Simultaneous Enhanced Mechanical Properties and Foamability of Biodegradable PBAT via Physical Cross-Linking through Reactive Blending

While fully biodegradable poly(butylene adipate-co-terephthalate) (PBAT) is considered to be one of the most promising materials, the application of PBAT materials is still hindered due to its intrinsic low mechanical strength and poor foamability. Herein, a strategy is addressed to construct PBAT-based supramolecular bionanocomposites of high strength and excellent foamability with homogeneous dispersion of UPy aggregates via quadruple hydrogen bonding. The biocomposite was prepared by direct melt-blending of isocyanate-terminal ureido-pyrimidinone (UPy-NCO) and PBAT. It was found that the terminal hydroxyl group of PBAT quickly reacted with the isocyanate group of UPy-NCO during the mixing and in-situ formed a dimerized supramolecular polymer (PBAT-UPy-UPy-PBAT) owing to quadruple hydrogen bonding. The PBAT-UPy-UPy-PBAT could be further folded via longitudinal hydrogen-bonding interactions between the ureido groups of UPy units, forming ordered needle-like UPy nanoassemblies in the PBAT matrix. Such particular nanoassemblies could function as physical cross-linking points for PBAT-based composites, resulting in simultaneous improved mechanical strength and foamability of PBAT. This work paves a feasible avenue for manufacturing high-performance PBAT biocomposites and corresponding foams, which is challenging in existing industrial technologies.