Preparation Of Novel Polysiloxane Containing Phosphorus And Nitrogen And Its Application To PP

Polypropylene（PP）,as a kind of thermoplastic polymer material with excellent integrative properties,is widely applied in industry and commerce.However,PP is highly flammable with high fire risk.Therefore,it is of great significance to decrease the inflammability of PP to increase its fire safety.Currently,melt blending of flame retardants（FRs）with PP is the most commonly used method to improve the flame retardancy of PP.Polysiloxane,as a kind of polymer combining excellent thermal stability,low toxicity or non-toxic and good compatibility with substrates,has promising application prospect in flame-retardant field.However,common polysiloxanes are oily liquids and preparation procedures are complicated,which limits the wide application of organsiloxanes in PP.In general,only high loadings of FRs can give PP good flame resistance,which usually damages the mechanical properties of PP.The flame-retardant coating is a novel and efficient flame-retardant method without adverse effect on the mechanical properties of PP.The factors including low surface energy and poor wetting ability of PP make it difficult for the flame-retardant coating to adhere to the surface of PP firmly and enduringly.Therefore,a novel thermally stable solid polysiloxane（APID）containing many nitrogen,phosphorus,silicon and benzene rings was obtained through hydrosilylation and ring-opening reaction.Then,APID with its synergistic agents was used to improve the flame retardancy of PP through melt-blending and flame-retardant coating with low loadings of FRs,and the effect of flame-retardant systerms on mechanical properties of PP was kept to a minimum.In addition,the flame-retardant mechanism and aging resistance were investigated.An intumescent flame-retardant system（IFRs）composed of APID and ammonium polyphosphate（APP）was used to improve the flame retardancy of PP.The results showed that PP/IFRs composite with 23 wt.%loadings of IFRs（APID:APP=2:3）passed UL-94 V0 rating,limiting oxygen index（LOI）being28.2 vol.%.The peak heat release rate（PHRR）and fire growth rate（FIGRA）of the composite compared with those of virgin PP dropped by 75.7%and 81.0%,while fire performance index（FPI）increased by 126.9%,respectively.When IFRs was faced with heat,a kind of integral,dense,stable,solid and intumescent char layer containing a large amount of-P（=O）-O-Si-linkages was formed to act as a protective barrier to insulate oxygen and heat and to protect the substrate.APID containing many-Si-O-CH₂CH₃ groups can improve the compatibility between APP and PP through surface modification of APP during melt-blending to reduce the negative effect of APP on PP and enhance the impact strength.When the flame-retardant coating was used to reatard PP,the acid treatment was adopted to enhance the surface energy of PP,and then PP samples with smooth intumescent flame-retardant coatings composed of APID,APP,KH550,polyvinyl formal-acetal and etc.were prepared by dip-coating.The coating owned good flame retardancy,adhesion and flexibility.A coating with an average thickness of 196μm contributed to PP’s excellent flame retardancy,passing UL-94 V0 rating and LOI value being up to 37.8 vol.%.The PHRR and FIRGA of the composite were reduced by 74.9%and 80.0%,while FPI increased by 281.8%,compared with those of PP.Interactions between the ingredients of coatings including surface modification of APP,hydrolysis condensation between silanes and a wide existing of hydrogen bonds gave rise to uniform and dense coatings with excellent thermal stability.The flame-retardant coatings left no negative effect on the mechanical properties of PP.In addition,the flame-retardant mechanism of intumescent flame-retardant coatings was investigated,and the aging resistance of the coatings was studied as well.