Stability of cross-linked acetic acid lignin-containing polyurethane

The thermo-oxidative stability of acetic acid lignin-containing polyurethane (LPU) that contains cross-linking agents, such as 1-aminopropyltriethoxy-silane (APTS) and/or trimethylolpropane (TMP) was investigated based on the thermogravimetric analysis (TGA) method, their kinetic parameters in the thermo-oxidative process was determined. FT-IR certified the occurrence of interaction between lignin and polyurethane (PU). It was found that continuous membrane can be formed when lignin concentration was 43.3%, but rupture took place when it increased to 50%. When the degradation was performed in nitrogen, TG and dynamic differential thermogravimetry (DTG) results demonstrated that the PU underwent three stages of degradation while the LPU involved one main degradation stage with a shoulder, and the degradation stability increased with the increase in the lignin concentration and PEG length. It was also found that the addition of a cross-linking agent is beneficial to the improvement of thermal stability and, in particular, APTS gave the best thermal stability for the LPU produced, among the cross-linking agents tested. Furthermore, LPU exhibited multistage degradation process in air and displayed higher thermo-oxidative stability than PU. At the same time, the kinetic study showed that LPU modified with APTS exhibited higher activation energy than LPU modified with TMP. And the maximum activation energy was found for the sample modified with the simultaneous addition of APTS and TMP.