Flexible polyurethane foams green production employing lignin or oxypropylated lignin

An innovative and green chemistry synthetic approach was developed in order to employ lignin for the production of flexible polyurethane foams. Soda lignin and oxypropylated soda lignin were tested and compared. Glycerol and PEG 400 were used as polyol fractions for lignin liquefaction by microwave irradiation, which represents a novel green processing technique. The samples were produced with the ‘‘one-shot’’ technique, using two types of chain extenders in combination with liquefied lignin: castor oil and polypropylene glycol triol. Water was used as a single natural blowing agent, and polymeric diphenylmethane diisocyanate (PMDI) was employed as the isocyanate fraction. The work was carried out keeping the NCO/OH less than one hundred, thus enhancing the flexibility due to a lower crosslinking degree; all the foams were produced in free and controlled expansion. Two of the most efficient chain extenders were individuated thus introducing flexible chains into the macromolecular structure that can reduce the glass transition temperature of the materials and therefore generate foams with higher flexibility. The properties of the produced foams were compatible with the technical requirements for applications in packaging and for the production of the interior part of car seats.