| Due to the excellent electrical insulation,comprehensive mechanical proprieties,chemical stability and adhesiveness,epoxy resin（EP）is currently one of the most widely used thermosetting resin materials.However,the deficiency of brittleness,ignitability,flammability with huge heat release limits some application in high-quality required industrial fields like electronics,transportation.Carbon nanotubes（CNT）harbor many advantages like large length-diameter ratio,superior specific strength,and high thermal stability,which can improve the mechanical properties of CNT reinforced polymers with only small amount of CNT.Moreover,the burning rate and heat release rate of CNT reinforced polymers composites also can be reduced,showing some flame-retardant effect.The problems are that the CNT reinforced polymers composites could not satisfy the industrially required reinforcement material for composite materials,can greatly improve the thermal flame retardancy with sole addition of CNT.Thus,exploring a facile and efficient strategy to enhance the flame-retarding,reinforcing and toughening properties of modified CNT reinforced polymers composites simultaneously is of great value to the scientific and industrial research.In this paper,the CNT was firstly in situ grafted with a layer of hyperbranched polyphosphoramide（HBPPA）,and then was in situ coated with molybdenum disulfide（Mo S2）and layered double hydroxides（LDH）respectively to form different CNT hybrid flame-retardants.They were added into the EP to fabricate different EP composites and then their flame-retarding,mechanical and thermal-stable performance were investigated to explore the relative flame-retarding,reinforcing and toughening mechanisms.The details are as follows:1.By using 4,4-diaminodiphenylmethane（DDM）and phosphorus oxychloride（POCl3）as raw materials,triethylamine as catalyst and acid binding agent,the hyperbranched polyphosphoramide（HBPPA）is in situ grown on the surface of CNT-COOH to form a hybrid CNT@HBPPA,whose thickness,thermal stability and char residue can be controlled by adjusting the mass ratio of DDM+POCl3 and CNT-COOH.It was found that the thickness of CNT@HBPPA was about 43nm with no crossing,the char residue at 700℃was 61.9%when the mass ratio was at 1:3.Meanwhile,the EP composites with 2wt%CNT@HBPPA（1:3）showed the best flame retarding properties withe the highest LOI value of 28.5%and UL94 V-1 rating.The investigation on the char morphologies revealed that more compact and high-quantity char yield（improved by 28.24%compared with pure EP）played the key role to enhance the flame retardancy.Further,the EP/2%CNT@HBPPA composites also exhibited the optimum mechanical properties,eg the tensile strength,impact strength,flexible modulus and Tg of above-mentioned composites achieved to be 102.48 MPa,16.56 KJ/m2,2022MPa,173.4℃,which are respectively 42.83%,65.93%,68.35%,44.52%.higher than those of pure EP.2.A new hybrid flame-retardant of CNT@HBPPA@Mo S2 was fabricated by using a hydrothermal reaction in an autoclave with CNT@HBPPA,molybdic acid and thiourea.A comparison of EP/CNT@HBPPA@Mo S2 and EP/CNT@HBPPA was explored on flame-retarding and smoke suppression performance.The chemical and morphologies of CNT@HBPPA@Mo S2 was informed by several equipment including FTIR,XRD,XPS,TEM,EDX and so on.The layered Mo S2 was evenly grown on the surface of CNT@HBPPA with the sulfur content ratio of 8.98%.The TG results showed that CNT@HBPPA@Mo S2 possessed higher thermal stability than CNT@HBPPA.EP composites with 4wt%CNT@HBPPA@Mo S2 showed the highest LOI of 30.5%and passed the UL94 V-1 rating with shortened total burning time of12s.Further,the total smoke release also reduced.The tensile and impact strength of the composite were 86.3MPa,10.42KJ/m2,which are still higher than those of pure EP（71.75MPa,9.98KJ/m2）.3.Another hybrid flame-retardant of CNT@HBPPA@LDH was prepared by using magnesium nitrate and aluminium nitrate as starting materials,whose structure and morphology were characterized by FTIR,XRD,TEM.The char residue at 700℃of CNT@HBPPA@LDH was 59.5%in the N2 atmosphere.The primary research showed that only 2wtt%CNT@HBPPA@LDH can make the EP composites to reach a LOI value of 28.5%and pass the UL94 V-1 rating with total burning time of 14s.However,the further increased loading of CNT@HBPPA@LDH brought bad results on the vertical burning test which may be caused by the unevenly dispersion of the above nano hybrids.More investigation of EP/CNT@HBPPA@LDH will be further conducted to make their flame-retarding and mechanical properties more clear. |
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