【作者】 洪宁宁；

【导师】 胡源； 宋磊； T.Richard Hull；

【作者基本信息】 中国科学技术大学 ， 安全科学与工程， 2014， 博士

【摘要】 石墨烯因其特殊的二维结构和优异的性质,在聚合物基复合材料领域应用十分广泛,仅需极少的添加量,就能显著提升复合材料的电学、力学和热学等性能。但是聚合物／石墨烯复合材料领域仍然面临着许多科学和技术问题。本文针对石墨烯的制备产率低和成本高、与基体中的相容性差以及对基体增强阻燃效率低等问题,开发了石墨烯的新型制备方法,结合纳米复合、分子设计以及催化成炭等理念,制备了阻燃剂接枝改性石墨烯、几种基于石墨烯负载纳米粒子杂化物,考察功能化修饰对改善石墨烯与基体相容性的作用,研究聚合物／功能化石墨烯纳米复合材料的力学性能、热稳定性和阻燃性能,从气相和凝聚相角度研究可能的阻燃机理。取得的研究进展如下：1.针对现有石墨烯的制备方法存在的成本高、产率低等问题,开发了一种催化裂解聚合物制备石墨烯的新方法,即以聚甲基丙烯酸甲酯(PMMA)为碳源,以镍粉(Ni)为催化剂,在有机改性蒙脱土(OMMT)形成的局限空间内,控制裂解制备石墨烯。所得石墨烯片层尺寸在几微米以上,具有均一的厚度(1-4nm),与传统热还原和化学还原氧化石墨法制备的石墨烯相比,产物具有较少的结构缺陷和较高的石墨化程度。研究发现：石墨烯的产量随着OMMT含量增加而增加；温度越高越有利于形成结构完整的石墨烯；微米级的金属Ni粉对形成石墨烯结构起决定作用。根据实验结果,提出可能的石墨烯形成机理。2.采用溶液共混法制备聚苯乙烯(PS)/石墨烯复合材料,由于石墨烯和PS之间存在较强的π-π作用,石墨烯在基体中主要以插层或插层-剥离状态存在。石墨烯的加入能够提高PS/石墨烯复合材料的玻璃化转变温度、热稳定性和阻燃性能,且随着石墨烯含量的增加而逐渐提高。大尺寸石墨烯(GNS-EG)比同含量的小尺寸石墨烯(GNS-NG)的改善效果更为明显,可能是前者对裂解气体有着更好的阻隔作用。进一步将石墨烯与膨胀型阻燃剂(IFR)结合,研究石墨烯对PS/IFR复合材料的热降解行为和阻燃性能的影响。随着石墨烯添加量的增加,PS/IFR复合材料的最大热分解温度(Tmax)不断提高。石墨烯与IFR在阻燃PS上存在拮抗效应,因为石墨烯的加入降低了PS/IFR复合材料的熔体黏度,造成体系不能有效发泡形成膨胀的多孔炭层。3.合成了一种膨胀型阻燃剂PPPB,并将其接枝到石墨烯(GNS)的表面得到GNS-PPPB,妾着通过与马来酸酐接枝聚乙烯(MAPE)反应得到GNS-MAPE,采用熔融共混法制备出线性低密度聚乙烯(LLDPE)/GNS-PPPB复合材料。研究发现,由于接枝阻燃剂与基体存在化学键作用,GNS-PPPB在基体中呈现均匀分散。与GNS相比,GNS-PPPB能明显提升复合材料的拉伸强度和断裂仲长率,这得益于GNS自身优异的机械性能以及与基体之间存在较强界面作用力。GNS-PPPB能够提高复合材料的热稳定性和阻燃性能,因为一方面均匀分散的GNS可以很好地阻隔易燃性气体逃逸和氧气扩散,另一方面GNS-PPPB能够促进LLDPE在燃烧时成炭。GNS-PPPB的加入能够显著提升材料的氧化诱导温度和氧化诱导时间,因为GNS-PPPB具有捕捉自由基的作用。研究结果表明,GNS-PPPB在LLDPE中形成网络结构,而导致体系熔融黏度增加,燃烧时通过促进基体形成炭层而起到保护内部基体,降低火灾危险性的作用。4.通过原位水热反应法制备石墨烯/镍铁双氢氧化物(GNS-LDH)纳米结构,采用溶液共混法制备丙烯腈-丁二烯-苯乙烯共聚物(ABS)/GNS-LDH复合材料,研究GNS-LDH对ABS复合材料的力学性能、热稳定性和阻燃性能的影响。NiFe-LDH纳米片均匀且致密地分布在GNS片层的表面,有效地抑制了GNS的团聚和重新堆积,因而制备的复合物中GNS-LDH呈现高度剥离的状态。同含量的GNS-LDH比GNS更能提高材料的力学性能,且随着添加量的增加,材料的拉伸强度、弯曲强度和储能模量均逐渐增加。GNS-LDH的添加能够明显改善ABS复合材料的热稳定性和阻燃性能。ABS基体的主要热裂解产物为碳氢化合物、烯烃、芳香族化合物,ABS/GNS-LDH的裂解产物成分基本类似,但其产物的浓度要远低于ABS。GNS-LDH通过促进基体形成致密结实的炭层,阻碍易燃性气体挥发和氧气扩散,从而达到阻燃的目的。5.通过化学共沉淀法制备Gs-NiCexOy杂化物,采用母粒-熔融共混法制备聚丙烯(PP)/Gs-NiCexOy复合材料,研究杂化物对PP复合材料的热稳定性、阻燃性能和有毒烟气释放的影响,探究可能的火灾安全性增强机制。Gs-NiCexOy均匀的分散在PP中,无团聚现象。与纯PP相比,PP/Gs-NiCexOy复合材料的Tmax升高了28℃,最大热分解速率降低近40%,最终残炭达到4.2wt%. Gs-NiCexOy对于提高PP复合材料的火灾安全性有积极作用,在添加2.5wt%的情况下,复合材料的热释放速率峰值(PHRR).总热释放量(THR)、总烟释放量(TSR)和CO产生速率(COP)分别下降了37%、17%、36%和49%。利用稳态管式炉(SSTF)模拟材料在氧气供应不足条件下烟密度随时间变化关系,发现Gs-NiCexOy能够降低PP复合材料燃烧过程中烟颗粒的产生。利用Py-GC/MS和TG/FTIR分析PP和PP/Gs-NiCexOy裂解产物,发现后者的可燃性气体的释放量要低于前者。炭渣表征结果表明,Gs-NiCexOy催化PP燃烧过程中气相产物成炭,形成保护炭层,起到阻碍气体挥发和氧气扩散的作用。更多还原

【Abstract】 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.更多还原