Preparation Of Rare Earth Hydrotalcite-like Compounds And Its Application In Flame Retardant And Smoke Suppression In Polylactic Acid

With the increasing oil crisis and white pollution,the research and development of bio-based degradable composite materials is imminent.Among them,polylactic acid（PLA）has been widely studied as a typical high-performance degradable plastic,but its flammability limits its application in fields with flame retardant requirements.Hydrotalcite-like compounds（LDHs）have high specific surface area and good thermal stability.Using LDHs as a flame retardant for PLA has the advantages of low price and no pollution,but its compatibility with PLA is poor and its flame retardant efficiency is low.Studies have shown that the flame retardant efficiency of LDHs can be effectively improved by optimizing the structure of LDHs.The unique electronic arrangement of rare earth elements makes them have unique properties and a wide range of uses.Therefore,the combination of LDHs and rare earth elements to synthesize rare earth doped LDHs with excellent performance has broad application prospects.In this paper,the modification based on rare earth doped LDHs and its application in flame retardant and smoke suppression in PLA are systematically carried out.The main work is summarized as follows:1.In this chapter,the rare earth RE（RE=La,Ce,Sm,Eu,Tb,Y）doped magnesium-aluminum hydrotalcites,denoted as MgAlRE-LDHs,were synthesized by hydrothermal-assisted co-precipitation method.The products were characterized by XRD,FT-IR,SEM,TEM and TG,and the effects of p H,type and ratio of rare earth ions on Mg Al-LDHs during the synthesis were discussed.The morphology and crystal form of MgAlY-LDHs synthesized under the conditions of p H=11 and n(Mg²⁺):n(Al³⁺):n(Y³⁺)of 2:0.9:0.1 are more uniform,and the dispersibility and thermal stability are better.The effects of MgAlY-LDHs on the thermal stability and flame retardancy of PLA were investigated by thermogravimetric analysis（TG）and cone calorimetry tests（CCT）.The results showed that the thermal stability and flame retardancy of PLA/MgAlY-LDHs were enhanced with the addition of MgAlY-LDHs,and the addition of 25 wt%MgAlY-LDHs made the carbon residue mass of the composites reach 15.2%,and the peak heat release rate（PHRR）decreased by 37.2%compared to pure PLA.2.In this chapter,stable dispersions of negatively charged Mo S₂nanosheets were prepared by solvothermal assisted ultrasonic exfoliation,and Mo S₂/LDHs nanohybrid materials were constructed by electrostatic interaction with positively charged MgAlY-LDHs nanosheets.Compared with LDHs,the material has better dispersion,thermal stability and better compatibility with PLA matrix.Compared with adding the same content of LDHs,Mo S₂/LDHs can significantly improve the thermal stability and smoke inhibition of PLA composites.The peak carbon dioxide release rate（CO₂P）decreased by 10.4%,8.3%and 19.8%,respectively.3.In this chapter,ammonium polyphosphate（APP）intercalated MgAlY-LDHs were prepared by one-step hydrothermal method.XRD,FT-IR,SEM-EDS and TEM confirmed that the target APP-LDHs were successfully synthesized,and PLA/APP-LDHs composites were prepared by melt blending.The flame retardant test results show that the introduction of 15 wt%APP-LDHs can make PLA pass the UL-94 V-0 rating and obtain a high LOI value of 24%,and due to the catalytic blocking effect of APP-LDHs,the PHRR and total heat release（THR）of the composites were reduced by 43%and 20%,respectively.