Plant Oil-Based Supramolecular Polymer Networks and Composites for Debonding-on-Demand Adhesives

The stimuli responsiveness of supramolecular polymers has recently been exploited for the development of adhesives that can be (de)bonded on demand when heated or exposed to UV light. However, it remains difficult to combine competitive solid-state mechanical properties and very low melt viscosity in one material. Here we report a new supramolecular polymer adhesives platform based on soybean oil as a multifunctional low-molecular-weight monomer (∼1500 g/mol) and isophthalic acid (IPA) groups that show hydrogen bonding and promote the formation of a reversible network. The polarity difference between the triglyceride backbone and the IPA groups leads to microphase separation, and the crystalline IPA domains act as physical cross-links. Heating the polymer above the melting temperature of the IPA-rich domains results in a dramatic viscosity reduction to 8 Pa·s at 120 °C. Once cooled to room temperature, the material properties are fully recovered as a result of the reassembly of the supramolecular network. Single lap joint adhesive tests performed at room temperature using glass and stainless steel substrates reveal shear strength values of 1.2 and 1.7 MPa, respectively, and heat and UV light can be used as external stimuli to debond on command. In addition, composites were prepared by adding 5 or 10 wt % microcrystalline cellulose (MCC) to the polymer, and this led to an increase of strength and modulus below the glass transition by up to 80% and 170%, respectively. Because the introduction of MCC partially hinders the crystallization of the matrix, the stiffness and tensile strength are reduced above the glass transition, while the elongation at break is significantly increased.