Abstract
Using nanoscience to solve the issues that limit the development of a sustainable society is one of the most important topics at present. Sustainable polymers play an important role in the construction of a sustainable society, but its large-scale application is usually limited by the poor mechanical and shape-memory properties of the commonly used epoxy resin. The utilization of nanoarchitectures to improve the shape-memory performance of composite materials is an effective approach. Graphene, among the used reinforcement materials for epoxy resin, is undoubtedly a fascinating example. In this paper, the shape-memory and mechanical properties of graphene-modified epoxy resins are described respectively for different response types. In this mini-review, we present an overview of the research results of graphene nanoarchitectonics in the modification of shape-memory epoxy resin composites. Besides, this paper has reviewed the properties of different types of graphene/epoxy composites, looking forward to the development of graphene/epoxy composites and future prospects.
Introduction
A sustainable polymer is a kind of material that can change shape and recover under certain conditions, such as heat, light, water, pH, and other external stimuli (; ). Shape-memory characteristics have broad application prospects in aerospace, biomedical, and other fields (; ; ). Among the sustainable polymer series materials, epoxy (EP) resin has attracted considerable attention both scholarly and popularly due to their excellent shape-memory properties, thermal properties, and mechanical properties ().
Related researches pointed out that the interaction between nanoparticles and polymer matrix can accelerate the movement of molecular chains, improving the shape-memory performance of materials (). Graphene has been considered as an irreplaceable reinforcing material because of its special structure and excellent properties and has great application value in the field of composite modification. introduced graphene into EP–cyanate ester nanocomposites, and the results confirmed that graphene could promote the shape recovery of EP cyanate nanocomposites. It should be noted that the doped size, surface modification, and dispersion of graphene as a filler will have a significant impact on the performance of composite materials (). For instance, functionalized graphene (FG) can obtain good bonding with the matrix, thereby enhancing the role of graphene as reinforcing filler (). A novel slippery film with tunable wettability based on a shape-memory graphene sponge was presented by . The shape-memory polymer was coated on the surface of porous graphene sponge, which was used to lock in inert lubricant and to construct a smooth surface to achieve good hydrophobicity. The superelasticity, high strength, and good conductivity of graphene sponge endow graphene/polymer hybrid films with good shape-memory properties. In fact, in addition to graphene, its derivatives, such as graphene oxide (GO) and thermally reduced graphene, are often used as fillers to modify composite materials (). At present, the use of graphene to modify shape-memory EP resins to prepare shape-memory graphene/EP resin composites with better shape-memory and mechanical properties has been widely investigated by scholars. Table 1 shows the literature summary of graphene-modified shape-memory EP resin. It can be seen from the table that different doping processes and dosage can improve the mechanical properties of shape-memory EP resin to a different extent. For different types of shape-memory EP resin, different graphene content can change its recovery performance correspondingly.
TABLE 1
| Doping methods | Graphene content | Performance | References |
| Ultrasonic dispersion | 5–15 wt% | Tensile strength and elongation were increased by 5.3 and 33.5%, respectively | ; ; |
| Vacuum-assisted resin transfer | 2–12 wt% | Enhance the structure of the nanofiber web (increased 15%) | ; ; |
| Solution casting | 1–3 wt% | Young’s modulus and tensile strength of nanocomposites prepared via R(GO-ISO) nanosheets have been improved (increased 51 MPa) | |
| Solution blending | 0.1–4 wt% | Moduli of the imidized graphene nanocomposites were 25–30% higher than those of unmodified graphene nanocomposites. The addition of graphene improved the recovery rate | |
| Compound aerogels | 0.5–0.8 wt% | Compared with pure epoxy, the electrical conductivity of the composite is improved by 13 orders of magnitude | |
| Coupling reaction | 2–6 wt% | A modulus of ∼339 MPa and a shape recovery ratio of 98% were achieved | |
| In situ polymerization | 0.5–1.5 wt% | Young’s modulus of PU/GQD nanocomposites increases with the addition of GQDs content at both room temperature and 60°C | ; |
| Condensation polymerization | 0.1–1.0 wt% | The nanocomposite film containing 0.25wt% GNPs showed the highest shape recovery ratio (92.4%) since the net-point effect |
Overview of shape-memory and mechanical properties of widely used graphene.
GQD, graphene quantum dot; PU, polyurethane; GNP, graphene nanoplatelete.
In this article, we summarized the recent developments of graphene nanoarchitectonics in a reinforcement of shape-memory polymers under various external stimuli like thermal, electrical, and other stimulations and discussed the problems of graphene in limiting the application of composites (Figure 1).
