Technical points of graphene water-based anti-corrosion coatings

Graphene is the thinnest corrosion-resistant material in the world and can be used for metal protection. A large number of research results show that graphene's oversized surface area, excellent barrier, high chemical stability and good conductivity and other properties, for the comprehensive performance of anti-corrosion coatings have a strong role in improving, such as enhancing the coating on the substrate adhesion, improve the paint wear resistance and corrosion resistance, at the same time has environmental safety, no secondary pollution and other characteristics.
recent years, graphene-based anti-corrosion application research has focused on pure graphene anti-corrosion coating and graphene composite anti-corrosion coating
China
. However, the simple use of graphene anti-corrosion coating has many limitations: high quality requirements for graphene, metal substrate restrictions, equipment requirements, difficult to large-scale, large-area preparation, difficult to industrialization.
Compared with pure graphene anticorrosion coatings, graphene composite anti-corrosion coatings can take into account graphene's excellent chemical stability, rapid conductivity, outstanding electrical properties and polymer resin strong adhesion, film-forming properties, can be combined to improve the comprehensive performance of coatings.
addition, the preparation method and coating process of graphene composite anti-corrosion coating can be based on the traditional coating production process, and show good controllability and construction in industrial synthesis and industrialization applications. Therefore, graphene composite anti-corrosion coatings will be the new anti-corrosion coating materials in the future.
the unique structural properties of graphene itself, which gives it an advantage in both physical and electrochemical corrosion protection.
(1) layer structure can form a "labyrinth" structure, which can effectively improve the physical barrier of the coating.
(2) due to its small size effect, the coating defects can be effectively filled, reducing porosity and enhancing tightness.
(3) layer structure can divide the coating into many small intervals, which can effectively reduce stress in the coating, consume break energy, and improve the flexibility, impact resistance and wear resistance of the coating.
(4) electronic migration rate is high, showing good conductivity.
graphene in water-based composite anti-corrosion coatings
water-based coatings due to low pollution, easy to purify, no stimulation and so on, has become the paint industry to develop green environmental protection coatings. However, the protective effect of water-based coatings is still not comparable to its corresponding solvent-based coatings, resulting in its application in the field of heavy corrosion is still not high.
water-based coatings have some technical problems: due to the different mechanism of film formation, compared with solvent-based coatings, water-based anti-corrosion coatings are difficult to form a highly edic, highly complete structure of high-quality coatings, its film-forming properties, abrasive performance is not good; The residual water-based group in the coating makes its shielding ability of water, oxygen and other corrosive media poor, because the surface of water is too strong, the water-based coating is difficult to achieve a high degree of immersion and dispersion of pigment fillers, so improving the corrosion resistance of water-based coatings has become the focus of the development of environmentally friendly coatings.
unique properties of graphene bring new ways to improve the tightness, barrier, mechanical properties and corrosion resistance of water-based coatings.
1.
graphene water-based polyurethane anti-corrosion coating
water-based polyurethane (WPU) has solvent-based polyurethane performance, but also overcome solvent volatile environmental pollution. However,
WPU
thermal stability, solvent resistance and technical performance, affecting its application range, so in order to provide the comprehensive performance of
WPU
, it is usually necessary to cross-link the modified, epoxy Resin modified, silicone modified and inorganic nanomaterials (
SiO2
,
TiO2
,
CNTs
) modified.
graphene as a new high-performance nano-enhancer, so that polyurethane water resistance, thermal properties, and aesthetic properties have been improved to varying degrees.
2.
Graphene water-based epoxy anti-corrosion coatings
After years of efforts by research and development workers, water-based epoxy coatings have overcome the disadvantages of poor water resistance/corrosion resistance, and gradually applied to solvent-based coatings involved in the field of heavy corrosion protection. To further improve its corrosion resistance, the researchers combined graphene into a water-based epoxy coating to develop a new composite coating.
3.
