Preparation Of DOPO Derivative/carbon Nanotube Compound Flame Retardant And Its Flame Retardant Property On PLA

In recent years,pollution caused by petroleum-based polymers has become a big burden on the global environment.With the increase of people's environmental awareness,biodegradable polymers have received more and more attention.Among many biodegradable polymers,polylactic acid?PLA?has become the first choice to replace petroleum-based polymers due to its good appearance,excellent mechanical properties,biodegradability,and low toxicity.But due to its inherent poor flame retardancy performance,the limiting oxygen index is only 19%?21%,and it is accompanied by flame droplets,which limit its application areas,especially in electronics and electrical appliances.For this reason,the development of flame retardant PLA has become a research hotspot in recent years.Relevant researchs have shown that the efficiency of adding a single flame retardant to flame retardant PLA is not high,and the amount of addition is usually large,resulting in a significant decrease in PLA mechanical properties.Therefore,the introduction of P and N elements to prepare organic-inorganic hybrid flame retardants has received widespread attention.To this end,starting from the design of molecular structure of flame retardant in this article,a DOPO derivative containing P and N elements was synthesized and added to polylactic acid in different proportions.The effects of flame retardant content on the performance and flame retardancy mechanism of polylactic acid composites are explored.And then the flame retardant was chemically grafted to the surface of carbon nanotubes to prepare the compound flame retardant.The effects of different types of flame retardants on the properties of polylactic acid and the flame retardant mechanism have been explored..The main works of this article are as follows:1?The flame retardant DOPO-NH₂ has been successfully prepared by FTIR,¹H NMR,³¹P NMR,and MS analysis.TG results showed that the thermal stability of DOPO-NH₂was significantly improved,and its initial decomposition temperature(T_5wt%)was 361 ^oC,which was 112 ^oC higher than that of DOPO.In addition,the residual of DOPO-NH₂ reached 22.7 wt%at 600 ^oC,showing good carbon forming ability.DOPO-NH₂ was added to PLA in the proportions of 5 wt%,7.5%wt and 10 wt%to prepare composite materials.TG results showed that the flame retardant DOPO-NH₂did not increase the thermal stability of PLA,and the initial thermal decomposition temperature was decreased,but the maximum thermal weight loss rate temperature increased by about 10 ^oC.The results of LOI,UL-94,and MCC tests showed that the PLA composites containing only 5wt%DOPO-NH₂ can reach UL-94 V-0,and the LOI value increased from 21%to 26%.In addition,the introduction of 5wt%DOPO-NH₂reduced the peak heat release rate?PHRR?of PLA by 22%and the total heat release?THR?by 18.7%.Rheological results showed that the addition of flame retardants will reduce the storage modulus,loss modulus and complex viscosity,which plays a certain plasticizing effect on PLA.2?TEM,XPS,FTIR and TG results showed that he flame retardant DOPO-NH₂was successfully grafted onto carbon nanotubes to prepare compound flame retardant?CNT-DOPO?.TG results showed that the initial thermal decomposition temperature(T_5wt%)of CNT-DOPO was 298 ^oC,and the residual was 54.8 wt%at 700 ^oC,which indicated the excellent char forming ability.In addition,based on the calculation results of XPS and TG,the grafting rate of the DOPO-NH₂ flame retardant is about 50%.CNT-COOH,DOPO-NH₂,and CNT-DOPO were added to PLA at the same ratio of 5 wt%to prepare composite materials.It has shown that carbon nanotubes caused premature degradation of PLA.However,by comparing the experiment and theory values of the residue of each composite,the experiment values of the residue of both PLA/5DOPO-NH₂ and PLA/5CNT-DOPO are larger than the theory values,indicating that DOPO-NH₂ and CNT-DOPO had the effect of promoting PLA to char formation.The cone calorimetry results showed that carbon nanotubes can effectively block the release of heat insulation and delay the fierce combustion of the materials.The PHRR of the three composite materials is 46%,3.4%,and 39.8%lower than that of pure PLA,respectively.Through quantitative analysis,it was concluded that the flame retardant mode of PLA/5CNT-COOH is mainly the barrier effect and promoting char formation,and the flame retardant mode of PLA/5DOPO-NH₂ is mainly the flame suppression and promoting char formation.The flame retardant mode of PLA/5CNT-DOPO is the same as that of PLA/5CNT-COOH.The barrier effect is dominant,accompanied by a certain promoting char formation.Rheological results showed that the influence of carbon nanotubes on viscoelastic transition is quite obvious.PLA/5CNT-COOH and PLA/5CNT-DOPO basically show elastic behavior.Because of the existence of carbon nanotubes,the viscosity of PLA composites increases,and a uniform network-like carbon layer is formed in the end of combustion,which has a certain role in promoting the flame retardancy.