Preparation Of Two-dimensional Covalent Organic Frame Materials And Their Application In Epoxy Resin Flame Retardant

Epoxy resin(EP)is a kind of thermosetting resin with excellent performances and wide applications,but it has poor flame retardant performance,which is difficult to meet the burning level requirements of some applications.In order to improve the flame-retardant properties of EP,researchers are constantly conducting relevant research.Covalent organic framework(COF)materials are a new class of organic porous materials with a wide range of applications.Since two-dimensional COF is similar in structure to graphene and may contain flame-retardant elements such as phosphorus and nitrogen,COF has attracted attention and research in the flame-retardant industry in recent years.This paper focuses on the preparation of COF and its application in epoxy resin flame retardant.The specific research contents are as follows:(1)A covalent organic framework material COF was synthesized by simple solvothermal method with melamine(MEL)and cyanide chloride(TCT)as raw materials.The morphology and structure of COF were characterized by infrared spectroscopy,scanning electron microscopy and other testing methods.The COF-EP flame-retardant composite material was prepared by the casting method.The test results showed that the flame retardancy of COF-EP were significantly improved compared with that of MEL-EP and EP.The limit oxygen index(LOI)of 20COF-EP increased from 24.8%to 29.3%,the vertical burning test(UL-94)reached V-0 rating from no rating,and without dripping.The Cone Calorimetry Test(CCT)showed that the peak heat release rate(PHRR)of 20COF-EP was reduced from 1185.5 kW/m2 to 395.0 kW/m2,a decrease of 66.7%;the total heat release(THR)was reduced by 19.4%;The total smoke release rate(TSP)and peak smoke release rate(PSPR)had been significantly reduced by 63.8%and 82.5%,and the 20COF-EP char residue had increased significantly.The tensile strength and impact strength of 20COF-EP decreased by 1 8.1%and 33.7%due to the large addition amount.However,the same amount of 20MEL-EP decreased the tensile strength by 44.3%and the impact strength by 44.2%,which showed that the effect of COF was better than that of MEL on the mechanical properties of EP.(2)Phosphorylated melamine(MP)MEL TCT was used as raw material to obtain the phosphorylated covalent organic skeleton material PCOF,which could be used as flame retardant and mechanical reinforcement of EP.The results showed that the introduction of phosphate did not cause great damage to the original layered structure,and the amount of PCOF char residue was higher than that of COF.Good flame retardant performance of PCOF has been shown for EP,the LOI value of 12PCOF EP was increased to 29.3%,and the UL-94 test was improved to V-0 rating.PHRR and THR were decreased by 79.2%and 68.9%respectively.The flame retardant efficiency of PCOF was higher than that of MP,and the UL-94 rating of 12MP-EP could only reach V-1 rating.In addition,PCOF had good water resistance.After soaking,the LOI value was slightly increased,and the self-extinguishing time of UL-94 was shorter.The residual char electron microscope showed that PCOF-EP had a more continuous and dense char layer.The tensile properties and impact resistance of 4PCOF-EP were improved by 37.4%and 7%respectively.This was because PCOF participated in the curing process of EP,improved the crosslinking network density of EP,and had better dispersion.(3)This part pioneered the growth of PCOF in situ on GO and CNT to form PCOF-coated carbon nanomaterials(PCOF@CM).The structure and morphology were characterized.The loading capacity of CM was about 5 wt%.The LOI value of 5PCOF@CM-EP had been increased by 8%and the UL-94 was V-1 rating.The PHRR and THR of 5PCOF@GOEP were decreased by 37.4%and 21.7%respectively.The PHRR and THR of 5PCOF@CNT-EP were decreased by 25.5%and 23.3%respectively.In addition,the TSP and PSPR of 5PCOF@GO-EP were reduced by 62.2%and 59.0%respectively.The TSP and PSPR of 5PCOF@CNT-EP were reduced by 55.0%and 56.4%respectively,which indicated that both of them had good effect on flame retardant and smoke suppression of EP,and there was little difference in efficiency between them.The mechanical properties were maintained with the addition of PCOF@CM,and the tensile strength and impact strength of 5PCOF@CM-EP were slightly reduced.