【作者】 牛磊；

【导师】 徐建林；

【作者基本信息】 兰州理工大学 ， 材料物理与化学， 2019， 博士

【摘要】 聚对苯二甲酸丁二醇酯（PBT）是一种半结晶热塑性聚合物材料,具有尺寸稳定、强度高、耐化学腐蚀以及结晶速度快等特点。由于其具有较好的机械性能、热学性能和化学性能等,成为许多工程应用的理想选择。然而,由于PBT材料遇火后容易燃烧,在燃烧过程中会释放大量的热量,导致火灾事故的增加,限制其在工程上的进一步应用。随着阻燃剂制备技术的发展,人们发现工业化使用的微米级阻燃剂已无法适应市场的需求,开发一种既具有高效阻燃性能又能改善基体材料力学性能和加工性能的纳米技术应运而生。而具有优异性能的纳米阻燃剂已引起研究者广泛关注,添加少量的纳米阻燃剂就会使复合材料的机械性能、热稳定性能和阻燃性能产生明显的变化。本论文采用机械化学法制备和改性nano-Sb₂O₃颗粒,将nano-Sb₂O₃颗粒、溴化环氧树脂（BEO）阻燃剂和PBT基粉体材料通过高能球磨机共混后,利用熔融共混和挤出成型的方法制备了nano-Sb₂O₃/BEO/PBT复合材料。通过差示扫描量热仪（DSC）、扫描电子显微镜（SEM-EDX）以及锥形量热仪（CCT）等设备对nano-Sb₂O₃/BEO/PBT复合材料的结晶动力学、热降解动力学以及阻燃机理等进行了系统的研究和探讨。主要研究内容和结果概括如下:1.采用机械化学法制备nano-Sb₂O₃颗粒并对其进行改性,经表征分析,高能球磨法制备的nano-Sb₂O₃颗粒形貌不规则,颗粒之间产生软团聚现象。经阳离子表面活性剂CTAB改性后,由于烷基长链在nano-Sb₂O₃颗粒的表面提供了空间位阻作用,nano-Sb₂O₃颗粒的分散性变好,分散度提高。在CTAB改性基础上,进一步采用硅烷偶联剂KH550对nano-Sb₂O₃颗粒进行复配改性,提升了nano-Sb₂O₃颗粒的分散效果,其平均粒径为59.36nm。复配改性降低了nano-Sb₂O₃颗粒的表面活性,其接触角达到132.5°,提高了nano-Sb₂O₃的表面亲油性,增加了其界面相容性。2.在制备和改性nano-Sb₂O₃颗粒的基础上,研究nano-Sb₂O₃颗粒和BEO阻燃剂的加入对PBT基复合材料结晶性能的影响。结果表明:nano-Sb₂O₃颗粒和BEO阻燃剂的加入并没有改变PBT基复合材料的α晶型结构,但会引起其成核及晶体生长方式发生变化,影响了PBT复合材料的结构规整性。仅加入BEO阻燃剂后,BEO/PBT复合材料的结晶度明显低于纯PBT材料的结晶度,并且随着BEO含量的增加,BEO/PBT复合材料的结晶度相应的减小。而随着nano-Sb₂O₃颗粒含量的增加,nano-Sb₂O₃/BEO/PBT复合材料的晶粒尺寸逐渐减小。Nano-Sb₂O₃颗粒加入后PBT复合材料的焓值减小,利于PBT复合材料进行结晶,nano-Sb₂O₃颗粒含量越高,PBT复合材料结晶的速率越快。Nano-Sb₂O₃颗粒的加入虽然起到了异相成核的作用,但其加入也阻碍了PBT分子链在结晶时候的规整运动,增大了PBT分子链在排入晶格时需要的能量,造成nano-Sb₂O₃/BEO/PBT复合材料的结晶活化能增大。3.PBT复合材料的结晶性能和nano-Sb₂O₃颗粒在基体材料中的分散性能对复合材料的力学性能具有重要的影响。本论文在保证力学性能不受影响的条件下,研究其阻燃性能。力学性能测试分析表明:BEO/PBT复合材料的拉伸强度和杨氏模量升高,但断裂伸长率和缺口冲击强度明显降低。当改性nano-Sb₂O₃颗粒加入BEO/PBT复合材料后,随着nano-Sb₂O₃颗粒含量的增加,PBT复合材料的拉伸强度和杨氏模量呈现先增高后降低的趋势。当nano-Sb₂O₃颗粒含量小于3 wt%时,其在PBT复合材料中具有较好的分散性,PBT复合材料的拉伸强度和冲击强度得到提高。但是,nano-Sb₂O₃颗粒对PBT复合材料冲击强度的贡献较小。相比于BEO/PBT复合材料,其缺口冲击强度的提升仅有7.2%。4.Nano-Sb₂O₃/BEO/PBT复合材料的热降解行为对分析复合材料的阻燃机理具有重要的意义。PBT复合材料的热降解主要分为快速降解和稳定碳层的缓慢降解两个阶段。BEO阻燃剂和nano-Sb₂O₃颗粒之间产生了明显的协效阻燃作用,随着nano-Sb₂O₃颗粒含量的增加,PBT复合材料的热降解速率峰值降低,热稳定性能逐渐提升,残碳率也明显提高。而PBT复合材料的热降解活化能则呈现出先升高后降低的趋势,当nano-Sb₂O₃含量为3 wt%时热降解活化能最高,此时PBT复合材料的热降解最为困难,nano-Sb₂O₃颗粒的加入阻碍了分子链的运动与规整堆砌,增强了PBT复合材料的热稳定性能。5.在前面章节分析基础上,研究nano-Sb₂O₃/BEO/PBT复合材料阻燃性能,探讨其阻燃机理。结果表明:单独添加nano-Sb₂O₃颗粒或BEO阻燃剂时,PBT复合材料均达不到阻燃性能的要求,保持BEO（16 wt%）阻燃剂一定的条件下,随着nano-Sb₂O₃颗粒含量的增加,nano-Sb₂O₃/BEO/PBT复合材料的阻燃性能逐渐提高,极限氧指数（LOI）值由22.9%增加到29.8%。并且在nano-Sb₂O₃颗粒含量为3 wt%时,样品的垂直燃烧（UL-94）等级达到V-0级。PBT复合材料的HRR、PHRR、THR、PCO₂P和PCOP值显著降低,最大降低率分别为57.6%、75.5%、43.7%、76.7%和10.1%。PBT复合材料在热裂解的过程中产生Br自由基和难燃气体,含Br自由基不仅可捕获燃烧区活泼自由基而抑制燃烧的反应,还可以猝灭链端的自由基而阻止复合材料进一步裂解,产生的难燃气体可稀释燃烧区的可燃气体和氧气,并带走燃烧过程中产生的热量,产生气相阻燃作用。同时,nano-Sb₂O₃颗粒促进了凝聚相的交联成炭,炭层形貌致密,热稳定性能好,有效阻止了挥发物的逸出和热量的传递,产生较好的凝聚相阻燃作用。更多还原

【Abstract】 Polybutylene terephthalate（PBT）is a semi-crystalline thermoplastic polymer with the characteristics of stable size,high strength,chemical corrosion resistance and fast crystallization rate.It has become an ideal choice in many engineering applications because of its good mechanical,thermal and chemical properties.However,PBT materials are easy to burn and a lot of heat will be released during the combustion process,which leads to the increase of fire accidents and limits its further application.With the development of flame retardant preparation technology,micron-scale flame retardants used in industy fail to meet the needs of the market.It has become an urgency to develop retardants with high flame retardancy and improved mechanical properties and processing properties of matrix,through nano-technology.Nano-flame retardants with excellent properties have attracted extensive attention of researchers since the addition of a small