Cure Behavior Changes and Compression of Carbon Nanotubes in Aerospace Grade Bismaleimide-Carbon Nanotube Sheet Nanocomposites

Abstract

Herein, we study the effects that carbon nanotubes (CNTs) have on the curing of the bismaleimide resin matrix (BMI), as well as the effects that the curing of BMI has on the CNTs, in the nanocomposites containing up to 40 wt % CNTs. Two different types of CNTs in the sheet form: unbaked and baked (termed as UB and B CNT), have been employed. Addition of only 10 wt % UB CNT (10 wt % UB − 90 wt % BMI) reduced the BMI cure temperature by up to 123 °C, compared to the cure temperature of neat BMI with no CNTs (100 wt % BMI). The 40 wt % UB − 60 wt % BMI demonstrated a 107 °C increase in the glass transition temperature, compared to the 100 wt % BMI. UB CNTs in the 10 wt % UB − 90 wt % BMI compressed upon the cure of BMI with an estimated compressive stress of 2.9 GPa while the UB CNTs in the 40 wt % UB − 60 wt % BMI were not compressed. The factors leading to these unprecedented effects have been discussed. The effect of the varying CNT content on the inter-CNT spacing and consequently the cure reactions of the BMI, compression of CNTs, and the thermomechanical properties of the nanocomposites has been discussed using an ideal CNT-BMI interaction model. Based on the thermomechanical results and the theoretical calculations, interphase thicknesses of at least 5.3 and 4 nm are estimated for the 30 and 40 wt % CNT nanocomposites, respectively. Since an optimum cure condition is critical to obtain the best mechanical properties in a CNT-BMI system, our results suggest that the optimum cure condition will likely vary for each unique CNT-BMI system. Thus, going forward, optimizing the cure conditions for each CNT-BMI system is critical in realizing the best mechanical properties from that system. Potential applications of the CNT-BMI nanocomposites include structural materials in the aerospace domain.

The effects of processing and carbon nanotube type on the impact strength of aerospace‐grade bismaleimide based nanocomposites

“…The tan δ plots demonstrated two thermal relaxations of the BMI in the 0.1 wt% f-CNT A -HSSM BMI, with glass transition (T g ) peaks at 288 and 328 C, a difference of 40 C. Relaxations in a similar temperature range were also observed through DSC (Figure S2). The two-step relaxation signifies the formation of interphase due to the noncovalent interactions between the f-CNT A and the BMI, where the interphase has restricted mobility compared to the bulk and thus relaxes at a higher temperature, [69,70] The peak of the bulk BMI relaxation in the 0.1 wt% f-CNT A -HSSM BMI and the HSSM BMI is at a similar temperature (~288 C). The two-step relaxation was also observed in the 0.2 wt% f-CNT A -HSSM BMI (Figure 5B).…”

“…SAXS has been used in prior studies to calculate the domain size associated with the molecular heterogeneity of the BMI [28] or CNT-BMI composites, [70,71] inter-CNT distance [72] and CNT bundle size. [72] In our prior work, [28] SAXS peak corresponding to Bragg's d-spacing of 15.5 nm was observed in the HSSM BMI.…”

Prediction of the Interfacial Properties of High-Performance Polymers and Flattened CNT-Reinforced Composites Using Molecular Dynamics

“…Using MD, this study focuses on modelling the polymer/flCNT interface of three high-performance polymers: glycidylamine-based epoxy, bismaleimide (BMI), and poly-benzoxazine. All the simulated systems are aerospace-relevant thermosets [13][14][15][16][17][18][19][20][21] and each system is unique in terms of reaction chemistry and molecular topology. This study compliments the results published by Patil et al [11] and Pisani et al [12].…”

Mechanical and thermal properties of synergistic modification of bismaleimide polymer composites with nano‐SiO2 and hyperbranched polyimide

“…Bismaleimide (BMI) is a thermosetting resin with active terminal group of unsaturated maleimide ring, which has good heat resistance, durable chemical resistance and radiation resistance. [1][2][3][4][5] It can be widely used in aerospace, marine engineering, mechanical and electronic industries. [6][7][8] However, BMI tends to form a threedimensional network structure with excessive crosslinking in the curing process, leading to the rise of cross-linked density, thereby significantly reducing the toughness of the material .…”