【作者】 张峰；

【导师】 张军；

【作者基本信息】 青岛科技大学 ， 材料学， 2008， 博士

【摘要】 传统的阻燃体系中含卤阻燃剂阻燃效果比较好,但由于在火灾中会放出腐蚀性、有毒的气体,对环境危害较大。而膨胀阻燃体系通过膨胀成炭隔热、隔氧起到阻燃作用,且有抑烟效果,对环境友好,已成为最有前途的阻燃技术之一。膨胀阻燃聚合物材料在火灾中的热行为变化以及热解化学反应过程、燃烧过程都非常复杂,至今仍然没有充分理解,因此有必要对其燃烧过程进行研究,以建立相应的理论模型。本文选取膨胀阻燃聚丙烯材料(IFR-PP)和纯聚碳酸酯(PC)作为典型材料,研究了两种材料的膨胀阻燃特性。TG/FTIR联用的分析结果表明,当温度高于290℃(在空气中)或440℃(在氮气中),由于添加剂的作用使IFR-PP聚合物材料热稳定性好于PP。通过调节膨胀阻燃剂的含量,可以使IFR-PP材料的阻燃级别达到V-0级,热释放速率大大降低。IFR-PP聚合物材料的炭渣分析结果表明,膨胀剂配方、含量的变化对炭层结构的致密性、整体性都有很大影响。IFR-PP在低辐射功率下比在高辐射功率下更容易形成致密、均匀的炭层。SEM分析表明,膨胀阻燃PP材料开始形成的炭层有利于起到有效隔热隔氧作用。辐射功率、样品厚度和样品的安装方式对纯PC的燃烧行为都有影响。纯PC的膨胀速度在燃烧过程中基本不变或有增加的趋势。本文还研究了IFR-PP和PC材料在锥形量热仪条件下的热传递过程。结果表明,辐射功率增加明显加快IFR-PP材料表面温度升高;膨胀阻燃剂的含量也对IFR-PP材料的表面温度有影响。IFR-PP材料和纯PP材料内部温度场分析结果表明,样品内部距离上表面越近的位置温度越高,距离上表面越远的位置温度越低。改变配方APP,PER的含量会影响IFR-PP材料内部的传热。IFR-PP材料外部温度场分析结果表明,当膨胀炭层膨胀到样品上方测温点位置,由于膨胀炭层的覆盖作用导致测温点温度曲线下降之后再上升。此外,对样品上方的测温点,离样品越远(即越靠近锥形加热器),所能达到的最高温度越大。纯PC的表面温度分析结果表明,不同辐射功率下PC样品上表面温度随时间都呈现先升高后保持平稳的趋势。纯PC的内部温度场分析结果表明,温度曲线中会出现转折现象。本文对IFR-PP的热物性也进行了分析和研究。建立了火灾环境下材料加热过程(聚合物分解之前)中估算材料热导率的方法。采用DRX—I热导率测试仪测量并分析了IFR-PP材料热导率在20℃~380℃的温度范围内的热导率随温度变化规律。膨胀阻燃聚合物材料比热容的测试结果表明,由于熔融和分解吸热导致膨胀PP材料比热容曲线中出现了两个峰值。膨胀PP材料燃烧后炭层比热容由于氧化分解放热使比热容在温度超过127℃后出现了下降的趋势。膨胀PP材料的热扩散系数随温度增加而不断减小;膨胀PP材料燃烧后炭渣的热扩散系数随温度增加下降趋缓。用理论公式计算和实验测量两种方法得到了材料的表面发射率。用直接测量法测定了IFR-PP的表观密度;炭渣的表观密度和真实密度,并由此计算出炭渣的孔隙率。本文通过实验研究和理论分析建立了可以描述膨胀阻燃聚合物材料膨胀燃烧过程的模拟模型。该模型在传统能量模型的基础上强调了膨胀过程所涉及到的热力学问题,并提出了相应的热力学吸热模型。选取典型膨胀聚丙烯材料,并将该材料的实验结果与模拟结果进行了比较。验证结果表明,利用本模型模拟出来的温度曲线、样品厚度、质量损失速率曲线与实验结果吻合很好。研究结果表明,本模型可以合理地描述聚合物材料的膨胀行为,可以比较准确预测材料在燃烧过程中的温度分布、样品厚度随时间变化、样品质量损失速率随时间的变化等。更多还原

