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Polymer composites with small amount of CNTs (< 5 wt%) have been studied as a light-weight wear-resistant material with low friction, among other applications, but their modulus improvement often plateaus or diminishes with increasing CNT fraction due to agglomeration. Here, polymer nanocomposites were fabricated with randomly oriented or aligned CNTs across their volume (up to 5 mm length) by CNT surface diazotization and by static magnetic field application (400 G for 40 min). With the improved CNT dispersion and thus less agglomeration, the reduced moduli of PNCs stayed improved with addition of up to 1 vol% (or 1.3 wt%) of CNTs. In this work, the PNCs with randomly oriented CNTs exhibited higher stiffness than the PNCs with magnetically aligned and assembled CNTs, indicating again the negative effect of CNT agglomeration on stiffness. In future, other CNT structuring methods with controlled inter-CNT contacts will be conducted to dissociate alignment from local agglomeration of CNTs and thus to simultaneously improve hardness and modulus of PNCs with small CNT addition.
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EFFECTS OF MAGNETIC ALIGNMENT AND CNT AGGLOMERATION ON REINFORCING FRACTURE TOUGHNESS OF POLYMERS
Reinforcing composite materials with carbon nanotubes (CNTs) has the potential to improve mechanical and/or multifunctional properties due to their nano-size. Research has been done on using CNTs to reinforce the interlaminar strength of carbon fiber reinforced composites (CFRPs), but most of the previous work is about randomly oriented carbon nanotubes. Currently, one of the main challenges regarding CNT integration into polymers is mitigating their agglomeration and controlling their dispersion in the polymer matrix. By aligning CNTs with an external field, more tailored structure control can be achieved, and a better understanding of how CNT agglomeration and dispersion relate to external field application and CNT concentration is needed. In this work, we studied the effects of magnetic field magnitude, CNT concentration, and matrix viscosity on CNT agglomeration and morphology. We measured the fracture toughness reinforcement of epoxy-CNT nanocomposites at various CNT concentrations (0.1 vol.% and 0.5 vol.%), magnetic field magnitudes (no field, 180 G, and 300 G), and matrix viscosities (older epoxy-hardener system with higher viscosity and newer epoxy-hardener system with lower viscosity). Our results demonstrated that aligning CNTs with a magnetic field can lead to extra reinforcement when compared to using randomly oriented CNTs if the field magnitude, CNT concentration, and matrix viscosity are selected accordingly. The maximum fracture toughness reinforcement achieved with the higher viscosity epoxy-hardener system (~72%) was with 0.5 vol.% of CNTs with a 180 G field, whereas the maximum reinforcement with the lower viscosity epoxy-hardener system (~62%) was observed for the samples fabricated with 0.1 vol.% of randomly oriented CNTs. COMSOL simulations were also conducted to understand the behavior of CNT agglomeration and alignment at different field magnitudes and CNT concentrations, and were compared with the experimental results. To maximize CNT reinforcement, more work needs to be conducted to address the challenge of CNT agglomeration and dispersion control in a polymer matrix, such as a more in-depth study of how different field magnitudes affect fracture toughness improvement and new methods to improve CNT dispersion.
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- Award ID(s):
- 1844670
- PAR ID:
- 10392412
- Date Published:
- Journal Name:
- Proceedings of the American Society for Composites - 37th Technical Conference, ASC 2022
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.12783/asc37/36418
