Wave-transparent and eco-friendly flame-retardant phosphorus-based phthalonitrile/quartz composites by a synchronized self-curing strategy with cyano and alkynyl groups

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2024-12, Vol.501, p.156885, Article 156885
• Main Authors: Zhang, Yabin, Zhang, Wenguang, Yin, Houxiang, Wang, Yanlin, Wang, Bingbing, Zong, Lishuai, Wang, Jinyan, Jian, Xigao
• Format: Article
• Language: English
• Subjects: Dielectric properties; Flame retardancy; High-temperature resistance; Phthalonitrile resin; Self-catalyzed; Wave-transparent composite
• ISSN: 1385-8947
• DOI: 10.1016/j.cej.2024.156885

[Display omitted] •P-ALK-PN monomers have high-efficiency self-curing characteristics.•Dual-curing functional group resulted in homogeneous and high crosslink density.•P-ALK-PN-420℃/QF displayed consistent dielectric properties from 25 °C to 600 °C.•P-ALK-PN resin shows intrinsic flame retardancy exceeding 1300 °C for 200 s.•The flame retardancy is attributed to the dual action of the condensed/gas phase. The robust human–machine interaction systems of the aerospace industry necessitate the development of thermal resistant wave-transparent composites, with a pivotal focus on organic resin matrix. However, enhancing the heat resistance of such materials while preserving other critical attributes has been a formidable challenge. In this study, a novel designed strategy of a dual-curing functional phosphorus-based phthalonitrile monomer (P-ALK-PN) has been proposed. The optimized curing temperatures for intra- or intermolecular Diels-Alder reactions of alkynyl groups and polyaddition reaction of cyano groups resulted in a homogeneous and highly crosslinked N-enriched phthalonitrile system. After curing at 450 °C, the resin, namely P-ALK-PN-450 °C, demonstrated exceptional thermal stability (T5% = 644 °C), thermo-oxidative stability (T5% = 554 °C), and char yield at 800 °C (90.7 % in N2 and 67.5 % in air). Their quartz fiber reinforced composites (P-ALK-PN/QFs) were subsequently fabricated by the hot-pressing process. Upon post-curing at 420 °C, P-ALK-PN-420 °C/QF displayed elevated glass transition temperature (550 °C), flexural strength (319 MPa), and relatively low dielectric properties with a dielectric constant (Dk) of approximately 4.2 and a dissipation factor (Df) less than 0.02 across a wide temperature ranging from 25 °C to 600 °C. Especially, it exhibited excellent flame retardancy (only a 6.7 % weight loss at ambient temperatures exceeding 1300 °C for 200 s) as well, stemming from release of eco-friendly inert gases (NH3) and formation of a graphitized protective layer during pyrolysis. These promising results highlight the potential applications of P-ALK-PN resins in aerospace and high-performance engineering fields.