|The choice of curing agent in the formulation design of epoxy resin building str|
Building repair and reinforcement, represented by the repair and reinforcement of 137m municipal buildings after the damage caused by the SAN fernando earthquake in California in 1971, is a subject of
Building repair and reinforcement, represented by the repair and reinforcement of 137m municipal buildings after the damage caused by the SAN fernando earthquake in California in 1971, is a subject of concern to the industry, while the repair and reinforcement of roads, Bridges and buildings after the hanshin earthquake in the 2nd century exposed epoxy resin to us. In China, in the 1980s, taking the opportunity of the development of JGN building structural glue of dalian chemical institute of Chinese academy of sciences and the practical application of foreign building structural glue in China, the construction structural glue of China's environmental oxygen resin and its application have entered the practical stage. After 20~30 years of cultivation, epoxy resin building structural glue has become the main adhesive used for building repair and reinforcement. This paper briefly introduces the classification, composition, characteristics and application of building structural glue, especially discusses the choice of curing agent in formula design, and looks forward to the future of building structural glue according to the market demand and application.
According to its application, it can be divided into: reinforcement, anchoring and anchoring, repair and other use of building structural glue; According to the construction status, it can be divided into: perfusion coating and special building structure glue (such as medicine package type).
There are many kinds of epoxy resin building structural glue in China, such as adhesive steel reinforcement building structural glue, structural pouring glue, planting reinforcement anchoring glue, crack low-viscosity filling and sealing glue, and special adhesive for carbon fiber reinforcement.
Through analyze the classic building structure glue formula, we found that the epoxy resin structural adhesive to roughly the following several kinds of materials, epoxy resin and its complex system (such as E44, E51, E20 and AG80 composite system), toughening agent, curing agent, filler and other additives, and to meet the performance requirements of building structure glue, some still need to add some other components, such as diluent, coupling agent and solvent, the curing agent determines the performance of the whole the basic properties of the epoxy resin structural adhesive. Therefore, the choice of curing agent is the key to the performance of epoxy resin.
Epoxy resin building structural adhesive has the following characteristics: High bonding strength of the upper part; With uniform force on the adhesive part, it is difficult to generate stress concentration, and has good fatigue resistance, crack resistance and integrity. The crossing bonding technology is simple, easy to operate, quick construction, high efficiency, short construction period, low cost and good effect. The curing time of sound building structure is short, which is suitable for strengthening and strengthening of various emergency and emergency repair projects.
Epoxy resin structural adhesive and steel can be widely used in structural reinforcement, carbon fiber paste reinforcement and concrete crack injecting maintenance and reinforcement, wet drilling preparetions in baotou steel reinforcement and concrete reinforcing steel bar (or bolt), table surface and internal defects of concrete repair, new and old concrete interface and concrete surface coating protection, etc.
Selection of curing agent
The properties of epoxy resin determine the important role of curing agent. As the most important determinants of formulation, curing agent should be carefully considered in formulation design. Due to the different application environments of epoxy resin architectural glue, the following key factors should be the top priority in formula design: Environmental factors: hydrophobic; Requirements of mesh structure: bonding strength and heat resistance; Factors for the first time construction: appropriate viscosity, operability and safety; Economic factors.
1. Open ring activity of epoxy resin
The epoxy resin used in the construction structure glue is generally bisphenol A type epoxy resin, and the amine curing agent formulation system is adopted, which is mainly based on the construction structure glue application environment and other factors. The open ring reactive activity of epoxy resin is determined by the electron effect of its own structure including substituents. Among all kinds of epoxy resins, glycidyl base epoxy resins have higher reactivity, and the resins of lipopyclic epoxy resins have much lower reactivity. Some of them can be cured with aromatic amine, and most of them can only be cured with organic anhydride or BF3. Bisphenol A epoxy resin can be cured at room temperature with modified amine or low molecular polyamide in certain proportion. Usually, using polyamide curing bisphenol A epoxy resin, room temperature tensile shear strength of 20 mpa, but at low temperature (< 10 ℃) curing incomplete; At 20 ℃, also need a long curing period.
