Formaldehyde-free dispersion adhesives for the production of wood-based materials

Project start / November 01, 2015

Currently, the adhesives used in the production of wood-based materials are predominantly formaldehyde-containing amino resins. The EU has classified formaldehyde as a mutagenic and carcinogenic substance. One alternative could be the dispersion adhesives on the basis of polyvinyl acetate (“white glue”) commonly used in the furniture industry. Whilst they are formaldehyde-free, their use in the production of wood-based materials is, however, currently very limited due to their thermoplastic properties. We are developing a formaldehyde-free dispersion adhesive with thermosetting properties on the basis of polyvinyl acetate (PVAc) and sugar derivatives. We are thereby creating the prerequisites for the future production of wood-based materials with formaldehyde-free adhesives using renewable raw substances.

Last modified: November 01, 2015

Stück einer MDF-Platte mit sichtbarer Sägekante liegt neben einem Haufen Holzfasern. — © Fraunhofer WKI | Manuela Lingnau
Example of particle bonding: medium-density fiberboard (MDF)

Stück einer Spanplatte mit sichtbarer Sägekante liegt neben einem Haufen Holzspänen. — © Fraunhofer WKI | Manuela Lingnau
Example of particle bonding: particle board

Conventional wood-based materials are produced using formaldehyde-containing thermosetting plastics that cure during pressing. Our approach involves using formaldehyde-free thermoplastics, such as white glue. As thermoplastics can deform under load and heat, we modify them with a new, bio-based building block. This building block is a radically polymerizable sugar derivative and can be copolymerized with polyvinyl acetate glue (white glue). The glass transition temperature is thereby increased and, consequently, the heat deflection temperature as well. In this way, we are able to match the thermoplastic properties of the glues to a thermoset.

We evaluate and optimize the bonding quality of the PVAc-sugar adhesive by means of mechanical material tests. With regard to health safety, we measure the emissions of volatile organic compounds (VOCs), in particular formaldehyde.

This project is a joint project between the Fraunhofer WKI and the adhesive manufacturer Jowat SE. In addition, four leading wood-based materials manufacturers are participating in the project, thereby representing the particle-board, fiberboard and plywood-manufacturing industries. The project is listed in the environmental database UFORDAT provided by the German Federal Environment Agency.

Results

Within the scope of the project, we succeeded in synthesizing a copolymer on the basis of polyvinyl acetate and a sugar acrylate as a new type of binder and to transfer the synthesis from laboratory scale (1 kg) to pilot-plant scale (60 kg). Our emission measurements showed that the final adhesive developed did not emit formaldehyde.

We were able to demonstrate that the new adhesive is suitable for the production of particle board. In comparison to the production with a conventional formaldehyde-containing amino resin, the mechanical properties of the particle boards are almost identical. Solely the swelling behavior continues to represent a deficit, despite the addition of wax as a hydrophobing agent. The application in damp rooms is therefore not yet possible and requires further research.

Furthermore, the new adhesive has been successfully used to produce dimensionally stable medium-density fiberboard (MDF) and (molded) plywood made from beech veneers.