Optimization of spray-coated nanochitin/nanocellulose films as renewable oxygen barrier layers via thermal treatment

Abstract

The demand for food and pharmaceutical packaging materials is increasing, but the most common materials used are non-renewable, non-biodegradable petroleum-based plastics, which has resulted in many end-of-life problems. Cellulose nanocrystals...

Aqueous-Based Recycling of Cellulose Nanocrystal/Chitin Nanowhisker Barrier Coatings

“…For instance, the polypropylene (PP) film coated with 20 bilayers of ChNW and TEMPO-oxidized CNF had an OP of 7.76 cm 3 ·μm/m 2 /day/kPa at 23 °C and 50% RH and a WVTR of 128 g·μm/m 2 /day at 30 °C and 50% RH . However, different substrates, coating structures (i.e., number of bilayers), and testing conditions make it difficult to directly compare the gas barrier properties of the coatings in different studies, which has been discussed in detail in our previous studies. , Additionally, the PET film coated with recycled materials as a bilayer had oxygen and water vapor barrier properties that are suitable for the packaging of many types of food. The normalized oxygen transmission rate (OTR) and WVTR for a 100-μm-thick film under room atmosphere are 1.4 cm 3 /m 2 /day and 1.36 g/m 2 /day, respectively, assuming 23 °C, 50% RH, and 21 kPa for the driving force of O 2 .…”

“…The suspensions were spray coated on the PET substrate by using the same setup as we previously reported . Briefly, the PET film was fixed along its four edges to a hot plate that was held vertically and maintained at 80 °C during the spray-coating process.…”

“…The film properties were characterized using the same methods as previously reported . The thicknesses were measured with a digital micrometer (Coolant Proof Micrometer Series 293, Mitutoyo).…”

“…The suspensions were spray coated on the PET substrate by using the same setup as we previously reported. 21 Briefly, the PET film was fixed along its four edges to a hot plate that was held vertically and maintained at 80 °C during the spray-coating process. For the PET-ChNW-CNC film, a volume of 25 mL of 0.5 wt % ChNW or 25 mL of 0.5 wt % CNC was spray coated on a 19 cm × 19 cm PET film in sequence.…”

“…Because nanochitin is usually cationic due to deacetylation treatment and nanocellulose is usually anionic due to acid hydrolysis or (2,2,6,6-tetramethylpiperidin-1-yl)­oxyl (TEMPO) oxidation, the electrostatic attraction between them promotes densification at their interface and improves the oxygen barrier properties. − For instance, a cellulose acetate (CA) film coated with a bilayer of ChNW and CNC had an OP that was 99, 22, and 84% lower than those of uncoated CA and CA coated with a single layer of ChNW or CNC, respectively . However, there remains much room for improvement in the water vapor barrier property to satisfy the requirements for food packaging applications. − Furthermore, cellulose and chitin are sensitive to humidity, and their gas barrier properties decrease significantly with elevated relative humidity (RH). , One approach to address these issues with water vapor in cellulose and chitin oxygen barriers is to use a conventional moisture barrier material as the substrate. , A drawback of this approach is the fact that most of the high-performing conventional water vapor barriers are petroleum-based and nondegradable. Promoting deconstruction of the coating and substrate at the end of life could enable recycling of the packaging materials to manage the dilemma.…”