Mechanical and thermal properties of polyoxymethylene-matrix composites filled with multi-walled carbon nanotubes-coated milled glass fiber

The advanced multifunctional filler has become one of the main challenges in developing high-performance polymer composites. In this study, the acid-treated multiwall carbon nanotubes (MWCNTs) were adhered to the surface of milled glass fiber under the combined effect of 3-aminopropyltriethyloxy silane and tetraethyl orthosilicate to fabricate a hierarchical fiber (MWCNTs-MGF). The morphologies of the hierarchical fibers were characterized using field-emission scanning electron microscope and transmission electron microscope, which showed evidence of a coating layer of MWCNTs on each fiber surface. The MWCNTs-MGF was employed as a multifunctional filler to prepare polyoxymethylene-based composites using a twin-screw extruder by melt blending. The obtained composites exhibited improved mechanical and thermal properties. The composite tensile strength and notched impact strength and Young's modulus increased by 10%, 32%, and 32%, respectively, as the MWCNTs-MGF content varies from 0 to 10 wt.%. Meanwhile, the reinforcing and toughing mechanisms of MWCNTs-MGF were also elaborated by analyzing the interfacial adhesion and fracture morphologies of the composites. Moreover, the study on thermal stability and crystallization behavior indicated that the polyoxymethylene/MWCNTs-MGF composites had higher thermal stability, crystallization temperature, and crystallinity as compared to the polymer matrix. The improvement of thermal stability originates from the unique surface structure of MWCNTs-MGF, while the increase in crystallization temperature and crystallinity is due to the strong heterogeneous nucleation ability of the hierarchical fibers.