Mechanical, optical, and photochromic properties of polycarbonate composites reinforced with nano-tungsten trioxide particles

This work attempts to explore the feasibility of developing photochromic polymer composite films for modern building applications, using polycarbonate resin, and nanocrystal tungsten trioxide (WO3) particles as raw materials. The metal oxide powder was synthesized, characterized, and then mixed with polymer resin, using a solution-based process. The aim of this work was to investigate the effects of silane treatment and concentration of the tungsten trioxide particles on mechanical, optical, and chromic properties of the composite products. Interestingly, after exposure to sunlight, it was found that the spectral response of the polycarbonate/tungsten trioxide composite films changed remarkably from a kind of near infrared reflective material to near infrared absorbing material, regardless of the metal oxide concentration. This resulted in the overall decrease of near infrared transmittance through the substrates. By using the silane-treated tungsten trioxide as a replacement of the normal tungsten trioxide powder for reinforcing the polycarbonate, near infrared absorbance of the composite film was further increased. The color contrast and bleaching rate of the polycarbonate/silane modified tungsten trioxide specimen were also superior to those of the normal polycarbonate/tungsten trioxide system. The discrepancies were ascribed to the changes in chemical structure on the surface of the metal oxide which altered the state of polarity and an affinity for moisture absorption of the metal oxide. These factors, in turn, affected the access-ability of the photo-induced proton to intercalate the tungsten trioxide.