| The development of halogen-free,low toxicity and high effective flame retardant has attracted wide attention in the last few decades.The flame retardant containing phosphorus and silicon is recognized as a green flame retardant,while Lewis acid metal can catalyze the formation of char to achieve flame retardant effect.Based on three elements of phosphorus,silicon and titanium,a series of flame retardants were designed and synthesized,and several kinds of flame retardant epoxy resin composites containing phosphorus-silicon-titanium were constructed.The main work of this paper is as follows:Firstly,we used NH2-POSS,DOPO and paraformaldehyde as raw meterials to synthesize POSS-bisDOPO consisting of one POSS and two unit of DOPO through a classic Kabachnik-Fields rection.And then,it was used as co-additive with tetrabutyl titanate(TBT)to construct a multi-element flame retardant epoxy system.The structure of POSS-bisDOPO was characterized by NMR,FTIR and MS.The flame retardancy,thermal and mechanical properties of epoxy composites were studied.The experimental results showed that there is a synergistic effect of phosphorus-silicon-titanium in the process of polymer combustion and thermal degradation.When the added TBT and POSS-bisDOPO had a same amount of 5 wt%,the LOI value increased from 26.3%(pure epoxy)to 31.0%(composite),UL-94 ratings up to V-0 and the peak heat release rate and total heat release were reduced to 28.4 W/g and 1.7 kJ/g,respectively.TGA showed that the introduction of TBT/POSS-bisDOPO can increase the amount of residual char and reduce the thermal decomposition rate of the matrix resin,thus enhancing the thermal stability of epoxy resin.Based on the analysis of residual char of epoxy resin during combustion and thermal degradation,it was found that residual char of TBT/POSS-bisDOPO modified epoxy resin had an alveolate inner layer and continual compact outer layer of phosphorus and silicon accumulation.The stable char can be attached to the matrix as a kind of physical protective layer,blocking the transfer of the thermal oxygen to the matrix resin,reducing the ablation of the material,so as to enhance the flame retardancy of epoxy resin.DMA and three-point bending test results showed the mechanical property of the EP composites had no decline.In a word,The flame retardant of TBT/POSS-bisDOPO not only improved the flame retardancy and thermal stability of epoxy resin,but also maintained the excellent mechanical properties of epoxy resin.Secondly,we used POSS-triOH and isopropyl titanate as raw materials to synthesize metal hybrid POSS(Ti-POSS)through a corner-capping rection.Amino modified POSS-Ti-ETA was synthesized by the transesterification reaction with ethanolamine in order to improve the compatibility between POSS and epoxy matrix.The structure of POSS-Ti-ETA was characterized by NMR and FTIR.It was used as co-additive with DOPO to construct a multi-element flame retardant epoxy system.The experimental results showed that this kind of metal hybrid POSS had better flame retardant effect than POSS.When the added POSS-Ti-ETA and DOPO had a same amount of 5 wt%,the LOI value increased from 25.2%to 32.7%and UL-94 ratings reached V-0.TGA showed that the introduction of POSS-Ti-ETA/DOPO can increase the amount of residual char and reduce the thermal decomposition rate of the matrix resin,thus enhancing the thermal stability of epoxy resin.After combustion and thermal degradation,the reesidue char can be attached to the matrix as a kind of physical protective layer,blocking the penetration of thermal and oxygen to the matrix resin,reducing the ablation of material.DMA,three point bending test and impact test results showed that POSS-Ti-ETA/DOPO can enhance the mechanical properties of epoxy resin composites.Finally,metal hybrid POSS containing phosphorus(Ti-POSS-bisDOPO)was synthesized by three steps including corner-opening rection,corner-capping rection and Kabachnik-Fields rection.The structure was identified by NMR,FTIR and MS. |
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