonstrated the feasibility of producing chemical admixtures from lignocellulosic biomass generated in biorefineries [28; 31; 69]. In this sense, the LBAs research can offer fundamental strategies for waste management in biorefineries, considering the high availability of biomass jointly with the increasing development of biofuels in the industry [45]. As expected, Kraft lignin is the most studied technical lignin in LBAs research. On the other hand, Organosolv lignins still need further studies on their modification and improvement of surfactant properties. Due to their high purity and the feasibility of being generated from a sustainable delignification process, Organosolv lignins are becoming popular and valued in the global market [3; 8]. Thus, developing new LBAs from Organosolv lignins generated by green chemistry approaches in the context of biorefineries is a research topic that needs to be explored. The use of residual black liquors is another strategy for producing new LBAs. This strategy aids in avoiding the improper disposal of black liquors and reduces costs in LBAs production since fewer modification processes are necessary. Previous studies used residual black liquors from different delignification processes to produce LBAs [20; 25; 68]. However, Figure 8 shows that these studies correspond to only 13% of the published articles on new LBAs, demonstrating that there is still room for further research. The LBAs research has a multidisciplinary character and must involve different tests and analyses. The science mapping allowed the identification of various journals related to civil engineering that publish on LBAs (see Table 1). However, most of the works involve commercial lignocellulosic-based admixtures. Discussions about the production and testing of new LBAs are more frequent in chemical engineering, materials engineering, and agricultural sciences journals. As a possible consequence, 92% of the studies on new LBAs performed a polymer characterization, while only 49% investigated the mechanical strength and 22% investigated the physical properties of LBA-containing composites. Mechanical and physical analyses of hardened cement matrices are essential to verify the feasibility of using LBAs and should be considered for near-future research on LBAs applied to cement-based composites. In addition, Figure 8 shows that only 22% of the studies on new LBAs analyzed the hydration properties of the cement matrices. Investigations on the hydration profile of LBA-containing composites (e.g., calorimetric and setting time analyses) are mandatory to assess the influence of LBAs on cement hydration since LBAs may present set-retarding properties. Results show that only 46% of the studies on LBAs were performed in concrete and mortar.