2.2. Preparation of the FTIR experiments
The infrared experiments were conducted on a FTIR Bomen Model MB104 (Quebec, Canada) working in the ATRmode. The ATR accessory from Graseby Specac (Smyrna, GA, USA) was equipped with a heater controller and a silicon crystal, amaterial optically denser than the polyurethane. In order to obtain a more stable background, the ATR optics was continuously purged with nitrogen during the experiments. Lignin and PCLwereweighed in an analytical balance in the desired proportions and the mixture homogeneized by stirring. Then, molten MDI was added by volume in one portion and the reactive species thoroughly mixed together during 30 s and rapidly transferred to the ATR cell. Time zero of the
reaction was taken as the addition moment of the MDI.