Research and Application of Adhesives (I)

0 Introduction <br>Adhesives are an old and young material. As early as thousands of years ago, human ancestors had begun to use adhesives. According to research [1], phosphate inorganic adhesives have been used in the manufacture of large painted bronze horses unearthed in the Qin Dynasty Museum. The white lumps of the silver joints of the parts of the earth were found to be the same as those of modern phosphate adhesives. The adhesive process was also used in the ink-making process described in Chapter 91 of the "Qi Min Yao Shu" written by Jiasi Yu of the Northern Wei Dynasty. At the beginning of the last century, the invention of synthetic phenolic resin created a modern history of adhesives. At present, compared with the output of the three major synthetic polymer materials, adhesives only accounted for the fifth place, but the annual growth rate ranked first. China's adhesives started in the 1950s. After entering the 1990s, the adhesives industry has grown by leaps and bounds. Today, adhesives have penetrated into various fields of industry, agriculture, transportation, medicine, national defense, and people's daily life. They have played an ever-increasing role in the national economy. The adhesive industry has developed into an independent and newly emerging sector. It is estimated that by 2005, the consumption of synthetic adhesives in China will reach 2.65 million tons, with an average annual growth rate exceeding 8%.

1 The type of adhesive According to incomplete statistics, more than 6,000 types of adhesive products have been available so far. Due to their wide variety and different composition, there is currently no unified classification method. According to different curing methods, the adhesive can be divided into melt-curing, volatile-curing, water-curing, and reaction-curing.

1.1 Melt-curing type melt-curing adhesive refers to a type of adhesive in which the adhesive is adhered in a molten state. Among them, EVA (polyethylene-vinyl acetate) hot-melt adhesives such as solder, silver solder, and low-melting-point metals such as rods, granules, and films are widely used.

1.2 Volatilely Cured Volatile Curable Adhesives are adhesives that naturally evaporate moisture or other solvents in the air and cure to form an adhesive. Such as water glass series adhesives, neoprene and so on.

1.3 The water-curable water-curable adhesive refers to a type of substance that undergoes a chemical reaction and solidifies and coagulates when it encounters water. Among them, plaster and various types of cement are representative.

1.4 Reaction Curing The reaction curing adhesive is a type of adhesive that is cured by chemical reaction of a material other than water and a binder. Phosphate adhesives, dental cements, alpha cyanoacrylate cyanoacrylates, acrylic diester anaerobic adhesives, etc., fall into this category.

2 Adhesive Features
2.1 Temperature resistance Temperature resistance is one of the fine characteristics of inorganic adhesives. Inorganic high-temperature adhesives are generally used in the range of 1500 to 1750°C, while copper phosphate adhesives have a wider temperature range and can be used in the range of 180 to 1400°C. However, the main aggregates used for inorganic high-temperature adhesives are zircon sand and fire-resistant earth. The price of zircon sand is relatively high, which is mainly due to imports. Fire-resistant earth is to be obtained at the expense of the land, which is costly. Therefore, it is imperative to look for inexpensive and readily available products to replace traditional aggregates to reduce production costs. Some organic adhesives have also achieved high temperature resistance through modification. For example, B4C modified phenolic resin adhesive can withstand high temperatures of 1500°C. The market demand for heat-resistant adhesives is constantly increasing, and thus this type of adhesive has a broad prospect for development.

