Multifunctional biobased water vapor barrier coatings for fiber-based packaging materials

Barrier coatings protect against spoiling in fiber-based food packaging

The continuous growth of the global population combined with the cultural and industrial shift towards convenience, mass-production and online shopping has led to a significant increase in the consumption of packaging materials. The high demand for fiber-based packaging can be attributed to an increased environmental awareness and new political campaigns supporting sustainability and limiting the production of fossil-based products. Despite the many inherent benefits of fiber-based substrates, including high availability, sustainability and versatility, they provide no significant protective barrier against gas or liquids permeation. This is critical, especially in the sector of food-packaging, because oxygen and moisture permeate and spoil the food.

Biobased barrier coatings are not multifunctional yet

The conventional solution to this problem is to coat fiber-based substrates with protective layers against gas and moisture permeation using fossil-based polymers like PE, EVOH, etc. These materials, however, are not only resource-limited and environmentally harmful, but also hinder the recyclability of the paper. Biobased solutions have therefore been proposed to replace these fossil-based compounds. Current approaches utilize renewable polymers such as polysaccharides, proteins and waxes as individual coating layers or a combination thereof. These coatings provide either sealability or a barrier functionality towards water vapor or oxygen. A biobased material that combines all relevant properties for the packaging of sensitive foodstuffs does currently neither exist on the market, nor are there any successful research approaches.

Innovative biobased coating derived from cork

The “BioBarrier4Fiber” project aims to address this challenge by developing a novel coating concept for fiber-based food packaging that, for the first time, combines an effective water vapor barrier with high flexibility, processability, and sealability. This multifunctional coating system is based on various suberin fatty acids (SFA), which are extracted from the cork of oak and beech trees in Germany and Turkey. Due to their chemical composition, suberin fatty acids are particularly well suited for this purpose. They consist of highly functional, polymerizable aliphatic acids of varying length and structure. In nature, they act as a hydrophobic polyester forming a protective layer around the periderm of plants. With BioBarrier4Fiber, this natural function is transferred to packaging applications.

Project Results – "BioBarrier4Fiber"

Process development – extraction of suberin fatty acids

To obtain suberin fatty acids (SFA) from cork bark, the researchers developed an extraction process based on alkaline depolymerization. This process was initially established at laboratory scale and subsequently successfully scaled up. Comparable quality of the SFA extracts was also achieved at larger production scales.

SFA coating with strong barrier properties

Fraunhofer IVV additionally evaluated the coating process for fiber-based substrates. SFA-based formulations were applied to various paper substrates using a roll-to-roll process. Compared to uncoated reference materials, the coated substrates exhibited a significantly improved water vapor barrier. Under practical test conditions (23 °C, 85% relative humidity), water vapor transmission rates (WVTR) in the range of 5–10 g/m²·d were achieved. For a purely bio-based coating material, these results represent a major success and clearly demonstrate the technology’s potential for future packaging applications.

SFA-coated paper bags extend shelf life

For the production of demonstration bags, an additional sealing lacquer layer was applied, as the extracted suberin fatty acids did not yet provide sufficient sealability at the current stage of development. Storage tests with cherry tomatoes showed that the fruits remained fresh longer in SFA-coated paper bags than when left unpackaged. Further optimization of the sealability of SFA is planned in subsequent research projects.

Close collaboration between research and industry

The selection and pretreatment of beech and oak bark, as well as the development and optimization of the extraction processes and coating materials, were carried out in close cooperation between Fraunhofer IVV and the Turkish research center TÜBİTAK. In parallel, eight industry associations – including the German Association for Food Technology and Packaging (IVLV) and the Association of Packaging Manufacturers in Turkey (ASD) – supported the project through an industry committee and evaluated the technical and economic potential of the developed solution.