【作者】 贾彩霞；

【导师】 陈平；

【作者基本信息】 大连理工大学 ， 高分子化学与物理， 2012， 博士

【摘要】 芳纶纤维增强高性能热塑性树脂基复合材料的耐热性能和力学性能优异,与传统的热固性树脂基复合材料相比,其突出的优点是具有较高的韧性、损伤容限、抗冲击性能,以及优良的加工性能,可应用于使用环境条件苛刻、承载能力要求较高的多种领域,例如航空、航天、国防军工等。然而,由于芳纶分子链的高度取向和结晶使纤维表面光滑平整、缺少化学活性基团,导致了纤维与树脂基体间的界面粘结性能较差,因此有必要对芳纶进行表面改性,以改善其增强树脂基复合材料的界面粘合强度,从而提高复合材料的整体性能。本论文选用空气介质阻挡放电(DBD)等离子体在常压条件下对芳纶(Twaron和Armos)纤维进行表面改性,并且研究了此改性手段对芳纶增强热塑性聚芳醚砜酮(PPESK)树脂基复合材料界面性能的影响。采用X-射线光电子能谱(XPS)分析纤维表面的元素组成和基团含量,衰减全反射红外光谱(ATR-IR)可对XPS测试结果进行辅助证明；采用扫描电子显微镜(SEM)、原子力显微镜(AFM)观察纤维表面的物理形貌和粗糙度变化；采用动态接触角分析(DCAA)测定纤维与水和二碘甲烷的接触角以及纤维的表面自由能；采用单丝纤维拉伸强度(SFTS)测试分析纤维的拉伸性能变化。对于等离子体改性前后芳纶纤维增强PPESK树脂基复合材料界面粘结性能的变化,主要采用层间剪切强度(ILSS)、断面SEM形貌、吸水率测试进行评估。论文首先研究了在常压空气DBD等离子体改性之前Twaron纤维的清洁处理对Twaron/PPESK复合材料界面性能及Twaron纤维表面等离子体改性效果的影响。研究结果表明：商业化Twaron纤维表面的涂层会在纤维与树脂基体之间形成一个弱界面层,使Twaron/PPESK复合材料的ILSS值(42.9MPa)相对于涂层经丙酮去除后(46.0MPa)要低；同时,由于等离子体本身也具有对涂层的清洁作用,会削弱作用于Twaron纤维表面的改性效果,因此在进行等离子体改性之前需用丙酮溶剂对纤维进行清洁处理,以使纤维的表面性能以及纤维增强复合材料的界面粘结性能得到最佳程度的改善。其次,论文讨论了常压空气DBD等离子体的放电参数,包括处理时间和功率密度对Twaron纤维的表面化学组成、物理形貌、浸润性能、拉伸性能,以及Twaron/PPESK复合材料的ILSS、破坏模式、吸水率等方面的影响。研究结果表明：经过适度(如12s-55.2W/cm3)的等离子体改性之后,Twaron纤维表面的O/C由0.177增长到0.233,引入了含氧官能团如C-P、C=O和O=C-O,同时,纤维的表面形貌发生了明显改变,粗糙度增加、比表面积增大,这两方面的变化均有助于改善纤维表面的浸润性能,使表面自由能由50.6mJ/m2显著增加至71.0mJ/m2,使PPESK树脂胶液在Twaron纤维表面的浸润行为得到明显改善；改性后Twaron纤维增强PPESK树脂基复合材料的ILSS值提高了34.1%,破坏模式向基体破坏转变且吸水率大幅度降低。而经过SFTS测试发现,改性之后Twaron纤维的拉伸强度下降仅有2.0%,本体性能不受影响。研究结果还表明：延长处理时间和增大功率密度均可以使纤维表面的改性效果增强,然而,过长的处理时间或过高的功率密度却会造成过度刻蚀,使引入的极性基团含量下降、纤维表面结构遭到破坏,从而影响到Twaron纤维表面及其增强PPESK树脂基复合材料界面的性能。然后,论文讨论了不同贮存环境对常压空气DBD等离子体改性之后的Twaron纤维表面时效性的影响。研究结果表明：将经等离子体改性后的Twaron纤维贮存于空气环境中48h后,Twaron/PPESK复合材料的ILSS由58.0MPa降低为47.3MPa,吸水率上升显著；而贮存于含03气氛的氧化性环境中48h后,Twaron/PPESK复合材料的ILSS仅降低为51.4MPa,吸水率上升幅度较小。复合材料ILSS的变化主要是由不同贮存环境中Twaron纤维表面所引入的含氧极性基团以及纤维表面浸润性的变化所导致的。由此可见,氧化性的贮存环境能够减缓等离子体改性效果的时效性。最后,论文进一步研究了常压空气DBD等离子体处理对具有更高性能的芳纶—Armos纤维表面浸润性及Armos/PPESK复合材料界面粘结性的影响,并分析了等离子体改性之后Armos纤维表面化学组成、物理形貌和粗糙度、以及拉伸性能的变化。研究结果表明：经适度(如18s-27.6W/cm3)的等离子体改性之后,Armos纤维的表面自由能由49.6mJ/m2增加至68.3mJ/m2, Armos/PPESK复合材料的ILSS值由60.9MPa增至71.4MPa,基本破坏模式也由界面脱粘转向基体破坏,表明了Armos/PPESK复合材料界面粘结强度的提高。而空气DBD等离子体作用于Armos纤维表面后,纤维表面O和N元素的含量增加,即含氧官能团C-O、C=O、O=C-O和含氮的极性基团的引入,以及纤维表面凹凸结构的增加,即表面的粗糙化,是使纤维表面浸润性能以及纤维增强复合材料界面粘结性能得以改善的主要原因。更重要的是,得到改性的Armos纤维拉伸性能并没有受到影响,表明了常压空气DBD等离子体是一种适于芳纶纤维表面改性的有效技术手段。更多还原

