| In this contribution,several halogen-free flame retardants have been prepared,and their flame-retardant application in the thermoplastic polymers has also been studied.The main contents are as follows:The melamine-formaldehyde prepolymer has been first synthesized using melamine and formaldehyde as raw materials,methanol as inhibitor and triethanolamine as pH value regulator.Subsequently,the microencapsulated red phosphorus(MRP) has been successfully prepared by in-situ polymerization using potassium persulphate(KPS) as initiator.It is found that KPS is useful in enhancing the reaction activity of the melamine-formaldehyde prepolymer,which can encapsulate well on the red phosphorus by the melamine-formaldehyde prepolymer and reduce the reaction time.The differential scan calorimetry(DSC) curves show that the peak temperature of oxidation reaction for MRP is 480℃,which is higher than that of RP,extending the applications for MRP.Polyproplene(PP) composites with different formulations have been prepared by melt extrusion.It is shown that if PP:MRP:magnesium hydroxide(MH)=100(phr):15(phr):50(phr),the limited oxygen index(LOI) of the composite is 26%,vertical firing ranking UL-94 V-0,and the use of flame retardants has less influence on the tensile strength of the composite.LDH-NO3-has been prepared by coprecipitation method using Al(NO3)3·9H2O,NaOH and Mg(NO3)2·6H2O as raw materials.The X-ray diffraction(XRD) results show that the purity of LDH-NO3-has a good relationship with the stirring time,and the intensities of impurity peaks for the resulting products decrease as the stirring time increased and almost disappeared when the reaction time reaches 100min.C18H35O2Na has been used to modify LDH-NO3-.It is shown that when the ratio of C18H35O2Na/Al(NO3)3·9H2O is 1,the quantity of C18H35O2-intercalated into the interlayer of LDH almost gets the maximum.Compared with the LDH-NO3-,the interlayer spacing of LDH is increased from 0.80 nm to 2.98 nm.The LDH modified with C18H35O2Na has a good thermal stability.Nylon-66(PA66) composites with different formulations have been prepared by melt extrusion.The results indicate that when PA6:LDH:MRP=100(phr):9(phr):9(phr),the limited oxygen index(LOI) of the composite is 28.5%,vertical firing ranking V-0,and the use of flame retardants has no influence on the tensile property of the composite.The sheet-like Cu3(MoO4)2(OH)2(CMH) powder has been prepared at lower temperatures by precipitation method using Cu(NO3)2·3H2O,Na2MoO4·2H2O and NaOH as raw materials.The results show the obtained CMH powders are sheet-like and well-crystalline with 50～100 nm width and 100～300 nm length.The CMH powders also have a good thermal stability,and its initial decomposing temperature reach around 320℃, which can satisfy machining requests of common plastics.Poly(ethylene-co-vinyl acetate) (EVA) composites with different formulations have been prepared by melt extrusion.It is indicated that there is good synergistic effect between CMH and MRP(or MH).In addition, when EVA:MRP:MH=100(phr):15(phr):60(phr),the limited oxygen index(LOI) of the MRP/MH/EVA composite is 39%and vertical firing rankes V-0.The expendable graphite(EG) particles with the size of≤30μm and high expanded volume have been prepared by chemical oxidation method with H2SO4 and KMnO4 as oxidant, H3PO4 as assisted intercalation agent.The XRD and scanning electron microscopic(SEM) results show that when the volume ratio between H2SO4 and H3PO4 is 2:1,the oxidation and intercalation effectiveness will be best,and the expanding volume gets to 102 mL·g-1.The energy dispersive X-ray spectrum(EDS) analyses and the Fourier transform infrared(FTIR) spectra indicate there could be H3PO4,H2SO4,dihydric phosphate and sulphate containing Mn in the layers of EG.It is also demonstrated that the initial expanding temperature of EG is about 160℃through TG-DTA curves.High density polyethylene(HDPE) composites with different formulations have been prepared by melt extrusion.The studies reveal that when HDPE:MRP:MH:EG-100(phr):15(phr):35(phr):5(phr),the limited oxygen index(LOI) of the MRP/MH/EG/HDPE composite is 28.5%,vertical firing ranking V-0,and the use of flame retardants has less influence on the tensile strength of the composite.High purity MH powder has been prepared by precipitation method with MgCl2·6H2O and NaOH as raw materials,CO(NH2)2 as coordination agent.The XRD and EDS results show the impurity could generate when the concentration of MgCl2 reaches 2 mol·L-1.Unless CO(NH2)2 is used,it would not decrease.After the concentration of CO(NH3)2 gets to 30 g·L-1,the impurity disappears and the obtained MH powder is lamellas with the size of (30～120) nm.The MH particles have been modified with C18H35O2Na.It is revealed that the modification effect could be best when the usage of C18H35O2Na reaches 5%(wt).Comparing with pre-and post modification,the morphology and the size of MH almost have no change. Nylon-66(PA66) composites with different formulations have been prepared by melt extrusion.The results indicate the modified magnesium hydroxide has a good compatibility with PA66,and small quantity of MRP or MH almost has no influence on the tensile strength. As PA66:MRP:MH=100(phr):10(phr):8(phr),the limited oxygen index(LOI) of the composite is 32%,and vertical firing ranksV-0.
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