Construction And Application Of Intumescent Flame Retardant System Based On Ionic Liquids

Ionic liquids(IL)have received extensive attention in the field of preparation technology of flame-retardant materials due to their excellent thermal stability,non-combustibility and infinite designable nature.Two ionic liquid flame retardants and two synergists were synthesized by simple and convenient methods.According to their composition and properties,they were combined with traditional intumescent flame retardants respectively,and a new intumescent flame-retardant system was constructed by combining their advantages and action mechanism in order to solve the problem of low flame-retardant efficiency of single flame retardant in high-density polyethylene(HDPE)and wood-plastic composite(WPC).Specific studies are as follows:1.Two functional ionic liquids,1-butyl-3-methyl-imidazole hypophosphite(BMP)and1-(3-triethoxysilylpropyl)-3-methylimidazole hypophosphite(SiMP)were synthesised,and the structural properties were characterized by FT-IR,¹HNMR,¹³CNMR and³¹PNMR.The impacts of the content of them on flammability and thermal decomposition behaviors of WPC were comprehensively investigated.When 10 wt%BMP was added,the LOI value reached a maximum of 24.2%,and the peak heat release rate(PHRR),total heat release(THR)and total smoke production(TSP)were reduced,but with an increase in BMP content,the flame retardancy decreased slightly.For the WPC/SiMP system,with an increase in SiMP content,the LOI values gradually increased.When 20 wt%SiMP was added,the LOI value reached a maximum of 24.8%,and the PHRR,THR and TSP were lower than pure WPC.The SEM-EDS and FT-IR analysis of the chars showed that both BMP and SiMP could catalyze the char-forming reaction in the condensed phase and promote the formation of chars.In particular,the chars layer of WPC/SiMP were more continuous and dense,forming a structure with thermal oxidation resistance such as P-O-C,Si-O-Si,Si-O-C and Si-O-P,which exerted an effective barrier effect,thereby inhibiting combustion and thermal degradation of underlying substrates.The results of TGA analysis showed that when 20 wt%BMP or SiMP was added,the yield of residual chars at 700?of WPC/BMP and WPC/SiMP increased by104.6%and 162.0%,showing a good catalytic effect of chars formation.2.The new intumescent flame-retardant system(EG-BMP)was prepared by heat treatment of BMP and expandable graphite(EG),and the impacts of content and proportion of EG-BMP on flammability and thermal decomposition behaviors of WPC were comprehensively investigated.When the weight ratio of EG and BMP was 2:1 and the total amount was 30wt%,the LOI value of WPC/EG-BMP system reached a maximum of 31.5%and achieved an UL-94 rating of V-0.Compared with pure WPC,the PHRR,THR and TSP decreased by64.9%,53.2%and 66.6%respectively,and it had a higher fire performance index(FPI)and a lower fire growth index(FGI),showing excellent fire safety.SEM-EDS and RS analysis of the chars showed that the combined effect of EG and BMP made the chars layer structure more compact,the degree of graphitization was significantly improved,thereby exerting a synergistic flame-retardant effect in the condensed phase.TGA and TG-IR analysis showed that EG-BMP had a better ability to catalyze char-forming reaction.When 30 wt%EG-BMP(EG:BMP=2:1)was added,the yield of residual chars at 700?increased by 226.3%compared to pure WPC.The barrier effect of the chars layer inhibited thermal degradation,and the volatile products were reduced accordingly.3.A polyoxometalate-based ionic liquid(SiPIL)was synthesized by anion exchange reaction,and the structural properties were characterized by FT-IR and H¹NMR.As a synergistic agent,it was used to form a new intumescent flame-retardant system with ammonium polyphosphate(APP)and pentaerythritol(PER).The effect of the content and proportion of them on flammability and thermal decomposition behaviors of HDPE composites was systematically investigated.When 0.5 wt%SiPIL and 24.5 wt%IFR(APP/PER)were added,the LOI value of HDPE/IFR/SiPIL reached a maximum of 26.3%,and achieved an UL-94 rating of V-0,the PHRR,THR,TSP,CO and CO₂production were further reduced compared to HDPE/IFR.SEM-EDS,TGA and TG-IR analysis showed that SiPIL could promote the char-forming reaction at elevated temperature,and the thermal decomposition activation energy of the HDPE/IFR system was increased,showing better thermal stability.Dynamic rheological measurements showed that SiPIL could promote the formation of a three-dimensional network structure in the system,which facilitated the formation of a stable chars layer.4.A polyoxometalate-based ionic liquid-doped sepiolite(SEP-PIL)was prepared by surface grafting and anion exchange reaction,the structure,morphology and thermal stability were characterized by FT-IR,solid-state NMR,XRD,ICP-OES,SEM,TEM,EDS and TGA.Compared to pure sepiolite(SEP),the combination of SEP-PIL and IFR(APP/PER)showed a better synergistic flame-retardant effect.When 1wt%SEP-PIL and 24.5 wt%IFR(APP/PER)were added,the LOI value of the HDPE/IFR/SEP-PIL reached a maximum of 27.6%,and achieved a UL-94 rating of V-0,the PHRR,THR,TSP,CO and CO₂production were further reduced compared to HDPE/IFR/SEP composite.SEM-EDS,TGA,TG-IR and dynamic rheological measurements showed that SEP-PIL could promote the cross-linking reaction to form chars at elevated temperature,play a role in stabilizing the chars layer,and further enhance the thermal decomposition activation energy of HDPE/IFR,showing good thermal stability.