Synthesis of bio-based polyurethane foam modified with rosin using an environmentally-friendly process

Abstract

Rosin is mainly composed of abietic acid, which enhances the properties of materials that have a high cost and which involve a complicated process. This study produces high-performance polyurethane (PU) foam at a normal temperature and pressure without the use of a solvent using a simple and environmentally-friendly process. A small amount of rosin is added as a raw functional monomer to modify the PU foam. Castor oil dissolves the rosin and can be used directly as a bio-based polyol. PU foams are prepared from castor oil with 0, 5 and 10% molar ratio rosin as a polyol and isocyanate Desmodur N. The molar ratio of NCO/OH is 1.5 and 2.0. The results show that increasing the molar ratio of rosin increases the density and compressive strength of PU foams. The compressive strength is increased more than three-fold in optimal conditions, which is a better result than previous studies. The wettability results show that the water contact angles of foams are 109°–115°, which dictates the surface is hydrophobic. The water absorption kinetics of foams obey Schott’s second-order kinetics and the results verify that adding rosin increases the initial water-aborted rate and decreases water absorption. The solvent resistance results show that the foams have good durability in water and solvents. The patterns for thermogravimetric analysis (TGA) show that a PU foam with a 5% molar ratio of rosin is most thermally stable. The improvement in mechanical and chemical properties is attributed to the hydrophenanthrene ring structure of rosin, and less related to the molar ratio of NCO/OH. This study demonstrates that bio-based PU foams are improved by adding only 2–4 wt% rosin to produce foams with excellent mechanical and chemical properties, controlled water absorption and thermal stability. The results show that this green synthesis process is a viable alternative to current manufacturing processes for high-quality foams.