amount of Nano-flame retardants will improve the mechanical properties,thermal stability and flame retardancy of composites significantly.In this paper,nano-Sb₂O₃ particles were prepared and modified by mechanochemical method.Nano-Sb₂O₃ particles,brominated epoxy resin（BEO）flame retardant and PBT-based powder materials were blended by high energy ball mill.Then,the mixtutre were melt-blended and extruded and PBT/BEO/nano-Sb₂O₃composites were prepared.The crystallization kinetics,thermal degradation kinetics and flame retardant mechanism of nano-Sb₂O₃/BEO/PBT composites were systematically studied by differential scanning calorimeter（DSC）,scanning electron microscope（SEM-EDX）and cone calorimeter（CCT）.The main research contents and results are summarized as follows:1.Nano-Sb₂O₃ particles were prepared and modified by mechanochemical method.The morphology of nano-Sb₂O₃ particles prepared by high-energy ball milling was irregular and there was soft agglomeration between the particles.After modification by cationic surfactant CTAB,nano-Sb₂O₃ particles have higher dispersibility due to the steric hindrance of long alkyl chains on the surface of nano-Sb₂O₃ particles.On the basis of CTAB modification,nano-Sb₂O₃ particles were modified by silane coupling agent KH550.The dispersion effect of nano-Sb₂O₃particles was further improved.The average particle size of nano-Sb₂O₃ particles was59.36 nm.The surface activity of nano-Sb₂O₃ particles was reduced by the compound modification,and the contact angle reached 132.5 degrees.The surface hydrophilicity and interfacial compatibility of nano-Sb₂O₃ particles was improved.2.The effects of nano-Sb₂O₃ particles and BEO flame retardant on the crystallinity of PBT matrix composites were studied based on the successful preparation and modification of nano-Sb₂O₃ particles.The results show that the addition of nano-Sb₂O₃ particles and BEO flame retardant does not change the alpha crystal structure of PBT matrix composites,but changes their nucleation and crystal growth mode,which affects the structural regularity of PBT composites.The grain size of PBT composites decreases gradually,with the increase of nano-Sb₂O₃ particle content.The crystallinity of BEO/PBT composites is lower than that of pure PBT composites after adding only BEO flame retardant.With the increase of BEO content,the crystallinity of BEO/PBT composites decreases.The enthalpy of PBT composites decreases with the addition of nano-Sb₂O₃ particles,which is conducive to the crystallization of PBT composites.The more nano-Sb₂O₃ particles are added,the faster the crystallization rate of PBT composites is.Although the addition of nano-Sb₂O₃ particles improves heterogeneous nucleation,it hinders the regular movement of PBT molecular chains during crystallization,increases the energy required for PBT molecular chains to be discharged into the lattice,and increases the crystallization activation energy of nano-Sb₂O₃/BEO/PBT composites.3.The crystallinity of PBT composites and the dispersibility of nano-Sb₂O₃particles in matrix materials are very important to the mechanical properties of PBT composites.The flame retardancy of PBT composites is studied under the condition that the mechanical properties are not affected.The results of mechanical properties test show that the tensile strength and Young’s modulus of BEO/PBT composites increase,but the elongation at break and notch impact strength decrease significantly.When modified