Regular Article
Facile immobilization of graphene nanosheets onto PBO fibers via MOF-mediated coagulation strategy: Multifunctional interface with self-healing and ultraviolet-resistance performance

https://doi.org/10.1016/j.jcis.2020.11.026Get rights and content

Abstract

The surface of poly (p-phenylene benzobisoxazole) (PBO) fibers with self-healing and ultraviolet (UV)-resistance performance play the key role in prolonging their service lifespan. Although great advances have been made in the single aspect of above two properties, integration of self-healing and anti-UV performance into the surface of PBO fiber is still a challenge. In this study, the coagulation strategy mediated by metal-organic framework (MOF) is proposed to construct the multifunctional surface of PBO fibers. The spindle-like iron (III)-based MOF (MIL-88B-NH2) nanocrystals are firstly immobilized onto the surface of PBO-COOH through hydrothermal reaction, then serving as the medium layer to further immobilize sufficient graphene oxide (GO) nanosheets. Benefitting from the favorable near-infrared (NIR, 808 nm) photothermal conversion performance of GO nanolayers, the monofilament composite-PBO@Fe-MIL-88B-NH2-GO-TPU (thermoplastic polyurethane) exhibited a stable and high self-healing efficiency (approximately 80%) within five cycle times. Meanwhile, the cooperative adsorption and shielding weaken effects of MOF-GO nanolayers enabled PBO fibers with excellent anti-UV properties that are superior to much reported literatures after 96 h aging time and eventually increased by 75% compared with untreated PBO fiber. In view of the varieties and multifunctionalities of MOFs and carbon nanomaterials, MOF-mediated coagulation strategy would provide guidance for preparing multifunctional composite materials.

Introduction

Among the fiber composites [1], PBO fibers capture wide attention because their wonderful thermal stability [2] and mechanical properties [3]. As is known to all, the interfacial region [4], designated as “interphase” [5] between fiber and resin [6], acts as the key roles in load transferring [7] and determining the overall mechanical performance of advanced composites [8], [9]. Owing to the inert surface of PBO fibers[10], the interface combination is weak and susceptible to generate microcracks or damages [11], [12]. Because the formed microcracks often continue to derive and extend at interfacial region and eventually penetrate into the deep structure [13], the detection and restore are often laborious and costly [14]. More seriously, once the interfacial damage has developed [15], the overall properties and operation lifespan of the composites will be greatly compromised [16]. Efforts should be focused on exploring new self-healing strategy that allow for in situ repairing the interfacial failure of the composites to prolong their service life.

Up to now, extrinsic and intrinsic strategy are two main types of self-healing systems [17]. The extrinsic method generally comes into force by pre-introduced healing agent into materials [18]. The breaks and cracks existed in the materials will induce healing agents release and then perform the healing programme [19]. The pioneering group of White and Sottos [20] showed that the fabrication of autonomic repairing interface by attaching capsules-encapsulated healing agent and catalyst onto the surface of fibers [21]. Since then, more extrinsically interfacial self-healing techniques are gradually developed including the single-capsule system [18], capsule/dispersed catalyst system [21], phase-separated droplet/capsule system, double-capsule system, and all-in-one microcapsules system [17], [21]. However, the healing numbers/times of capsule/microcapsule are finite [22], hindering the application of extrinsic strategy in the repair of fiber reinforced composites [21]. Alternatively, intrinsic repair strategy realized by introducing reversible dynamic bonds such as Diels-Alder bonds [23], thiuram disulfide groups [24], alkoxyamine [25], coumarin units [26], acylhydrazone bonds [18], disulfide units [27], Csingle bondC bonds reshuffle with the aid of Ru-catalyzed [18], and hydrogen bonds [28] into the materials has been extensively applied [17]. Despite the intrinsic strategy involving the breakage and reformation of chemical bonds could be operated repeatedly [29], it still suffers from more or less severe drawbacks for instance much cost, complicated self-healing process and degraded mechanical properties of materials [21]. To overcome the above shortcomings, the self-healing materials induced by external stimulation [30], for example heating [31] and photo-irradiation [26], arise enormous interests among scientific researchers [30]. Meanwhile, the light with advantages of easily available, clean, inexpensive, unparalleled, remote activation and productive was especially captured much interest and has been greatly applied in self-healing materials [32], [33]. Moreover, several self-healing interfaces in resin-based composites have been successfully constructed by anchoring the photothermal nano-agents including Ag/Cu2S nanoparticles[6], and PDA/BN nanosheets [34] on the PBO fiber surface in previous works of our group. Although some progresses have been made, finding a facile and valid strategy that can fabricate stable and multifunctional interface to overcome the potential defects existed in the PBO fiber and corresponding composites is still a great challenge.

