Non-Isocyanate polyurethane from the extracted tannin of sumac leaves: Synthesis, characterization, and optimization of the reaction parameters

Abstract The extracted tannin from Sumac leaves (Rhus coriaria L.) as a bioresource was utilized for Non-isocyanate Polyurethanes (NIPUs) synthesis. The extracted tannin pre-reacted with dimethyl carbonate. Subsequently, NIPUs were synthesized via the reaction of carbonated tannin with hexamethylene diamine. The condition of the reaction was optimized for different parameters including tannin/DMC weight ratio, reaction time, and reaction temperature by response surface methodology (RSM). The results indicate the influence of the mentioned variables on the polyurethane synthesis yield was negative, positive, and ineffective, respectively. The structural, thermal, and mechanical properties of the synthesized materials were investigated by FTIR, MALDI-TOF, GPC, DSC, DMTA, TGA analyses, and tensile testing. The successful synthesis of NIPUs was confirmed by MALDI-TOF and FTIR spectroscopies. Tannin as a polyphenolic material contains many aromatic benzene rings. During thermal degradation due to benzene rings fusion, these rings convert to thermally stable materials and increase the char yield (36 wt% at 800 °C). Also, the synthesized NIPU demonstrated a high value of Tg (DSC: 75 °C, DMTA: 79 °C) which can be attributed to the existence of intermolecular hydrogen bonding, high crosslinked density, as well as restriction of the molecular segments mobility due to benzene rings rigidity. Finally, the Higher mechanical properties of the optimum sample confirm the efficiency of the optimization process. The results exhibited that the extracted tannin from the biobased resource can be a good alternative material for the NIPUs synthesis.