Effects of Molecular Weight on the Miscibility and Properties of Polyurethane/Benzyl Starch Semi-Interpenetrating Polymer Networks

We successfully prepared a series of semi-interpenetrating polymer networks (semi-IPNs) from castor oil-based polyurethane (PU) and 20 wt % benzyl starch (BS) with different weight-average molecular weights (M(w)), coded as the PU/BS films. The M(w) values of a series of BSs were determined by size-exclusion chromatography combined with laser light scattering. The effects of the BS M(w) on the miscibility and properties of the resulting PU/BS films were investigated using reflection Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, scanning electron microscopy, optical microscopy, ultraviolet-visible spectroscopy, and tensile testing. The results revealed that the PU/BS films possessed much higher optical transmittance and tensile strength than the pure PU film. Interestingly, with a decrease of the BS M(w) from 1.69 x 10(7) to 5.70 x 10(5), the optical transmittance, tensile strength, and elongation at break of the PU/BS films increased from 82% to 89%, from 11.7 to 15.7 MPa, and from 121% to 180%, respectively. Therefore, the M(w) of BS plays an important role in the improvement of the miscibility and properties of the semi-IPN materials. On the basis of the analysis of the miscibility and the morphology of the PU/BS films, the interaction between the PU and the BS with relatively low M(w) was stronger than that with high M(w).