【作者】 刘大兴；

【导师】 孟令辉；

【作者基本信息】 哈尔滨工业大学 ， 高分子化学与物理， 2009， 硕士

【摘要】 通过液晶纺丝得到的聚对苯撑苯并二噁唑（PBO）纤维具有高比强度、高比模量、低密度、耐烧蚀、耐高温等优异性能,因而是一种理想的复合材料增强体。但是由于其表面光滑,活性官能团含量少,PBO纤维与树脂之间的界面粘接性能较差,因此对其进行表面改性是非常有必要的。鉴于超临界流体临界区的特性,选用其作为介质对PBO纤维进行处理改性实验。本文主要通过两个方面进行研究:一是通过超临界二氧化碳（scCO2）临界区的处理使PBO纤维的本体强度得到增强;二是通过超临界苯胺+环己烷体系处理使PBO纤维界面粘接性能增加。实验首先通过热力学的方法确定混合介质的临界操作参数,并通过控制临界区域内波动频率和波动幅度来控制实验的可重复性。经过scCO₂对纤维在临界区进行处理后,发现处理后的PBO纤维的单丝拉伸强度比未处理提高9.71%,拉伸模量提高6.54%;热失重（TG）的分析表明处理后PBO纤维的热分解温度由650℃提高到700℃,等温TG反映出处理后的PBO纤维热分解速率降低一半并且最终残留率提高2.2倍,由此可见处理后的PBO纤维的耐热性能得到了提高;XRD表明纤维的结晶度提高3.18%,处理样的晶粒比未处理样的晶粒平均增大9.69%,由此可见scCO2的处理可以提高了纤维的结晶度,使晶粒长大,从而使纤维的力学性能和耐热性能提高。为了验证scCO2处理方法的普适性,实验对碳纤维T700进行了处理,发现处理样的拉伸强度比未处理的提高13.39%,拉伸强度与拉伸模量的分散性减小,从而证明了scCO2临界区处理是一种对纤维本体强度增强的低温后处理方法,该方法具有很大的实际应用价值。通过微观分析发现拉伸强度的增加主要是由于平均再取向次数增加所致,并通过模型建立了通过结晶度计算模量的经验公式。实验还研究了表面涂层对纤维表面粘接性能的影响,在此基础上又研究了scCO2处理对PBO纤维表面粘接性能的影响,发现总体上均为降低,但在scCO2中引入氨水后发现纤维的粘接性能与抽提处理相比有所提高。此后实验研究了碱性介质体系超临界苯胺+环己烷处理对PBO纤维表面粘接强度的影响。经超临界苯胺+环己烷处理的PBO纤维制备的复合材料再经scCO₂后处理之后ILSS值由原来的42.52MPa最高提高到58.84MPa,提高38.38%,通过单丝拔出仪测试得到的IFSS值由未处理样的38.95MPa提高到63.73MPa,平均提高63.62%。通过处理前后纤维与环氧树脂的接触角降低6.3°,表明环氧树脂在纤维上的浸润性提高,铺展性变好。结合第一方面的研究结果,把scCO2处理作为一种缓释界面应力的后处理方法来应用到复合材料中,最终确定了一条PBO纤维表面处理的可行方案:未处理样→乙醇抽提处理→超临界苯胺+环己烷体系处理→复合材料制备→scCO2后处理。更多还原

【Abstract】 Poly(p-phenylenebenzobisoxazole)(PBO) fiber obtained by liquid crystal spinning shows superior tensile strength, tensile modulus, excellent thermal stability, and flame resistance with low density, which make PBO an ideal reinforcing materials for fabricating advanced composites. However, the interfacial adhesion between PBO fiber and resin matrix is not satisfied for the practical usage. The composites containing PBO fiber demonstrate the poor adhesion attributing to the chemically inert surface and/or smooth surface of PBO fiber. Therefore, it is necessary to modify the surface of PBO fiber to increase the chemical activity for better properties of composites.The supercritical fluid is applied as reaction medium for its special properties in the critical region. This study focuses on two aspects: one is to enhance the strength of PBO fiber by supercritical carbon dioxide (scCO2) treatment; another is to improve the interfacial strength between PBO fiber and resin matrix by treatment in the hybrid system of supercritical aniline and cyclohexane.Initially, the critical parameters of supercritical treatment are determined by a thermodynamic method; and the experimental stability is controlled by the vibrate frequency and amplitude. The scCO2 treatment of PBO fiber can improve the tensile strength and the tensile modulus by 9.71% and 6.54% respectively. Furthermore, the thermal stability of PBO fiber after scCO2 treatment has been enhanced base on the results of thermal gravity (TG) analysis, and the decomposing temperature of PBO fiber increases from 650℃to 700℃. The results of XRD illustrate that the crystallinity of PBO fiber increases about 3.18% and the crystalline grain grows about 9.69%, which improve the mechanical properties and thermal resistance of PBO fibers. For verifying the universal applications of this novel method, carbon fiber (T700) has been treated by the same approach in scCO2. The 13.39% increment of tensile strength of T700 has been verified and the statistical data of tensile strength and modulus become much stable. The above results indicate that the scCO2 treatment of fibers is an effective method to enhance the fiber strength. It is also found that, to a large extent, the tensile strength of PBO fiber is affected by the chain reorientation. The relationship between modulus and crystallinity is established.The affect of coating on the surface adhesion properties of fiber has been studied and the surface modification of PBO fiber in scCO2 has been investigated. The performance of PBO fiber by scCO2 treatment is negative except using the ammonia and scCO2 hybrid system. By the way, the surface properties of PBO fiber treated in supercritical aniline and cyclohexane have been significantly modified which can reflected by the ILSS and IFSS of PBO composite. The ILSS of PBO/epoxy composites has been improved by 38.38% and the IFSS 63.62% after supercritical aniline and cyclohexane treatment. It is shown more soakage between epoxy and fiber after treated that the contact angle between PBO fiber and epoxy decreased about 6.3°. Combined with the effectiveness in scCO2 treatment for enhancing the fiber strength, a feasible route for surface modification of PBO fiber has been verified which is as following: raw fiber→ethanol clear→surface modification in supercritical aniline and cyclohexane→PBO composite preparation→treatment in scCO2.更多还原