Synthesis and properties of an efficient self-healing material based on Eucommia ulmoides gum

Abstract

The unique molecular chain and aggregation structures of Eucommia ulmoides gum (EUG) lead to unique mechanical and thermal behavior. By regulating the microstructure of EUG via chemical reactions, changes in the mechanical and thermal behavior as well as the addition of specific functionalities of EUG can be achieved. Herein, we report a simple method to prepare intrinsic, autonomous, low-temperature self-healing materials by introducing pendent polyol moieties onto the chain of epoxidized EUG (EEUG). The relationship between the microstructure and properties of the resultant hydroxyl-functionalized EEUG (FEEUG) was analyzed by Fourier transform infrared spectrometry (FTIR), nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), tensile tests, and lap shear tests. As the modification degree of FEEUG increased, the mechanical behavior of FEEUG gradually changed from plastic to elastic and then to viscous, and the material showed highly efficient self-healing behavior. The self-healing efficiency was 77.8 % after 1 h of free contact at 30 °C and reached up to 90.2 % after 4 h. During five repeated lap shear tests, the adhesive strength of FEEUG28.6 (sample with a modification degree of 28.6 mol. %) decreased by only 10.9 %. The specific high chain mobility due to the diffusion and randomization of EUG at low temperatures and the reversible recovery of hydrogen bonds are believed to be the main causes for this phenomenon.