Composite films obtained from a waterborne biopolyurethane. Incorporation of tartaric acid and nanocellulose

Abstract

Unmodified castor oil (CO) and tartaric acid (TA), a dihydroxy acid that can be obtained from various by-products of the grape processing to wine, were used in order to obtain bio-based waterborne polyurethanes (WBPUs). Isophorone diisocyanate (IPDI) was incorporated to the formulation to obtain transparent films. The effect of the incorporation of polycaprolactone diol (PCL), a biodegradable diol was investigated in order to increase the flexibility of the WBPU. Additionally, cellulose nanocrystals (CNC) were used as bio-reinforcement for these polyurethanes (thus, increasing the use of bio resources). The final neat and composite material films were characterized by ATR-FTIR, XRD, DMA and TGA. The addition of PCL in the polyurethane formulation was confirmed by FTIR and led to the decrease of the Tg of the films, thus to a more flexible material. CNC addition resulted in an increase of the storage modulus of the material, at all the temperatures tested. CNCs interact and generate a three-dimensional network of the reinforcement (>2 wt.%), improving the ability of the films to maintain structural integrity when they were immersed in water.