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

Christian Harito,Dmitry V. Bavykin,Brian Yuliarto,Frank C. Walsh,Hermawan K. Dipojono

doi:10.1007/s10924-019-01443-w

Christian Harito, Dmitry V. Bavykin + Show 3 more

Open Access

https://doi.org/10.1007/s10924-019-01443-w

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Abstract

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 1 h. In contrast, TiNT/PI composite demonstrated a much slower rise in concentration of adsorbed MB even after 4 h 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 (≈ 40 µm long) appeared in TiNT/PI composites whereas macro cracks (> 100 µm) were visible in neat PI after 3 h 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 3 h 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 Photodegradation of a titanate nanotubes/polyimide composite can lead to cross-linking of broken polymer chains by nanostructured material, resulting in increased hardness.

Highlights

Ultraviolet (UV) exposure is one of the most common environmental threats to polymer materials since it can lead to deterioration of properties and degradation
Polyimide film is widely used in technological uses ranging from space applications and electronics, in which exposure to UV light can be the subject of photostimulated degradation, usually occurring via scission of polymer chains and formation of active radicals, relaxation of which can lead to formation of phenol, amine, isocyanic and carboxylic functional groups [17]
The amount of methylene blue (MB) sorbed by photodegrading polymer for neat and composite polymer material after their UV exposure was calculated by combining Eqs. (2)–(4)

Summary

Graphical Abstract

Photodegradation of a titanate nanotubes/polyimide composite can lead to cross-linking of broken polymer chains by nanostructured material, resulting in increased hardness. Keywords Mechanism of photodegradation · Nanocomposites · Ceramics · Early detection · Dye staining

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