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Mechanical and thermal properties and crystallization behavior of PA66 composites reinforced with MWCNTs-coated milled glass fiber

Constructing a hierarchical structure of nanomaterials on the surface of reinforcing fibers is the best strategy to obtain other desired functions while improving the mechanical properties of polymers. In this article, acid-treated multiwall carbon nanotubes (MWCNTs) were introduced to the surface of milled glass fiber (MGF) under the combined action of tetraethyl orthosilicate and 3-aminopropyltriethyloxysilane to prepare a hierarchical fiber (MWCNTs-GF). The surface morphology and microstructure of this hierarchical fiber were characterized by field-emission scanning electron microscope and transmission electron microscope, and a composite coating with MWCNTs as the main component was observed on each fiber surface. Fourier transform infrared and Raman spectroscopy revealed the presence of the specific interactions between MWCNTs and MGF. Polyamide 66 (PA66) composites with different content of MWCNTs-GF were fabricated by melt blending. The resulting composites exhibited improved mechanical properties relative to pure PA66, in which the tensile strength and notched impact strength of the composite filled with 3 wt% MWCNTs-GF increased by 23.3% and 69.0%, respectively. Subsequently, by analyzing fracture morphology and interfacial adhesion of the composites, the strengthening and toughening mechanisms of MWCNTs-GF were elaborated in detail. In addition, the results of thermogravimetric analysis and differential scanning calorimetry showed that MWCNTs-GF possessed strong heterogeneous nucleation ability, and its addition could refine the grain size of PA66 and significantly increase the crystallization temperature and thermal stability of the corresponding composites. Compared to PA66 composites reinforced with neat MGF, it was found that the unique surface structure of MWCNTs-GF was likely responsible for improved thermal properties of this hierarchical fiber-reinforced PA66 composites.