Efficient production of ultrafine poly-p-phenylene benzobisoxazole nanofibres for high-performance polyurea nanocomposites

The superb properties of poly- p -phenylene benzobisoxazole nanofibres (PNFs) have been realized in research institutes for advanced applications, such as military and aerospace industries. However, PNFs experiences major challenges in production and retaining their integrity after breaking into nanoscale. The current study succeeded to efficiently prepare reinforcing PNFs within considerably short time via ball-milling sol-gel disruption (BM-SGD) method. The BM-SGD method was able to produce ultrafine PNFs with diameters of 20 ± 5 nm at a concentration of 1 wt% in only 24 min; the method is ready for rapid and scalable production of PNFs. The intense collisions and shear forces during ball milling improve contact between fibres and reactants, accelerating the dissolution of fibres into a PNF sol. A wall-breaking step is used to disrupt PNF network to be integrated into polyurea matrix. The ultra-high specific surface area and surface functional groups of PNFs facilitate strong physical and chemical cross-linking with polyurea (PUA), leading to significant enhancement in its mechanical properties; tensile strength and Young's modulus of polyurea increased by 111.75 % and 106.10 %, respectively upon adding only 0.25 wt% PNFs. Additionally, the PUA/PNF nanocomposite demonstrates excellent corrosion resistance, as evidenced by the Tafel polarization test. The PUA/PNFs demonstrated high recyclability achieving 85 % recycling efficiency after the third cycle. This research pioneers a cost-effective strategy for the mass production of ultrafine PNFs, paving the way for advanced elastic and functional nanocomposites with broad industrial applications.