Sustainable Boron Nitride Nanosheet-Reinforced Cellulose Nanofiber Composite Film with Improved Mechanical Properties and Oxygen Barrier without the Cost of Color and Brittleness

Abstract

Herein, we introduce a boron nitride nanosheet (BNNS)-reinforced cellulose nanofiber 19 (CNF) film as a sustainable oxygen barrier film that can potentially be applied in food packaging. 20Most of commodity plastics are oxygen-permeable. CNF exhibits an ideal oxygen transmittance rate 21 (OTR) of <1 cc/m 2 /day in highly controlled conditions. A CNF film typically fabricated by the air 22 drying of a CNF aqueous solution reveals an OTR of 19.08 cc/m 2 /day. The addition of 0-5 wt% BNNS 23 to the CNF dispersion before drying results in a composite film with highly improved OTR, 4.7 24 cc/m 2 /day, which is sufficient for meat and cheese packaging. BNNS as a 2D nanomaterial increases 25 the pathway of oxygen gas and reduces the chances of pin-hole formation during film fabrication 26 involving water drying. In addition, BNNS improves the mechanical properties of the CNF films 27 (Young's modulus and tensile strength) without significant elongation reductions, probably due to 28 the good miscibility of CNF and BNNS in the aqueous solution. BNNS addition also produces 29 negligible color change, which is important for film aesthetics. An in vitro cell experiment was 30 performed to reveal the low cytotoxicity of the CNF/BNNS composite. This composite film has great 31 potential as a sustainable high-performance food packaging material. 32 Keywords: cellulose nanofiber; boron nitride nanosheet; oxygen barrier; food packaging 33 34 1. Introduction 35 Synthetic polymers such as polyethylene (PE), polypropylene (PP), and polyethylene 36 terephthalate (PET) have been widely used as food and medicine packaging materials owing to their 37 high strength, low cost, viscoelastic properties, and chemical resistance. The oxygen barrier 38 properties of food and medicine packaging films are vital to prevent the oxidation of food and 39 medicine. However, most polymeric films are oxygen permeable and exhibit a high oxygen 40 transmission rate (OTR) of 40-1000 cc/m 2 /day [1-5]. 41Halogenated and metalized polymeric films can achieve an OTR of 0.1-10 cc/m 2 /day [6][7][8][9]. 42However, these polymer films pose many environmental and health threats [6][7][8][9]. For example, the 43 incineration of aluminum-coated PET films and polyvinylidene chloride (PVDC) produces fine dust 44 and dioxins, respectively. In general, metalized polymeric films are not recyclable.Cellulose nanofiber (CNF) is a sustainable and biocompatible nanomaterial [10] and is a 46 potential food and medicine packaging material [11][12][13][14][15][16][17][18][19]. It is produced by mechanically 47 disintegrating highly crystalline nanofibrils in cellulose bulk, the most abundant biomass [10,20]. 48Coatings and films composed of CNF can achieve an OTR of less than 1 cc/m 2 /day, which is suitable 49 for the packaging of most foods and medicines [11][12][13][14][15][16][17][18][19]. 50It is questionable whether the oxygen barrier performance of CNFs can be reproduced in an 51 industrial setting. CNF films are typically produced from an aqueous dispersion by air d...