A Humidity-Insensitive Waterborne Polyurethane Pressure-Sensitive Adhesive Modified by Castor Oil and Siloxane
Graphical The long hydrophobic fatty acid chains of natural castor oil and low surface energy siloxane can form drainage structures that would displace water from the surface of the substrate to make PSA effectively contact with the substrate surface. Subsequently, some polar groups such as ester, urea, urethane and Si-OH will form hydrogen bonds with the active groups on the surface of the substrate to achieve effective bonding on the wet substrate. Although waterborne polyurethane pressure-sensitive (PSA) has achieved great progress, achieving robust effective adhesion on the wet substrate surface is still challenging. Herein, we developed a humidity-insensitive waterborne polyurethane pressure-sensitive adhesive through the modification of bio-based castor oil and 3-aminopropyl triethoxysilane (APTES) as the end-capper. Improved bonding property on wet substrate via drainage of hydrophobic groups led to better humidity-insensitive adhesiveness. The results exhibited exceptional bonding performance (∼3.3N/25 mm) on the moist surface of the steel in the environment with a humidity of 100 % RH (Relative Humidity). Especially, the 180° peel forces of siloxane-terminated castor oil-based waterborne polyurethane (SCWPU) respectively enhanced by 13.33 % and 73.68 % compared with the blank sample when the air humidity increased from 50 % RH to 100 % RH. Silicone had the advantages of low surface energy, good heat resistance and good oxidation resistance. The heat resistance could be improved by introducing silicone into waterborne polyurethane. Tested by the TGA, the SCWPU3 PSA demonstrated great thermal stability (T HRI =144.32 °C). Besides, the PSA also exhibited low water absorption (20.6 %), and eligible viscoelasticity properties. These findings provided an impetus for the development of humidity-insensitive PSA.
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