【Abstract】 Traditional halogen-based fire retardant systems will release corrosive and toxic gases in fire and do harm to environment. The Intumescent technology is an alternative means to impart flame retardancy to polymer materials. Intumescent fire retardant materials generate intumescent char on the surface, which protects the underlying material from the insults of heating from fire. However, the mechanisms involved with the intumescence behavior, the thermal behavior and decomposition occurred in the burning process have not been fully understood yet. Therefore, it is important to study their burning process and to develop a prediction and simulation model.In this study, intumescent fire-retardant polypropylene (IFR-PP) and polycarbonate (PC) materials were selected to be typical intumescent fire-retardant polymer materials and their intumescent behaviors in fire were investigated firstly. The results from the analysis of TG/FTIR show that the IFR-PP composites are more thermally stable than PP because of the incorporation of intumescent flame additives at temperature higher than 290℃in air and 440℃in nitrogen. The fire retardancy level of IFR-PP materials can reach V-0 grade with UL-94 test at appropriate content levels of intuemscent fire reatardant. Simultaneously the heat release rates and mass loss rates will decrease remarkably. The analysis results of intumescent char formed from IFR-PP materials indicate that different formulation and contents will affect the densification and unity of the char. The formed char for IFR-PP materials tend to be denser and more uniform at lower incident heat flux than higher incident heat flux. The examination of IFR-PP materials by scanning electron microscope (SEM) shows that, compared to intumescent char layer after the complete combustion, the char formed after the material burnt for 10 s is more fine and compact, which can provide a better shield to inhibit the heat and oxygen penerating the char effectively. The burning behavior of PC is affected by many factors such as incident heat flux, sample thickness and sample mounting and so on. The intumescent velocity is nearly constant or tends to increase during burning.The heat transfer process for IFR-PP and PC materials were studied using the cone calorimeter. The results show that the surface temperatures for IFR-PP materials will increase faster in high incident heat flux than that in low incident heat flux. The surface temperatures for IFR-PP materials are also influenced by the change of intumescent fire retardant contents. According to the analysis results of temperature distributions inside the sample for IFR-PP materials, the temperature measured near the top surface is much higher than the temperature measured far from the top surface. The heat transfer process inside the IFR-PP materials is affected by difference in the formulations such as the contents change of APP and PER. The temperature distributions above the IFR-PP samples show that the temperature increases gradually with time before the intumescent char forms. The temperature values of the sample decrease sharply due to the formation of char cap and accumulating gases. The surface temperature distributions for PC materials indicate that the temperature will increase with time and then keep almost constant. A bending point in the temperature curves was observed for internal temperature distribution of PC sample.The thermal properties for IFR-PP materials were analyzed and studied. A method used to calculate thermal conductivity for polymer materials was proposed, which is used for the heating stage in cone calorimeter fire condition. At the same time, thermal conductivities for IFR-PP materials versus temperature in the range of 20℃~380℃were measured using DRX-I thermal conductivity test instrument. Specific heat capacities for IFR-PP materials were measured by differential scanning calorimetry NETZSCH DSC204. Two peak values appear in the specific heat capacity curve for IFR-PP materials due to melt and pyrolysis heat. The specific heat capacity values for the char formed from IFR-PP will decrease when the temperature beyond 127℃because of the oxidized pyrolysis heat. Thermal diffusivities of IFR-PP materials will decrease with the increase of the temperature. Thermal diffusivities of the char formed from IFR-PP will also decrease with increase of temperature but more gently. Surface emissivities of IFR-PP materials were measured using two different methods. One is to calculate surface emissivities with mathematical model and another is to measure it in experiment. The apparent densities of IFR-PP and its char were measured and the porosity of their char was calculated.A prediction model for the intumescence process in fire for intumescent flame retardant PP was developed. The model emphasizes the thermodynamic aspect of the intumescence process and a corresponding submodel is deduced. The intumescent fire-retardant polypropylene materials were selected to obtain experimental data such as MLR. The validation results showed that the temperatures, intumescent thicknesses and mass loss rates predicted by the model were in reasonably good agreement with the experimental results. The study shows that the present model can appropriately describe the intumescent behavior of polymer and numerically predict their intumescent thickness, temperature distribution and mass loss rates in fire.更多还原