Electrospun Semi-Alicyclic Polyimide Nanofibrous Membrane: High-Reflectance and High-Whiteness with Superior Thermal and Ultraviolet Radiation Stability for Potential Applications in High-Power UV-LEDs

• Main Authors: Xinxin Zhi, Huasen Wang, Xinying Wei, Yan Zhang, Yuancheng An, Haoran Qi, Jingang Liu
• Format: Article
• Language: English
• Published: MDPI AG 2021-07-01
• Series: Nanomaterials
• Subjects: polyimide; electrospinning; nanofibrous membrane; reflectivity; UV-LED
• Online Access: https://www.mdpi.com/2079-4991/11/8/1977

Polymeric nanofibrous membranes (NFMs) with both high whiteness and high thermal and ultraviolet (UV) stability are highly desired as reflectors for ultraviolet light-emitting diodes (UV-LEDs) devices. In the current work, a semi-alicyclic and fluoro-containing polyimide (PI) NFM with potential application in such kinds of circumstances was successfully fabricated from the organo-soluble PI resin solution via a one-step electrospinning procedure. In order to achieve the target, a semi-alicyclic PI resin was first designed and synthesized from an alicyclic dianhydride, 3,4-dicarboxy-1,2,3,4,5,6,7,8-decahydro-1-naphthalenesuccinic dianhydride (or hydrogenated tetralin dianhydride, HTDA), and a fluoro-containing diamine, 2,2-bis[4-(4-amino-phenoxy)phenyl]hexafluoropropane (BDAF), via an imidization procedure. The derived PI (HTDA-BDAF) resin possessed a number-average molecular weight (<i>M</i>_n) higher than 33,000 g/mol and was highly soluble in polar aprotic solvents, such as <i>N,N</i>-dimethylacetamide (DMAc). The electrospinning solution was prepared by dissolving the PI resin in DMAc at a solid content of 25–35 wt%. For comparison, the conventional high-whiteness polystyrene (PS) NFM was prepared according to a similar electrospinning procedure. The thermal and UV stability of the derived PI and PS NFMs were investigated by exposure under the UV-LED (wavelength: 365 nm) irradiation. Various thermal evaluation results indicated that the developed PI (HTDA-BDAF) NFM could maintain both the high reflectance and high whiteness at elevated temperatures. For example, after thermal treatment at 200 °C for 1 h in air, the PI (HTDA-BDAF) NFM exhibited a reflectance at a wavelength of 457 nm (<i>R</i>₄₅₇) of 89.0%, which was comparable to that of the pristine PI NMF (<i>R</i>₄₅₇ = 90.2%). The PI (HTDA-BDAF) NFM exhibited a whiteness index (<i>WI</i>) of 90.88, which was also close to that of the pristine sample (<i>WI</i> = 91.22). However, for the PS NFM counterpart, the <i>R</i>₄₅₇ value decreased from the pristine 88.4% to 18.1% after thermal treatment at 150 °C for 1 h, and the sample became transparent. The PI NFM maintained good optical and mechanical properties during the high dose (2670 J/cm²) of UV exposure, while the properties of the PS NFM apparently deteriorated under the same UV aging.