S. Varanasi, G. Simon, G. Garnier, W. Batchelor
Keywords: nanocellulose, micro fibrillated cellulose, packaging, composite
Summary:There is a need to develop sustainable packaging of controlled gas and water vapour permeability. Conventional paper is well known packaging material. However, the hydrophilic nature of cellulose and poor water-vapour and oxygen barrier properties due to high network porosity limits papers use in certain packaging applications. Paper packaging also easily absorbs water from the environment, or from the food it contains, thereby losing its physical and mechanical strength. Water vapour and oxygen can easily diffuse through the void spaces in paper. To mitigate these limitations, commonly plastic materials, wax and aluminium are incorporated to the paper for packaging, leading to multilayer materials. However, these materials can have serious environmental issues and the addition of these materials to paper makes the paper very difficult and inefficient to recycle as different phases cannot be separated. Cellulose nanofibers (CNF) can be produced from macro fibres through mechanical fibrillation combined with chemical or enzymatic pre-treatment. Films/sheets prepared with CNF showed superior barrier properties compared to macro fibres because of reduction in network porosity and pore size. Cellulose nanofibre sheets have low OP due to low porosity compared to films made from both commercially available petroleum based polymeric materials such as low density polyethylene (LDPE) and high density polyethylene (HDPE) and biopolymers. However, WVP of nanofibre sheet is high because of the inherent sensitivity to water vapour (hydrophilic nature) of cellulose and high diffusion of water molecules. Barrier properties of nanofibre sheets depend on the size of nanofibres, sample crystallinity, and hydrophilicity. Modifying the structure of the pore network by decreasing pore size or increasing sample crystallinity should reduce the WVP. Reducing the WVP while keeping low OP is a key challenge to the utilisation of cellulose nanofibres for barrier applications. We developed a simple and novel method to prepare a nanofibre/nanoparticle composite. Nano particles acts as pore fillers to reduce the porosity of sheet. Barrier properties of composites, water vapour and oxygen permeability of composite one order of magnitude less than nanofibre sheets.