Electrochemical Method For Preparation Of Functional Graphene And Study On Retardant Performance Of Its Polystyrene Composites

Polystyrene is one of the widely used thermoplastic polymers with low cost and excellent mechanical properties.However,its flammability limits its application in many applications.How to prepare highly efficient flame retardant for polystyrene has always been an important issue.The content of this thesis is to design electrochemical method to prepare functionalized graphene and graphene hybrid,and apply it to the flame retardancy for polystyrene.Specified research methods and contents are as follows:1.The graphene modified by sodium p-styrene sulfonate was obtained by exfoliating and stripping graphene in an electrochemical method with sodium p-styrene sulfonate as the electrolyte.Then the polymerization of the p-styrene sulfonate was initiated to form polystyrene on graphene.The structure of the functionalized graphene/polystyrene nanocomposite was characterized by SEM,TEM and XRD,and it was proved that the functionalized graphene had better dispersion in the polystyrene matrix.The combustion properties of the polymer composites were tested by cone calorimeter.The tensile strength and impact strength of the composites were also tested by mechanical properties tester.The results show that graphene functionalized with sodium polystyrene sulfonate can improve the thermal stability of polystyrene more effectively and has a better flame retardant effect on polystyrene.And the mechanical properties of polystyrene have also been improved.The flame retardant mechanism was studied by Raman,SEM and XPS analysis of char residue.The well-dispersed graphene sheets block the outward diffusion of volatile pyrolysis products in the condensed phase,forming a carbon layer,isolating oxygen and small molecular combustible pyrolysis products,thus improving the flame retardant property.2.Using cyanuric acid as the electrolyte to fabricate graphene nanosheets by electrochemical exfoliation in hot water,and then melamine was added to fabricate generate melamine cyanurate(MCA)through molecular self-assembly,so as to obtain the MCA and graphene(MCA@Gr)hybrid.The products were characterized by TEM,XRD,Raman and TGA,and the results showed that the MCA@Gr were successfully prepared.The graphene/melamine cyanurate hybrid(MCA@Gr)prepared by the above method was added into polystyrene to obtain nanocomposites.Meanwhile,the nanocomposites with only MCA and Gr were prepared respectively as a contrast.The structure of the nanocomposites was characterized by SEM and XRD,and it was proved that the nanocomposites were prepared successfully.The thermal stability and combustion behavior of the composites were tested by thermo gravimetric analyzer and cone calorimeter.Results showed that MCA@Gr/polystyrene composites has lower peak heat release rate and lower total amount of heat release compared to the composites with only MCA or Gr,the explanation is that MCA and Gr can play roles of fire inhibitor in a synergetic way,so as to achieve better flame retardant effect.3.Using 9,10-dihydro-9-oxa-10-phenanthrene phosphate 10 oxide(DOPO)and trimethyl methyl phosphine oxide(THPO)to obtain the product(DOPO-THPO)as phosphorus flame retardant.The DOPO-THPO and the MCA@Gr prepared in the previous chapter were blended into polystyrene to obtain a composite material.The vertical combustion and limiting oxygen index were tested and the flame retardant mechanism was discussed.The results show that the synergistic use of MCA@Gr and phosphorus-containing flame retardants can increase the oxygen index of polystyrene to a certain extent and reduce the heat release of polystyrene combustion.DOPO-THPO exerts its flame retardant effect mainly in gas phase with synergistic effect with MCA@Gr.