AbstractThe purpose of this study is to develop a low-formaldehyde-emitting resin system for medium density fibreboards (MDF). A combination of polyamines with phenolic resins seems to be suitable for this purpose. To produce panels with such a resin system, polyethylenimine, and a phenolic resin were separately applied on fibres and subsequently made into boards in a thermal pressing process. It was demonstrated that thickness swelling and the mechanical properties of the boards produced with the new adhesive system were comparable to those conventionally manufactured with urea-formaldehyde resins. Even with adhesive contents of just 2 to 3%, the panels attained satisfactory internal bond strength. MDF panels with a total adhesive content of between 1.25 and 5% were produced from a mixture of polyethylenimine and phenolic resins (resol type) at different ratios. All boards were tested for physical (thickness swelling and water absorption) and mechanical properties (internal bond, modulus of elasticity, flexural strength). It was demonstrated that thickness swelling and the mechanical properties of the boards produced can be improved by a combination of polyethylenimine and phenolic resin.