Role of starch nanocrystals and cellulose whiskers in synergistic reinforcement of waterborne polyurethane

Starch nanocrystals (SN) and cellulose whiskers (CW) were fabricated successfully from the sulfuric acid hydrolysis of waxy maize starch granules and cotton linter pulp, respectively, and were characterized by transmission electron microscopy, atomic force microscopy and wide-angle X-ray diffraction. The nanocrystals and whiskers were embedded in waterborne polyurethane (WPU) matrix using a casting/evaporation technique. A synergistic reinforcing role of SN and CW in WPU was observed for the first time. With incorporation of 1 wt.% SN and 0.4 wt.% CW, the tensile strength, Young’s modulus and tensile energy at break of the WPU based nanocomposites were significantly enhanced by 135%, 252% and 136%, respectively, and the elongation at break remained basically compared to pure WPU. WPU/1% SN/0.4% CW system also exhibited a much better reinforcing effect than all of WPU/SN and WPU/CW systems. Furthermore, the WPU based nanocomposites possessed greater thermal resistance. The results clearly revealed that the different polysaccharide nanocrystals and whiskers combined together to form strong hydrogen bonding networks, leading to the synergistic reinforcement of WPU. This work provides a new eco-friendly pathway to prepare polymer nanocomposites with high performance by using natural nanocrystals and whiskers together.