Investigation Of The Effect Of MOFs On Flame Retardancy And Smoke Suppression For Soft Polyvinyl Chloride Materials

Soft polyvinyl chloride（PVC）has been widely used in wire,cable and other fields due to its excellent chemical resistance,electrical insulation and so on.However,PVC releases large amount of heat and smoke during combustion,thus it should be modified for enhancing the smoke suppression performance.Metal oxides are currently used for smoke suppression agents in PVC,but there are some advanges such as poor compatibility in the polymeric matrix and the smoke suppression efficiency need to be improved.In recent years,metal-organic framework materials（MOFs）are developed and they have high specific surface,good compatibility and dispersion in polymer and so on.It has been attracted a lot of concern,but their application in the smoke suppression for PVC has been seldom reported.In this thesis,three MOFs containing different metal ions were prepared and used in PVC.The effect of MOFs on the flame retardant and smoke suppression for PVC were investigated.The related contents as following:Based on the excellent smoke suppression performance of iron oxides for PVC,the organic framework materials containing iron ions（Fe-MOF）was prepared,and terephthalic acid acted as an organic ligand.It was introduced into PVC.Compared with pristine soft PVC,the maximum smoke density(D_max)of PVC/3wt%Fe-MOF was reduced from 924 to 485,with a reduction of 47.5%.The limiting oxygen index（LOI）value was increased from 26.8%for PVC to 29.0%.Cone calorimetry（CONE）tests revealed that the total smoke production（TSP）of PVC/3wt%Fe-MOF was reduced from 28.8 m² for PVC to 16.2 m²,with a reduction of43.8%.The addition of a small amount of Fe-MOF improved the flame retardant and smoke suppressing properties for soft PVC.For the comparatively investigation,the iron oxide with same amount of iron ions was added in PVC.The D_max and TSP values of PVC/Fe-MOF were reduced by 26.1%and 13.8%,respectively.The fact indicated that Fe-MOF possessed more excellent flame retardant and smoke suppression efficiency for PVC.Due to the presence of organic ligands,Fe-MOF was well dispersed in PVC matrix,and its high specific surface properties benefited to exert excellent catalytic effect for PVC.Consequently,PVC/Fe-MOF composites presented good flame retardant and smoke suppression performance.Copper oxide possesses excellent suppression properties for PVC materials,and the copper ion-containing organic framework materials（Cu-MOF）was synthesized based on the organic ligand of 1,3,5-benzene tricarboxylic acid.Compared with pristine PVC,the D_maxvalue of PVC/3wt%Cu-MOF was reduced from 924 to 514,with a reduction of 44.4%,and the LOI value was increased from 26.8%to 30.6%.The TSP value of PVC/3wt%Cu-MOF was reduced from 25.2 m² to 13.9 m².Besides,the D_max and TSP values of PVC/Cu-MOF were reduced by 25.9%and 13.7%compared with that of PVC/Cu O composites with the same copper ion content.As a result,Cu-MOF has excellent catalytic and smoke suppression properties for soft PVC.Molybdenum oxide usually worked as a common smoke suppression agent for polymeric materials,and Mo-MOF was prepared based on the organic ligand of imidazole.When 3wt%Mo-MOF was added in PVC,the D_max value decreased from 918 to 471,and the TSP value decreased from 25.2 m² to 12.0 m².The LOI value was increased from 26.8%to 30.3%.It indicated that a small loading amount of Mo-MOF effectively reduced smoke release and improved flame retardant performance to a certain extent.Compared with PVC/Mo O₃,the D_max and TSP of PVC/Mo-MOF composites were reduced by 39.1%and 31.5%,under the same molybdenum ion content.The above investigation of PVC smoke suppression with different three MOFs revealed that Mo-MOF presented superior smoke suppression performance for soft PVC materials,the nano-scale Mo O₃ generated during combustion reacted with HCl and then formed the strong Lewis,which accelerated the removal of HCl from PVC materials,and then cross-linking and charring.Consequently,the smoke release of soft PVC was obviously reduced.