Metal-organic frameworks [35], which is constituted by metal nodes and organic linkers [36], have shown huge potential in different fields for instance adsorption [35], catalysis [37] and sensing [38] result from high specific surface areas, excellent thermal and chemical stability, controllable pore sizes and extensive structural diversity [39], [40]. Recently, several MOF materials constituted by metal/transition metal ions (Zr4+, Ti4+ and In3+) and benzene ring-containing organic linkers have been successfully introduced onto the PBO fibers and other fibers/fabrics via in situ growth methods in our previous publications [41] and few findable works [42], [43], simultaneously enabling the fibers/fabrics with remarkably improved surface energies, roughness and anti-UV properties [41], [44]. Hence, loading the suitable MOF nanocrystals can be regarded as a feasible and promising strategy to make up the potential defects (surface inertness, poor UV stability and weak combination with resin) of PBO fibers. Besides, the UV-adsorption properties of MOFs are mainly depending on the physical structures and chemical compositions of organic ligand components [42], [45]. Generally, the MOF crystals bridged by organic linkers composed of pure/functional group-substituted benzene ring and carboxyl, such as terephthalic acid and 2-aminoterephthalic acid, will exhibit excellent absorbance in the UV or even visible regions. In the family of MOF materials, Fe-MIL-88B-NH2 [46] built by Fe3+ and 2-aminoterephthalic acid with the spindle-like topology [47], [48], possesses wide and strong light response and adsorption in the wavelength ranging from 200 to 600 nm [49], commendably covering the UV and visible light regions. Moreover, one more interesting fact is that the water-stable MOFs can act as efficient coagulants for sufficient heteroaggregation and destabilization of GO sheets from aqueous solutions, providing a cost-efficient and promising procedure to reduce the toxicity of GO in natural aquatic systems and fabricate the MOF-GO hybrids, which is mainly based on the comprehensive effects including hydrogen-bonding/π-π/acid-base interactions and electrostatic attraction (adjusting pH values) between MOF crystals and GO sheets [50]. Combining the above-mentioned discussions, we speculate that in situ growing well-defined Fe-MIL-88B-NH2 nanocrystals (chemical stability, UV–visible light adsorption and shielding) as the medium layer/coating to further introduce enough GO sheets (auxiliary UV–visible light adsorption and shielding, favorable NIR photothermal conversion) onto the surface of PBO fibers, could be a simple and feasible strategy to well resolve the known shortcomings of PBO fibers and construct stable multifunctional interfaces in composites.

As a proof of proposed conceive, an iron (III)-based MOF (MIL-88B-NH2)-mediated coagulation strategy is developed in the present study to construct a stable and multifunctional (UV-resistance and repeatable self-healing) surface of PBO fibers. Specifically, the spindle-like/rod-shape Fe-MIL-88B-NH2 are in-situ formed onto carboxylated PBO fibers surface (PBO-COOH) in the first place by a well-known one-step hydrothermal method. Then, numerous micron-scale GO sheets are further immobilized onto the PBO fiber surface via the mediated effects of Fe-MIL-88B-NH2 nanocrystals-the hydrogen-bonding/π-π/acid-base (Lewis) interactions between them. As expected, the resulting composites fibers, denoted as PBO@Fe-MIL-88B-NH2-GO, present excellent UV-resistance properties and improved by 75% compared with untreated PBO fibers which is result from the effect of synergetic adsorption and shielding/refection between Fe-MIL-88B-NH2 nanocrystals and coagulated GO sheets. Meanwhile, on the basis of favorable NIR photothermal conversion of introduced GO layers [51], PBO@Fe-MIL-88B-NH2-GO-TPU monofilament composites also display stable and repeatable self-healing interfaces, which is conducive to prolong the service life of PBO-related composites. On the whole, the developed MOF-mediated coagulation strategy in current work will potentially enable PBO and other high-performance fibers for valuable applications in sensors, functional fabrics, advanced composites and so on.

Section snippets

Materials

PBO fibers (12 μm in diameter) were cleaned through Soxhlet extraction prior to use. Guangdong. Iron (III) chloride hexahydrate (FeCl3·6H2O, 99%), 2-aminoterephthalic acid (NH2-BDC, 98%), glacial acetic acid (CH3COOH, 99.7%), Pluronic F127 and ethanol (CH3CH2OH, 95%) were obtained from Aladdin and Innochem Reagent Company.

Fabrication of PBO@Fe-MIL-88B-NH2 fiber

PBO-COOH fibers were prepared refer to the method in previous literature [52]. The detailed fabrication process was as follows. First of all, iron (III) chloride hexahydrate

Results and discussion

As has been noted, the high-performance PBO fibers are still faced with several deficiencies including surface inertness [52], vulnerable to UV light irradiation and poor binding affinity with resin matrix [41] seriously limiting the application of PBO fibers. Meanwhile, the improved methods reported so far remain unsatisfactory and the main shortages are as follows: complex preparation process, inhomogeneous modification effects and low coverage of UV-protection materials. Under this

Conclusions

In conclusion, one-dimensional (1D) versatile PBO@Fe-MIL-88B-NH2-GO fiber is achieved by hydrothermal treatment and MOF-mediated coagulation strategy. Herein, numerous GO sheets can be simply and effectively immobilized onto the surface of PBO fiber due to the hydrogen-bonding/π-π/acid-base (Lewis) interactions between Fe-MIL-88B-NH2 nanocrystals and GO sheets. The PBO@Fe-MIL-88B-NH2-GO-TPU monofilament composite exhibited stable interfacial self-healing properties. More importantly, the SE

CRediT authorship contribution statement

Qing Shao: Conceptualization, Formal analysis, Methodology, Visualization, Writing - original draft, Investigation, Project administration, Visualization. Fei Lu: Conceptualization, Formal analysis, Methodology, Visualization, Writing - original draft, Investigation, Project administration, Visualization. Long Yu: Validation. Xirong Xu: Validation. Xinghao Huang: Validation. Yudong Huang: Funding acquisition, Resources, Project administration, Supervision, Writing - review & editing,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank the Basic Strengthening Program of Science and Technology (no. 2019-JCJQ-JJ-302), the National Natural Science Foundation of China (no. 51673053), the Natural Science Foundation of Heilongjiang Province (no. LC2017024), the Aeronautical Science Foundation of China (No. 2019ZF077009).

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