The overall objective of the ECOAT project is to select, extract, and functionalize molecules (proteins, polysaccharides, cutin) from highly available, low valorized biomass such as tomatoes, legumes, and sunflowers for the development of new bio-based coating materials. These coating materials will be applied to two different substrates (cellulosic and plastic based), with the objective of improved performance compared to currently available products and at the same time more sustainable end of life options. The products to be developed include, for example, paper and cardboard (packaging for fresh products such as pasta, paper plates,…), plastic substrates (bio-polyesters) for active packaging, cutin based formulations for water repellent coatings (paper cups, service paper, etc.), water vapor barrier packaging, and non-food packaging with protective properties.
Plant-based micellar proteins as alternative to petrochemical-based polymers
In the ECOAT project the Fraunhofer IVV is responsible for developing protein based coatings, the identification of protein sources, the extraction of proteins and selection of polymers, formulation development, and coating characterization. The application of the coatings will be carried out using the Fraunhofer IVV pilot plant facilities.
The Fraunhofer IVV has expertise in the development of plant-based micellar proteins which can be used as an alternative to petrochemical-based polymers. The main function of micellar proteins in a packaging is to replace petrochemical-based polymers, such as ethylene vinyl alcohol copolymer (EVOH), that are used as oxygen barriers in conventional packaging. Micellar proteins have been shown to have good barrier properties against oxygen and also very good adhesive properties. A special protein precipitation process enables the recovery of micellar protein structures. However, up until now water has been used as the solvent for the micellar protein formulation. When the protein is used in polymer-polymer multilayers, water cannot be adequately removed after the lacquering process and thus remains in the adhesive. As a consequence, no adhesive force is obtained.
Use of the micellar protein in plastic packaging
A novel solvent system will be developed for using the micellar protein in plastic packaging. This solvent system must meet the following requirements: high solubility of the protein, no or minimal impact on the micellar structure of the protein, low viscosity, high vapor pressure (e.g. similar to ethanol) and thus easy to evaporate, non-toxic, and environmental friendly. In the next step, a reactive crosslinking system will be developed. By careful selection of the chain length as well as the reactive groups of the crosslinker and thus the functional protein groups involved in crosslink formation, various properties of the protein-based adhesive can be customized. These include the solubility of the layer, the mechanical strength, and the barrier properties. The crosslinking reaction will be triggered after the coating or lamination process, for example by temperature or by exposure to UV light.
Development of a suitable coating formulation
Once these challenges are overcome, a suitable coating formulation will be developed. The change of the solvent system as well as the addition of crosslinking agents has a significant impact on processing properties such as the viscosity and shear sensitivity. The formulation development includes the selection of a suitable plasticizer as well identification of the optimum protein and plasticizer concentration. Newly developed plasticizers based on hydroxyl acid copolymers (based on lactic, tartaric, or glycolic acids) to improve the processing of proteins will be tested in different concentrations.
The final formulation will then be applied on both a laboratory and pilot plant scale. Key parameters for the coating process are, for instance, the temperature of the formulation, the wet coat weight, the coating speed, and the drying temperature and interval.
The resulting laminates will be characterized for their oxygen and water vapor barriers, bond strength, and mechanical stability in the Fraunhofer IVV laboratories.