In some formulations, epoxides such as resorcinol formaldehyde resin and epoxidated phenolic resin are often added to improve crosslinking degree and high temperature performance. Some additives, such as double or single epoxy active diluents, are added to reduce the viscosity of the main epoxy resin, which has little effect on the high temperature properties of the epoxy resin. Some toughening agents, such as liquid polysulfide rubber, can be added to increase flexibility. Aromatic amine can compensate for the poor performance of low molecular polyamide curing system at high temperature.
It has been proved that in the reaction of bisphenol A epoxy resin with modified amine, if 25% resorcinol is added, the reaction speed can be increased 10 times. But this kind of material can affect high temperature strength and medium resistance. The hydroxyl group is directly introduced into the epoxy resin structure. For example, A hydroxymethyl group is introduced at the epoxy site of bisphenol A epoxy resin. The cyclic opening activity of this epoxy is 10 times higher than that of bisphenol A dihydrated glycerol ether epoxy. This can be used as room temperature, even in the epoxy - 5 ~ 10 ℃ low temperature fast curing epoxy structural adhesive. This provides a good idea for the design of epoxy resin building gels used at low temperature.
The reactivity of curing agent
At room temperature, it is not difficult to cure epoxy resin from a few seconds to a few minutes. However, due to the short time and poor performance of the curing system, it lacks practical value. The commonly used curing agent of epoxy resin at room temperature is fatty amine, modified fatty amine, etc. This kind of curing agent is often used to solidify epoxy resin for the reinforcement of DAMS and culverts in large-scale civil buildings and water conservancy projects. In addition, there are low molecular polyamide and epoxy resin as the base of the adhesive, in the building structure adhesive can be used to bond steel.
Due to climate change, all the year round brings complexity to room temperature curing, summer air temperature above 25 ℃ can solidification structure glue formula, outdoor average - 5 ~ 10 ℃ in winter the temperature of the following conditions may not be able to cure. Such as aliphatic amine and low molecular polyamide may at 20 ℃ about curing epoxy resin, the curing speed is slow, cannot satisfy the requirement of rapid solidification, nor in the low temperature curing epoxy resin; In addition, due to high water solubility, it cannot be used on high wet surfaces and under water. Some of the modified fatty amines have similar disadvantages. For example, the addition of diethylenetriamine and ethylene oxide will cause water-absorbing deterioration, the activity of cyanoethyldiethylenetriamine is low, and the curing speed is slower than that of diethylenetriamine.
In the process of renovation and repair of construction projects, the environment is sometimes not as suitable as people expect for the application of architectural glue. Water or humid environment is often encountered problems. Lipoamine curing agents are generally water-soluble and tend to cure slowly and with low strength in water or humid environment. Using low molecular polyamide as curing agent, the whitening in water is also more serious. All of these will have adverse effects on the strength and comprehensive performance of building structural glue. Phenolic modified amine epoxy resin curing agent due to the presence of benzene in the molecular structure
The existence of ring, its hydrophobicity has been better expressed.
High activity and hydrophobic curing agent
The curing agents that meet the above requirements are: phenolamine series, ketoimide series, aliphatic amine or aromatic amine and epoxide addition, polyamine and thiourea condensation, polymercaptan, etc.
4.1 phenolic aldehyde amine
The typical representative of this type of curing agent is T31 epoxy resin curing agent. Since the molecular structure contains hydroxyl and hydroxyl methyl, which promotes curing, curing speed is significantly faster than polyethylene polyamine. The addition of accelerant can obviously promote the curing of phenolic amine curing agent. In the domestic epoxy curing agent, this kind of products and the output of the proportion. In order to strengthen the comprehensive performance of building structural glue, phenolic amine curing agent is often mixed with other curing agents such as low molecular polyamide.
