Mechanical and thermal enhancements of benzoxazine‐based GF composite laminated by in situ reaction with carboxyl functionalized CNTs

Abstract

An easy and efficient approach by using carboxyl functionalized CNTs (CNT-COOH) as nano reinforcement was reported to develop advanced thermosetting composite laminates. Benzoxazine containing cyano groups (BA-ph) grafted with CNTs (CNT-g-BA-ph), obtained from the in situ reaction of BA-ph and CNT-COOH, was used as polymer matrix and processed into glass fiber (GF)-reinforced laminates through hot-pressed technology. FTIR study confirmed that CNT-COOH was bonded to BA-ph matrices. The flexural strength and modulus increased from 450 MPa and 26.4 GPa in BA-ph laminate to 650 MPa and 28.4 GPa in CNT-g-BA-ph/GF composite, leading to 44 and 7.5% increase, respectively. The SEM image observation indicated that the CNT-COOH was distributed homogeneously in the matrix, and thus significantly eliminated the resin-rich regions and free volumes. Besides, the obtained composite laminates showed excellent thermal and thermal-oxidative stabilities with the onset degradation temperature up to 624 C in N 2 and 522 C in air. This study demonstrated that CNT-COOH grafted on thermosetting matrices through in situ reaction can lead to obvious mechanical and thermal increments, which provided a new and effective way to design and improve the properties of composite laminates.

Effect of bisphenol-A on the structures and properties of phthalonitrile-based resin containing benzoxazine

“…Moreover, the absorption intensity of nitrile groups decreased with increasing the content of BPA, suggesting the obvious catalysis. The wide and intensive absorption band at around 3364 cm -1 corresponding to the association state of hydroxyl were observed in all of the samples, reported previously [15,16]. The absorption peak at 2969 cm-1 was assigned to the stretching vibration of -CH 3 and no obvious changes were observed.…”

“…However, the wide endothermic transition started from 200°C and peaked at 250°C was attributed to the evaporation of BPA monomer. In Figure 4b (curve a) for pristine BA-ph, the double exotherm bands were peaked at 230°C and 263°C, corresponding to the ring-opening polymerization of oxaznine rings and the ring-forming polymerization of nitrile groups, respectively [14,15]. With the introduction of BPA, the exotherm bands shifted to a lower temperature range, shown in Figure 4a.…”

“…For thermosetting resin, long time curing and elevated temperature treatment were necessary. In the previous work, BA-ph/GF systems were treated for 11 h and the temperature was up to 280°C [15,16]. Phthalocyanine/GF systems were generally treated at 320°C for 2 or 4 h to obtain the laminates with good properties.…”

“…On the one hand, the active phenolic hydroxyls generated from ring-opening of benzoxazine can be used as a kind of curing agent to achieve the cross-linking networks, thus realizing the self-promoted copolymerization. On the other hand, the active phenolic hydroxyls allowed BA-ph to be used as hydroxyl-functional phthalonitrile to achieve good processability and desirable properties of the composites [14][15][16]. In addition, the initial curing temperature and postcuring temperature of BA-ph were 200~220 and 280°C, respectively, which significantly improved the processibility of phthalonitrile-based resins.…”

Active diluents effects of 4-nonylphenoxy-1, 2-dinitrilbenzene on phthalonitrile containing benzoxazine and their copolymerization behaviors

“…On the one hand, the active phenolic hydroxyls generated from ring-opening of benzoxazine can be used as a kind of curing agent to achieve the cross-linking networks, thus realizing the selfpromoted copolymerization. On the other hand, the active phenolic hydroxyls allowed BA-ph to be used as hydroxyl-functional phthalonitrile to achieve good processability and desirable properties of the composites [8][9][10][11]. Therefore, these merits accompany their excellent processability (low melting point, low viscosity), outstanding thermal stabilities and cost-effectiveness have made BA-ph resin attract increasing interests in the field of composites compared with the traditional heat resisting resins and can find their potential applications in the future [12][13][14][15].…”