The influence of wood extracts on the rheological properties of urea-formaldehyde adhesive during cure.

Rheological analysis was used to evalute the influence of the wood species of beech, fir and poplar on the gelation time of commercial urea-formaldehyde (UF). The UF adhesive samples were mixed with hot water extracts of selected wood species. Two series of samples were prepared, one without the catalyst addition and the other with the addition 0,2% of amonium chloride, per dry adhesive mass. Both series included the control UF adhesive samples, without the addition of wood extracts. Measurements of the viscoelastic properties of UF adhesive samples during cure were conducted at the temperature of 80C, and at the constant frequency of 1Hz. The addition of wood extracts had a positive catalytic influence in the case of the UF adhesive samples without the catalyst addition. Contrary, wood extracts have retarded the curing of the UF adhesive samples with catalyst.