Preparation Of MOFs/Phosphorus Lignin-based Flame Retardant And Its Application In Epoxy Resins

With the development of the social economy,more and more polymer materials with excellent mechanical properties and processing properties are widely used in daily life,including epoxy resins(Epoxy Resins).However,epoxy-based polymer materials are often flammable and will release a lot of heat and toxic and harmful gases when burning,which poses a great threat to the natural environment and human safety,and this flammability greatly limits the wide application of epoxy resin materials.Therefore,research on the improvement of flame retardant properties of epoxy resins is imminent.In this paper,lignin was modified by phenol and amination,and then9,10-dihydro-9-oxa-10-phosphophenanthrene-10-oxide(DOPO)was introduced to prepare a lignin-based flame retardant(Lignin-N-DOPO)containing nitrogen and phosphorus flame retardant elements.On this basis,three MOFs structures HKUST-1,ZIF-67 and ZIF-8 were successfully introduced to prepare HKUST-1/lignin-based flame retardant(F-lignin@HKUST-1),ZIF-67/lignin-based flame retardant(F-lignin@ZIF-67)and ZIF-8/lignin-based flame retardant(F-lignin@ZIF-8).According to the analytical test results of infrared spectroscopy(FT-IR),X-ray diffractometer(XRD),X-ray photoelectron spectroscopy(XPS),and field emission electron microscopy(SEM).It was found that DOPO was successfully coated with lignin,and HKUST-1 also grew on the surface of Lignin-N-DOPO.The results of thermogravimetric(TG)test analysis showed that the carbon residue(18.24 wt.%)of the modified nitrogen and phosphorus-based lignin(Lignin-N-DOPO)flame retardant was lower compared with that of lignin(41.57 wt.%),indicating that the flame retardant mainly decomposed to form volatile products,but its maximum weight loss temperature was elevated to 354.7 ℃ higher than that of lignin(333.3 ℃).The carbon residues of the flame retardants after the introduction of the MOFs structure were also improved,and the maximum weight loss temperature was also higher than that of Lignin-N-DOPO,which indicated that the addition of the MOFs structure enhanced the thermal stability of the flame retardants.Different types of flame retardants were introduced into the epoxy resin system by physical blending,and then the flame retardant properties were investigated by thermogravimetric analysis as well as by vertical combustion rating test(UL-94),oxygen index test(LOI)and cone calorimetric test.Thermogravimetric test results show that the carbon residues of EP/F-lignin@HKUST-1,EP/F-lignin@ZIF-67 and EP/F-lignin@ZIF-8 are higher than those of pure epoxy at 800 ℃.The limiting oxygen index(LOI)test results show that the LOI value of pure epoxy-based thermosetting materials was 26.1 %.,while the LOI value of the epoxy-based thermoset composites kept increasing(30 % ～ 33 %)with the increase of the flame retardant dosage.The EP/15% F-lignin@HKUST-1 successfully passed the vertical combustion V-0 test and achieved the best flame retardant performance index.The results of cone calorimetry test showed that the peak heat release rate(PHRR)and total heat release(THR)of EP/15%F-lignin@HKUST-1 are reduced by 41.2 % and 33.8 %,respectively,compared with pure epoxy-based thermosets.In addition,F-lignin@HKUST-1 can effectively reduce the release of carbon monoxide(av-COY)and carbon dioxide from the composites.Raman spectroscopy analysis showed that the graphitization degree of the residual carbon of EP/15%F-lignin@HKUST-1 composite was significantly increased,which helped to form a protective layer with shielding effect in the epoxy resin.The pyrolysis process of the composite is a solid-state reaction process.In this thesis,the thermogravimetric analyzer was used to analyze the EP/15% Lignin-N-DOPO and EP/15%F-lignin@HKUST-1 at different ramp rates.Two different kinetic analysis methods,the Kissinger-iterative method,and the Ozawa-iterative method were used for kinetic analysis,and their activation energies at each stage of pyrolysis were obtained.When the conversion rate reaches 70%,the activation energies of EP/15% Lignin-N-DOPO and EP/15%F-lignin@HKUST-1 obtained by the two kinetic analysis methods are 164.55 k J/mol ～ 164.51 k J/mol and 350.50 k J/mol ～ 351.51 k J/mol,respectively.It was found that the activation energy of the material added with F-lignin@HKUST-1 was much higher than that of the material added with Lignin-N-DOPO.Their pyrolysis process was mainly composed of three parts,which are the pre-decomposition(0.05<α<0.25): the initial decomposition of DOPO and lignin;the mid-decomposition(0.3<α<0.65): the decomposition of DOPO and HKUST-1 and the further degradation of lignin leads to dehydration of the condensed phase;and the post-decomposition(0.7<α): the formation of a large number of carbon residues and the action of HKUST-1decomposition products make the carbon layer denser.