Preparation And Performance Study Of POSS-based Flame Retardants And Flame Retardant Butyl Tapes

Butyl tape is a self-adhesive tape prepared from isobutylene-isoprene rubber（IIR）,polyisobutylene（PIB）,and other additives such as precipitated calcium carbonate（PCC）,carbon black（CB）,and stearic acid（SA）.It exhibits excellent sealing,adhesion,and chemical resistance properties,making it widely used in construction,automotive,and processing equipment industries.However,butyl tape is a flammable material with a limiting oxygen index（LOI）of21.3%.It has a fast burning rate,high heat release and smoke generation,and can produce molten droplets,posing significant risks to human life and property safety.These limitations greatly restrict the application of butyl tape.Although research has been conducted on flame retardant modifications of butyl tape,the current studies in this area have certain limitations.Cage-like polyhedral oligomeric silsesquioxane（POSS）is often used as a flame retardant and reinforcing filler in polymer matrices due to its high thermal stability and compatibility with polymers.In this study,phosphorus-containing cage-like polyhedral oligomeric silsesquioxane flame retardant（DP-POSS）was successfully synthesized using vinyltriethoxysilane（VTES）and9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide（DOPO）as raw materials.It was compared with commercial POSS flame retardant（Si-87M）for flame retardant modification of butyl tape,and their flame retardant effects were evaluated along with the investigation of flame retardant mechanisms.Furthermore,a synergistic flame retardant system was developed by combining DP-POSS with melamine hypophosphite（MHS）for flame retardant modification of butyl tape,and the effects of different ratios on the flame retardant performance of butyl tape were explored.Additionally,further research was conducted to investigate the flame retardant mechanisms of the DP-POSS/MHS system.Firstly,the synthesized DP-POSS was characterized by nuclear magnetic resonance spectroscopy（NMR）,Fourier transform infrared spectroscopy（FT-IR）,matrix-assisted laser desorption/ionization time-of-flight mass spectrometry（MALDI-TOF MS）,and thermogravimetric analysis（TGA）.The successful synthesis of the T8 structure of DP-POSS was confirmed.The T_5%of DP-POSS was found to be 423.3°C,with a T_max of 527.0°C,and the residual char content at 800°C was 50.7 wt.%.Furthermore,with the increase in DP-POSS content,the limiting oxygen index（LOI）and UL-94 rating of the flame-retardant modified butyl tape improved from 21.3%in B-D₀ to 25.9%in B-D₁₅,achieving a V-1 rating.Compared to B-D₀,B-D₁₅ exhibited reductions of 36.6%in peak heat release rate（PHRR）,28.4%in total heat release（THR）,45.2%in peak smoke production rate（PSPR）,and 31.1%in total smoke production（TSP）.In contrast,B-S₁₅ had an LOI of only23.8%without a UL-94 rating,and it showed decreases of 14.4%in PHRR,8.5%in THR,20.5%in PSPR,and 14.8%in TSP compared to B-D₀.The analysis suggests that the flame-retardant mechanism of DP-POSS in the butyl tape involves the synergistic effect of silicon and phosphorus,promoting dehydration and carbonization of the matrix,enhancing the thermal stability and strength of the char layer,thus improving heat and oxygen barrier properties.Simultaneously,it enhances flame retardancy,reduces heat release and smoke generation,thereby reducing the potential fire risk.The contact angle on the surface of the butyl tape increased from83.3°to 107.4°,indicating improved hydrophobicity.With the increase in DP-POSS content,the tackiness and peel strength of the butyl tape increased from 32.45 min and 1.14 N·mm^-1 to 42.12min and 1.42 N·mm^-1,respectively.To further enhance the flame-retardant performance,partial substitution of MHS with DP-POSS resulted in improved dispersion of the flame-retardant modified butyl tape,as evidenced by the absence of significant agglomeration in the SEM and EDS images.With increasing DP-POSS content,the LOI and UL-94 rating increased from 22.3%in B-D₀M₂₀ to 28.5%in B-D₇M₁₃,achieving a V-0 rating.The system exhibited maximum reductions of 42.2%in PHRR,29.2%in THR,35.9%in PSPR,and 32.8%in TSP.The analysis suggests that the flame-retardant mechanism involves the formation of an expanded char layer containing a silicon protective layer in the solid phase,as well as the generation of non-combustible gases and phosphorus-oxygen radicals in the gas phase.This synergistic effect improves the LOI and UL-94 rating of the butyl tape while reducing its heat release and smoke generation,effectively lowering the combustion risk.With the increasing DP-POSS content,the contact angle on the surface of the butyl tape increased from 95.1°in B-D₀M₂₀ to 119.4°in B-D₉M₁₁,indicating improved hydrophobicity.Due to the excellent compatibility between DP-POSS and the organic matrix,the partial substitution of MHS resulted in an increase in tackiness and peel strength of the butyl tape from 23.04 min and 0.80 N·mm^-1 in B-D₀M₂₀ to 31.59 min and 1.33 N·mm^-1 in B-D₉M₁₁,respectively.