| In this work one kind of basic magnesium salt, magnesium oxychloride (MOC),was synthesized and used as flame retardant agent in epoxy resin (EP) and low pressure sheet molding compound (LPMC).The flame retardancy, structure, thermal decomposition and mechanical properties of MOC/EP and LPMC composites, ammonium carbonate hydroxy hydrate (AACHH) and basic magnesium carbonate /EP composites were studied by LOI, TG-DTG, DSC, XRD, SEM and mechanical test. The main results are as follows:1. Active MgO was obtained by calcinations of basic magnesium carbonate. As the temperature increased, the activity of MgO decreased. The average grain size and lattice distortion of MgO were calculated by Hall method. At 650℃,850℃and 950℃, the average grain sizes of MgO were 20 nm,63nm and 69nm respectively and the average lattice distortions of MgO were 4.00×10-4,2.16×10-4 and 1.68×10-4 respectively.2. Thermal decomposition of MOC in the air was investigated by TG-DSC and XRD. Kissinger method was used to analyze the thermal decomposition DSC curves of MOC at different heating rates. Kissinger and Crane method were used to calculate thermal decomposition kinetic parameters by investigating TG curves of EP/MOC composites at different heating rates. The activation energy of EP in EP/MOC composites is higher than that of pure EP. In other words, MOC enhanced thermal stability and increased pyrolysis temperature. The thermal decomposition reaction orders of EP-in EP/MOC composites and pure EP are basically the same, indicating both reactions are similar.3. Endothermic temperature of MOC matched with decomposition temperature of EP. Water vapor and HCl were released when decomposition of magnesium oxychloride. The flame retarded mechanism of MOC was the synergies of.diluting, cooling, catalyzing char forming, capturing free radical and obstructing effects. MOC can decrease the decomposition heat of MOC/EP composites, enhance the thermal decomposition stability and anti-melting capacity of EP, promote the mass of residual char, and have flame-retardant effect.MOC performed well as an inorganic flame-retardant in EP. When the content of MOC was 50%, the LOI of EP reached 29.6% and mass of residual char reached 9.6%. Moreover, the initial and terminal decomposition temperature of EP increased by 10℃and 50℃respectively. At 50% loading of MOC and 2% loading of KH550, the tensile strength and bending strength of MOC/EP composites increased by 12% and 17% respectively.4. Endothermic temperature of basic magnesium carbonate matched with decomposition temperature of EP. Water vapor and CO2 may have synergistic flame retardant effect. Basic magnesium carbonate has more flame retarding effects by diluting, cooling, isolating and their synergies. At 56.5% loading of basic magnesium carbonate, the LOI of the epoxy resins increases to 29.7%. Flame-retardant effect of basic magnesium carbonate is better than that of magnesium hydroxide. The termination thermolysis temperature of magnesium carbonate/epoxy resin is below 100℃. Intermediate decomposition products, Mg3O (CO3) 2, may accelerate the termination thermal decomposition of epoxy resin and produce a stable carbon-containing residues.5. Particle morphology of basic magnesium carbonate was analyzed by SEM. Viscosity of basic magnesium carbonate/EP composites was measured by viscometer. The results showed that the coarse basic magnesium carbonate particles with squamaes and holes on their loose surfaces possessed strong adsorbability, which increased the viscosity and curing time by 30.2% and 34.6%.Coupling agent KH550 can improve mechanical properties of MOC/EP composites. The mechanical properties of basic magnesium carbonate/EP composites and dispersive properties of basic magnesium carbonate treated with silane were the best.6. During combustion, the NH4+, CO32- and OH- groups in AACHH decompose into NH3, CO2 and water vapor, which dilutes the flammable gas and oxygen and reduce the combustion temperature. These gases have very good flame-retardant effect and may have a synergistic flame retardant. NH3 may play a key role. At relative low temperature,AACHH break down into highly active amorphous Al2O3 completely which has strong capacity of adsorbing carbon residue and catalyze the formation of char. Not only reducing the decomposition heat of EP, AACHH can also enhance the thermal stability and the anti-melting capacity of EP. At 47.34% loading of AACHH, the LOI of AACHH/EP composites reached 32.2% and mass of residual char reached 5.1%. Moreover, the initial and terminal decomposition temperature of EP increased by 48℃and 40℃respectively. The flame retarded mechanism of AACHH is due to the synergic flame retardant effects of diluting, cooling, decomposition resisting and obstructing. AACHH exhibited excellent flame-retardant properties in epoxy resin.7. The tensile property, flame retardancy and thermal behavior of MOC/LPSMC composites were studied. MOC matched well with decomposition temperature to LPSMC. HCl may have synergistic and capturing free radical effects. The flame retarded mechanism of MOC was due to the synergies of diluting, cooling, catalyzing char forming, capturing free radical and obstructing effects. The results indicate that at 40% loading MOC the integrated performances of LPMC are optimal.The LOI of the MOC/LPMC composites increaseed to 31.5 and UL-94 reached-V-0 grade, tensile strength and flexural strength were 79.6 MPa and 153.7 MPa respectively. Due to it's special structure of crystalline water, Magnesium oxychloride crystal salt is very promising as high efficiency flame retardant additives. It has good water resistant properties, excellent heat stability and comprehensive physical and chemical properties, and is a new inorganic flame retardant suitable for LPMC. |
PDF Full Text Request