Study On The Preparation Of Hydroxylated Eucommia Gum And The Modification Of UV-Curable Polyurethane Self-Healing Coating

The self-repair of polymer materials refers to the ability to self-repair part or all of its properties under certain conditions after being damaged.Self-repair is divided into foreign aid type and intrinsic type.Intrinsic self-healing materials mainly rely on reversible covalent bonds and reversible non-covalent bonds to achieve self-repair,it has the advantages of mild repair conditions and repeated repairs many times,but it also has the disadvantage of low strength.Eucommia Ulmoides Gum is a bio-based polymer material with a unique "rubber-plastic" duality,and has good fatigue resistance,abrasion resistance,shock resistance and tear resistance,it also has the advantages of strong insulation,water and humidity resistance,and excellent shape memory.But it's high molecular weight makes it difficult to directly use as coatings,adhesives and composite materials.It is urgent to carry out its modification research to promote its application in the fields of rehabilitation medicine,marine equipment anti-corrosion,and sports goods.Reversible covalent bonds such as disulfide bonds and hydrogen bonds have poor self-repairing ability and weak mechanical strength,while Eucommia Ulmoides Gum has a large molecular weight and is difficult to directly use as a polymer material.In view of the above problems,this thesis has carried out research from three aspects:UV-curable polyurethane self-healing coating,hydroxylated Eucommia Ulmoides Gum and hydroxylated Eucommia Ulmoides Gum modified UV-curable polyurethane self-healing coating.The specific content is as follows:(1)Study on preparation and performance of UV curing Polyurethane self-healing coating.Based on the reaction mechanism of isoc yanate and polyol,a UV curable polyurethane self-healing resin containing disulfide bonds was prepared.Through FI-IR,TG-DSC,tensile test and scratch test,the effects of different hard segment content and different disulfide bonds on the mechanical pro perties,solvent resistance,adhesion and self-repairing properties of DSPU coatings were studied and compared.The results showed that with the continuous increase of the hard segment content of DSPU resin,the adhesion,elongation and solvent resistance of DSPU coatings decreased,but the mechanical properties of the coatings continued to increase.When the hard segment content of DSPU resin is 69.26%,the maximum tensile strength of the coating is 10.45 MPa,but the elongation is only 74.9%,the adhesion is only Grade 2 and the solvent resistance is also poor.In addition,with the continuous increase of the disulfide bond content in DSPU resin,the self-repairing ability of DSPU coating improves,but when the hard segment content exceeds a certain limit,the self-repairing performance is also weaker.This is because the high content of hard segments in the polyurethane segment is not conducive to the movement of the molecular chain,reducing the probability of sulfur atoms forming disulfide bonds with sulfur atoms at the damage site,thereby reducing the self-repair performance.Considering the self-repair efficiency and performance comprehensively,the hard segment content of the best DSPU resin formulation is 54.03%,and the disulfide bond content is 6.58%.At this time,the tensile strength of the coating is8.65 MPa,and the elongation is 129.5%,after 15 minutes at 60°C,the scratches on the DSPU coating surface disappeared obviously,with the characteristics of low self-repair temperature and high repair efficiency.(2)Study on synthesis of hydroxylated Eucommia Ulmoides Gum based on thiol-ene click chemistry.Under 365 nm ultraviolet light irradiation,mercaptoethanol reacts with the carbon-carbon double bonds on the molecular chain of Eucommia gum to synthesize hydroxylated Eucommia Ulmoides Gum(HEUG).Using chemical titration and nuclear magnetic resonance,the effects of different solvents such as water,N,N-dimethylformamide,chloroform,molar ratio of carbon-carbon double bond to sulfhydryl group and reaction time on the degree of hydroxylation modification of Eucommia gum were studied.The results show that the hydroxylation degree of HEUG obtained with chloroform as the solvent is higher,while with water is lower.This is because Eucommia Ulmoides Gum can be dissolved in chloroform and the reaction proceeds in the same phase.The optimal reaction time is 6 hours and the optimal molar ratio ? is 3:1.At this time,the hydroxyl value of the prepared hydroxylated gutta-percha gum can reach 156 mg KOH/g,and the higher hydroxyl value makes it very soluble in ethyl acetate Common solvent for esters and acetone.The reaction has the advantages of simplicity,controllability,and high efficiency.We provide a new idea for the modification of hydroxylate d Eucommia Ulmoides Gum,which has certain application value.(3)Study on the properties of hydroxylated Eucommia Ulmoides Gum modified UV-curable polyurethane self-healing coating.In order to improve the mechanical properties,self-healing properties,adhesion and solvent resistance of DSPU coatings,hydroxylated gutta-percha glue is dissolved in ethyl acetate and then added to DSPU resin to obtain a UV curable polyurethane modified by hydroxylated Eucommia Ulmoides Gum Self-healing coating(HEUG/DSPU).The effects of different amounts of hydroxylated Eucommia Ulmoides Gum on the mechanical properties,solvent resistance,heat resistance,and self-repair properties of DSPU coatings were studied and compared by using infrared spectroscopy,Raman spectrosco py,TG-DSC,scanning electron microscopy,and pulling Stretch test and scratch test methods.The results show that with the continuous increase of HEUG addition,the tensile strength,self-healing performance,adhesion and solvent resistance of DSPU coatin g continue to increase.the tensile strength of the coating is 12.90 MPa and the elongati on is306.99% when the mass fraction of HEUG is 5%(DSPU-5wt HEUG),and the self-repairing efficiency can reach 90.71%.Meanwhile,the scratches can be completely repaired after being placed at 60? for 15 min.Instantaneous repair at room temperature can support a weight of 2 Kg items.When the amount of HEUG is increased again,the performance of all aspects of the coating will be reduced.This is because the compatibility of the HEUG/DSPU coating is reduced when the amount of addition is too large,thereby reducing the performance of the coating.In addition,the addition of HEUG does not reduce the transparency of the original resin.