在芳纶无定形区构筑纳米颗粒及其抗光降解分子机理研究

Aramid fiber is an important strategic material for the nation, however, photodegradation happens to aramid fibers lowering the service life of its products outdoor application The photodegradation of aramid fibers is still a problem. For aramid fibers composed of crystalline and amorphous regions, the failure accoured at the weak point, amorphous region of the fiber under the load. As the photo oxidation generally happens in amorphous region and surface, making the amorphous region more easily to be damaged, and as a result the mechanical properties decrease significantly. In the early study of applicant, a new method is reported, that is infiltrating hexamethylene diisocyanate (HDI), a crosslinker, to enhance the amorphous phase of aramid fibers with the aid of supercritical carbon dioxide (ScCO2), and the tensile strength and modulus were simultaneously improved. The purpose of this project is interfilling the precesors of nano particles into the amorphous regions and coating on the surface of fibers, and then using hydrazine under reflux to create nano particles in situ formation on the surface and in the amphormous regions of aramid fabric to improve its photostability, strength and modulus. In this project, the ScCO2 effects on the soulibilty of precesors and the amount impregation into the fibers will be studyed. The development rule of the microstructure of fibers and the effect on the mechincal properties during the ScCO2 treatment will be researched. The effects of hydrazine under reflux carried out in the confinement of rigid chains in the amorphous region, on nano particles microstructure, particle size and particle size distribution will be discussed. The relathionship on the nano particle structure on the photostability of fiber will be investigated. The molecular mechanisms of anti-photodegradation will be explored and offer an theoretical direction about the optimization of anti-photodegradation.

芳纶是重要战略物质，但易光降解，影响其在室外空天使用寿命，是长期未解的难题。芳纶由晶区和少量无定形区组成，无定形区是薄弱点，载荷下容易破坏；光降解一般发生在无定形区（和表面），使无定形区更容易被破坏，力学性能急剧下降。因此如何防止无定形区分子链光降解是关键。申请者前期研发了一种用超临界CO2(ScCO2)携带亚甲基二异氰酸酯浸入无定形区发生扩链，加强无定型区，可以同时提高纤维强度和模量的新方法。本项目拟用ScCO2携带光稳定剂前躯体渗入芳纶无定形区和亚表面，原位水解形成纳米光稳定剂，期望建立同时提高芳纶强度、模量和抗光降解性的新方法。研究前躯体分子结构与其在ScCO2中的溶解性及其携带效果关系；ScCO2处理过程纤维凝聚态结构及其力学性能演变；无定形区中刚性分子链限域下前躯体水解与纳米颗粒尺寸及分布关系及其对抗光降解性关系，研究芳纶抗光降解分子机理，为优化抗光降解性能提供理论指导。

芳纶具有低密度、高强度、高模量和高耐热性等性能，广泛应用于交通运输、防弹背心、电缆和国防等领域。但是芳纶纤维易发生光老化，长期紫外光照射下会影响其使用寿命，制约其应用；同时芳纶纤维分子链结晶度高，表面光滑，表面惰性，与基体之间的界面结合性能差，影响其在复合材料中的应用。项目采用超临界CO2（ScCO2）的携带作用及强的扩散和干燥作用，在芳纶纤维表面及纤维内部制备具有抗光老化性能的纳米颗粒（TiO2、ZnO和SiO2及混合的纳米粒子）。成果如下：利用ScCO2将前驱体正硅酸四乙酯（TEOS）和钛酸四丁酯（TBT），携带到芳纶纤维表面和纤维内部，再进行原位水解，在芳纶纤维表面或内部原位合成纳米SiO2、TiO2纳米粒子。通过研究对超临界压力、温度等因素对SiO2、TiO2纳米粒子对纤维形貌、结构、光稳定性以及与树脂界面结合性能的影响，得到最佳的处理条件。研究发现发现超利用ScCO2处理改性时，不会破坏纤维的结构，纤维的力学性能提高，且纳米粒子可以在纤维表面和内部微纤之间同时形成。与未处理AF比，SiO2改性纤维的IFSS提高了64％，拉伸强度提高9.6%，且在216 h-UV辐射后，强度保持率为91.5％。压力为15Mpa时制备TiO2的改性效果较好，改性后168h-UV光照后，拉伸强度保持率为86.34%，IFSS提高了57%。在此基础上利用Sc-CO2将涂覆有Sol-gel法的 ZnO溶胶溶液的AF进行萃取和干燥，调节Zn2+浓度控制纤维表面纳米ZnO的分布和尺寸。浓度为0.015 mol/L时，ZnO颗粒分布最均匀，216 h-UV光照后的强度保持率为93.1%，未处理纤维仅为73%，IFSS提高68.2%，拉伸强度增加13.7%。由于纳米粒子对纤维的遮蔽效果，降低光照对纤维的透过率，提高其抗光降解性能，此改性方法可以同时提高纤维的力学性能和界面结合性能，此方法可以推广应用至其他有机纤维或高分子材料。