Bio-based Pressure Sensitive Adhesives Derived from Cardanol, Vanillin, and Sebacic Acid for Removable Nonstructural Applications

Green and sustainable pressure sensitive adhesive (PSA) with higher biomass content is an upcoming area in the adhesive industries, owing to its potential to replace crude-oil-based nonrenewable PSAs. Herein, we report a novel bio-based PSA with 89-92% biomass content, majorly derived from cardanol, a component derived from cashew nut shell liquid (CNSL) and from vanillin, a lignin derivative. The control PSA copolyesters were synthesized by the copolymerization of epoxidized cardanol with sebacic acid. Vanillin epoxide (VE) was incorporated into the prepolymer in different proportions (10-30 wt %) to tune its functional behavior through ring opening esterification and etherification. A single glass transition temperature (Tg) of all the samples revealed good miscibility of the system with desired transition temperature range (-16 to -21 degrees C) as applicable for PSAs. The 90 degrees peel strength of the formulations gradually improved upon an increase in VE loading with an optimum value of 4.82 +/- 0.38 N/25 mm, revealing their suitability for nonstructural and semistructural applications. A similar trend is noticed for the lap shear analysis of metal joints, wherein the PSA with 30% VE loading showcased excellent shear resistance of 2.61 +/- 0.08 MPa. The PSA showed reasonable shear adhesive performance for plastics joints and also good adhesion even after exposure to water and liquid nitrogen. The viscoelastic properties of uncured PSA formulations were found to satisfy the criteria for removable PSAs. The samples are found to be thermally stable up to 180 degrees C without any sort of degradation, indicating potential for high temperature PSA applications. Thus, vanillin and cardanol incorporated PSAs with similar to 90% biomass content pave the way for substituting the petro-based PSAs for nonstructural and semistructural applications being renewable and eco-friendly.