STUDY ON EFFECTS OF ISOCYANATE INDEX ON THE PROPERTIES OF LIGNIN-BASED POLYURETHANE FROM HYDROXYPROPYL OXYGEN-ALKALINE LIGNIN

The lignin-based polyurethane films are prepared by solution casting from hydroxypropyl oxygen-alkaline lignin, hexamethylene diisocyanate (HDI) or methylene diphenyl diisocyanate (MDI). The effects of NCO/OH molar ratio (Isocyanate index R), the type of diisocyanate, glass transition temperature and tensile properties are studied. It is found that the R value and the type of diisocyanate influences the properties of prepared polyurethane film greatly. The glass transition temperature of MDI series based films increases more significantly with excessive diisocyanate than that of HDI series based films. The swelling of HDI series films in dimethyl formamide decreases with the increase of isocyanate index R. The effects of isocyanate index R on tensile strength of polyurethane film are obvious. The tensile strength of MDI series films are greater than that of HDI series. The strengths of the prepared polyurethanes are higher, and they are potential engineering plastics.