Fast-Processable Non-Flammable Phthalonitrile-Modified Novolac/Carbon and Glass Fiber Composites

Abstract

Phthalonitrile resins (PN) are known for their incredible heat resistance and at the same time poor processability. Common curing cycle of the PN includes dozens hours of heating at temperatures up to 375 °C. This work was aimed at reducing processing time of phthalonitrile resin, and with this purpose, a novolac oligomer with hydroxyl groups fully substituted by phthalonitrile moieties was synthesized with a quantitative yield. Formation of the reaction byproducts was investigated depending on the synthesis conditions. The product was characterized by 1H NMR and FT-IR. Curing of the resins with the addition of different amounts of novolac phenolic as curing agent (25, 50 and 75 wt.%) was studied by rheological and DSC experiments. Based on these data, a curing program was developed for the further thermosets’ investigation: hot-pressing at 220 °C and 1.7 MPa for 20 min. TGA showed the highest thermal stability of the resin with 25 wt.% of novolac (T5% = 430 °C). The post-curing program was developed by the use of DMA with different heating rates and holding for various times at 280 or 300 °C (heating rate 0.5 °C/min). Carbon and glass fiber plastic laminates were fabricated via hot-pressing of prepregs with Tg’s above 300 °C. Microcracks were formed in the CFRP, but void-free GFRP were fabricated and demonstrated superior mechanical properties (ILSS up to 86 MPa; compressive strength up to 620 MPa; flexural strength up to 946 MPa). Finally, flammability tests showed that the composite was extinguished in less than 5 s after the flame source was removed, so the material can be classified as V-0 according to the UL94 ratings. For the first time, fast-curing phthalonitrile prepregs were presented. The hot-pressing cycle of 20 min with 150 min free-standing post-curing yielded composites with the unique properties. The combination of mechanical properties, scale-up suitable fast-processing and inflammability makes the presented materials prospective for applications in the electric vehicle industries, fast train construction and the aerospace industry.

Optimizing the thermal properties of fiber reinforced phthalonitrile composites

“…where x ij and z ij are the elements of the matrixes X and Z, respectively. The entropy weight method was utilized to determine the weights of each indicator, as presented in Equation (9).…”

“…With the modernization and intelligent development of high technology sectors such as aerospace, electric motors, electronics and automobiles, polymer‐based composites with better overall performance are increasingly in demand. Phthalonitrile (PN) resin, a new type of high‐temperature resistant resin, has attracted a wide range of interest, 1 for its high glass transition temperature, 2 outstanding thermal and mechanical properties, 3–6 low water absorptivity 7 and superior flame resistance 8–10 . As one of the promising matrix materials for advanced composites, the mechanical properties of phthalonitrile can be further improved through fiber reinforcement 11 .…”

“…Phthalonitrile (PN) resin, a new type of hightemperature resistant resin, has attracted a wide range of interest, 1 for its high glass transition temperature, 2 outstanding thermal and mechanical properties, [3][4][5][6] low water absorptivity 7 and superior flame resistance. [8][9][10] As one of the promising matrix materials for advanced composites, the mechanical properties of phthalonitrile can be further improved through fiber reinforcement. 11 With years of exploration, PN composites have had a lot of theoretical and experimental basis in terms of the fabrication process, and some works of literature have been reported on the innovations and breakthroughs of curing mechanisms, and resin as well as fiber modification.…”

Effect of post‐curing temperature on the retention of mechanical strength of phthalonitrile thermosets and composites after a long‐term thermal oxidative aging

“…Phthalonitrile resins are the class of high performance polymers that is characterized by outstanding thermal stability, high mechanical properties, low water absorption and superior fire resistance. [1][2][3][4][5][6][7] Thermal curing of phthalonitriles is initiated by addition of curing agents such as metal salts and metals, 8 phenols, 9 strong organic acids 1 and organic amines. 10 Aromatic diamines are widely used because of their outstanding reactivity with phthalonitrile groups, good compatibility, and low volatility at resin curing temperatures.…”

“…Phthalonitrile resins are the class of high performance polymers that is characterized by outstanding thermal stability, high mechanical properties, low water absorption and superior fire resistance 1–7 . Thermal curing of phthalonitriles is initiated by addition of curing agents such as metal salts and metals, 8 phenols, 9 strong organic acids 1 and organic amines 10 .…”