Inhibition of Polyimide Photodegradation by Incorporation of Titanate Nanotubes into a Composite

摘要

The effect of UV light exposure on the properties of hexafluoroisopropylidene-diphthalic anhydride-oxydianiline (6FDA-ODA) polyimide (PI) and polyimide-titanate nanotube (TiNT/PI) composites has been studied using Raman spectroscopy, optical microscopy, nanoidentation and TEM. The degree of polymer photodegradation was estimated by measuring the change in affinity to a positively charged dye (methylene blue, MB). The mechanism of photoassisted transformations in polyimides usually involves scission of polymer chains accompanied by appearance of active radicals, which undergo further rapid transformations to more stable phenol, amine, and carboxylic functional groups. The accumulation of these groups can increase the degree of adsorption of charged dyes in the photodegraded polymer. It was found that neat PI showed a significantly increased capacity to adsorb MB after irradiation with UV, reaching a plateau after 1h. In contrast, TiNT/PI composite demonstrated a much slower rise in concentration of adsorbed MB even after 4h of UV exposure. Raman spectra indicated cleavage of C=O and C-F bonds in PI while only the C-F bond was damaged in TiNT/PI. Shorter cracks (approximate to 40 mu m long) appeared in TiNT/PI composites whereas macro cracks (100 mu m) were visible in neat PI after 3h of UV exposure. Brittleness was studied by comparing plasticity index which varied from 0 to 1 (0 corresponding to the most brittle material and 1 the most ductile one). Plasticity index reduced by 51% and 2% for PI and TiNT/PI, respectively after 3h UV irradiation, indicating that TiNT can protect underlying PI from further damage. The hardness of neat PI decreased whereas, for TiNT/PI, it increased under UV, suggesting crosslinking of broken polymer chains with nanotubes.Graphical AbstractPhotodegradation of a titanate nanotubes/polyimide composite can lead to cross-linking of broken polymer chains by nanostructured material, resulting in increased hardness.[GRAPHICS].