Synergist Flame Retardancy And Smoke Suppression Effect Of Ultrafine Zinc Borate On LDPE/IFR System

Low-density polyethylene (LDPE) applies many fields owing to its advantages such as good electrical insulation, low cost and easy process. It is essential to improve its fire resistance because of the fire hazard result from its easy combustibility and melt drip during combustion. LDPE treated with traditional halogen-contained flame retardant will produce hydrogen halide and dense smoke during combustion. It is essential to study the application of halogen free flame retardant (HFFR) on LDPE. Intumescent flame retardant (IFR) and inorganic flame retardant are important HFFR. Although the studies of IFR focus on the application of polypropylene (PP), the application of IFR on PE has attracted much concerning. Zinc borate (ZB) is an excellent inorganic flame retardant that possesses flame retardancy, smoke suppression, anti-melt drip and char promotion. It is essential to reduce the particle size and its distribution in order to improve its compatibility to polymer matrix. It is significant to study the preparation of ultrafine zinc borate (UZB) and its synergist flame retardancy and smoke suppression on LDPE/IFRIn order to compare the compositions of IFR on the flame retardance and mechanical properties of LDPE, IFR which composed of synthesized product such as phosphoramide (PAD), ammonium polyphosphate (APP) and melamine polyphosphate (MPP) or high polymerization APP with pentaerythritol (PER) were employed to treat LDPE. IFR composed of APP and PER is of good flame retardancy based on LOI test, IFR composed of PAD and PER is of good mechanical properties based tensile strength and elongation at break. IFR composed of high polymerization APP with PER was chosen to treat LDPE and the optimum ratio and content was obtained based on flame retardancy and mechanical properties. The LOI of LDPE treated with 30% IFR(based on LDPE) is 24.5 compared to 17.8 of virgin LDPE. In order to solve the problem of the decreasing of mechanical properties and the smoke result from IFR introducing to LDPE, Ultrafine zinc borate (UZB) was prepared through high speed stirring emulsified reaction for the first time. Synthetic condition and the characteristics of UZB was also studied. The composition of UZB is ZB2335; its average particle size is 73nm and 90% of particles below 100nm. The shape of particle is irregular sphere. The flame retardance and mechanical properties of LDPE/IFR was improved when the mass ratio of UZB to IFR is 4.2:25.8 and the content of complex flame retardant composed of UZB and IFR is 30% ( based on LDPE), The smoke decreased substantially when UZB incorporating to LDPE/IFR system. Ultrafine zinc borate is of the advantageous on improving the flame retardancy and mechanical properties of LDPE/IFR compared to general zinc borate.TG-DTA, cone calorimetry, SEM and EDS, FTIR,XRD,PY-GC-MS were employed to study the synergist flame retardancy and smoke suppression of UZB on LDPE/IFR system. The mechanism of synergist flame retardancy and smoke suppression of ultrafine zinc borate on LDPE/IFR system was proposed for the first time.The TG-DTA studies imply that heat stability was improved and the residual mass of 800℃was increased obviously, which result from the lower thermal degradation rate when UZB incorporating to LDPE/IFR system. Thermal dynamics show apparent activity energy increased and reaction rate constant decreased. UZB can promote char forming and protect the charring layer and this provides the positive evidence of its synergist flame retardance on LDPE/IFR.The results of cone calorimeter indicated the peak of heat release rate (pk-HRR) and total heat release (THR) decreased substantially when UZB incorporating to LDPE/IFR. The synergist flame retardancy of UZB on LDPE/IFR result from the mass loss rate decreased and combustible gas reduced during combustion, in addition the effective heat of combustion (EHC) decreased. This implies the main role of UZB is condensed phase and its role on gas phase can not be neglected. SEM micrograph of residual char indicated the structure of residual char was improved when UZB incorporating to LDPE/IFR. The worm like graphite structure protected the char layer and the better protection to polymer matrix was obtained. Zinc contained compound and boron orthophosphate (BPO₄) were proved in residual char by EDS and XRD, which play an important role to improve the properties of char structure and improve the heat stability at higher temperature. FT-IR proved the complex structure of char layer containing P-O-P,P-O-C,B-B and aromatic compounds possesses good protection.Cone calorimetry was employed to study the effect of ultrafine zinc borate on the smoke and the toxicity of smoke of LDPE/IFR for the first time. The results indicated that smoke production rate (SPR), total smoke release (TSR), CO yield and total CO (T_CO) were suppressed substantially when UZB incorporating to LDPE/IFR. These suppression of UZB can be explained from the following mechanisms: One is the amount of combustible gas decreased obviously owing to the forming vitreous protection layer and improve the quality of char layer. The second is the absorption of smoke and CO owing to the UZB has huge specific surface area and surface energy.PY-GC-MS was employed to analyze the pyrolysis gas composition and content of LDPE/IFR/UZB and LDPE/IFR for the first time. The results indicate the amount of ethylene decreased and the amount of water increased in the pyrosis gas when UZB incorporating to LDPE/IFR. This indicates UZB can promote dehydration and charring of LDPE/IFR system. The numbers of components decreased in pyrosis gas when UZB incorporating to LDPE/IFR system.