Graphene water-based acrylic anti-corrosion coatings
water-based acrylic anti-corrosion coatings are cheap, with safety and environmental protection, excellent aging resistance, good alkaline resistance, simple synthetic processing and so on, but due to the residual hydrophobic group, its water resistance is poor, easy to flash erosion. However, the water-based graphene coating made by adding graphene has outstanding water resistance and salt spray resistance, and its anti-corrosion effect is significantly better than that of other carbon-based materials filled with water-based coatings.
4.
Graphene water-based inorganic zinc-rich primer
water-based inorganic zinc-rich primer is a silicate solution as an important film-forming substance, with high content of zinc powder (in order to improve the performance of the coating film, can be mixed with some sheet aluminum powder, mica powder, phosphorus iron powder, phosphorus iron-zinc silicon powder, etc.) for anti-corrosion pigment water-based heavy anti-corrosion primer.
Due to the high zinc content, zinc powder in the air prone to whitening, reducing the adhesion of the coating, the coating in the process of use easy to foam and dry cracking, corrosion resistance is reduced, but by adding graphene can improve the film's salt spray resistance.
At home and abroad corrosion protection workers in graphene water-based composite anti-corrosion coating performance research has done a lot of work, graphene water-based composite anti-corrosion coatings show the effect, indicating that water-based coatings modified by graphene, performance has improved.
However, most of the research is laboratory results, research content fragmentation, and the research focus on how to prepare graphene composite protective coating and verify the corrosion resistance of graphene, ignoring the graphene selection, graphene water-based composite coating supporting system research, especially graphene on the water-based coating corrosion performance between the structure of the relationship and graphene and coating dispersion, interface problems and other lack of understanding. difficulty in the application of graphene in the field of water-based anti-corrosion
1.
to solve the problem of graphene selection and water-based coatings
graphene preparation methods are different, its physical structure, chemical properties are not the same. Although the structure of graphene oxide GO, reduced graphene oxide
RGO
is similar to graphene
GNP
but due to the influence of chemical modification, there are a large number of structural defects on its surface, resulting in its conductivity, machinery, mechanics and other properties are not
GNP
excellent.
in hydrophobicity, affected by the surface effect, GNP has a poor immersion of water and shows good hydrophobicity, compared with
GNP
,
the
,
RGO
surface because it contains a large or small amount of oxygenated organic energy groups, showing good hydrophobic. When
GNP
and
GO
are added to the resin as fillers, hydrophobic
GNP
will prevent or delay the penetration of corrosive media such as water and oxygen, while hydrophobic
GO
will promote the penetration of corrosive media to some extent.
go, go, and other countries in terms of
RGO
because the surface contains some organic organ groups (carboxyl, carboxyl, epoxy-based) have a certain reaction activity, can react with some of the resin groups to produce chemical bonds, showing better interface compatible than
GNP
and resin.
in terms of conductivity, GNP, due to its good conjugate structure, exhibits excellent conductivity, which is similar to
Compared
GNP,
GO
,
RGO
surface due to the presence of organic organ groups destroyed its original conjugate structure, conductivity is far less than
GNP
.
addition, there is a direct relationship between graphene thickness, chip size, curling of the sheet structure, and surface area. At present, there are hundreds of domestic graphene-related research institutions, manufacturers, the use of preparation methods, production processes are not the same, the performance of graphene products produced vary, in the use of graphene for anti-corrosion coatings, the effect must be different, so choose which graphene is the first consideration of researchers.
coating is a complex supporting system, the various groups play a protective role. At present, the research on graphene water-based composite anti-corrosion coating tends to diversify, not only graphene selection is diverse, but also film resin, pigment, additive selection is also diverse, so for different corrosion environment to choose which graphene and water-based anti-corrosion coating to form a complete supporting system is the focus of research.
To this, it is necessary to establish a comprehensive evaluation system of graphene and anti-corrosion coatings, to examine in detail the effect of graphene materials of different structures and materialization on the protective properties of different parts of water-based coatings, to explore its mechanism of action in depth, and to provide theoretical and experimental basis for the selection of graphene for subsequent water-based anti-corrosion coatings.
