| During the molding process and long-term use of polymer materials,micro-cracks are easily caused by external factors such as external force extrusion and impact.If the crack is not effectively repaired in time,it will inevitably lead to a reduction in the service life of the material and a decline in mechanical properties,thereby increasing the potential safety hazards of the material during use.According to the principle of bionics,when an organism is injured,it autonomously recognizes the location of the wound and transforms physical properties into chemical energy and physical response capabilities that can heal its own injuries through the supply of materials and external stimulation.Therefore,it is of great research significance to prepare intelligent polymer materials with self-diagnosis,identification and autonomous repair capabilities by introducing new self-healing technology into polymer materials.In this paper,the effect of different content of microcapsules on the mechanical properties and repair properties of self-healing materials was studied by filling epoxy resin microcapsules in Nano-Si O2 modified epoxy resin substrates.In addition,Diels-Alder dynamic covalent bonds was introduced into epoxy resin and polyurethane systems,an intrinsic self-healing polymer material with multiple repair capabilities was prepared,and the effects of reprocessing properties and repair times on the repair properties of self repairing materials were further studied.The details are as follows:（1）The one-step in-situ polymerization method was used to prepare epoxy resin microcapsules（EP-UF）that with urea-formaldehyde resin（UF）as the core material and bisphenol E-51 epoxy resin（EP）as the core material,and the average particle diameter is 146μm.With the help of KH-550 as a bridge,Nano-Si O2 and epoxy resin were bonded together through chemical bonding,and Si-O-C bond was successfully introduced into the epoxy resin to form an inorganic-organic framework.The mixture of epoxy resin microcapsules and latent curing agent dimethylimidazole was uniformly filled into the Nano-Si O2 modified epoxy matrix material,and the effect of different contents of epoxy microcapsules and Nano-Si O2 on the mechanical properties and repair performance of the epoxy matrix composite was studied.The results show that when the epoxy microcapsule content is 10 wt%and Nano-Si O2 content is 8 wt%,the mechanical properties such as the flexural strength,flexural modulus,impact strength and tensile strength of Nano-Si O2 modified epoxy resin microcapsule-filled self-repairing composite are 108.29 MPa,4704.40 MPa,5.91 KJ·m-2,and 78.67 MPa,respectively,which are 40.86%,37.16%,217.74%and 31.53%higher than the unmodified self-repairing composites in various mechanical properties,respectively.In addition,its repair rate reached 94.6%.（2）Polyethylene glycol diglycidyl ether（PEGDE）was synthesized by one-step method.Each factor is tested and analyzed by the controlled variable method to obtain the optimal set of synthetic schemes.When n（ECH）/n（PEG-400）is 6,the reaction temperature is 40℃,the amount of catalyst is 1.6 g,the amount of sodium hydroxide is 9 g,and the reaction time is 12 h.The synthesized polyethylene glycol diglycidyl ether had the best epoxy value and yield,the epoxy value is 0.38 mol/100 g,and the yield is 91%.Furan amine was used to link the hard segment EP and the soft segment PEGDE into linear macromolecules,which were reacted with bismaleimide to synthesize an intrinsic self-healing epoxy resin EP-DA containing a thermoreversible DA dynamic covalent bond.By adjusting the content of EP and PEGDE,soft-hard-soft structural polymers with better mechanical properties were prepared.When the content of PEGDE and EP in the EP-DA segment each accounts for 50%,its heat resistance and mechanical properties reach the best,and its tensile strength can reach 24.26 MPa.The DSC test determined that the optimal temperature for the DA reaction and the DA reverse reaction are 60℃and 122℃,respectively.At the same time,the tensile test of the sample shows that the DA reaction was basically complete when the sample repair time is 4 h.In addition,EP-DA is thermally reversible,thus giving it good reworkability and self-repairing properties.After heat treatment at 122℃for 0.5 h and heat treatment at 60℃for 4 h,it was found that scratches with a depth of 3 mm have basically healed.The maximum repair rate can reach 88.41%.After three repairs of the sample,the repair rate can still reach more than 68%.（3）FGE-FA containing binary furan group was prepared by the reaction of furfuryl glycidyl ether（FGE）with FA;Polytetrahydrofuran（PTMG）and isophorone diisocyanate（IPDI）were used to prepare IPDI-PTMG with isocyanate groups at a molar ratio of 1:2.The polyurethane（PU-DA）containing quaternary furan group was prepared by the reaction of FGE-FA with IPDI-PTMG,and then reacted with bismaleimide（1,8-BMI）to prepare the intrinsic self-healing polyurethane（PU-DA）containing thermo reversible Diels-Alders dynamic covalent bond.The DSC test determined that the optimal temperatures for the DA reaction and the DA reverse reaction are 70℃and 132℃,respectively.The swelling and dissolution test was performed on PU-DA,and it was immersed in DMF for 72 h.It was found that PU-DA placed at 30℃hardly dissolved in DMF solvent,while the sample placed at 90℃was basically dissolved in In the solvent,PU-DA was shown to be thermally reversible.Based on this property,additional tests were performed on the sample,and the long PU-DA sample was cut into several small pieces,which were placed at 132℃and 70℃for 30 minutes and 4 hours,respectively,and the pieces were processed.The results show show that PU-DA can be reprocessed.A tensile test was performed on the PU-DA sample and the repair rate was analyzed.The tensile strength of the original PU-DA sample is 4.20 MPa,the elongation at break is 305.59%,and the first repair rate of the sample is 94.76%.After the sample is stretched three times,the elongation at break can still reach 264.74%,and the repair rate can still reach more than 70%. |
