Comprehensive characterization and human toxicological assessment of nanocellulose along its life cycle for reliable risk evaluation and safe use in environmentally friendly packaging materials
Nanocellulose as a sustainable barrier coating
Cellulose is the most abundant organic material on earth and has always been used in a whole variety of ways. In modern food packaging, it is mainly used in the form of paper or cardboard. As a rule, such packaging is readily recyclable as well as biodegradable. One disadvantage, however, is its high permeability to gases such as oxygen, as an effective oxygen barrier is crucial for the protection of many products. Conventionally, plastic films are used to provide such barrier properties and to protect food products from spoiling. However, such films are either made of multilayer composites, which are difficult to recycle, or are coated with hydrocarbon-based barrier coatings such as the copolymer ethylene vinyl alcohol (EVOH). A lack of an effective refuse-collection system or the unintentional release of plastic waste into the environment results in the formation of micro plastics, which then lead to long-term global problems for the environment.
An alternative here is to use crystalline nanocellulose (CNC) as a coating material to be applied to substrates with a high gas permeability, such as paper or the majority of bioplastics. CNC has very low permeability to oxygen and mineral oils. It can therefore replace barrier coatings and materials made of hydrocarbon-based raw materials, making it one of the promising new materials to emerge from the bioeconomy sector. Moreover, its use as packaging does not compromise its biodegradability. As such, it offers a promising route towards reducing the use of poorly degradable plastic waste. In addition, several studies indicate that CNC as a paper coating is more compatible than other materials commonly used for this purpose and that it therefore causes fewer problems in the recycling process.
The characterization and human toxicological assessment of CNC
The project is looking into a number of issues that have so far slowed or hampered a market launch of nanocellulose. Investigations here are focusing on smart strategies for the production of CNC from different sources of cellulose fiber and on a scale-up of synthesis methods so as to significantly reduce the cost of industrial production. In turn, the CNC suspensions thereby produced are being examined for their use in processes to produce film or paper coatings, their barrier properties, and for their suitability as coatings for materials used as packaging for food.
The project is also assessing the potential hazards resulting from an oral or pulmonary ingestion of CNC by the processor or end user. This involves the development and use of smart test strategies based on novel in vitro and in silico methods. Such work includes an investigation of the toxicological effects of CNC using newly developed cell models (gastrointestinal tract and lung) and chip-based high-throughput methods, and also the simulation of the chemical degradation and uptake of nanocellulose in human cells.
Another key aspect of the project is the development of standardized analytical strategies for the investigation of CNC in solution, on substrates and in complex biological matrices. This includes the development of quantitative analytical methods for the characterization of CNC on the basis of electron microscopy and field-flow fractionation (FFF) in conjunction with a variety of detection methods such as multi-angle light scattering (MALS), dynamic light scattering (DLS) and refractive index (RI) detection.
CNC suspension as food packaging
Activities at the Fraunhofer Institute for Process Engineering and Packaging IVV focus primarily on the processing and characterization of aqueous CNC suspensions for use as food packaging. Once the coatings have been formulated, they are then applied to suitable substrates using a variety of processes. As a rule, such coatings are either laminated with a sealing film or sealed with a special lacquer. This is to protect the nanocellulose coating from moisture and physical damage, and to protect the product and the consumer from any nanoparticle abrasion. Any properties relevant to packaging performance, such as the oxygen transmission rate (OTR) of the composite or the bonding strength between composite layers, are also taken into account during the development process. In addition, the project involves the development and application of methods to test for the migration of contaminants such as mineral oil residues during paper processing. A further interesting aspect that has emerged in the course of this project is the development of a chemical process to modify nanocellulose and thereby improve, for example, a coating’s vapor barrier properties or its adhesion to hydrophobic substrates such as polypropylene.