**4. Conclusions**

This study has investigated the Pickering emulsion polymerization of styrene using SD-ChNFs as stabilizers to fabricate nanochitin/polystyrene composite particles. The SD-ChNFs used as stabilizers efficiently formed Pickering emulsions with styrene in aqueous acetic acid, even under higher weight ratios of SD-ChNFs to styrene (e.g., 1.4:1). Radical polymerization of styrene in the resulting emulsions was then conducted in the presence of a radical initiator to fabricate the desired composite particles. Their average diameters decreased with increasing weight ratios of SD-ChNFs to styrene to a minimum of 84 nm. The resulting nanochitin/polystyrene composite particles can be converted into hollow particles composed of nanochitin/polystyrene shells by dissolving the inner polystyrene. The obtained materials have potential to be used as carriers for the controlled release of hydrophobic medical drugs owing to their biocompatibility and hydrophobicity, respectively. In the future, the approach described in this study will be employed in Pickering emulsions using other monomers to obtain nanochitin-based composite particles with functional polymers such as biodegradable and biocompatible polymers.

**Author Contributions:** J.-i.K. and K.Y. contributed to the methodology and writing of the paper. R.W. and K.I. performed the experiments and analysis. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable. **Data Availability Statement:** Not applicable.

**Acknowledgments:** Not applicable.

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