2.2 Low pollution As the global environment continues to deteriorate, people gradually start using some environmentally friendly products. Although the adhesive is not a huge chemical product, the harm to the environment can not be ignored. Those non-environmental adhesives will gradually be abandoned. Polyethylene formaldehyde adhesive (commonly known as "107 glue") is harmful to human health because it contains free formaldehyde. It has long been banned in developed countries, but in China, due to its low price, there is still a considerable market share. However, its use has gradually decreased and will be completely eliminated in the near future. How to make a non-environmental adhesive into an environmentally friendly adhesive through modification is imperative. Japanese DJK company has successfully developed a formaldehyde-free adhesive that can replace plywood manufacturing. DJK pointed out that common urea formaldehyde and melamine adhesives contain formaldehyde that can cause allergic reactions in humans, and DJK claims that the strength, water resistance, and cost of the adhesive are similar to those of melamine adhesives. With the increasing demand for environmental protection, more and more people are now working on the development of biodegradable adhesives. Biodegradation of polymers is accomplished by hydrolysis and oxidation. Most of the degradable polymers contain degradable groups in their backbone, such as amine groups, hydroxyl groups, urea groups, and the like. Sharak et al. reacted with dihydroxy and ether to synthesize methylol-containing polyesters as substrates to produce biodegradable adhesives. They also used hydroxyl-containing butyrate, valerate, cellulose, and starch esters as substrates. Sucrose esters are used as viscosifiers to produce biodegradable or hydrolyzed adhesives. In addition, Kauffman et al. used starch or sulfonated esters as the base and added polar waxes to produce polar, water-sensitive adhesives that can be hydrolyzed by water and reduced or eliminated during disposal. Environmental pollution

2.3 Bonding Non-destructive materials are mainly connected by bolting, riveting, welding, and bonding. Although bolting can be used to achieve quick connection, the materials are destroyed due to emptying or local heating of material components. , and in use can not avoid stress concentration. In contrast, the bonding technology is a non-destructive connection technology, and increases the load capacity and prolongs the service life because of the overall load on the bonding interface.

2.4 Lightweight adhesives have a low density, mostly between 0.9 and 2, which is about 20% to 25% of the density of metal or inorganic materials, and thus can significantly reduce the weight of the attached material. This has the important value of reducing weight and saving energy in aerospace, aviation, missiles, and even automobiles and navigation.

3 Application of Adhesives <br>Adhesives In addition to being used in conventional bonding, there are some new, clever applications.

3.1 Anti-corrosion At present, the ship’s steam pipe uses aluminum silicate and rock wool to achieve heat insulation. However, condensation or leakage occurs due to leaks or hot or cold heat, which collects on the outer wall of the steam pipe at the bottom. The steam pipe is subjected to high temperatures for a long time. The effect of soluble salts, external wall corrosion is very serious. For this purpose, a series of water silicate glass adhesives can be used as the coating material for the aluminum silicate bottom layer to form a coating of the enamel-like structure. The coefficient of thermal expansion is similar to that of the pipes, and the thermal stress is small and will not crack. In mechanical installations, components are often bolted. The bolted device is exposed to air for a long period of time and crevice corrosion occurs. During mechanical work, bolts are sometimes loosened due to violent vibrations. To solve this problem, the connecting members can be first bonded with an inorganic adhesive in a mechanical installation and then bolted. This can not only play a role in strengthening, but also play a role in anti-corrosion.

3.2 Used as biomedical material Hydroxyapatite Ca10(PO4)6(OH)2(abbreviated as HA) bioceramic composition close to the inorganic components of human bone, has good biocompatibility, and can form a strong bond with bone Chemical bonding is an ideal hard tissue replacement material. However, currently prepared HA implants have high general elastic modulus and low strength, and their activity is not ideal. Phosphate glass adhesives were used to bond the HA raw material powder below the traditional sintering temperature through the action of the adhesive, thereby reducing the elastic modulus and ensuring the material activity. Cohesion Technology Co., Ltd. recently announced that they have developed a Coseal sealant that can be used for heart bonding and have been successfully used in the clinic. In Europe, 21 cases of cardiac surgery were compared and found that the use of Coseal surgical sealant significantly reduced surgical adhesions compared to other methods. Subsequent preclinical studies showed that Coseal sealant has a tremendous development in heart, gynecology and abdominal surgery. Potential [13]. The application of adhesives in medicine is praised as a new growth point for the adhesive industry.