*Article* **Emulsion Stabilization by Cationic Lignin Surfactants Derived from Bioethanol Production and Kraft Pulping Processes**

**Avido Yuliestyan <sup>1</sup> , Pedro Partal 2,\* , Francisco J. Navarro <sup>2</sup> , Raquel Martín-Sampedro <sup>3</sup> , David Ibarra <sup>3</sup> and María E. Eugenio <sup>3</sup>**

	- <sup>3</sup> Forest Research Center (INIA, CSIC), Ctra. de la Coruña km 7.5, 28040 Madrid, Spain; raquel.martin@inia.csic.es (R.M.-S.); ibarra.david@inia.csic.es (D.I.); mariaeugenia@inia.csic.es (M.E.E.)
	- **\*** Correspondence: partal@uhu.es

**Abstract:** Oil-in-water bitumen emulsions stabilized by biobased surfactants such as lignin are in line with the current sustainable approaches of the asphalt industry involving bitumen emulsions for reduced temperature asphalt technologies. With this aim, three lignins, derived from the kraft pulping and bioethanol industries, were chemically modified via the Mannich reaction to be used as cationic emulsifiers. A comprehensive chemical characterization was conducted on raw lignin-rich products, showing that the kraft sample presents a higher lignin concentration and lower molecular weight. Instead, bioethanol-derived samples, with characteristics of non-woody lignins, present a high concentration of carbohydrate residues and ashes. Lignin amination was performed at pH = 10 and 13, using tetraethylene pentamine and formaldehyde as reagents at three different stoichiometric molar ratios. The emulsification ability of such cationic surfactants was firstly studied on prototype silicone oil-in-water emulsions, attending to their droplet size distribution and viscous behavior. Among the synthetized surfactants, cationic kraft lignin has shown the best emulsification performance, being used for the development of bitumen emulsions. In this regard, cationic kraft lignin has successfully stabilized oil-in-water emulsions containing 60% bitumen using small surfactant concentrations, between 0.25 and 0.75%, which was obtained at pH = 13 and reagent molar ratios between 1/7/7 and 1/28/28 (lignin/tetraethylene pentamine/formaldehyde).

**Keywords:** lignin; amination; emulsion; bitumen; rheology; microstructure
