Castor oil-derived sustainable poly(urethane urea) covalent adaptable networks with tunable mechanical properties and multiple recyclability based on reversible piperidine-urea bond

Castor oil-derived polyurethanes are usually limited by their poor mechanical properties, non-processability, and non-recyclability due to their permanent crosslinking structures with soft backbone and high crosslink density. It is highly desired to fabricate mechanically robust, reprocessable, and recyclable polyurethane from renewable castor oil (CO) for sustainable development. Herein, we report sustainable poly(urethane urea) covalent adaptable networks (CANs) containing novel reversible piperidine-urea bonds with CO and commercially available isophorone diisocyanate (IPDI) and 1,3-bis(4-piperidinyl) propane (PIP) as raw materials. PIP with two six-membered rings as a structural modifier can adjust the network stiffness and crosslink density of PPU, which allows the mechanical properties of PPU to be tuned easily in a wide range from soft to tough and hard. Furthermore, the reversible piperidine-urea bonds formed by PIP and isocyanate endow PPU with stable reprocessability, exceptionally recyclable and strong weldability. Both the chemical structure and physical properties of the PPU network were almost restored completely after repeated processing. The mechanical properties of broken PPU can be recovered to higher than 88% of original PPU by thermal welding. In addition, the PPU can be recycled (or dissolved) chemically via deconstruction of the polymer network by exposure to PIP solution. The deconstructed polymer network can be reconstructed by addition of IPDI to the solution. The reconstructed PPU exhibited enhanced mechanical strength compared to the original PPU. In general, this investigation presents a facile, universal, and environmentally friendly approach to fabricate sustainable PUs with tunable mechanical properties, excellent malleability and multiple recyclability.

Automated summary

The study presents a method to fabricate sustainable polyurethanes from renewable castor oil, which exhibit good mechanical properties, reprocessability, and recyclability.