Preparation And Properties Of Self-healing Polyurethane Without External Stimulation

Due to its excellent characteristics,polyurethane materials are used in all aspects of life.However,damage will inevitably occur during the use of materials.Therefore,people have started to research self-repairing polyurethane materials to extend the service life of materials and meet special application requirements.The introduction of reversible acylhydrazone bonds will make the material self-repairing,but it cannot be completely autonomously repair and it needs a certain external stimulus to achieve the self-repairing.In this paper,a self-repairing polyurethane material without external stimulus is synthesized.A synthetic reversible acylhydrazone bond-containing chain extender is introduced into the polyurethane chain,and the diisooctyl phosphate component is introduced into the system,so that the obtained polyurethane can achieve self-repair without external stimulation.In this dissertation,dimethyl succinate was used as a raw material to obtain amino-terminated succinic acid dihydrazide.The amino-terminated succinic acid dihydrazide and p-hydroxybenzaldehyde were used to obtain a dihydroxy chain extender.Because the reaction is a Schiff base reaction,that is easy to produce liquid crystal phase.In the experiment,the chain extender was dissolved in dimethyl sulfoxide solution.When the solution reached a certain concentration,a liquid crystal phase appeared and a lyotropic liquid crystal was formed.FTIR and 1HNMR were used to determine the molecular structure of the target product.polarizing microscope(POM)and digital viscometer were used to characterize the liquid crystal properties of the chain extender.FTIR and 1HNMR indicate that the target product has been successfully synthesized;polarized light microscope results show that the presence of liquid crystals is not observed until the concentration of the chain extender solution reaches 8% at the temperature,the liquid crystal was subjected to heating treatment again,it was found that the liquid crystal would gradually disappear when the temperature was raised above 90 °C.The results of the digital viscometer showed that as the solution concentration increased,the viscosity of the formed lyotropic liquid crystal also increased,and the fluidity of the solution became worse.After reaching 20% concentration,it is no longer fluid.In this thesis,the synthetic acylhydrazone bond-containing chain extender is introduced into the polyurethane to synthesize self-repairing polyurethane.It is reacted with hexamethylene diisocyanate(HDI)and polyethylene glycol(PEG-1000)to obtain a polyurethane prepolymer,and HDI trimer was added to crosslink to obtain selfrepairing polyurethane.The performance test of the synthetic polyurethane is as follows: FTIR shows that the synthesis of the prepolymer and its reaction with the chain extender have been successfully completed;DSC test shows that the material has two glass transition temperatures,the glass transition temperature of the soft segment(Tg1)is-24.87 °C and the glass transition temperature of the hard segment(Tg2)is 52.45 °C.TG test shows that the synthesized material has good thermal stability with the temperature range of 0-200 °C.The average tensile strength of the repaired polyurethane material was 0.82 MPa,and the average elongation at break was 223.74%,and the repair efficiency of the elongation at break and tensile strength reached 74.18% and 86.21% respectively after 72 h of acid stimulation,that shows the introduction of acylhydrazone bonds can achieve a good repair effect.It can swell without dissolving in N,Ndimethylformamide solution,the equilibrium swelling rate reaches 187.20%,and the gel content is 80.98%.Finally,a self-repairing polyurethane without external stimuli was synthesized and its properties were studied.In the last step of the synthesis of self-repairing polyurethane,different content of diisooctyl phosphate was added to synthesize selfrepairing polyurethane materials with different acid contents.It is compared with unacidified polyurethane,the test shows that: the more the amount of diisooctyl phosphate is added,the longer the gel time of the material,the Tg1 and Tg2 are more lower and the degree of microphase separation of the polyurethane is reduced in the DSC test.The material's heat resistance is reduced,the tensile strength is reduced in the mechanical test,and the elongation at break is increased.After cutting the material and leaving it at room temperature for 72 hours,it was found that materials containing 0.6% by weight,0.8% by weight,and 1.0% by weight of diisooctyl phosphate can perform self-healing,the highest repair efficiency reaches 9.86%.This proves that the addition of diisooctyl phosphate enables the synthesized polyurethane materials to perform a certain degree of self-repair without external stimulation.This study can provide a route for the preparation of self-repair materials without external stimulation.