| Since graphene was first discovered in2004, extensive research has been earried out on the applications in various fields, due to its unique electronic, thermal, and mechanical properties arising from the strictly two-dimensional (2D) atomic carbon sheet structure. One of the most promising applications of graphene was polymer/graphene composites, in which graphene caused significant improvements in various properties. However, there were still challenges remained in the academic research and practical application of polymer/graphene composites:preparation of graphene, poor compatibility between polymer matrix and graphene, and low efficiency of flame retardancy. In order to solve those problems, this work developed a novel method to prepare graphene. Based on the ideas of nanocomposites, molecular design and catalytic charring, flame retardant grafted graphene and graphene supported nanoparticle hybirds were prepared. The dispersion, mechanical properties, thermal stability and flammability behaviors of polymer/functionalized graphene nanocomposites were investigated, and also the flame retardant mechanism was clarified. The main progress of this work was illustrated as follows:1. A simple method was developed for the production of multi-layer graphene by pyrolyzing poly (methyl methacrylate)(PMMA) on Ni particles in the presence of orgar.ophilic montmorillonite (OMMT). Compared to the graphene prepared by chemical reduction or thermal reduction of graphite oxide, the crumpled graphene with the size of1mm and the thickness of1-4nm had fewer defects and higher degree of graphitization. The yield of graphene was increased with the increased OMMT content; high temperature favored the formation of perfect graphene structure; the size of Ni played a critical role on the formation of graphene. Based on the experimental observations, a possible formation process was proposed.2. Polystyrene (PS)/graphene composites were prepared by solution blending method, where the graphene nanosheets were intercalated and intercalated-exfoliated in the matrix due to the strong π-π interaction between PS and graphene nanosheets. The incorporation of graphene improved the glass transition temperature, thermal stability and flame retardancy of PS matrices, and the reinforcement was enhanced by increasing graphene contents. Graphene with larger diameter (GNS-EG) was superior than that with small diameter (GNS-NG) on the flame retardancy of the nanocomposites, which can be explained by the fact that GNS-EG had better barrier effect on the pyrolysis gases. Then graphene was combined with intumescent flame retardant (IFR) to investigate the effect on the thermal degradation and flame retardant behaviors of PS composites. The maximum decomposition temperature (Tmax) of PS/IFR was increased with the increased content of graphene. It was found that graphene had antagonistic effect with IFR on the flame retardancy because low melt viscosity of PS/IFR caused by graphene made the system not effectively foam to form porous char.3. Intumescent flame retardant PPPB was synthesized and grafted onto the surface of graphene to obtain GNS-PPPB. GNS-PPPB was then covalently reacted with maleic anhydride grafted polyethylene (MAPE) and series of LLDPE/functionalized graphene nanocomposiies were prepared by melt blending method. TEM results demonstrated that GNS-PPPB was well dispersed in the matrix due to the chemical bonding effect between GNS-PPPB and LLDPE matrix. Compared with GNS, GNS-PPPB can obviously improve both tensile strength and elongation at break of the composites, owing to the excellent mechanical properties of GNS as well as strong interfacial interaction between matrix and GNS-PPPB. GNS-PPPB can visibly improve the thermal stability and flame retardant properties of the composites. On one hand, the well dispersed GNS formed good physical barriers to prevent the escape of volatile gases and the spread of oxygen; on the other hand, GNS-PPPB promoted the formation of graphitized and compact char layers. The incorporation of GNS-PPPB can significantly improve the oxidation induction temperature and oxidation induction time, dueto the role of GNS-PPPB that captured free radicals during combustion. The research results indicated that GNS-PPPB formed a network structure in LLDPE, causing an increase in melt viscosity of the system. GNS-PPPB promoted the formation of char layers with high thermal oxidative resistance and compact structure, which could effectively inhibit the energy and mass transfer between the flame and matrix, delay the degradation of inner polymer, and thus reduce the fire hazards.4. Graphene/NiFe-layered double hydroxide (GNS-LDH) nanostructures were synthesized through in situ hydrothermal reaction. Due to the inherent agglomeration tendency of graphene, the Acrylonitrile-Butadiene-Styrene copolymer (ABS) nanocomposites were prepared by solution blending. The effect of GNS-LDH on the mechanical properties, thermal stability and flame retardant properties of ABS has been investigated. The uniform distribution of NiFe-LDH on the GNS could effeciently avoid the aggregation of graphene, which was beneficial for the molecular-level dispersion in ABS. Compared with GNS, incorporated GNS-LDH could improve the mechanical properties of the compositess more obviously. With the increase of GNS-LDH content, the tensile strength, bending strength and storage modulus of ABS/GNS-LDH increased gradually. The introduction of GNS-LDH can obviously improve the thermal stability and flame retardancy of ABS nanocomposites. TG/FTIR results showed that the main decomposition products of ABS/GNS-LDH were hydrocarbons, alkene and aromatic compounds, which were similar to those of pure ABS; however, the release amount of the flammable and toxic products from ABS/GNS-LDH was much lower than those from ABS. This dramatical reduction in fire hazards was mainly attributed to the synergestic effect of GNS-LDH nanostructure:graphene promoted the formation of graphitized and compact char layer, while NiFe-LDH improved the thermal oxidative resistance of the char layer.5. A hybrid graphene/Ni-Ce mixed oxide (Gs-NiCexOy) was fabricated using a co-precipitation method, and then incorporated into PP matrix through masterbatch-melt blending method to prepare PP/Gs-NiCexOy composites. Compared to pure PP, the obtained composites exhibited significantly enhanced thermal stability, flame retardancy and smoke suppression, including decreased maximum mass loss rate by40%, peak heat release rate (PHRR) by37%, total heat release (THR) by17%, total smoke release (TSR) by36%and CO production rate (COP) by49%, and increased Tmax by28℃. Thus, it was concluded that Gs-NiCexOy was beneficial for the fire safety of F?. The steady state tube furnace (SSTF), which was used to study the relationship between smoke density and time under anaerobic atmosphere, revealed that the addition of Gs-NiCexOy reduced the evolution of smoke particle during the combustion of composites. The analysis of Py-GC/MS and TG/FTIR indicated that the amount of flammable gase from PP/Gs-NiCexOy composites was lower than that of PP. Furthermore, based on the char analysis, it was found that Gs-NiCexOy can catalyze the char formation of PP, which inhibited the escape of flammable gases and the transfer of oxygen. |
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