Cellulose nanocrystals (CNC) are nano-sized cellulose extracted from natural fibres, with unique strength and optical properties, and have a promising future in the packaging field, with the following specific advantages:
Enhancement of barrier properties Gas barrier: CNC can effectively reduce the oxygen permeability of packaging materials, such as Rampazzo et al. prepared CNC with wood fibre as raw material for the oxygen barrier coating of food packaging film, its gas barrier properties are similar to pure cellulose raw material, and better than the performance of ordinary barrier polymers, which can better prevent the deterioration of food products due to oxidation, and prolong the shelf-life of food products.
Barrier to water vapour and oil: CNC can improve the barrier property of packaging materials to water vapour and oil, reduce moisture and oil seepage from the contents, and maintain the taste and quality of food. For example, the ternary polysaccharide polyelectrolyte complex material containing 5wt% CNC prepared by Chi et al. has a low water vapour transport rate, which can prevent the liquid from penetrating the cardboard substrate, and it is an excellent barrier coating.
Enhancement of mechanical properties Improvement of tensile strength: CNC has high crystallinity and high strength, which can significantly enhance the tensile strength of the packaging material, making it tougher and more durable, not easy to rupture and damage, and better able to withstand a variety of external forces in the process of transport and storage, and reduce the loss caused by the breakage of packaging. For example, the CNC/PLA composite film prepared by Shi Junhua et al. with oil tea husk cellulose, compared with the pure PLA film, the tensile strength increased by 30.1%.
Increase the modulus of elasticity: It can improve the rigidity and deformation resistance of packaging materials, which makes it easier to form and maintain the shape during the packaging process, and also better protects the contents from extrusion and deformation, which is of great significance for some fragile or shape-demanding products.
Antimicrobial properties Inhibit the growth of microorganisms: CNC can inhibit the growth of common spoilage bacteria and pathogenic bacteria such as Staphylococcus aureus and Escherichia coli during acid hydrolysis, thus prolonging the shelf-life of food, reducing the risk of spoilage due to microbial contamination, and improving the safety of food.Sanwar et al. prepared PVA/CNC/Ag nano-composite film with 8% CNC, can effectively protect the contents from extrusion and deformation, which is important for some broken or shaped products. The PVA/CNC/Ag nanocomposite film prepared by Sanwar et al. can effectively inhibit the growth of Staphylococcus aureus and Escherichia coli with the addition of 8% CNC and can be used for antibacterial food packaging.
Reduce the use of preservatives: its antimicrobial properties can reduce the use of preservatives in food packaging to a certain extent, to meet consumer demand for natural, healthy food, but also in line with the development of the food packaging industry to the direction of green, environmentally friendly trends.
Good biocompatibility and degradability Environmentally friendly: CNC from natural cellulose, is a renewable resource, has good biocompatibility and degradability, can be decomposed into harmless substances faster in the natural environment, will not be like the traditional plastic packaging that causes long-term environmental pollution, help reduce the pressure of packaging waste on the environment, in line with the requirements of sustainable development. High safety: It is non-toxic and biocompatible, and when used in food packaging, it will not have harmful chemical reactions with food or release harmful substances, so it is harmless to human health and can be used as packaging materials in direct contact with food.
Giving packaging materials special properties Optical properties: CNC has unique optical properties, such as polarisation, birefringence, etc., and can be used to prepare packaging materials with special optical effects, such as anti-counterfeiting packaging, decorative packaging, etc., to enhance the added value of the packaging and aesthetics, and to enhance the market competitiveness of the product.
Multi-layer structural design potential: CNC composites with multi-layer structural design have great potential in the field of food packaging, through the combination of different levels of materials, can achieve a variety of functions, such as barrier, antibacterial, preservation of freshness, etc., to meet the personalised needs of different food packaging, and to promote the development of green food packaging.
Abundant and renewable resources Wide range of sources: cellulose is the most abundant bio-based polymers on earth, widely present in plant cell walls, rich sources, can be obtained through the extraction of a variety of biomass resources, such as wood, crop residues, husks, leaves, etc., the raw materials are readily available and the cost is relatively low, with a good economic viability, and can reduce the cost of production of packaging materials.
Renewable and sustainable: Unlike petroleum-based packaging materials, the production of CNC does not consume limited non-renewable resources, and its production process is relatively environmentally friendly, with less impact on the environment, so it can realise the sustainable use of resources, which helps to alleviate the shortage of resources and environmental pressure.
