insiGlue:
Formaldehyde-free, bio-based in-situ adhesive system for the production of MDF for low-emission and sustainable furniture, construction products and other applications

Project start /

Medium-density fiberboard (MDF) is widely used in furniture construction. It has a very homogeneous surface that can be coated particularly smoothly. Furthermore, it can be produced economically and sustainably from regionally available wood and recycled waste wood. As a result, it also plays a major role in the construction industry - for example as a substrate for floor coverings or wall panels. Through this research project, we are aiming to make MDF and similar fiberboards even more sustainable. In collaboration with industrial partners, we are developing a formaldehyde-free adhesive system with bio-based materials that are available on the market at low cost. The special highlight: The new adhesive system functions without conventional adhesives.

The photo shows a small piece of MDF, a small pile of wood fibers, a laboratory beaker containing a colorless liquid, a small laboratory dish containing pale-blue powder and a laboratory dish containing white powder.
© Fraunhofer WKI | Manuela Lingnau
Constituents for the MDF of the future: hydrogen peroxide (H2O2), iron(II) sulphate (FeSO4) and a bio-based dicarboxylic acid as the starting substance for the pre-adhesives as well as beech-wood fibers from climate-resilient mixed forests.

The project is based on a pilot study carried out at the Fraunhofer WKI on the subject of Auto-adhesively bonded wood-based materials. The fundamental idea of the pilot study was to chemically treat the fibers in order to increase the wood’s own binding forces to such an extent that MDF can be produced with significantly less adhesive or even completely without adhesive.

The basic feasibility was demonstrated in the pilot study; however, this process has not become established on an industrial scale. Reasons include:

  • Moderate mechanical and hygric properties of the auto-adhesively bonded MDF
  • Lack of process reliability

Building on the pilot study, our aim in this research project is the development of a reliable process for the production of particularly sustainable, low-emission MDF with marketable material properties.

Functional principle of the new adhesive system

  • The inherent binding forces of the wood fibers are increased with the aid of inexpensive and readily available activation chemicals (Fenton reagent made from hydrogen peroxide and iron salts).
  • The activated wood fibers are coated with bio-based pre-adhesives and pressed to form boards.
  • During the hot-pressing process, the actual adhesive substances are formed on the fiber surface (“in situ”).
     

Utilization of sustainable wood species

The chemical and physical properties of wood fibers are heavily dependent on the species of wood. Within the scope of the development work, various species of wood that are readily available in Germany are being tested. The focus is on hardwood, in particular beech and birch. With a proportion of 16.6 percent, beech is the most common deciduous tree species in German forests (fourth Bundeswaldinventur 2022, English: Federal forest inventory). Birch is suitable as a pioneer tree for the quick reforestation of bare areas. Furthermore, with a rotation period of 60 to 80 years, it is one of the so-called “other deciduous tree species with a short lifespan” (German: ALN). This means that it reaches harvesting maturity relatively quickly compared to other tree species. For comparison, the softwood species currently predominantly used for MDF – spruce and pine – are included in the development.

The aim is to determine whether and to what extent the constituents of the different species of wood support or block the activation and, in particular, the in-situ bonding. As hardwoods have proven to be particularly suitable for the activation of wood by means of Fenton reagent, the project work is increasingly focusing on hardwood as a raw material.

The utilization of hardwood has a further advantage: Up until now, it has been used much less than softwood for the production of particle-bound wood-based materials, but will be increasingly available in the future. This is because forest owners, in the face of the extinction of spruce due to climate change, are increasingly turning to more resilient mixed forests. In the course of the increase in deciduous and mixed forests, ALN tree species such as birch will gain in importance – for example as companion tree species and as a readily available assortment of first growth on, for example, calamity areas. The development of the untapped potential of hardwood for the production of MDF and other wood fiberboards could provide a significant contribution towards easing the tense situation on the softwood market.
 

Unique selling points of the new in-situ adhesive system

  • The new adhesive system is formaldehyde-free.
  • No adhesive in the conventional sense is required.
  • With the exception of the iron salts used catalytically, the activation chemicals and pre-adhesives can be produced entirely from renewable raw materials.
  • The bio-based pre-adhesives have a hydrophobic effect.

The new process steps should be easily transferable to existing facilities in order to keep the cost of implementing the process to a minimum. In this way, a high level of acceptance of the new in-situ process within the wood-based materials industry should be created from the outset.

Last modified: