Valorization of Lignin Side-Streams into Polyols and Rigid Polyurethane Foams—A Contribution to the Pulp and Paper Industry Biorefinery oleh João A. Pinto, Isabel P. Fernandes, Virginia D. Pinto, Elson Gomes, Cátia F. Oliveira, Paula C. R. Pinto, Luís M. R. Mesquita, Paulo A. G. Piloto, Alírio E. Rodrigues, Maria-Filomena Barreiro