Improving adhesion and antiaging properties of soybean oils-based pressure sensitive adhesives by phenolic acids grafting

Abstract

Three representative natural phenolic acids (ferulic acid: 1 hydroxyl group, caffeic acid: 2 hydroxyl groups, and gallic acid : 3 hydroxyl groups) were selected to investigate the effects of phenolic acids grafting on adhesion and antiaging properties of soybean oils-based pressure sensitive adhesives (PSAs). The grafting of gallic acid and ferulic acid led soybean oils-based PSAs to occur cohesive failures due to their large sterohindrance, while the grafting of caffeic acid did not. The optimal conditions for caffeic acid-grafted soybean oils-based PSA preparation were 0.6% caffeic acid, 7% phosphoric acid, reaction temperature of 50 °C and reaction time of 6 min. Under the optimal conditions, caffeic acid-grafted soybean oils-based PSA had the shear adhesion of more than 99 h, 180˚ peel strength of 2.30 N/cm, and loop tack of 0.97 N, which are approximately 5 and 3 times the control (soybean oils-based PSA without caffeic acid grafting: 180˚ peel strength of 0.46 N/cm and loop tack of 0.35 N), respectively. The grafting of caffeic acid significantly slowed down the aging rate of soybean oils-based PSAs as the peel strength residue reduced from 871.29% to 157.06% (82% decrease). Characteristic results showed that caffeic acid-grafted soybean oils-based PSA had better optical transparency (light transmittance: >100% vs. >95%), higher thermal stability (rapid decomposition temperature: 365 vs. 350 °C; maximum decomposition temperature: > 850 vs. 481 °C) and lower glass transition temperature (−12.70 vs. −5.40 °C) than the control. • Phenolic acids were grafted onto epoxidized soybean oils for PSA preparation. • Gallic or ferulic acid grafting led soybean oils-based PSA to occur cohesive failure. • Caffeic acid grafting enhanced the 180˚ peel strength and loop tack by 5 and 3 times. • Caffeic acid grafting delayed PSA aging with peel strength residue reduced by 82%. • Resulting PSA had higher thermal stability and lower glass transition temperature.