**4. Conclusions**

The impact of CNC surface properties on the crystallization behavior of PBS in CNC-reinforced PBS composites was investigated using differential scanning calorimetry. The surface properties of the CNCs were tailored by grafting alcohols of different chain lengths on their surface using TDI as a linker. The water contact angle of the modified CNCs increased to 34◦, 52◦, 104◦, or 120◦ using ethanol, 1-butanol, 1-hexanol, or 1-octanol, respectively. Compared to neat PBS, the crystallization thermograms of the PBS composites showed a heterogeneous crystallization behavior with increased crystallization temperature as a result of CNC nucleation activity, which was proportionally dependent on the contact angle of the CNCs. However, the estimated Avrami kinetic parameters and Kissinger activation energy of crystallization showed that the impeding effect of CNCs is prevailing, resulting in retarded crystallization. The impeding effect was less significant for the CNCs with higher contact angles. Overall, the surface properties of CNCs had a crucial role in the crystallization behavior of PBS and can be advantageous to tailor its properties.

**Author Contributions:** Conceptualization, H.A. and J.M.; methodology, H.A. and J.M.; formal analysis, H.A. and J.M.; investigation, H.A. and J.M.; writing—original draft preparation, H.A. and J.M.; writing—review and editing, H.A. and J.M.; funding acquisition, H.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Fraunhofer Institute for Wood Research (WKI) through the Wilhelm-Klauditz Fellowship.

**Acknowledgments:** Many thanks to Nadine Nöcker from the Fraunhofer Institute for Surface Engineering and Thin Films (IST) for the contact angle measurements and to Martin Eichler from the Fraunhofer Institute for Wood Research (WKI) for performing the DSC measurements.

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