UV-Curable Bio-Based Pressure-Sensitive Adhesives: Tuning the Properties by Incorporating Liquid-Phase Alkali...

Renewable pressure-sensitive adhesive (PSA) is an emerging field in adhesive industries as it is an excellent green alternative to depleting petroleum-sourced adhesives. Herein, we report the development of novel bio-sourced UV-curable PSAs with ∼50% biomass content originating from alkali lignin, cardanol, and linseed oil. Bio-based prepolymers cardanoldiol acrylate (CDA) and acrylated epoxidized linseed oil (AELO) were synthesized and used to prepare polyurethane acrylate (PUA)-based PSA systems. Alkali-lignin-based acrylates (LAs) in the liquid phase were incorporated into the PUA/AELO PSA system at 10-30 wt % loading to tune the functional properties. The Fourier transform infrared spectroscopy (FTIR) analysis showed weakened cross-linking in the PSA systems on LA addition, which is desirable for removable PSA applications. The single glass-transition temperature (T_g) noticed in all of the PSA formulations revealed good miscibility among the oligomers/prepolymers. The viscoelastic window also confirmed that the incorporation of 10-20% LA could improve the viscoelastic properties effectively to be used as removable PSAs. The addition of 20% LA into the PUA-based PSA system showed reasonable tackiness, lap shear adhesion (166 kPa), and 180° peel strength (∼2.1 N/25 mm) for possible nonstructural or semistructural applications. Lignin improved the thermal stability by hindering the degradation rate even at higher temperatures. Therefore, lignin-based PSAs with a high bio-based content paved the way of replacing petro-sourced PSA by proper tuning of the lignin content and modifications.