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Effects of cell structure and density on the properties of high performance polyimide foams

机译：泡孔结构和密度对高性能聚酰亚胺泡沫性能的影响

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Activity at the NASA Langley Research Center (LaRC) has focused on developing low density polyimide foam and foam structures which are made using monomeric solutions or salt solutions formed from the reaction of a dianhydride and diamine dissolved in a mixture of foaming agents and alkyl alcohol at room temperature. Monomer blends may be used to make a variety of polyimide foams with varying properties. The first foaming process developed consisted of thermal cycling the polymer precursor residuum and allowing the inflation of the particles to interact to create the foam. This process has resulted in foam structures with higher percentages of open cell content. Another innovative foaming process has been developed that begins with partially inflated microspheres, "friable balloons", with incomplete polymer molecular weight gain, which when fully cured into a foam results in more closed cell structures. In a research study performed by NASA Kennedy Space Center (KSC) and LaRC, two closely related polyimide foams, TEEK-H series and TEEK-L series, (4,4'-oxydiphthalic anhydride/3,4'-oxydianiline and 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride/4,4'-oxydianiline) were investigated for density effects and closed versus open cell effects on the thermal, mechanical, and flammability properties. Thermal conductivity data under the full range of vacuum pressures indicate that these materials are effective insulators under cryogenic conditions. Contributing factors such as cell content, density, and surface area were studied to determine the effects on thermal conductivity. Cone calorimetry data indicated decreased peak heat release rates for the closed cell system, TEEK-H friable balloons, compared to the TEEK foams with higher open cell content. Mechanical properties including tensile strength and compressive strength indicated that the materials have good structural integrity. Foams with more open cell content resulted in greater tensile and compressive strengths than the closed cell foams. The maximum closed cell content achieved in the "friable balloon" system was 78% at a foam density of 0.048 gm/cm{sup}3.
机译：NASA兰利研究中心（LaRC）的工作重点是开发低密度聚酰亚胺泡沫和泡沫结构，这些结构是使用二酐和二胺在泡沫剂和烷基醇的混合物中溶解而得的单体溶液或盐溶液制得的。室内温度。单体共混物可用于制备各种具有不同性能的聚酰亚胺泡沫。开发的第一个发泡过程包括热循环聚合物前驱体残渣并允许颗粒膨胀相互作用以产生泡沫。该过程导致具有较高百分比的开孔含量的泡沫结构。已经开发出另一种创新的发泡方法，该方法以部分膨胀的微球“易碎的气球”开始，聚合物分子量增加不完全，当完全固化成泡沫时，泡沫会形成更密闭的孔结构。在NASA肯尼迪航天中心（KSC）和LaRC进行的一项研究中，两种密切相关的聚酰亚胺泡沫TEEK-H系列和TEEK-L系列（4,4'-氧二邻苯二甲酸酐/ 3,4'-氧二苯胺和3，研究了3'，4,4'-二苯甲酮四甲酸二酐/ 4,4'-羟二苯胺的密度效应以及闭孔与开孔对热，机械和可燃性的影响。在整个真空压力范围内的导热系数数据表明，这些材料在低温条件下是有效的绝缘体。研究了诸如泡孔含量，密度和表面积之类的影响因素，以确定对热导率的影响。锥形量热数据表明，与具有较高开孔含量的TEEK泡沫相比，闭孔系统TEEK-H易碎球囊的峰值放热速率降低。包括抗张强度和抗压强度的机械性能表明该材料具有良好的结构完整性。与闭孔泡沫相比，具有更多开孔含量的泡沫具有更大的拉伸和压缩强度。在0.048gm / cm {sup} 3的泡沫密度下，在“脆性气球”系统中获得的最大闭孔含量为78％。

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