Carbon nanotube reinforced biobased poly(urethane urea) covalent adaptable network composite

A solvent-free approach was developed to incorporate carbon nanotube (CNT) into castor oil derived poly(urethane urea) (PPU) covalent adaptable network (CAN) based on dynamic piperidine-urea bonds to fabricate CNT reinforced PPU composites. The approach includes two steps i.e., pre-polymerization of castor with isophorone diisocyanate in flask and subsequent chain-extension with 1,3-bis(4-piperidinyl)propane (PIP) in the presence of CNT in an internal mixer. The effect on CNT content of the morphology, mechanical property, stress relaxation, and reprocessability of the PPU/CNT composites was investigated in detail. The results demonstrated that CNT dispersed well in the PPU networks due to the applied strong shear force which facilitated the dispersion of CNT in the PPU matrix before cross-linking. The well-dispersed CNT reinforced the mechanical properties of PPU significantly and the Young's modulus (E) of the composites were enhanced significantly when the content of CNT was >= 6 wt% due to the formation of CNT network in the PPU matrix. When the content of CNT was 10 wt%, the E of PPU-10%CNT was 927.59 +/- 149.05 MPa, which was improved by similar to 60% compared to PPU. The reprocessability of the PPU network was remained although the stress relaxation rate was reduced with incorporation and increasing content of CNT. In addition, the PPU/CNT composites could be degraded chemically to recycle CNT through reaction of the dynamic piperidine-urea bonds with additional PIP.