| Layered double hydroxides(LDHs),also known as hydrotalcites,have a unique nano-layered structure and excellent stable physicochemical properties.In recent years,it has been widely used in the fields of catalysts,adsorbents,polymer nanomaterials and halogen-free flame retardant materials.In this thesis,the carbonization catalyst was used to study the catalytic carbonation of polyolefin materials.The flame retardancy of the carbon-forming polymer materials and the microstructure,graphitization degree and application properties of the obtained carbon material were tested.In this paper,a NiAl-LDHs was first synthesized by microwave hydrothermal crystallization.The layered structure and phase state of NiAl-LDHs were characterized by X-ray diffraction(XRD).It was confirmed that the synthesized NiAl-LDHs is a typical LDHs structure and consists of Ni(OH)2 and Al(OH)3 phases.The catalytic carbonization performance of NiAl-LDHs on polyolefins[polypropylene(PP),linear low density polyethylene(LLDPE),polystyrene(PS),polyethylene glycol(PEG200)and polyvinyl alcohol(PVA)]was investigated by model carbonation experiments.It was found that NiAl-LDHs have the characteristics of general Ni-based catalysts,that is,they have better catalytic carbonization properties for non-oxygenated polyolefins in the presence of trace amounts of chlorides.The results of carbonization confirmed that when 20 wt%NiAl-LDHs catalyst and 0.5 wt%NH4Cl promoter were added,the carbonization conversion rate of LLDPE reached 49.6%,the carbonization conversion rate of PP was 46.8%,and the carbonization conversion rate of PS was 44.2%.The formation of carbon can effectively improve the flame retardancy of the polymer.This paper next studies the flame retardant effect of NiAl-LDHs combined with NH4CI on LLDPE.The results of limiting oxygen index(LOI)and cone calorimetiy(CONE)show that the addition of NiAl-LDHs catalyst and trace NH4CI promoter have a great influence on the flame retardant properties of LLDPE.When 20 wt%NiAl-LDHs and 0.5 wt%NH4CI promoter were added,the peak heat release rate(PHRR)of LLDPE decreased by about 80%,and the LOI value increased to 26.5%.The microstructure and morphology of carbon residue were characterized by X-ray diffraction(XRD),transmission electron microscope(TEM)and scanning electron microscope(SEM).It was found that NiAl-LDHs can catalyze the formation of multi-walled carbon nanotubes by LLDPE.These carbons form a carbon barrier layer with the layered NiAl-LDHs to effectively flame retard the LLDPE.In this paper,a CuAl-LDHs was synthesized by the same method.The layered structure and phase of CuAl-LDHs were characterized by XRD.It was confirmed that the synthesized CuAl-LDHs also have a typical LDHs structure and are composed of Cu(OH)2 and Al(OH)3 phases.Model carbonization experiments show that CuAl-LDHs have higher carbonization properties for oxygen-containing polyolefins,while catalytic carbonization efficiency for non-oxygenated polyolefins is lower.When the addition amount of CuAl-LDHs(CuAl-4)was 20 wt%,the carbonization ratio of PEG200 was 14.5%.Similarly,when the amount of CuAl-4 added was 20 wt%,the carbonization rate of PVA was 9.8%.In the case of the same addition amount,the catalytic carbonization rates for PP,LLDPE,and PS were 2.1%,1.9%,and 2.6%,respectively.The PEG200 carbon product was selected for characterization.The microstructure and morphology of the carbon products were characterized by XRD,TEM,SEM,Raman and specific surface area(BET).The results confirmed that the carbon product is a porous carbon material,and the pore diameter is basically composed of micropores and mesopores;the specific surface area is up to 877.65 m2·g-1.The porous carbon material is applied to an electrode material of a supercapacitor.At a scan rate of 2 mVs-1,cyclic voltammetry(CV)tests found that its specific capacitance can reach 376.32 F·g-1.This result indicates that the porous carbon material has high electrochemical performance. |
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