Study Of Self-healing Thermosetting Benzoxazine Resins

In the process of manufacture and utilization of a polymer material, the mechanical properties often decrease due to partial injuries or micro-cracks, which caused by thermal, mechanical, light or other reasons. Self-healing materials can heal the damages by the healing agents filled in microcapsules or hollow fibers previously embedded in the polymer matrix. However, the self-healing process is irreversible and non-repeatable. By contrast, the intrinsic self-healing materials contained reversible covalent bonds or other dynamic interactions have advantages in rapider healing rate, and repeatable healing manner.In the present work, we attempt to achieve self-healable polybenzoxazines using reversible transesterification. Bisphenol F based benzoxazines(BZ-F), succinic anhydride(SA) and zinc acetate(Zn(Ac)2) were used to synthesize the SA/BZ-F thermosetting resin(PSA-BZ). Then the self-healing processes of the PSA-BZ resins were observed by an optical microscope. The results showed that the PSA-BZ resins could heal micro-cracks(60μm) closed with a heating at 140 °C for about 40 min.The Dynamic Mechanical Analysis(DMA) and tensile tests indicated that the modulus of the PSA-BZ based composites could be increased by 1.5 GPa, and the glass transition temperature(Tg) could be decreased by about 10 °C, just by adjusting the BZ-F:SA molar ratio from 1:0.25 to 1:0.5. However, the content of Zn(Ac)2 in the PSA-BZ resins did not significantly affect the modulus and the Tg values. Moreover, the healing tests indicated that the weakened mechanical strength of the fatigued PSA-BZ composites after a repeat bending process can be recovered to 90 % of the initial by heating at 140 °C for 1 h. Furthermore, the transesterification reaction in the BZ-F networks was studied using thermo-gravimetric analysis(TGA) with dimethyl phthalate/BZ-F resin as a model. The activation energy of the transesterification reaction in the BZ-F networks energy was calculated by Arrhenius equation.Our polybenzoxazine self-healing materials have various advantages, including great heat resistance, low water absorption, near-zero volumetric shrinkage, no byproduct release on polymerization and so on. It provides an experimental and theoretical basis for expanding the application of polybenzoxazine resins.