Effect of gamma and neutron irradiation on properties of boron nitride/epoxy resin composites

https://doi.org/10.1016/j.polymdegradstab.2021.109643Get rights and content

Highlights

  • The mechanical property and Tg of the EP were improved by introducing h-BN.

  • The low contents of h-BN were favorable to enhance the radiation resistance of EP.

  • h-BN could weaken oxidative degradation of EP under γ irradiation.

  • h-BN endowed the EP with excellent neutron shielding by absorbing neutrons.

Abstract

Improving the radiation resistance of epoxy resin (EP) is pivotal for the reliability of equipment and the safety of facilities in the nuclear industry. Hexagonal boron nitride (h-BN) is attractive in the preparation of radiation-resistant materials due to its good radiation stability and neutron shielding capability. In this work, h-BN/EP composites with enhanced radiation resistance were fabricated by solution blending. The tensile strength and thermal properties of the composites after γ-ray and neutron irradiation were investigated. The results showed that the addition of h-BN improved the mechanical property and the glassy transition temperature of the resin. The presence of low-level h-BN was favorable to enhance the radiation resistance of EP. As for composites with the 0.05% mass percentage of h-BN, the absorbed dose required to decrease relative tensile strength by 50% was about 300 kGy, which was higher than that of neat EP. The intrinsic mechanism of radiation resistance was attributed to the oxygen barrier effect as investigated by XPS and EPR. Then, benefiting from the absorbing neutrons capability of boron atoms, an addition of 0.55% h-BN to the EP resin could reduce the neutron transmittance of the resin by 5.6%. This study demonstrates that the blending with h-BN can increase the radiation-resistant property of EP resin, meanwhile augmenting the neutron shielding ability.

Introduction

Polymer materials are widely used in nuclear power plants and other nuclear facilities owing to their low density, high strength and specific modulus. However, they will inevitably be affected by ionizing radiation, such as γ-ray, electron beam and neutron beam [1,2]. The ionizing radiation can cause atomic displacement and electronic excitation of materials, which severely worsen the critical properties of structural material [3,4]. Being high-performance thermosetting resin, epoxy resin (EP) has been widely used as encapsulation materials for electronic devices, embedding materials for low and intermediate level radioactive waste and organic coatings for the containment, thanks to its excellent electrical and mechanical property [5]. Yet the high-dose irradiation generally degrades the properties of EP and even causes serious engineering accidents [6]. Therefore, the development of radiation-resistant EP possesses crucial theoretical significance and engineering value for enhancing the reliability of equipment and ensuring the safety of nuclear facilities.

The radiation effect and radiation-damage mechanism of EP have been extensively studied in the world over the past 50 years [7,8]. It is confirmed that the incorporation of some special inorganic or organic radiation-resistant substances into EP can markedly raise the radiation stability, such as lead, tungsten, and aromatic compounds [9,10]. Unfortunately, the poor compatibility between the filler and EP leads to the substantially decreased strength of the composite with the increase of the additives. In addition, the radiation resistance of EP can be improved by adding another polymer material with good compatibility with the EP and containing radiation resistant groups, or by directly modifying the EP and introducing aromatic groups [11]. Although these techniques enhance the radiation stability of materials, they cause somewhat decrease of the mechanical properties before irradiation. It is desirable to prepare EP composites with excellent mechanical properties and radiation resistance.

Two-dimensional materials have been proved to be fascinating fillers for the construction of functional composites with numerous applications [12]. As a structural analogue of graphite, hexagonal boron nitride (h-BN) shows the excellent mechanical property, thermal stability, and neutron shielding [13], [14], [15], which has been regarded as a promising candidate to fabricate EP composites with integrated performance. Introduction of hydroxylated h-BN can enhance the thermal stability, flame retardancy and smoke suppression of EP. The char yield and the temperature at 50 wt% mass loss of composites increased, and the peak heat release rate, total heat release, and release of smoke and toxic gases decreased [16]. The EP nanocomposites with tannic acid-modified h-BN nanosheets showed the excellent anticorrosion effect on the metal substrates and good anticorrosion stability after being immersed in 3.5 wt% NaCl aqueous solution for 120 h [17]. To the best of our knowledge, most of the research focusing on the thermal and corrosion properties of h-BN/EP. There are very few reports on its radiation protection performance. Saiyad et al. dispersed h-BN uniformly into EP by gravity casting method, resulting in the neutron linear absorption coefficient of h-BN/EP was 1.16 times as high as lead/EP [18]. The neutron shielding performance of h-BN/EP has been documented, yet no information is available on the radiation stability of h-BN/EP exposed to γ-rays.

In this study, di-glycidyl 4,5-epoxycyclohexane-1,2-dicarboxylate (TDE-85) with high reactivity and excellent electrical insulation performance was selected as a monomer of EP. h-BN/EP composites were prepared by solution blending. The tensile strength and thermal stability confirmed the radiation resistance enhancement in the case of the addition of h-BN. X-Ray photoelectron spectroscopic (XPS) and Electronic paramagnetic resonance (EPR) analysis were employed to investigate the mechanism of enhanced radiation resistance. The small angle neutron scattering (SANS) spectrometer was employed to investigate the neutron shielding capability, further understanding the effect of h-BN.

Section snippets

Materials

The h-BN powder (~ 325 mesh, 99.5%) was obtained from Shanghai Alfa Aesar Co. Ltd. TDE-85 was brought from Hubei Xinkang Pharmaceutical Chemical Co. Ltd. Methyl hexahydrophthalic anhydride (MHHPA, 98%) was purchased from Shanghai Macklin Biochemical Co. Ltd. The molecular structure of TDE-85 and MHHPA was shown in Scheme S1. The 2,4,6-tris (dimethylaminomethyl) phenol (DMP-30, 95%) was obtained from Shanghai Aladdin Bio-Chem Technology Co. Ltd. High purity nitrogen (≥ 99.999%) was supplied by

Mechanical and thermal properties of h-BN/EP composites

The photograph of neat EP and h-BN/EP (Fig. 2a) revealed that the transparency of strips decreased as the h-BN content increased. The transmittance of the samples in the wavelength range from 300 to 800 nm (Fig. S2) decreased with increasing h-BN content, confirming well the same trend of coloration. This photograph indicated that h-BN had been successfully added into the EP. The tensile properties of the neat EP and h-BN/EP composites were measured as shown in Fig. 2b. With increasing h-BN

Conclusion

In this study, h-BN/EP composites were synthesized, and their radiation resistance towards γ-ray and neutron beam was evaluated. It had been shown that the addition of a small amount of h-BN (0.05%) enhanced the mechanical property. After γ-ray irradiation, the tensile strength of composites increased first and then decreased with the increase of absorbed dose. Furthermore, radiation degradation of composites was inhibited with the addition of h-BN. The absorbed dose of h-BN/EP-0.05% was about

CRediT authorship contribution statement

Limin Jiao: Data curation, Validation, Conceptualization, Writing – original draft. Yi Wang: Investigation, Formal analysis. Zhihao Wu: Conceptualization, Writing – review & editing. Hang Shen: Formal analysis. Hanqin Weng: Writing – review & editing, Funding acquisition. Hongbing Chen: Funding acquisition, Resources. Wei Huang: Funding acquisition, Resources. Mozhen Wang: Writing – review & editing. Xuewu Ge: Writing – review & editing. Mingzhang Lin: Supervision, Project administration,

Declaration of Competing Interest

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled.

Acknowledgments

This work was supported by the Science Challenging Project (TZ2018004) and the National Natural Science Foundation of China (No. 11775214 and 51803205).

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