Monocomponent aqueous adhesive composition, useful as a binder composition for fibrous substrates, characterized in that the adhesive composition comprises: (A) from 5 wt.% to 75 wt.% of a formaldehyde-based resin, obtained by reaction of formaldehyde with a second component, and comprising from 0,5 wt.% to 30 wt. % of at least one formaldehyde scavenger, and comprising 0,1 wt. % or less of free formaldehyde as determined by the method ISO 11402:2004; wherein - said second component consists of phenol, the molar ratio of formaldehyde with regard to phenol in the formaldehyde-based resin being between 1,5 and 3,0; or - said second component is a mixture of phenol and at least one of lignin, lignosulfonate, tannin, cardanol, pyrolysis oil of biomass, or hydrochar obtained by thermal treatment of agroforestry residues, wherein in a formaldehyde-phenol resin having a molar ratio of formaldehyde with regard to phenol between 1,5 and 3,0, up to 50 wt. % of the phenol is replaced by an amount in weight, of at least one of lignin, lignosulfonate, tannin, cardanol, pyrolysis oil of biomass, or hydrochar obtained by thermal treatment of agroforestry residues, said amount in weight being exactly the same amount in weight of replaced phenol or up to 25% more or less than the amount in weight of replaced phenol; (B) from 0,5 wt.% to 10 wt.% of at least one compound selected from resorcinol, methylresorcinol, ethylresorcinol or tannin, which is not condensed with the phenol-formaldehyde resin; and in that the adhesive composition has a free formaldehyde content of 0,1 wt. % or less, as determined by the method ISO 11402:2004. (A) from 5 wt.% to 75 wt.% of a formaldehyde-based resin, obtained by reaction of formaldehyde with a second component, and comprising from 0,5 wt.% to 30 wt. % of at least one formaldehyde scavenger, and comprising 0,1 wt. % or less of free formaldehyde as determined by the method ISO 11402:2004; wherein - said second component consists of phenol, the molar ratio of formaldehyde with regard to phenol in the formaldehyde-based resin being between 1,5 and 3,0; or - said second component is a mixture of phenol and at least one of lignin, lignosulfonate, tannin, cardanol, pyrolysis oil of biomass, or hydrochar obtained by thermal treatment of agroforestry residues, wherein in a formaldehyde-phenol resin having a molar ratio of formaldehyde with regard to phenol between 1,5 and 3,0, up to 50 wt. % of the phenol is replaced by an amount in weight, of at least one of lignin, lignosulfonate, tannin, cardanol, pyrolysis oil of biomass, or hydrochar obtained by thermal treatment of agroforestry residues, said amount in weight being exactly the same amount in weight of replaced phenol or up to 25% more or less than the amount in weight of replaced phenol; - said second component consists of phenol, the molar ratio of formaldehyde with regard to phenol in the formaldehyde-based resin being between 1,5 and 3,0; or - said second component is a mixture of phenol and at least one of lignin, lignosulfonate, tannin, cardanol, pyrolysis oil of biomass, or hydrochar obtained by thermal treatment of agroforestry residues, wherein in a formaldehyde-phenol resin having a molar ratio of formaldehyde with regard to phenol between 1,5 and 3,0, up to 50 wt. % of the phenol is replaced by an amount in weight, of at least one of lignin, lignosulfonate, tannin, cardanol, pyrolysis oil of biomass, or hydrochar obtained by thermal treatment of agroforestry residues, said amount in weight being exactly the same amount in weight of replaced phenol or up to 25% more or less than the amount in weight of replaced phenol; (B) from 0,5 wt.% to 10 wt.% of at least one compound selected from resorcinol, methylresorcinol, ethylresorcinol or tannin, which is not condensed with the phenol-formaldehyde resin; <EOS>