nano-Sb₂O₃ particles were added into BEO/PBT composites,the tensile strength and Young’s modulus of PBT composites increased first and then decreased with the increase of nano-Sb₂O₃ particles content.The dispersion of nano-Sb₂O₃ particles in PBT matrix has an important influence on the mechanical properties of the composites.When the content of nano-Sb₂O₃ particles is less than 3wt%,the nano-Sb₂O₃ particles disperse in PBT composites,and the tensile strength and impact strength of PBT composites are improved.However,nano-Sb₂O₃ particles can’t improve the strength of PBT composites significantly.The notched impact strength of nano-Sb₂O₃/BEO/PBT composites increases only by 7.2%,compared with that of BEO/PBT composites.4.It is of great significance to study the thermal degradation of nano-Sb₂O₃/BEO/PBT composites when analyzing of flame retardant mechanism of composites.The thermal degradation of PBT composites can be divided into two stages:rapid degradation and slow degradation of stable carbon layer.The synergistic effect between BEO flame retardant and nano-Sb₂O₃ particles is obvious.With the increase of nano-Sb₂O₃ particle content,the peak thermal degradation rate of PBT composites decreases,the thermal stability increases and the residual carbon rate increases.With the increase of nano-Sb₂O₃ content,the thermal degradation activation energy of PBT composites increases at first and then decreases.When nano-Sb₂O₃ content is 3 wt%,the thermal degradation activation energy of PBT composites is at the highest and the thermal degradation of PBT composites is the most difficult.The addition of nano-Sb₂O₃ particles hinders the movement and orderly stacking of molecular chains and enhances the thermal stability of PBT composites.5.The flame retardant properties of nano-Sb₂O₃/BEO/PBT composites were studied and the flame retardant mechanism was discussed,based on the analysis of the previous chapters.The results show that the flame retardancy of PBT composites can not meet the requirements,when only adding nano-Sb₂O₃ particles or only adding BEO flame retardants.When BEO is 16 wt%,the flame retardancy of PBT composites increases gradually with the increase of nano-Sb₂O₃ particles content,and the LOI value increases from 22.9%to 29.8%.When the nano-Sb₂O₃ particle content is 3 wt%,the vertical combustion（UL-94）grade of the sample reaches V-0 grade.The HRR,PHRR,THR,PCO₂P and PCOP values of PBT composites decreased significantly,with the maximum reduction rates of 57.6%,75.5%,43.7%,76.7%and 10.1%,respectively.Br free radicals and nonflammable gases are produced in the process of thermal cracking of PBT composites.Br free radicals not only capture the active free radicals in the combustion zone to inhibit the combustion reaction,but also quench the free radicals at the end of the chain to prevent the further cracking of the composites.The flammable gases and oxygen in the combustion zone are diluted by the nonflammable gases,and the heat generated in the combustion process is taken away because of gas phase flame retardant effect.At the same time,nano-Sb₂O₃particles promote the cross-linking of the condensed phase to form carbon.The carbon atom structure in the carbon layer changes into graphite crystal structure.The carbon layer has compact morphology and good thermal stability,which effectively prevents the volatile matter from emitting and heat transfer,and produces better flame retardant effect of the condensed phase.更多还原