The aim of the present review is to summarize the current state of research in the field of sustainable bio-based adhesives used for production of eco-friendly wood composite materials. The article is focused mainly on the use of lignin, starch and tannins as raw materials and alternatives to the existing conventional adhesives. It is expected that increased amounts of bio-based adhesives will be used in the production of wood composites in order to meet the current needs for development of sustainable and innovative materials which will make the wood-based panel industry more sustainable and lower its dependence on fossil fuels. However, there are still substantial challenges for the complete replacement of petroleum-based wood adhesives with bio-based adhesives, mainly because of their relatively poor water resistance, low bonding strength and large natural variations due to different growing conditions. In this respect, fundamental research is still need in order to determine the factors for formulating bio-based adhesives with optimal properties and broaden their application in wood-based panel industry.
In this work, wet-process fibreboards (hardboards) were produced in the laboratory using industrial wood fibres of the species European beech (Fagus sylvatica L.) and Turkey oak (Quercus cerris L.) at the total volume of 40%, and white poplar (Populus alba L.) at 60% volume. The effects of hot pressing pressure (varied from 3.3 MPa to 5.3 MPa) and pressing time (from 255 s to 355 s) on the physical and mechanical properties of hardboards were investigated and optimal values of the parameters for fulfilling the European standard requirements were determined. It was concluded that hardboards with acceptable physical and mechanical properties may be produced from 60% poplar wood waste and residues, combined with 40% hardwood raw materials (beech and oak) by regulating the hot pressing regime only, i.e. pressure and pressing time. The following minimum parameters for producing hardboards from mixed hardwood tree species were determined: a pressure of 4.6 MPa and a pressing time of 280 s.