Effect of glycerol polymerization degree on the structure and humidity response of cellulose nanocrystals composite iridescent films

In order to investigate the effect of glycerol with different polymerization degrees on mechanical and humidity response of cellulose nanocrystalls (CNC), CNC were mixed with glycerol, triglycerol, hexamylglycerol and decaglycerol at different mass ratios to prepared a series of CNC/polyglycerol composite iridescent films by evaporation-induced self-assembly. The effect of glycerol polymerization degrees on structural color, mechanical and humidity response property of CNC composite iridescence film was systematically studied. The iridescent color of the composite iridescent film is blueshifted with the increase of the degree of polymerization due to the decrease of pitch of CNC chiral nematic sturcture, the maximum reflective wavelength decreases by up to 40 nm. The addition of glycerol (and polyglycerol) significantly improved the humidity response ability of CNC films. For the composite film with the same amount of addition, the lower the degree of polymerization of polyglycerol, the stronger the humidity response ability and the redder in high humidity enviroment. The color of 20wt% sample with glycerol change from cyan to red in relative humidity 98%, redshift about 170 nm. Compared with pure CNC film, the mechanical properties of the composite films were significantly improved. And compared with glycerol, the elongation at break and the tensile strength of decaglycerol composite films increased by 1.58 times and 2.48 times, respectively.