2.
Resol the problem of the amount of graphene in water-based coatings
when graphene fillers are not added, pure resins are prone to cracks in the film-forming process, the coating is micro-porous, and the corrosive medium is easy to spread through voids and cracks. When the ideal content is added, the layer structure of graphene is superimposed and staggered up and down, which can form tens to hundreds of dense physical barrier layers in the coating, greatly improving the anti-permeability of the coating.
When the amount of graphene filler is too large, on the one hand, due to its surface effect, graphene aggregation occurs, a large number of disorderly accumulation in the coating, forming a hard reunion body becomes a paint defect; In short, graphene content is too low or too high to provide good protection performance, so it is necessary to investigate the impact of graphene dosage on the microstructure, viscosity, adhesion and protective properties of the coating, and select the ideal amount of graphene added for a specific coating system.
3.
Resol the problem of dispersion and compatibility of graphene in water-based coatings
Graphene's high surface area, strong Vanderbilt and π
-
π effect make it easy to reunite, and water, organic solvents and polymers can not form a stable chemical bond binding, resulting in its interface with resin binding force is weak, poor compatibility, easy separation, seriously affecting the performance of the coating.
At present, more research technology of graphene dispersion includes chemical dispersion and physical dispersion, that is, the functionalization of graphene through co-priced bond and non-common-price bond modification, graphene and coating resin fusion mainly through conferencing method and poly-legal.
3.1 comix method
mix method is to disperse graphene directly in the coating, the mixture form can be a solution or melt mix. Generally using high-speed magnetic stirring process, shear emulsification process, ball grinding or sanding dispersion process, the use of shear force to make polymer chain adsorption into the graphene sheet layer, the main application of the substrate is polyurethane (PU), polystyrene (
PS)
), polymethyl acrylates (
PMMA
), polycarbonate (
PC
) and ethyl polyphenyl xylene (
PET
).
, however, the method has some defects. On the one hand, graphene has a high surface free energy, easy to self-reunion, on the other hand, graphene and polymers do not have chemical bond action, the relative position is not strong, so in the process of mixing, it is inevitable that graphene accumulation.
To solve this problem, before mixing, the researchers used non-common bond modification method, through hydrogen bonding, electrostectric action and π
-
π interaction, etc., to achieve the modifier (additives, stabilizers, etc.) pre-immersion of graphene, in order to improve the solubility of graphene and its compatible with coatings, and the method does not destroy the conjugate structure of graphene, can maintain its excellent performance.
e.g., in the process of graphene reduction, add water-soluble small molecules or aromatic polymers (e.g. pyridine, sulfonate-based polyphenylamine, polystyrene sodium sulfonate, polyethylene pyridoxine, etc.) as stabilizers, through the π
-
π interaction between stabilizers and graphene, the preparation of dispersed stable graphene nanochips.
3.2 Poly-legal
In recent years, researchers have used synthesis methods such as in-place polymerization, emulsion polymerization or controlled free-form polymerization to transfer active substances with specific functional groups to the surface of graphene by co-price bonding, realizing the cutting of graphene surface structure, improving its reaction activity and effectively improving the solubility, dispersion and compatibility of graphene inormeric nanofillers in the coating substate.
can ensure that polymer molecular chains are connected and wound to the surface of graphene, and there is a strong interface interaction between the two, which can effectively solve the problem of dispersion and compatibility of graphene in coatings. However, the requirements of poly-legal response are high, and it is difficult to realize the effective control of the position, proportion and thing rate of the official group in the reaction process, which is not suitable for large-scale application. Summary and Outlook
Water-based anti-corrosion coatings modified by graphene, mechanical properties, chemical stability and anti-corrosion properties have been improved, there have been a lot of relevant research work and patents published, the momentum of development is better. However, most of the application research of graphene in water-based coatings is laboratory results, the research is still in its infancy, there are still many difficult scientific problems and technical problems graphene water-based composite anti-corrosion coating application development boom continues to heat up, its further development can be expected.