Effect of the blocked ratio on properties of natural fiber-waterborne blocked polyurethane composites

In this paper, natural fiber/waterborne polyurethane composites were prepared from the imidazole blocked waterborne polyurethane and eucalyptus fiber mats. The related properties of blocked waterborne polyurethane and natural fiber/polyurethane composites were, respectively, measured by differential scanning calorimetry, dynamic mechanical analysis, dynamic contact angle, water absorption, and scanning electron microscope. The results showed that blocked waterborne polyurethane readily improved storage modulus (G') and dynamic loss (tan) of the composites. The blocked ratio determined the density of the cross-linking structure in natural fiber/polyurethane composite and significantly affected natural fiber/polyurethane composite's properties. With the increase of the blocked ratio, dynamic mechanical properties showed up a maximum value and the water absorption ratio reached a minimum value. The deblocking reaction of blocked waterborne polyurethane took place between 107.5? and 124.5?. Due to these results, blocked waterborne polyurethane used as a matrix improved the dynamic mechanical properties of natural fiber/polyurethane composite.