Homogeneous reinforcement as a strategy for the efficient preparation of high-strength, insulating and high heat-resistant PBO composite paper

Poly(p-phenylene benzobisoxazole) (PBO) fibre-based specialty paper has become a promising candidate for high-performance insulating materials due to the remarkable properties of PBO fibres. However, the porous structure and poor interfacial interaction of PBO paper seriously weaken its mechanical strength and greatly limit its practical application. Herein, proposed for the first time, a homogeneous reinforcement strategy is developed to regulate the microstructure of PBO paper and efficiently enhance its overall properties. For this reason, flexible ortho-hydroxy polyamic acid (HPAA) was first synthesized and used to impregnate PBO paper. Subsequently, HPAA was thermally converted into a benzoxazole-containing resin, manifesting excellent interfacial compatibility with PBO paper. As a result, the compact structure and solid interface endow the composite paper with impressive performance. The tensile strength, modulus, and electrical breakdown strength of the composite paper are 116.86 MPa, 5.47 GPa, and 63.7 kV mm−1, respectively, increasing by 33.1, 8.1, and 1.1 times compared with those parameters of the original paper (3.43 MPa, 0.60 GPa, and 30.5 kV mm−1). Moreover, the composite paper also exhibits an ultra-low dielectric constant and loss tangent (1.6 and 0.004 at 106 Hz, respectively), as well as superhigh thermal stability (maximum decomposition temperature, Tmax ≈ 600 °C) due to the elaborate design of the structure. Thus, the mechanical strength has been successfully integrated with the outstanding insulation and thermal properties, rendering the lightweight PBO composite paper promising in the field of high-temperature and high-voltage electrical insulation.Graphical abstract