Preparation Of Isocyanate-based Polyimide Foams Material And Flame Resistance Study

Polyimide foam(PIF)material is a type of high performance engineering material with excellent thermal stability,high and low temperature resistance,thermal insulation,acoustic absorptions,high fire resistance,and low smoke toxicity.Other polymeric foamed materials do not compare with its excellent combination property.Thus,PIF material is widely used in advanced technological applications,including spacecraft and aircraft.Isocyanate-based PIF(IBPIF)material is a new type of PIF material prepared by the free-foaming process,which involves the use of multi-anhydride or its derivatives and multi-isocyanate as raw materials.Because the free-foaming preparation technology of IBPIF material possesses the advantage of simple technological process,needless special function equipment,and low price of raw materials,the market price of PIF material can effectively be reduced.Thus,PIF material can be promoted for widespread use in advanced and commonly technological applications,then obtain the attention of scientists.However,the IBPIF material with neat cellular structure prepared by existing free-foaming preparation technology has bad flame resistance and use security,cannot match the use security requirement of advanced applications and common applications for polymeric foamed materials.Thus,IBPIF material cannot be widely used in national industry.To address the bad flame resistance and use security of IBPIF material,we rely on free-foaming preparation technology in this thesis,by simple formula adjustment of foaming white and black slurries realize the enhancement of flame resistance and use security of IBPIF material,which has neat cellular structure.The main research contents are as follows.Relying on the first free-foaming preparation technology of IBPIF materials,by a simple method that directly refilled 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride(BTDA)to the foaming white slurry,the reaction degree between amino and isocyanate group was effectively restrained,the polyimide proportion in IBPIF with neat cellular structure was effectively enhanced.With increasing refilled BTDA dosage,the flame resistance of IBPIF materials increased,the burning behavior and smoke release behavior significantly improved,burning velocity and flame spread speed were controlled effectively,and the use security of IBPIF materials significantly improved.When the ratio of BTDA refilled dosage and precursor solution mass reached 25:20,the generation of polyimide reached its maximum,the material composition remained constant,the limiting oxygen index(LOI)of IBPIF material reached 30%,and the material reached retardant grade.Relying on the second free-foaming preparation technology of IBPIF material,we grafted the two free-foaming preparation technology of IBPIF materials together.The preparation process of foaming black slurry was the same as the second free-foaming preparation technology,but the multiple carboxylic ester was introduced to the foaming white slurry.This grafting method can effectively improve the controllability of the free-foaming process and reduce IBPIF material density.It can effectively decrease the generation of uredio in the matrix resin and ensure the flame resistance of IBPIF material.When the ratio of multi-anhydride dosage used to prepare the foaming black slurry and total multi-anhydride dosage ranged from 0.4 to 0.8,IBPIF materials with high flame resistance and low density could be obtained.The density and LOI value of IBPIF material was essentially consistent with the polyimide foams prepared by powder preparation technology.Relying on the first free-foaming preparation technology of IBPIF material,by simply adjusting ratio of foaming slurry mass and airtight container cavity volume,density of IBPIF material could be freely adjusted.Test results showed that increasing density of IBPIF material enhanced its mechanical property and flame resistance.However,when polyimide proportion reached a certain extent,the effect of density on flame resistance weakened.Relying on the first free-foaming preparation technology of IBPIF materials,by a simple method that directly add liquid tri(1-chloro-2-propyl)phosphate(TCPP)/micro-sized hydrotalcites(LDHs)to the foaming white slurry,the flame resistance of IBPIF was enhanced.Experiment results showed that although the use of solid LDHs could effectively maintain the micro and macro cellular structures and thermal stability of IBPIF materials,its flame retardant efficiency for IBPIF materials was low,the use of liquid TCPP could effectively enhance the flame resistance of IBPIF materials and improve the burning behavior and smoke release behavior of IBPIF,but the slather of TCPP would heavily damage the micro and macro cellular structures and thermal stability of IBPIF materials.But,when solid LDHs and liquid TCPP were used as a complex,IBPIF with high flame resistance,high use security,and neat cellular structure was obtained.