纳米纤维素对环氧/聚砜共混体系层状结构调控及性能影响研究

Epoxy resins have been widely used as the matrices for fiber-reinforced composites due to their superior adhesive and mechanical properties. However, the highly-crosslinked nature of cured epoxy resins normally produces an undesirable characteristic: cured epoxies are brittle and show poor resistance to crack growth. Hence, epoxy resins must be modified in order to improve their performances. Enhancing fracture toughness of epoxy resins by the incorporation of high performance thermoplastic polymers has been paid increased attention in both research and application fields for decades. Layered structure, which was found in the thermoplastic modified epoxy resin blends, may provide a new approach for the interlayer toughness of the fiber-reinforced composites. Nevertheless, the poor interfacial adhesion and large domain size of the layered structure restricts the toughening effect. This project plans to introduce nano-cellulose (the environment-friendly reinforced material) into the polysulfone modified epoxy system, where morphological structure and interfacial property can be regulated and improved by the selective localization and entanglement of the nano-cellulose with high ratio aspect during reaction induced phase separation process. Therefore, mechanical property of the epoxy resins can be remarkably reinforced by nano-cellulose and meanwhile toughing effect of polysulfone can be enhanced. Influences of nano-cellulose on viscoelastic effect, phase separation process and mechanism of polysulfone/epoxy blends will be analyzed and then the optimum conditions for the layered structure regulation can be established. Consequently, the layered structure can be applied in the fiber-reinforced composite successfully.

环氧树脂由于粘结力强、固化后力学性能优异等特点，在纤维复合材料中具有不可替代的地位。然而，由于固化后通常质脆、耐冲击性差，环氧树脂成为纤维复合材料层间最薄弱的部分，要改进就必须对其增韧。通过向环氧树脂中引入热塑性树脂的增韧改性方法一直受到研究和应用的关注。热塑性树脂改性的环氧树脂体系中层状结构的发现为纤维复合材料层间增韧的研究提供了一种新思路。然而，层状结构中界面粘结力不强及相结构尺寸大等特点会影响热塑性树脂的增韧效果。本项目拟将性能优异的绿色增强材料纳米纤维素加入到聚砜改性的环氧树脂体系中，通过高长径比纳米纤维素在共混体系中的选择性分布及缠结作用，调控形貌结构，进而改善界面粘结力，发挥纳米纤维素对环氧树脂显著增强的同时提高聚砜本身对环氧树脂的增韧效果。分析纳米纤维素对体系粘弹性效应、相分离过程及机理的影响，探寻层状结构调控的最佳条件，真正发挥层状结构在纤维增强复合材料中的应用价值。

环氧树脂(EP)由于具有高模量、粘结性强、良好的耐化学性、尺寸稳定性和热稳定性等，作为高性能复合材料基体广泛应用在航天航空和汽车领域。然而，由于环氧树脂固化后本身质脆，限制其广泛应用。采用热塑性树脂(TP)可以克服这一缺陷，但是由于界面粘结较差改性效果往往不理想。. 本项目中我们将纤维素纳米纤维(CNF)通过溶剂交换和熔融共混相结合的方式引入到聚砜(PSF)改性的EP体系中，研究纳米纤维对体系固化反应、相分离、流变行为、机械和热性能的影响。结果表明，PSF/EP二元体系有三种典型的相分离结构。然而，层状结构中界面粘结力不强及相结构尺寸大等特点影响改性效果。均匀分散的CNF与聚合物基体有较好的相互作用，并且在不同相区间相互贯穿从而起到桥联作用而改善界面粘结性，同时，CNF对相分离起到一定的抑制作用，随着CNF含量增加，相区尺寸减小。界面粘结性的提高和相区尺寸的优化使低含量CNF的加入明显改善体系拉伸和冲击强度。差示扫描量热法(DSC)数据显示，PSF对环氧和双胺的固化反应起到阻碍作用而CNF在初始阶段对反应具有一定的促进作用。此外，动态热机械分析(DMA)和热重分析(TGA)数据显示CNF使体系玻璃化转变温度和热性能均有升高。另一方面，制备CNF改性的聚己内酯(PCL)/EP复合体系并考察CNF的加入对体系形貌结构、自修复性能和机械性能的影响。随着CNF的加入，体系相分离尺寸减小并且PCL相连续性增强。由于CNF的均匀分散和在聚合物基体中的桥联作用，自修复性能和机械性能均得到改善。CNF的含量为0.2%时，自修复性能提高26%，同时拉伸强度、断裂伸长率和冲击强度分别提高了27%, 38% 和 38%。该项目的开展为TP/EP二元体系的形貌和性能调控提供了一种新的方法，从而开阔了环氧树脂在工业领域的应用。