【Abstract】 Aramid fiber reinforced high-performance thermoplastic composites have excellent heat-resistance and mechanical properties. When compared to traditional thermoset resin-matrix composites, they have the outstanding advantages of high toughness, damage tolerance, impact resistance and excellent processability, which can be used in extreme conditions with high loads and high temperatures, for example, aeronautical and astronautical field, national defense and military industry. However, surface of aramid fiber is smooth and chemically inert due to the high orientation and crystallization of their molecular chains. Therefore, surface modification of aramid fiber is necessary, in order to enhance the interfacial adhesion and improve the whole performance of their composites.In this thesis, aramid fiber (Twaron and Armos) was treated by air dielectric barrier discharge (DBD) plasma at atmospheric pressure, and the relation between interfacial adhesion in aramid reinforced thermoplastic poly(phthalazinone ether sulfone ketone)(aramid/PPESK) composites and this surface treatment had been established and discussed. X-ray photoelectron spectroscopy (XPS) was used to analysis fiber surface elements and functional groups, attenuated total reflectance infrared spectroscopy (ATR-IR) was selected to confirm XPS results, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to observe the changes of fiber surface morphology and roughness, dynamic contact angle analysis (DCAA) was used to measure contact angles and surface free energy, and single fiber tensile strength (SFTS) was used to detect changes of fiber tensile property before and after the plasma treatment. The interfacial adhesion properties of aramid/PPESK composites were determined by interlaminar shear strength (ILSS) measurement, failure mode and water absorption testing.Firstly, this thesis reported the influence of cleaning treatment before plasma modification on interfacial properties of Twaron fiber reinforced PPESK composites and effectiveness of air DBD plasma treatment on Twaron fiber surface. Results show that ILSS of composites reinforced by Twaron fiber with oily finish on the surface is lower (42.9MPa) than that after the removal of surface finish (46.0MPa) because of the potential weak boundary layer, and meanwhile the plasma modification on fiber surface will be weakened by the cleaning effect. Therefore, aramid fiber needs to be rinsed by acetone before plasma treatment in order to insure the modification effectiveness on fiber surface and composite interface properties.Secondly, influence of atmospheric air DBD plasma discharge parameters, including sample treatment time and discharge power density, on surface composition, physical topography, surface wettability, tensile property of Twaron fiber and ILSS, failure mode, water absorption of Twaron/PPESK composites was studied. Results show that the moderate (for example12s-55.2W/cm3) plasma treatment is responsible for the increase of O/C from0.177to0.233and the introduction of oxygen-containing groups, such as C-O, C=O and O=C-O, and for the increase of surface roughness and specific surface area. Both the chemical and physical changes result in the noticeable enhancement of fiber wettability with surface free energy increasing from50.6to71.0mJ/m2, and the improvement of wetting behavior of PPESK resin on plasma treated Twaron fiber; the ILSS of plasma treated Twaron fiber reinforced PPESK composites increases by34.1%, the failure mode changes, and meanwhile the water absorption of composites declines sharply. Note that the decrease of SFTS is only2%and the bulk property is not affected. Results also show that extending treatment time and increasing power density can both enhance plasma modification effectiveness; however, excessive treatment will decrease the incorporated polar groups and damage the fiber surface, impairing the properties of fiber surface and Twaron-PPESK interface.Then, this thesis reported the influence of different storing environment on aging effect of Twaron fiber after the air DBD plasma modification. Results show that ILSS of composites reinforced by Twaron fiber stored in air for48h declines from58.0MPa to47.3MPa and water absorption increases evidently while the ILSS of composites reinforced by Twaron fiber stored in ambiance including O3active particle only decreases to51.4MPa and water absorption has a less increase. The main reason is the changes of oxygen-containing polar groups introduced to Twaron fiber surface by the plasma treatment and the fiber wettability in different storing ambiance. Meanwhile the results indicate that aging effect after the plasma treatment might be weakened by the oxidising storing environment.Finally, the thesis further discussed the influence of atmospheric air DBD plasma treatment on wettability of aramid with better properties, Armos fiber, and interfacial adhesion of Armos/PPESK composites. Then, the changes of surface chemical composition, morphology and roughness, tensile property of Armos fiber were analyzed. Results show that after the moderate (for example18s-27.6W/cm3) plasma treatment, surface free energy of Armos fiber increases form50.6to71.0mJ/m2, ILSS of Armos/PPESK composites increases from60.9to71.4MPa, failure mode changes from interface debonding to matrix fracture, indicating the enhancement of composite interfacial adhesion, which results from the increase of O and N, i.e. the generation of C-O, C=O,O=C-O and some nitrogen-containing polar groups, and the increase of surface roughness. More important, the tensile strength of plasma treated Armos fiber is not affected, indicating that the atmospheric air DBD plasma is an effective technique for aramid surface modification.更多还原