Study On The Preparation And Properties Of UHMWPE Flame Retardant Based On Modified Expandable Graphite

Ultrahigh molecular weight polyethylene(UHMWPE)usually refers to polyethylene with a molecular weight of more than 1.5 million.This extremely high molecular weight makes the molecular chains entangled in a large amount.The high entanglement degree resluts superior performance compared with conventional polyethylene,especially wear resistance,self-lubricating and impact-resistant properties.It widely used in aviation,aerospace,marine,airport transportation,military protection and other fields.However,when it encounters a fire,it also has the same problems as polyolefins,which are extremely flammable and then threaten people's lives and property.Therefore,designing and developing a flame retardant suitable for UHMWPE to obtain high flame retardancy is the key to solving the above problems.In this paper,UHMWPE was mixed with expandable graphite(EG)and ammonium polyphosphate(APP)for halogen-free flame retardant modification.The combustion properties and mechanical properties of the composites were investigated.Owing to EG and APP have the problems of high flame retardant addition which could deteriorate mechanical properties,the surface modification of EG must carry out for high performance by grafting small molecule flame retardant,coating silicone resin and coating polydopamine.The various properties of modified EG are tested by vertical combustion,limiting oxygen index,cone calorimeter,scanning electron microscopy,thermogravimetric analysis,Fourier transform infrared spectroscopy,Raman spectroscopy and X-ray photoelectron spectroscopy.And the characterization and analysis of the combustion performance and mechanical properties of UHMWPE/APP/EG.The main conclusions obtained are as follows:(1)UHMWPE is blended with expandable graphite(EG)and ammonium polyphosphate(APP)for flame retardant modification to discuss the minimum addition amount,the best compounding ratio and synergy effect of EG and APP.The results showed that EG and APP had a certain synergistic flame retardant effect,and the combination of EG and APP significantly improved the char formation.When the total addition amount was 25%,the UHMWPE/APP/EG composite could reach the V-0 level;the ratio of EG to APP is 2:1;the limiting oxygen index of UHMWPE/APP/EG composites is 31.8% and the heat release rate is the lowest.With the increase of EG ratio,the mechanical strength of UHMWPE/APP/EG composites also decreases.(2)EG was selected as the main modification object.DOPO modified expandable graphite(EG-g-DOPO)was prepared by grafting small molecule phosphorus-based flame retardant(DOPO)on the surface of EG.The maximum grafting ratio of DOPO was 6.54%.Then EG-g-DOPO and APP were added to UHMWPE in a ratio of 2:1.When the addition amount was 20%,UHMWPE was able to reach V-0 level,and the limiting oxygen index reached 30.6%.Thermogravimetric residual carbon reached 16.1%.EG-g-DOPO can also significantly reduce the heat release rate of flame retardant materials,increase the amount of residual carbon in combustion products,and form a dense carbon layer.(3)The surface of EG treated with a new bio-based flame retardant polydopamine(PDA)was carried out to prepare expanded graphite coated with polydopamine(EG@PDA),which has very good thermal stability and carbon residue at high temperature compared with EG.Then EG@PDA and APP are added to UHMWPE.20% of the total addition can make UHMWPE reach V-0 level and the limiting oxygen index is up to 29.2%.The free radical flame retardant mechanism of EG@PDA can significantly reduce the heat release rate and smoke emission of the flame retardant material.The presence of PDA can also solve the problem of poor compatibility between EG and UHMWPE,and improve the mechanical properties of UHMWPE composites.(4)EG(SEG)coated with silicone was prepared by coating EG with tetraethyl orthosilicate(TEOS)and a silane coupling agent(MPS).SEG and APP are used for flame retardant UHMWPE.Since Si element and MPS of SEG have smoke suppression and coupling effects,UHMWPE can reach V-0 level when the total addition amount is 15%.SEG can obvious increase smoke suppression effect and the tensile strength.The SEG can be decomposed to form silica at a high temperature to make the carbon layer denser and reduce the heat release rate of the flame retardant material.