A relative newcomer in the materials arena, nanocellulose is being investigated for applications in packaging, medicaine, composite, transport and electronics. We take a look at the market.
Over the past two decades, nanotechnology has come to the forefront of scientific research and development. However, despite being the most available natural polymer on earth, it is only recently that cellulose has gained prominence as a nanostructured material, in the form of cellulose nanocrystals (CNC) and micro/nanofibrillar cellulose (MFC/NFC). Today there is a substantial amount of research on these materials.
Cellulose is a biopolymer consisting of long chains of glucose with unique structural properties whose supply is practically inexhaustible. Nanocellulose is natural and renewable, biodegradable, biocompatible, has high strength and modulus, high surface area, high aspect ratio, chemical functionality (e.g. for modification), dimensional stability, moisture absorption properties and thermal stability (~200oC) amongst others. Advantages of nanocellulose are:
- Abundant, natural nanomaterials
- Renewable, biodegradable & biocompatible
- High strength & modulus
- High aspect ratios & high surface areas
- Chemical functionality & modification
- Dimensional stability.
From a basic chemical structure (two molecules of anhydroglucose composing a cellulobiose unit), a 3D network formed by hydrogen bonds results in a complex structure formed by nano-domains of crystalline structure co-existing with amorphous cellulose. This crystalline structure is responsible for its intrinsic strength and its relatively high chemical stability. The potential for exploiting it supramolecular structure, plus its availability and renewability have resulted in cellulose being increasingly investigated for use in high-performance materials applications. Properties of Nanocellulose are:
- Diameter: 5 nm – 500 nm
- Length: 10s nm – 100s mm
- Specific surface area: 10s – 100s of m2/g
- Surface modification: anionic, cationic, grafted, carboxymethylated, etc. (analogue to cellulose macrofibers)
- High aspect ration 100-150 (Birch 45)
- High mechanical strength
Nanocellulose is being developed for applications in composites, construction materials, porous materials, fibre web structures (e.g. paper and board), coatings, functional surfaces and functional additives (e.g. rheological modifiers). Its biodegradability is important when the current environmental, societal and political issues regarding the development of innovative, sustainable and recyclable materials. Applications of nanocellulose include:
- Composites: Strength enhancing additives for renewable and biodegradable composites, with the cellulosic nanofibrillar structures as a binder between the two organic phases are being produced for improved fracture toughness and prevention of crack formation for application in packaging, construction materials, appliances and renewable fibres. They are attractive because of their wide abundance, their renewable and environmentally benign nature, and their outstanding mechanical properties.
- Electronics: Nano fibrillated cellulose is being developed for transparent and dimensional stable strength-enhancing additives and substrates for application in flexible displays, flexible circuits, printable electronics and flexible solar panels. Nanocellulose is incorporated into the substrate-sheets are formed by vacuum filtration, dried under pressure and calandered. In a sheet structure nanocellulose acts as a glue between the filler aggregates. The formed calandered sheets are smooth and flexible.
- Construction: Composite and cement nanocellulose additives allow for crack reduction and increased toughness and strength.
- Packaging: Strength enhancement with nanocellulose increases both the binding area and binding strength for application in high strength, high bulk, high filler content paper and board with enhanced moisture and oxygen barrier properties.
- Filters: Porous nanocellulose is used for cellular bioplastics, insulation and plastics and bioactive membranes and filters.
- Medical: Bacterial nanocellulose can be used as biocompatible, highly porous scaffolds for tissue engineering in bone implants, artificial blood vessels and organs for embryonic stem cells
- Coatings and surfaces: Nanocellulose can be used as coating materials as they have a high oxygen barrier and affinity to wood fibres for application in food packaging and printing papers. Nanocellulose films/coatings have been shown to have excellent mechanical and barrier properties. Nanocellulose has also been used as an additive in water-based polyurethane varnishes and paints. Nanocellulose improves the durability of a coat of paint, and protects paints and varnishes from attrition caused by UV radiation.
- Rheological modifiers: Nanocellulose can be used as thixotropic, biodegradable, dimensionally stable thickener (stable against temperature and salt addition); in low-calories food application; Thickener in cosmetics; Pharma (tablet binder, diagnostics): bioactive paper; Pickering stabilizer for emulsions & particle stabilized foam; Paint formulation; Enhanced oil recovery
- Other: Flexible Energy Storage Devices (Battery membranes, supercapacitors); Adaptive, biomimetic nanocomposites.
A number of techniques have been developed for the production of micro- or nano-fibrillated cellulose. In most cases, chemical or enzymatic pre-treatments are needed in order to weaken the structure of the fibre walls before the isolation of the microfibres. Methods of functionalization are:
- Functionalization of NFC using polymers
- Chemical modification of NFC surface
- Functionalzation using nanoparticles
- Nanocellulose modified with inorganics and surfactants
- Biochemical modification
- Enabling drying & redispersing
The separation of cellulose microfibrils is performed by different equipments able to disintegrate the ultrastructure of the cell wall while preserving the integrity of the microfibrils.
Cellulose nanocrystals are different products composed only by the crystalline portion of the microfibrils. They are obtained by acidic hydrolysis using concentrated sulphuric acid and are formed by cellulosic elements measuring few hundreds of nanometres of length depending on the starting raw material.
Scale-up of these technologies for larger production is nowadays under way. Innventia AB is constructing the world’s first pilot plant to produce nanocellulose, mainly for paper and board applications. Production volumes are 100kg per day.
The National Research Council’s (NRC) Biotechnology Research Institute, has produced an adaptable high-grade nanocrystalline cellulose (NCC) using a novel environment-friendly extraction process that uses an oxidizer to produce a higher quality fibre called ‘carboxylated NCC’. The technology is being used by Bio Vision Technology Inc , which is supplying NCC to research institutions and companies exploring applications in automotive panels, aircraft parts, paint, adhesives, resins, bandages and gauze. EMPA in Switzerland and The Finnish Centre for Nanocellulosic Technologies have also developed production technologies.
Nanocellulose based composites are widely regarded as the most promising bio-based products for high performance products and along with other nanomaterials may soon replace glass and carbon fibre reinforced plastics in a industries ranging from transportation, wind turbines, sport and consumer goods to biomedicine.
