**Christoph Metzger 1, Solange Sanahuja 1, Lisa Behrends 1, Sven Sängerlaub 2,3, Martina Lindner 2,3 and Heiko Briesen 1,\***


Received: 2 March 2018; Accepted: 12 April 2018; Published: 14 April 2018

**Abstract:** Cellulose nanocrystals (CNC) and starch nanoparticles (SNP) have remarkable physical and mechanical characteristics. These properties particularly facilitate their application as high-performance components of bio-based packaging films as alternatives to fossil-based counterparts. This study demonstrates a time-efficient and resource-saving extraction process of CNC and SNP by sulfuric acid hydrolysis and neutralization. The yields of the hydrolyzed products were 41.4% (CNC) and 32.2% (SNP) after hydrolysis times of 3 h and 120 h, respectively. The nanoparticle dispersions were wet-coated onto poly(lactic acid) (PLA) and paper substrates and were incorporated into starch films. No purification or functionalization of the nanoparticles was performed prior to their application. Techno-functional properties such as the permeability of oxygen and water vapor were determined. The oxygen permeability of 5–9 cm<sup>3</sup> (STP) 100 μm m−<sup>2</sup> d−<sup>1</sup> bar−<sup>1</sup> at 50% relative humidity and 23 ◦C on PLA makes the coatings suitable as oxygen barriers. The method used for the extraction of CNC and SNP contributes to the economic production of these nanomaterials. Further improvements, e.g., lower ion concentration and narrower particle size distribution, to achieve reproducible techno-functional properties are tangible.

**Keywords:** cellulose nanocrystals (CNC); starch nanoparticles (SNP); biopolymers; packaging; barrier films; nanomaterials; nanocomposites; bio-coatings; oxygen barrier; water vapor barrier