FIGURE 1
Thermo-Active Graphene/Epoxy Composites
Thermo-induced shape-memory materials are the most widely studied type of shape-memory polymers. The shape-memory EP can be divided into the stationary phase and reversible phase, in which the stationary phase is used for shape-memory and recovery. When the temperature rises above the glass transition temperature (Tg), the material can deform under the effect of external load, and the reversible phase molecular chain is frozen when cooled, to obtain a stable morphology. When the temperature rises above Tg again, the reversible phase molecular chain recovers its activity and releases the stored strain energy, and the material returns to its original state gradually under the recovery of the stationary phase (
Recently, studies have shown that carbon nanomaterials can improve the thermally activated shape-memory properties of materials (
To solve the brittleness of the EP resin matrix,
In addition to the dual shape-memory effect, the triple-shape-memory composite materials have also attracted great interest from researchers. Triple-shape-memory polymers refer to shape-memory polymers capable of memorizing two temporary shapes in one shape-memory cycle (
Electro-Active Graphene/Epoxy Composites
Thermal-active shape-memory polymer materials are limited by the direct heating temperature when excited, whereas electro-active shape-memory polymer is motivated by applying voltage, so it is more convenient to use than thermal-active shape-memory polymer materials (
Other Types of Graphene/Epoxy Composites
Shape-memory materials that can be remotely and wirelessly driven have broad application prospects in space engineering, which has attracted widespread attention. Microwave-active shape-memory material is one of them. Microwaves can trigger this kind of shape-memory materials because the dipoles in the materials are oriented and polarized under the action of microwaves. During the deformation process, there will be friction loss and heat generation during the excitation of the microwave-responsive shape-memory material (
In addition to microwave-active shape-memory materials, photo/thermal-active shape-memory material is also one of the materials that facilitate remote driving (
Conclusion
In summary, recent researches on graphene/EP composites have brought up a great deal of government and social attention and support. The research results showed that graphene/EP composite material is an intelligent material with important application potential. In addition to its excellent shape-memory function, it also has the characteristics of high strength, wide adjustable range of stiffness, and easy processing and forming. However, the current research on shape-memory graphene/EP composites also has many problems that need to be solved:
- •
The content of graphene has a great influence on the shape-memory performance of the material. Improper content of graphene can agglomerate in the shape-memory materials, and the aggregation of graphene significantly reduces the strengthening effect of graphene. Therefore, improving the dispersibility of graphene in EP resin and the interface compatibility of shape-memory composites is still a technical problem that needs to be urgently solved.
- •
To accurately realize the specific deformation of the shape-memory polymer structure in practical applications, according to the special properties of the shape-memory composite material, the thickness dimension of the shape-memory graphene/EP resin should be limited. In the design of the shape-memory material structure, to prevent the fiber-reinforced material from falling off the resin matrix due to the irrational dimensional structure when the structure is deformed, it is necessary to limit the parameters such as outer size, thickness, and bending radius. Therefore, the application range of shape-memory composites will inevitably be affected.
- •
At present, the researches on shape-memory graphene/EP resin only focus on the static properties of the material. The dynamic changes of parameters such as glass transition temperature, elastic modulus, and thermal expansion coefficient caused by the preparation method and the graphene doping process are ignored. Also, the temperature change rate and temperature decrease rate in the preparation process may also have a certain effect on the memory performance of the material. Therefore, studying the properties of composite materials under dynamic conditions is also a problem that researchers need to solve.
Shape-memory graphene/EP composites still have a broad development space. If the previously discussed problems can be effectively solved, the application of shape-memory graphene/EP composites will be more extensive in the future.
Statements
Author contributions
LC and YZ produced and wrote the manuscript. LC and WL edited the manuscript. LC and ZL edited the manuscript and supervised. All authors read and approved the manuscript.
Funding
This work was supported by the 13th Five-Year Plan Equipment Pre-Research Fund under Grant No. 61402060404, the Natural Foundation of Shandong Province under Grant No. ZR2019BEE068, the State Key Laboratory of Mechanical System and Vibration under Grant No. MSV-2019-13, and the Fundamental Research Funds of Shandong University under Grant No. 2018GN034.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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Summary
Keywords
graphene, nanoarchitectonics, composites, sustainability, polymers
Citation
Chen L, Zhang Y, Liu W and Liu Z (2020) Graphene Nanoarchitectonics: A New Material Horizon for Reinforcement of Sustainable Polymers. Front. Mater. 7:276. doi: 10.3389/fmats.2020.00276
Received
21 April 2020
Accepted
24 July 2020
Published
18 August 2020
Volume
7 - 2020
Edited by
Brahim Aissa, MPB Technologies & Communications, Canada
Reviewed by
Adnan Ali, Qatar Foundation, Qatar; Mahyar Mohammadnezhad, Université du Québec, Canada
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© 2020 Chen, Zhang, Liu and Liu.
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*Correspondence: Long Chen, 812612937@qq.com
This article was submitted to Smart Materials, a section of the journal Frontiers in Materials
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