## 7 Conclusions  
Different approaches on synthesizing non-isocyanate polyurethanes (NIPUs) from lignin and tannin were comprehensively presented. Lignin and tannin have the potential to be used as an alternative material for polyols in the manufacture of polyurethane as wood adhesives. The polycondensation pathway synthesis of NIPUs is linked to the reaction between di-or polycarbamates and diols, di-or polycarbonates and amino alcohols or diamines, polychloroformate and polyamines, as well as polycarbamoyl chloride and polyol. Carbonation of lignin and tannin with dimethyl carbonate and a further reaction with hexamethylene diamine was reported, resulting in NIPUs based on lignin and tannin. Several studies confirmed that they have good characteristics as an alternative to the petroleum components concerned. The addition of Na\({}_{2}\)SO\({}_{3}\), KH560 (Silane coupling agent), and NaIO\({}_{4}\) could enhance the adhesion strength of lignin-based NIPUs adhesives, while the incorporation of cellulose nanofibers and furfuryl alcohol remarkably improved the adhesion performance of tannin-based NIPUs.  
The development of a non-isocyanate method for the production of NIPUs and their application in wood-based composites and plastic industry industries were also outlined. Different chemical approaches have been explored to synthesize new polyols and multi-isocyanates with triglycerides or fatty acids as starting materials. 5,5-dihydroxyroximethyl furoin, 5,5-bihydroxymethyl furil, and 5,5-bihydroxymethyl hydrofuroin could be converted into NIPUs. Oleic acid could also be used to manufacture 1,7-heptamethylene diisocyanate and 1,16-diisocyanateohex-8-ene. The properties of NIPUs based on 1,7-heptamethylene diisocyanate-derived oleic acid are similar to those of petroleum-derived 1,6-hexamethylene diisocyanate. Further, the NIPUs-based on 1,16-diisocyanateohex-8-ene exhibited an even higher tensile strength than those typically derived from petroleum-based 1,7-heptamethylene diisocyanate. All the above examples demonstrate that bio-renewable products can be used to produce NIPUs as an alternative to the petroleum-derived polyol and polyisocyanate.  
Methodology, M.A.A., M.A.R.L.; validation, M.A.R.L., S.M.Y., W.F., A.H.I., and M.I.; investigation, M.A.A., M.A.R.L., W.F., A.H.I, M.I., and P.A.; writing--original draft preparation, M.A.A., M.A.R.L., W.F., A.H.I., M.I, and P.A.; writing--review and editing, M.A.R.L., S.M.Y., A.P., P.A., and A.N.P.; visualization, M.A.R.L. and P.A.; supervision, M.A.R.L., A.P., and A.N.P. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
Authors are grateful to the research grant from Ministry of Research and Technology of Indonesia (No. 172/E1/PRN/2020) for the financial support and the Integrated Laboratory of Bioproducts (iLaB), Research Center for Biomaterials, and Indonesia Institute of Sciences for the facilities support. This publication is also supported by Deputy for Strengthening Research and Development, Ministry of Research and Technology/National Research, and Innovation Agency year of 2021, with a grant for research title \"Karakteristik Komponent Rumah Berbasis Komposit Panel Kayu Tahan Api\". This publication is also the result of the implementation of the project No. HHC-B-1145/04.2021 \"Development, Properties and Application of Eco-Friendly Wood-Based Composites\" carried out at the University of Forestry, Sofia, Bulgaria.  
The authors declare no conflict of interest.