Covalently-functionalized Graphene Oxide Via Introduction Of Bifunctional Phosphorus-containing Molecules As An Effective Flame Retardant For Polystyrene

Polystyrene?PS?with prominent thermal and chemical resistance,low density,good mechanical properties and convenience of processing and molding,has been widely applied in industrial fields?e.g.,packaging material,electrical setting and house-hold appliances?.However,PS is prone to be ignited with a high peak heat release rate?PHRR??about 1300 kW/m²?in burning.Moreover,it can release a large amount of toxic gases and black smoke when forming a streamer fire,with multi-directional propagation.When PS-based materials are applied in construction and electrical facilities as well as other fields,the potential fire risk regard the life and public property safety must be taken into account greatly,and this issue constrain the application of these materials in certain industrial fields.Therefore,it is imperative to develop high-performance flame retardants to reduce the flammability of PS.Generally,there are two approaches to improve the flame retardancy of polymer materials,known as the‘additive'approach and the‘reactive'approach.Additive flame retardants are incorporated into polymers by blending.This is a facile way in promoting flame retardancy for commercial polymers.However,a great variety of problems,such as unfavorable matrix-additive interfacial relationship,leaching,and a severe degradation of mechanical properties,decrease the attraction.In contrast,via designing intrinsically flame retarding polymers or introducing flame-retardant units into the backbone of existing polymers,reactive approaches demonstrate desirable characteristics of tailoring the properties of the material and optimizing its overall performance.In addition,graphene has been extensively applied in various polymers to improve the performance because of its special two-dimensional structure and excellent physical and chemical properties.The single addition of graphene,however,is prone to agglomerate.This drawback will further weaken the properties enhancement of graphene-based nanocomposites and limit the utilization of graphene to a great extent.To solve this issue,based on the physical barrier effect of GO and condensed and gas phases actions of phosphorus-containing flame retardants,we successfully fabricated a covalently-functionalized graphene oxide?FGO?via grafting a novel phosphorus-containingflameretardant,[2-??6-oxidodibenzo[c,e][1,2]oxaphosphinin-6-yl?methoxy?acryloxyethylchlorophosphate,PACP],to graphene oxide?GO?,and the resulting FGO further copolymerized with styrene to produce FGO/PS nanocomposites.The research work of this dissertation is presented as follows:1.Firstly,DOPO-OH was synthesized via paraformaldehyde and DOPO,and further used with POCl₃,hydroxyethyl acrylate?HEA?and DOPO-OH to synthesize PACP.The effects of reaction conditions were studied,and the molecular structure was well characterized by FTIR and ¹H NMR,corroborating that PACP has been successfully synthesized.2.Hummers method is employed for the preparation of GO,and GO was further modified by PACP to synthesize FGO.The structure and morphologies of GO and FGO are characterized by XRD,FTIR and TEM.The XRD results show the intercalation of PACP molecules in FGO,which react with the hydroxyl groups and covalently bond on GO surface.The phosphate characteristic peaks of FGO is observed in FTIR measurements.Different from the surface morphology of GO,surface of FGO is found with some black shadows,as demonstrated by TEM.Further,FGO exhibits hydrophobicity and can be stably dispersed in organic solvent DMF.3.The polystyrene/graphene oxide?PS-GO?nanocomposites were prepared by in situ polymerization via the combination of chemical bonds between FGO and styrene.DSC,TG,MCC and LOI tests were used to investigate their thermal properties and combustion performance.The TGA results revealed that incorporation of FGO into PS can remarkably promote the char yield at high temperatures and reduce the maximum mass loss rate?MMLR?,contributing much improved thermal and thermo-oxidative stability.Meanwhile,due to the physical hindrance of FGO and its strong covalent linkages with PS chains,a notable increase in glass transition temperature?T_g?was observed for PS-FGO nanocomposites.Moreover,much lower values of heat release capacity?HRC?and total heat release?THR?were seen for samples with FGO from MCC test,in conformity with an enhancement of the LOI value;4.TG-FTIR,SEM,Raman spectroscopy and FTIR were employed to gain insight into the flame-retardant mechanism of PS-FGO nanocomposites,which explicitly described the different decomposition reactions in PS after incorporation of FGO and corroborated that the presence of FGO in PS can not only decease gaseous volatiles and inhibit the combustion chain reactions in gas phase,but also serve as physical barrier and further react with the polymer molecule chains to catalyze the formation of char residue with improved microstructure,exerting flame retardant action in condensed phase.