Elsevier

Applied Surface Science

Volume 464, 15 January 2019, Pages 509-515
Applied Surface Science

Full Length Article
Methylpiperidine-functionalized graphene oxide for efficient curing acceleration and gas barrier of polymer nanocomposites

https://doi.org/10.1016/j.apsusc.2018.09.086Get rights and content

Highlights

  • MP-GO was prepared by introducing 4-amino-1-methypiperidine.

  • The MP-GO can act as a curing catalyst for polyimide nanocomposites.

  • The oxygen barrier property of PI/MP-GO 1 wt% was 80% better than pristine PI.

Abstract

We synthesized methylpiperidine-functionalized graphene oxide (MP-GO) by introducing 4-amino-1-methylpiperidine into reactive epoxy and/or carboxylic acid groups on pristine GO. Then, we applied the MP-GO as a curing catalyst for polyimide (PI) nanocomposites. The MP-GO was found to be an effective base-catalysts for the thermal conversion of polyamic acid (PAA) precursor to PI. Interestingly, when 3 wt% of MP-GO was added to the PI matrix, the complete imidization of nanocomposites was achieved at a temperature lower than 200 °C. In addition, the PI/MP-GO nanocomposite films exhibited reinforcement of the oxygen barrier properties which were even better than those of pristine PI, due to the excellent dispersion state of MP-GO and the favorable non-covalent interaction between MP-GO and the PI matrix. Comparison to pristine PI, the oxygen permeability of nanocomposite films that contained only 1 wt% of MP-GO loading was significantly decreased, by about 80%. Furthermore, all the PI/MP-GO nanocomposites exhibited high thermal stability.

Introduction

Polymer nanocomposites with well-defined architectures are attracting much attention because they have synergistic properties as well as tailored to specific industrial applications such as microelectronics, the aerospace industry, and optoelectronics [1], [2], [3], [4], [5], [6]. Particularly in the area of nanocomposite reinforcements, polyimide (PI) nanocomposites made with carbon nanomaterials such as carbon black [7], carbon nanotubes [8], [9], graphene [10], [11], [12], [13], and carbon nanofibers [14], [15] have recently drawn considerable interest owing to their exceptional mechanical strength, electrical conductivity, thermal stability, and gas barrier properties.

Among these carbon families, graphene oxide (GO), an oxidized version of graphene presenting epoxides, hydroxyls, ketones, and carbonyl on its edges and surface, has been employed in biosensors, catalysts, composites, membrane, and coatings due to its unique and physicochemical properties [16], [17], [18], [19]. Although GO sheets have high solubility in water and polar organic solvents owing to their hydrophilic nature, they have some limitations such as low compatibility with most organic polymers, which can reduce the reinforcing effects in the polymer matrix [20], [21], [22], [23]. Given the above issues, to produce high quality graphene polymer composites (GPCs), it is important to design and synthesize customized GO-derived materials in ways that the interface between the GO and polymer matrix can be modulated using various approaches.

Recently, we reported graphene-derived PI nanocomposites which incorporated chemically functionalized graphene (CFG), and had a variety of organic functional derivatives on the surface of the graphene, to improve the dispersibility of a graphene in polymeric matrix [24]. The PI nanocomposite filled with CFG exhibited a considerably reinforced mechanical strength and gas barrier ability compared to pristine PI. However, it was necessary to treat it at a temperature of over 300 °C for full imidization of the PAA [25], [26]. This high curing temperature may lead to several defects, which are produced by the partial destruction of the polymer and/or thermal elimination of organic functional groups on the filler surface during the transformation of the PAA precursor to the final PI product. Most importantly, not only might the physical properties of the PI nanocomposites deteriorate, but the components may also deteriorate when the PIs are used in industrial applications [27], [28]. Therefore, lowering the curing temperature in the manufacturing process of the high-performance PI nanocomposites is highly desirable.

This study highlights an effective way to develop low temperature curable PI barrier nanocomposite films with high thermal resistance using methylpiperidine-functionalized graphene oxide (MP-GO). The MP-GO was prepared by a facile single step functionalization by the reaction of 4-amino-1-methylpiperidine with pristine GO. Afterwards, PI nanocomposites with different MP-GO loading were produced by in-situ polymerization, followed by thermal curing of the polyamic acid (PAA) precursor. The MP-GO could be well dispersed in well-known organic solvents such as N,N-Dimethylacetamide (DMAc) and homogeneously dispersed within a polymer matrix, because of the presence of methylpiperidine functional groups on the surface of the GO. In particular, the methylpiperidine groups, one of the effective base-catalysts, not only acted as a dehydrogenation catalyst for PI but could also effectively enhance the degree of imidization. Moreover, the homogeneous dispersion of MP-GO which can block the pathway of oxygen molecules within the PI matrix, can effectively improve the gas barrier property. All the PI/MP-GO nanocomposite films were found to exhibit high storage modulus and thermostability, which are of paramount importance in the field of GPCs.

Section snippets

Materials

Natural graphite flakes (natural microcrystal grade, 99.9995%) were purchased from Alfar-Aesar (USA). The 4-amino-1-methylpiperidine, pyromellitic dianhydride (PMDA, >99%), and 4,4′-oxydianiline (ODA, >98%) were purchased from Tokyo Chemical Industry (Tokyo, Japan). N,N-Dimethylacetamide (DMAc) was obtained from Sigma-Aldrich (St Louis, MO, USA). Common organic solvents were purchased from Dae-Jung Chemicals (Siheung, Korea).

Synthesis of methylpiperidine-functionalized graphene oxide (MP-GO)

Scheme 1 depicts the preparation procedure for MP-GO. First, the

Synthesis and characterization of MP-GO

FT-IR spectroscopy was conducted to confirm the chemical modification of pristine GO by 4-amino-1-methylpiperidine. Fig. 1(a) shows the FT-IR spectra of the pristine GO and MP-GO. The GO spectrum displays the presence of bands associated with Osingle bondH groups at 3410 cm−1, Cdouble bondO stretching at 1722 cm−1, Csingle bondO alkoxy stretching at 1230 cm−1, Csingle bondO epoxy stretching at 1200 cm−1. The FT-IR spectra of MP-GO reveals a new peak at 2920 cm−1 corresponding to Csingle bondN bonds, the peak at 1610 cm−1 corresponding to the amide

Conclusion

In summary, we designed and synthesized methylpiperidine-functionalized graphene oxide (MP-GO) by introducing 4-amino-1-methylpiperidine to improve curing efficiency, oxygen barrier properties, and thermal stability of PI nanocomposites. The resulting MP-GO exhibited good dispersibility in various organic solvents, because of both the methylpiperidine groups and oxygen derivatives. A series of PI nanocomposites with different MP-GO loading were then prepared by in-situ polymerization. The MP-GO

Acknowledgements

This work was supported by a grant from the Korea Institute of Science and Technology (KIST) Institutional Program & Open Research Program and the Nano Material Technology Development Program through the National Research Foundation (NRF) of Korea funded by the Ministry of Science, ICT and Industrial Fundamental Technology Development Program (10052838) by the Ministry of Trade, Industry and Energy (MOTIE) of Korea and Space Core Technology Development Program through the National Research

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