Flexible polyurethane foams green production employing lignin or oxypropylated lignin

Flexible polyurethane foams were produced via microwave irradiation of lignin or oxypropylated lignin by using glycerol and polyethylene glycol (PEG 400) as liquefaction solvents, and polypropylene glycol triol (PPG triol) or castor oil as a chain extender. The produced foams were then characterized according to their thermal, chemical and mechanical properties and resulted comparable with those same properties of commercial PU foams based on fossil polyolic sources. [Display omitted] •Lignin and oxypropylated lignin liquefaction was carried out by microwave heating.•Liquified lignin was used as polyol for producing flexible polyurethane foams.•Castor oil and polypropylene glycol triol resulted effective chain extenders. 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.