Graphene And Graphitic Carbon Nitride Based Hybrids/Polyurethane Composites:Preparation And Study On Flame Retardant Properties

Thermoplastic polyurethane elastomer(TPU)is widely applied in various areas,such as sports equipment,cable,automotive,medical industry,tube,film,etc due to its outstanding properties such as high strength,high toughness,wear resistance,oil resistance and other excellent comprehensive performance.However,several fatal drawbacks,such as high flammability,evolution of a large amount of smoke and combustible volatiles together with severe melt-dripping during combustion greatly limit its further application.The flame retardants used in TPU could be simply classified into organic and inorganic flame retardant,both of them have its own advantage and drawback.Generally speaking,organic flame retardant has good compatibility and poor thermal stability,and inorganic flame retardant needs high loading,which brings negative impact on mechanic properties of the matrix.It is expected that the combination of organic-inorganic flame retardant hybrid can contribute to improvements in thermal stability and flame retardancy of TPU,simultaneously endows TPU with better smoke suppression.It is essential to improve the flame retardancy and smoke suppression of TPU.Organic-inorganic hybrids has been widely employed to lower the flammability of polymers,because they could combine the superiority of organic and inorganic flame retardants,furthermore,it could provide a method to adjust the structure and properties of compound at molecular level.Besides,the problem of compatibility between additive and materials matrix will also be settled.In this dissertation,three kinds of organic-inorganic hybrid were successfully fabricated and the structures were characterized.Since then,the hybrids were incorporated to the TPU matrix through solvent mixing and melt blending method.Therefore,this dissertation focuses on enhancement of 2D material based organic-inorganic hybrid/TPU composites on flame retardancy,compatibility and smoke suppression.1、A facile in situ method of synthesis and immobilization of a copper(salen)complex onto graphene oxide(GO)support has been developed.Then the nanohybrids were added into the thermoplastic polyurethane(TPU)matrix to prepare TPU nanocomposites using a master batch-melt compounding approach.Enhancements in the thermal stability and flame retardancy were ascribed to the explanations that graphene oxide nanosheets showed the physical barrier effect,and that both copper chelates and Schiff bases catalyzed the decomposition reaction to obtain increased char residues.Thermogravimetric analysis-Fourier infrared spectra results showed that the generation of total gaseous products and toxic gas CO obviously decreased by the Cu(salen)-f-GO.2、Graphite-like carbon nitride(g-C3N4)was innovatively modified by diethylphosphinic acid through hydrogen bonding;g-C3N4/organic aluminum diethylhypophosphites(g-C3N4/DAHPi)hybrid(denoted as CDAHPi)was synthesized by salification reactions,and subsequently incorporated into TPU matrix to prepare composites through melt blending method.Thermal data showed that g-C3N4 could protect DAHPi from external heat,leading to improved thermal stability of DAHPi.Moreover,it was found that the introduction of the hybrid reduced the values of heat release rate(HRR)and total heat release(THR)of the composites.The extra addition of lactic acid-stabilized copper nanoparticles into TPU matrix reduced the HRR and smoke production rate(SPR).3、Polyphosphoramides(PDMPD)oligomer with-NH2 terminal was successfully synthesized and well characterized by 1H NMR.Then polyphosphoramides/g-C3N4 hybrid(CPDMPD)was formed through hydrogen bonding.Structural and morphological analysis indicated the successful synthesis of and its hybrids.Thermal data showed that g-C3N4 could protect PDMPD from external heat,leading to improved thermal stability of PDMPD.Subsequently,these hybrids were incorporated into TPU matrix to prepare composites through melt compounding method.It was found from cone calorimeter testing that pHRR of PDMPD/TPU composites did not reduce a lot,the possible reason is that PDMPD released a large quantity of heat on the early-combustion stage before the carbonaceous layer formed.As for g-C3N4,it cannot play the barrier effect when the molecular skeleton collapsed,beside,g-C3N4 cannot effectively catalyze the formation of char layer of TPU.The introduction of the hybrids reduced the HRR,THR and smoke production,because in the early stage g-C3N4 could play a barrier effect and protect PDMPD,in the later period,the hybrid could form a great amount of free-radical capture agents and the continuous and dense char residues when exposure to flame.These improvements could be attributed to the combination of gas phase mechanism and physical barrier effect.