Study On The Preparation Of Epoxy Matrix Aeronautical Gelcoat And Its Cracking Resistance Properties Underthermal Shock

Because of the reducation of grinding work of composites structure,gel coat is used more and more widely.Aeronautical gel coat has not been reported inthe market recently and some higher performance is needed to meet the particularity of aeronautical condition.In this paper,the formulation of epoxy matrix aeronautical gel coat was confirmed.Then,the thermal shock（-50℃/30 min+90℃/30 min）cracking resistance properties of PEG modified epoxy gel coat were studied for the later application of gel coat in extreme aeronautic condition.Firstly,the usage amount of the diluent,thixotropic agent,nano TiO₂ and mica powder were fully studied to determine the formula of epoxy gel coat part A.Then,the crack properties of PEG modified epoxy gel coat under thermal shock were investigated by using a thermal shock specimen model and it was verified by analyzing the changing tendencies of thermal expansion and storage modulus.Finally,diethylenetriamine and modified DDM were used as gel coat part B with different proportion.The perfect proportion was determined by the impact toughness,mechanical property,HDT,thermal shock cracking resistance of cured gel coat.The experimental results indicated:1.The infrared spectrogram and Tg of PEG modified epoxy gel coat indicate that PEG has good compatibility with epoxy.5wt%PEG-1000 modified epoxy gel coat exhibits the highest impact strength of 4.97 kJ·m^-2,the impact strength is enhanced by 31.8%than that of neat epoxy gel coat.The thermal properties of epoxy gel coat show a decline trend with the increase of the molecular weight and content of PEG.2.The macroscopic initial cracking performance of 15wt%PEG-400 modified epoxy gel coat under thermal shock reaches the best,average initial crack needs conducting 10.4 cycles.The properties of crack extension resistance of modified epoxy gel coat are basically improved with the increase of PEG molecular weight and content.However,the crack width will be amplified with the increase of PEG molecular weight.3.Epoxy gel coat exhibits more excellent comprehensive performance when modified DDM as a part of gel coat part B.When the ratio of active hydrogen of diethylenetriamine and modified DDM is 8:2,the HDT,impact strength,tensile strength and tensile modulus reaches 97.3℃,4.89kJ·m^-2,32.2Mpa,2.28Gpa respectively,which is enhanced respectively by 27.36%,27.68%,9.38%,21.28%than that of cured epoxy gel coat with diethylenetriamine only.The crack width is smaller with the increase of the content of modified DDM,even though there is no obvious improvement of the crack resistance of epoxy gel coat under thermal shock.