(118i) Structural Composites with Multiple Functionalities

Polymer-based composites are susceptible to many different types of mechanical damage that may reduce their structural reliability, thermal conductivity, optical transparency, and surface qualities, thereby potentially decreasing the overall lifetime of these products.[1-5] We have previously reported on the fabrication of epoxy-based transparent composite coatings consisting of tailored halloysite nanotubes (HNTs) orientations.[6, 7] Mechanical reinforcement (i.e., stiffness and hardness) and wear-resistance of the resultant composites were correlated to the specific alignment of the HNTs. Composites displaying a high transparency of 90% even at a high halloysite concentration of 20 wt% can be achieved by matching the refractive index between the HNTs and polymer matrix (n ~ 1.5 for both) [6, 7]. These transparent coatings with well-controlled thickness are very attractive for fabricating multi-functional composites. However, it is challenging to find polymer additives that can be incorporated into epoxy resins with appropriate epoxy miscibility, and that result in high transparency, and unaffected mechanical robustness of the final composite.[8] The currently used self-healing additives in industry are not compatible with epoxy at macromolecular level, thus blocking the light transmittance and leading to low transparence in coatings. Examples of the self-healing additives include polycaprolactone (PCL),[9, 10] polyethylene-co-methacrylic acid (EMAA),[11, 12] and poly(bisphenol A-co-epichlorohydrin) (PBE).[12-14]

In this research, we studied the self-healing mechanisms that recovers mechanical robustness and light transparency in epoxy-based composite coatings. By demonstrating that the inclusion of cellulose derivatives can be utilized to produce self-healing composites, self-cleaning properties were also studied. Cellulose derivatives in our material system is an ideal candidate to compound with epoxy because of its solubility in a wide range of solvents compatible with our epoxy precursor formulations, excellent miscibility with the epoxy resin, high mechanical rigidness, and manageable self-healing transition temperatures and viscosities.[15] Importantly, the refractive index, ~ 1.5, closely matches each component of the epoxy/HNT composites. We showed a useful strategy for producing multifunctional material systems with enhanced mechanical durability, transparent optical properties, reversible self-healing behavior, as well as self-cleaning ability, which is practically applicable in optical systems.

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9. Rodriguez ED, Luo X, and Mather PT. ACS applied materials & interfaces 2011;3(2):152-161.

10. Luo X and Mather PT. ACS Macro Letters 2013;2(2):152-156.

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12. Pingkarawat K, Wang C, Varley R, and Mouritz A. Composites Part A: Applied Science and Manufacturing 2012;43(8):1301-1307.

13. Hayes S, Jones F, Marshiya K, and Zhang W. Composites, Part A: Applied Science and Manufacturing 2007;38(4):1116-1120.

14. Meure S, Wu DY, and Furman S. Acta Materialia 2009;57(14):4312-4320.

15. Gooch JW. Cellulose Acetate Butyrate. Encyclopedic Dictionary of Polymers, vol. 1. New York: Springer, 2011. pp. 128-128.