Research On Preparation And Properties Of The Kevlar Nanofiber Composite Films

As a high-performance aramid fiber after nylon-6 developed by Du Pont company, Kevlar, it’s high strength, good thermal stability drew lots of people’s attention. But the weak interactions between kevlar and polymer limit its applications in composite materials. Based on the particularity of nanomaterials, Kevlar nanofiber is expected to bring about exceptional mechanical and optical properties and allowed the emergence of an innovative nanoscale building block with great potential for engineering novel high-performance polymer nanocomposites.The amide groups of macro Kevlar can be deprotonated in strong alkaline solvent. By this method, Kevlar aramid nanofibers(ANF) were obtained and then we prepared pure ANF nanofilm using filtration method. Through characterization and analysis, we found that even though being nano-sized, the structure of Kevlar nanofibers were not destroyed. Besides, the length of ANF was 5-10 μm and the diameter was 10-20 nm. Mechanical property test of ANF film showed an ultimate strength of 180 MPa and elastic modulus of 14 GPa.Due to unique structure and excellent properties, polyurethane has always been a hot research topic. The waterborne polyurethane has the advanta ges of low cost, no pollution and good flexibility, which make broad application prospect. However the waterborne polyurethane material has many defects: low tensile strength and poor heat resistance, which limit its application. The addition of traditiona l fillers typically results in a moderate improvement. ANF represents one of the most promising nanoscale building blocks for high-performance nanocomposites. In this work, waterborne polyurethane(PU) has been reinforced with ANF using two solution processing methods, namely, layer-by-layer(LBL) assembly technique and the vacuum-assisted flocculation(VAF) method. Record-high modulus of 5.275 GPa and ultimate strength of 98.02 MPa are obtained among all the reported PU based nanocomposites. We attribute such achievement to the similar molecular structures of ANF with PU which ensures a high affinity made possible by the manifold interfacial interactions. The formation of multiple hydrogen bonds due to the presence of amide groups with appropriate spacing in both components is confirmed by the computer simulation. Compared with the VAF method, it is found that LBL assembly allows a better load transfer, resulting in higher ultimate strength and stiffness. The VAF method shows advantages in improving the ultimate strength at low loadings of ANF.Then, we explored that both ANF and C lay as fillers composited with PU and prepared PU/ANF/PU/C lay nanocomposites using LBL method. After testing, we found that the coordinating role of the ANF and C lay greatly improve the mechanical, thermal and flame-retardant properties of the nanocomposites.We believe our work may not only lead to a new practical combination within the field of composite materials but also provide important implications for the future design of nanocomposites based on the innovative nano fillers.