Structure and properties of cellulose films coated with polyurethane/benzyl starch semi-IPN coating

A series of water-resistant cellulose films was prepared by coating castor oil based polyurethane (PU)/benzyl starch (BS) semi-interpenetrating polymer networks (semi-IPN). All of the coated films, with a very thin coating layer of about 0.4 mu m, exhibited much better optical transmittance, water resistance, and mechanical properties than the original regenerated cellulose (RC) film, suggesting a strong interface interaction between PU/BS coating and cellulose substrate. The BS concentration in the coating had a significant effect on the properties of the coated films. With an increase of BS concentration in the coating from 10 to 70 wt %, the tensile strength and storage modulus of the coated films increased. Especially, as the tensile strength achieved a maximum value of 102 MPa, the elongation at break of the coated film still maintained a relatively higher value of 10%. Meanwhile, the coated films displayed good biodegradability, and the biodegradation rate increased with increasing BS concentration in the semi-IPN coating. Therefore, the BS component in the PU/BS coating plays an important role in the simultaneous enhancement of physical properties and biodegradability of the coated films. The good water-resistance character of the coated films could effectively extend the applying area for cellulose.