4.2 ketone imide
The polyamine and ketone reactions were used to prepare the enone condensate. This type of curing agent has a long life and is very suitable for use in a humid environment. Such curing agents are stable when no contact with water, and reversible reaction occurs when water is encountered. The imine bond is broken down and phenolamine curing epoxy resin is released. Another way is by direct reaction of polyethylene polyamine with ketamine, which can also cure epoxy resins in the same way.
4.3 addition of fatty amines or aromatic amines to epoxides
It is shown that such curing agents also have low temperature curing performance under the action of promoters. Such as DDM and isooctyl glycidyl ether of reaction product at 0 ℃ can be cured epoxy resin, and it has excellent dielectric resistance; When used with polyamide, a kind of building structure adhesive with good performance can be obtained.
4.4 polyamine and thiourea condensate
Such curing agents are characterized by their fastness. It is rarely used alone in the market, and is generally used as an accelerator of modified amine curing agent.
4.5 gather mercaptan
This kind of curing agent is characterized by low temperature and rapid curing. Classical approach is to gather mercaptan promoter and tertiary amine as curing agent, such as coordination, even using bisphenol A epoxy resin under - 20 ~ 0 ℃ temperature can also be cured. However, the data showed that the properties of polymercaptan and tertiary amine promoters alone were not satisfactory. The new technology shows that the combination of the modified amine and the system can achieve good results.
4.6 the other
As mentioned above, the use of polyamide alone has some adverse effects on the construction of structural adhesives, but it can be used in conjunction with other rapid and hydrophobic curing agents. The compound technology of curing agent has been almost universally applied in today's building structural glue, such as 650 polyamide and 810 underwater epoxy curing agent, 650 and 593, 810 and polymercaptan, etc. In future practice, a variety of different curing agent combinations will emerge to obtain better performance.
Looking forward to
Building structural adhesives have been developing rapidly in recent years, and their application fields are becoming more and more extensive. With the further development of the application field of architectural structural adhesives and the gradual maturity of the industry standards, many more demanding adhesives still need further development and research. As a high-performance curing agent directly determining the performance of adhesives, the development work is also placed in front of the practitioners. It is necessary for the following types of curing agent and great efforts in research and application development: (1) low temperature type of curing agent, the northern region winter construction difficulties, need to be in even lower - 15 ℃ temperatures construction use, for 10 days completely curing, comprehensive performance comprehensively. The problem remains. (2) temperature curing high-temperature curing agent, curing agent can be room temperature curing, can be in high temperature (150 ℃) under the conditions of use for a long time. How to improve the temperature resistance and strength needs further efforts. The high strength solidification agent requires shear strength greater than 30MPa and tensile strength greater than 50MPa, which can make some fields that cannot be strengthened realize bonding reinforcement. It is necessary to further reduce production cost and expand application.
Environmental curing agent is a new field of development of curing agent. The water-based epoxy adhesive with low toxicity and low VOC has good permeability to concrete and can solidify on moist surface. The viscosity can be adjusted during construction, but the curing strength of water-based curing agent needs to be further improved. In addition, the single component latent curing agent is easy to use, environmentally friendly and energy-saving, and contains moisture-sensitive latent curing agent, which has achieved good results in the field of precast concrete components and civil building of the wet working surface. However, it still needs to further improve its water-resistance, damp-heat resistance and toughness.
The rapid development of building structural glue also brings a good opportunity for the development of epoxy stabilizer. Energy saving, efficiency and environmental protection should be the first principles for our research and development.
From the perspective of application, the application of epoxy resin architectural glue has been expanded to many fields. Researchers should design and select architectural structural glue according to the actual situation on the site, so as to have a clear aim in repairing and strengthening the project, making it foolproof and responsible for people's life and property. In the future design and selection of building gelling glue, we should focus on solving the problem of moisture and heat resistance of gelling. From the construction quality problem that appears in current market, solve this problem already extremely urgent, this waits for expert of course of study and business to treat seriously.
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