Synthesis Of New Tin-based Flame Retardants And Their Flame Retardant Applications In Polyamide 6

Long-term development of flame retardant and flame retardant technology has put forward new and more stringent requirements for the flame retardant industry.Nowadays,new flame retardants with characteristics of high efficiency,non-toxic,harmless,low addition and smoke suppression have become a hot topic.Tin-based flame retardants have attracted much attention of the researchers due to their remarkable metal ion catalysis and excellent smoke suppression effect.In order to further develop the potential and fully explore the flame retardant effect of tin-based flame retardants,two new tin-based flame retardants,which were named as stannous2-[(6-oxido-6H-dibenzo[c,e][1,2]oxaphosphinin-6-yl)methyl]succinate(SDDP)and stannous hypophosphite(SHP)respectively,were synthesized from sodium hypophosphite(Na H₂PO₂)?stannous chloride dihydrate(Sn Cl₂·2H₂O)and 2-[(6-oxido-6H-dibenzo[c,e][1,2]oxaphosphinin-6-yl)methyl]succinic acid(DDP)by neutralization and double decomposition reaction.Their structures were characterized by Fourier transform infrared spectroscopy(FTIR),elemental analysis,X-ray diffraction(XRD)and nuclear magnetic resonance(NMR).The thermal properties of SDDP and SHP were also determined by thermogravimetric analysis(TGA)and differential thermal analysis(DTG).In the synthesis of SDDP,the optimum synthetic conditions were as follows.Solvent was chosen to be a mixture of deionized water and ethanol while the volume ratio is 10:3.Reaction temperature was controlled at 60?with a 4 hours'reaction time.Under these conditions,the product SDDP was white solid powder with a yield of 70.95%and a thermal decomposition temperature(T_-5%,N₂)of 309?,which satisfied the processing requirements of most thermoplastic resins.The appearance of SHP were similar to SDDP.The differences between these two flame retardants were that the optimum reaction temperature of SHP decreased to 50?,the optimum reaction time reduced to 4 hours and T_-5%decreased to 275?with the yield of 68.86%.Flame retardant composites(SDDP/FRPA6)were prepared by blending SDDP into polyamide 6(PA6).The thermal properties of all FRPA6 were obtained by TGA and DTG.The flame retardancy of FRPA6 was tested by vertical burning(UL94),limited oxygen index(LOI)test and glow-wire test.At the same time,the mechanical properties of the sample were tested.The results showed that the flame retardancy of PA6 was improved by adding SDDP.When the addition amount of SDDP was 30wt%,the sample could reach UL 94 V-2 rating(3.2mm)and its LOI was increased to 24.7%.Meanwhile the glow-wire flammability index(GWFI)reached 960?.Besides,SDDP and SHP were separately compounded with MCA and the effects of the compounding system of SDDP/MCA and SHP/MCA on the flame retardancy were studied as well.The results showed that in SDDP/MCA system,when the mass ratio of SDDP to MCA was 1:1and the total addition amount was 20%,the best flame retardancy was achieved with a UL 94 V-2rating.At the same time,the LOI value was 26.4%which was 1.9%higher than that of adding 20wt%SDDP alone and GWFI was over 960?.In SHP/MCA system,the optimum ratio was 1:1too.When adding 30wt%flame retardant,FRPA6 reached V-2 rating.LOI value was increased by7.9%to 28.9%compared with pure PA6.It is worth noting that the glow-wire test results of SHP/MCA system were better than SDDP/MCA.Its glow-wire ignition temperature(GWIT)had also passed 750?test which meant that it had better adaptability in the field of flame retardant polyamide for electrical appliances.In terms of the thermal properties and mechanical properties,the initial decomposition temperature and maximum decomposition rate temperature of FRPA6 with the above flame retardant systems,whether DDP or SDDP/MCA or SHP/MCA,were lower than pure PA6.This phenomenon indicated that the pre-decomposition of the flame retardant in FRPA6 absorbed a large amount of heat which maintained the stability of the substrate and thus exerted a good flame retardant effect to preven the material from continuing to burn.The addition of flame retardant also reduced the mechanical properties in varying degrees,especially in SDDP system.The lowest values of tensile strength is about 30%lower than those of pure PA6 which should be paid more attention in practical using.The mechanical properties of the composite system were relatively good.The value of mechanical properties of SDDP/MCA and SHP/MCA systems decreased by less than 10%.The combination of MCA did not only improve the flame retardancy of tin-based flame retardant,but also maintain good mechanical properties which could meet the application requirements in engineering field.