The Preparation Of Expansible Graphite Coupled With Borate And It’s Effects On Flame Retardancy And Mechanical Property Of Polymer Materials

As an intumescent flame retardant (IFR), expandable graphite has been more mature day byday in the fast-changing researches, and its application fields are wider and wider. However,the low expansion properity and mechanical strength of intumescent residual carbon of theexpandable graphite manufactured by single intercalator affected its flame retardant efficiency.At the same time, due to the worse compatibility between the expandable graphite and basematerials, its addition would make the mechanical property of the materials obviouslyreduced. Borate was an inorganic and environment friendly flame retardant, and when heated,it would form a glass-like coating on the surface of materials to resist the transfer of heat andmass. However, in order to guarantee the flame retardancy of materials, the adding amount ofborate was relatively high, and then it leaded to the decrease of material mechanical property.In this research, a new kind of flame retardant of borate couple with expandable graphite (EG)was prepared through graphite intercalation reaction. Firstly, EG with higher expansionproperty was prepared, and then its flame retarding efficiency for linear low densitypolyethylene (LLDPE) and acrylonitrile–butadiene–styrol copolymer (ABS) was investigated,respectively. Its flame retarding efficiency was compared with ordinary expandable graphiteintercalated with single sulfuric acid, mixture of ordinary expandable graphite and boratemechanically. The synergistic flame retarding efficiency of EG with ammoniumpolyphosphate (APP) was tested at the same time, and the influence of flame retardant onmaterials mechanical property was investigated. The research contents and results were listedas follows:During oxidation and intercalation reaction of the50mesh nature flake graphite, potassiumpermanganate was used as the oxidizing agent, sulfuric acid as the intercalator and sodiumtetraborate as the auxiliary intercalator; the appropriate mass ratio to prepare EG50, confirmedthrough single factor experiments, was: flake graphite: potassium permanganate: sulfuricacid (98%): sodium tetraborate equalling1.0:0.4:5.5:0.6, and the mass concentration ofsulfuric acid in the reaction was adjusted as80%, the reaction was maintained40min at40°C,and EG50with the initial expansion temperature of155°C and a expansion volume of515mL/g could be prepared. Through characterization of XRD and FTIR, it could be conformedthat sulfuric acid and sodium tetraborate had been inserted into layer structure of EG50.The flame retarding efficiency of the EG50, EG50/APP (I), ordinary expansible graphite (EG1),EG1/sodium tetraborate for LLDPE had been investigated. The experimental results indicatedthat: addtion30%EG50could make limiting oxygen index (LOI) of LLDPE increase from17.1%to28.4%, which was better than that of EG1and the mechanical mixture ofEG1/sodium tetraborate. However, the synergistic efficiency of20%EG50/10%APP wasobvious, which could make the LOI increase to30.5%. The thermogravimetic (TG),differential thermal (DTA), and FTIR for carbon residue and scanning electron microscope(SEM) results verified that: the formation of the expanded graphite residue was the importantcondition making EG50exhibit excellent flame retardancy, and the addition of APP couldimprove the density and mechanical strength of carbon residue. Whereas, the addition ofEG50/APP made the tensile strength of LLDPE obviously reduced.In order to improve mechanical property of the materials flame retarded by expandablegraphite, the EG80, with a little grain size, was prepared with80mesh nature flake graphiteused as the raw materials, potassium permanganate as oxidizing agent, sulfuric acid as theintercalator, and sodium tetraborate as the auxiliary intercalator. EG80was reunited with IFR[the mixture of APP, pentaerythritol ester rosin (PER) and melocol (MEL)] and formed a newIFR, named n-IFR, and its the flame retardancy for ABS was investigated. The experimentresults indicated that: the addition of n-IFR (EG80/APP/PER/MEL=15/7.5/4.5/3) could makethe LOI of ABS system increase from19%to32.6%, UL-94Level reach V-0. Compared withsingle addition of EG80, the residual carbon of ABS flame retarded by n-IFR were morecompact, and with no molten drops at the same time. Addition of n-IFR could change thethermal degradation behavior of ABS, physical effect and chemical reaction happenedbetween the n-IFR and ABS in burning process. The tension experiment indicated that thediminishment of grain size of EG80could make the mechanical property of ABS systemimprove greatly.To increase the compatibility of flame retardant and polymer material, polyethylene glycol(PEG-20000) was select to replace PER as the carbon source of IFR system, and the flameretardancy of EG80/APP/PEG for EVA was investigated. Researches showed that whenEG80/APP/PEG was added at the mass ratio of15/11.25/3.75, the LOI of flame retarded EVAreached32.9%, and the UL-94Level was improved to V-0, which made the residual carbonof EVA system become more compact. And even more, compared with the single EG80, nomolten drops produced. But too much or less amount of PEG would make the LOI of flame retarded composite decline. PEG showed better compatibility with EVA than APP and PEG,but the addition of EG80/APP/PEG made the tensile strength of EVA obviously reduced, andit changed the thermal degradation behavior of EVA composite, the physical synergy effectand chemical reaction happened at the same time in combustion process.