**4. Conclusions**

A series of fully biobased epoxy resins made from renewable resources were prepared, and their thermo-mechanical properties were analyzed. Lignin, rich in aromatic structures, gives stiffness and consistency to the epoxy resins, which are otherwise soft, flexible, and breakable due to long aliphatic chains of the fatty acid derivatives. Solvent extracted Kraft lignin was used due to its more defined profile. At a low lignin content, the effects were barely noticeable, but at a 12.5 weight% of lignin both the glass transition temperature and the Young's modulus increased, and the rise was even more pronounced at a 22 weight%. It is thus not a linear but an exponential correlation. Higher amounts of lignin could not be incorporated if solvent-extracted Kraft lignin was used. Depolymerized and subsequently solvent-extracted lignin, liquid and with low Mw, could be used in higher amounts (36.4%), leading to harder epoxy resins. The fact that all the components of the resin are bulk chemicals opens the door to the production of fully biobased resins on an industrial level.

### **5. Patents**

Ortiz, P.; Vendamme, R. Bio Based Epoxy Resin. PCT/EP2019/075067.

**Supplementary Materials:** The following are available online, <sup>31</sup>P NMR characterization of lignin S1–S3; GPC characterization of lignins S4–S8; Proof of epoxy curing S9–S10; Plot of equiv. of diamine vs. Young's Modulus of cured samples S11; DSC of cured samples S12–S13; TGA of cured samples S14.

**Author Contributions:** Conceptualization, P.O. and R.V.; methodology, P.O.; investigation, P.O.; writing—original draft preparation, P.O.; writing—review and editing, P.O., R.V. and W.E. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the province of Noord-Brabant (The Netherlands) in the framework of the activities at the Shared Research Center Biorizon.

**Acknowledgments:** The authors would like to thank BASF for providing epoxidized soybean oil (Efka® PL 5382); Valtris for providing epoxidized linseed oil (Lankroflex™); Croda for providing dimer diamine (Priamine 1074®); Innventia Institute for providing Lignoboost® Kraft lignin. West Fraser for providing West Fraser Kraft lignin; Fraunhofer Institute for providing base-catalyzed depolymerized (BCD) solvent-extracted eucalyptus lignin oil.

**Conflicts of Interest:** The authors declare no conflict of interest.

### **References**


**Sample Availability:** Samples of the cured epoxy resins are available from the authors.

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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