Designing a low-temperature curable phenolic/benzoxazine-functionalized phthalonitrile copolymers for high performance composite laminates

A low-temperature curable phenolic/benzoxazine-functionalized phthalonitrile (SH/BZ-CN) copolymer system with well processability is designed and applied in high performance glass fiber (GF) composite laminates. Differential scanning calorimetry (DSC) results showed that plenty of phenolic hydroxyl groups on SH could catalyze the oxazine ring-opening and triazine/phthalonitrile ring-forming reaction of BZ-CN. The ring-opening peak and ring-forming peak of SH/BZ-CN systems are reduced by 47.1 °C and 17.0 °C than those of BZ-CN, respectively. The processability of SH/BZ-CN copolymers were improved and could be controlled by tuning SH content, processing temperature and time. These parameters provided ground for preparing SH/BZ-CN/GF composite laminates under a relatively mild condition. All SH/BZ-CN/GF composite laminates exhibit excellent flexural strength more than 500 MPa and flexural modulus over 22.0 Gpa. SH/BZ-CN/GF composites showed immiscible structures and double Tgs, and they could stand high temperature up to 350 °C. Low temperature curing, short processing time and low processing pressure are beneficial to large-scale manufacturing and application of SH/BZ-CN/GF composites.