Composition,interfacial Structure Regulation And Mechanism Study Of Layered Double Hydroxides Based Flame Retardant And Smoke Suppressant For Flexible PVC

The flammable and combustible characteristics of polymer materials are the main evocators and triggers of many fires in today’s society,resulting in a large amount of loss of life and property.Polyvinyl chloride(PVC),one of the five common plastics,will release heavy smoke when forced to crack or burn under heat.Furthermore,the flammability and smoke density of flexible PVC are significantly increased due to the addition of a large amount of plasticizer.Therefore,the flame retardant and smoke suppression modification of flexible PVC(especially smoke suppression modification)plays an important role in expanding the application field and improving the safety of PVC.Layered double hydroxides(LDHs)is an ideal environment-friendly flame retardant and smoke suppressant due to its many excellent properties such as surface basicity,gradual thermal decomposition and adsorption capability.However,traditional LDHs still has some serious shortcomings,such as low efficiency and high dosage,which need to be solved urgently.In this thesis,the composition,structure and interfacial properties of LDHs-based flame retardant and smoke suppression materials were designed and prepared in a controlled manner,and the properties of LDHs-based flame retardant and smoke suppression materials on the flexible PVC were investigated when they were used as additives.The specific research contents are as follows:1.Cu-Al layered double hydroxides(CuAl-LDH)was prepared by introducing transition metal elements based on the adjustability of laminate and lattice confinement effect.The material efficiently combines the catalytic performance of Cu element with the excellent characteristics of LDHs and has good smoke suppression and flame retardancy:It can reduce the maximum smoke density of flexible PVC by about 25%in static flameless combustion mode,and reduce the peak heat release rate from 337.16 kW/m2 to 247.90 kW/m2(about 26.5%reduction)and the total smoke production by 14.6%in dynamic combustion mode.Then Cu-Mg-Al layered double hydroxides(CuMgAl-LDH)was synthesized.The doping of Mg can not only improve the dispersibility of the metal catalytic center,but also realize the synergistic effect of the catalytic center and the alkali center.The comprehensive properties of this material are superior to CuAl-LDH and Mg-Al layered double hydroxides(MgAl-LDH):CuMg2Al-LDH reduced the maximum smoke density for flexible PVC by about 32.7%with the addition amount of 3%(weight percentage);and the temperature corresponding to the weight loss of 5%for flexible PVC was increased by 28℃ after incorroperating 4%CuMg2Al-LDH into PVC matrix.Finally,Cu-Mg-Al layered double hydroxides/reduced graphene oxide hybrid material(CuMgAl-LDH/rGO)with hierarchical honeycomb micro/nano-sheet array structure was prepared from the viewpoint of regulating the interface structure and interface contactability of LDHs.The array structure features can effectively prolong the diffusion path of combustible materials and the like.Meanwhile,the synergistic effect between LDHs and graphene matrix further can improve the flame retardant and smoke suppression performance of the composite material compared with disordered powder materials.2.Based on the lattice confinement effect,a series of highly dispersed Fe-LDHs were prepared.The test results demonstrated that Cu-Fe layered double hydroxides(CuFe-LDH)has the best smoke suppression performance and can significantly improve the char residue of flexible PVC.After incorroperating CuFe-LDH into flexible PVC,the maximum smoke density and the maximum average rate of smoke emission of flexible PVC in static flameless combustion mode were reduced by about 36.5%and 68%,respectively;the peak heat release rate and the total smoke production of flexible PVC in dynamic combustion mode were reduced by about 20.5%and 21.1%,respectively.Pyrolysis analysis and carbon residue analysis both demonstrated that the synergistic effect of highly uniformly mixed Cu and Fe double catalytic centers is the key to the efficient smoke suppression of CuFe-LDH:Dehydrochlorination reaction and ionic crosslinking reaction can be promoted by the catalysis of Lewis acid CuCl2/FeCl3,which represses the output of aromatic compounds and hence emits less smoke.