Development of Plywood Binder by Partial Replacement of Phenol-Formaldehyde Resins with Birch Outer Bark Components

Abstract

The apparent shift in climate has resulted in the pursuit of environmentally friendly bio-based products to reduce the carbon footprint. In the scientific literature, there are many attempts to make phenol-formaldehyde resins (PFR) more sustainable by using bio-based phenolics in the synthesis instead of petroleum-based phenol. However, it is also important to reduce the content of formaldehyde in the binder, the vapours of which are toxic and even carcinogenic to the human body. One of the technologically simplest solutions could be the incorporation of another bio-based wood composite binder into the completed industrial PFR. In turn, birch outer bark suberinic acids are an effective, ecological, thermosetting binder to produce mechanically durable and moisture-resistant wood composites. The aim of the study was to adapt the components of birch outer bark (suberinic acids and betulin-based extractives) for their incorporation into industrial PFR and to find the optimal degree of resins replacement in practical experiments. At the same time, to keep a similar level of the bending strength and moisture resistance (shear strength) of the plywood bonded with the modified binder compared to pure industrial PFR. As a result, it was found that it was possible to replace up to 30 wt% (dry basis) of the industrial PFR with birch outer bark components to obtain birch plywood without significant loss of the bending strength and moisture resistance. In this way, it would be possible to significantly reduce the carbon footprint of the synthetic PFR binder in the birch plywood industry by using birch processing residues.