Natural adhesives are commonly used adhesives in our lives. According to different sources, it can be divided into animal glue, vegetable glue and mineral glue. Animal glue includes skin glue, bone glue, shellac, casein glue, albumin glue, fish bladder glue, etc.; vegetable glue includes starch, dextrin, rosin, gum arabic, natural rubber, etc.; mineral glue includes mineral wax, asphalt Wait. Due to its abundant sources, low price and low toxicity, it is widely used in furniture, bookbinding, packaging and handicraft processing.

starch adhesive

After the starch adhesive enters the 21st century, the good environmental performance of the material will become a major feature of the new material. Starch is a non-toxic, harmless, low-cost, biodegradable and environmentally friendly natural renewable resource. It is widely used in various industries. Especially in recent years, the world’s adhesive industrial production technology is developing in the direction of energy saving, low cost, no amount of harm, high viscosity and no solvent.

As a kind of green environmental protection product, starch adhesive has attracted extensive attention and great attention in the adhesive industry. As far as the application and development of starch adhesives are concerned, the prospect of starch adhesives oxidized by corn starch is promising, and the research and application are the most.

Recently, starch as an adhesive is mainly used in paper and paper products, such as carton and carton sealing, labeling, plane gluing, sticking envelopes, multi-layer paper bag bonding, etc.

Several common starch adhesives are introduced below:

Oxidized starch adhesive

The gelatinizer prepared from the mixture of modified starch with low degree of polymerization containing aldehyde group and carboxyl group and water under the action of oxidant by heating or gelatinizing at room temperature is a loaded starch adhesive. After the starch is oxidized, oxidized starch with water solubility, wettability and adhesiveness is formed.

The amount of oxidant is small, the degree of oxidation is insufficient, the total amount of new functional groups generated by starch decreases, the viscosity of the adhesive increases, the initial viscosity decreases, the fluidity is poor. It has a great influence on the acidity, transparency and hydroxyl content of the adhesive.

With the prolongation of reaction time, the degree of oxidation increases, the content of carboxyl group increases, and the viscosity of the product decreases gradually, but the transparency is getting better and better.

Esterified starch adhesive

Esterified starch adhesives are non-degradable starch adhesives, which endow starch with new functional groups through the esterification reaction between the hydroxyl groups of starch molecules and other substances, thereby improving the performance of starch adhesives. Due to the partial cross-linking of esterified starch, so The viscosity is increased, the storage stability is better, the moisture-proof and anti-virus properties are improved, and the adhesive layer can withstand high and low and alternate action.

Grafted starch adhesive

Grafting of starch is to use physical and chemical methods to make starch molecular chain generate free radicals, and when encountering polymer monomers, a chain reaction is formed. A side chain composed of polymer monomers is generated on the starch main chain.

Taking advantage of the feature that both polyethylene and starch molecules have hydroxyl groups, hydrogen bonds can be formed between polyvinyl alcohol and starch molecules, which play the role of “grafting” between polyvinyl alcohol and starch molecules, so that the obtained starch adhesive has more Good adhesiveness, fluidity and anti-freezing properties.

Because starch adhesive is a natural polymer adhesive, it is low in price, non-toxic and tasteless, and has no pollution to the environment, so it has been widely researched and applied. Recently, starch adhesives are mainly used in paper, cotton fabrics, envelopes, labels, and corrugated cardboard.

Cellulose adhesive

Cellulose ether derivatives used as adhesives mainly include methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose and other ethyl cellulose (EC): is a A thermoplastic, water-insoluble, nonionic cellulose alkyl ether.

It has good chemical stability, strong alkali resistance, excellent electrical insulation and mechanical rheology, and has the characteristics of maintaining strength and flexibility at high and low temperatures. It is easily compatible with wax, resin, plasticizer, etc., as paper, rubber, leather, Adhesives for fabrics.

Methyl cellulose (CMC): ionic cellulose ether. In the textile industry, CMC is often used to replace high-quality starch as a sizing agent for fabrics. Textiles coated with CMC can increase the softness and greatly improve the printing and dyeing properties. ‘In the food industry, a variety of cream ice creams added with CMC have good shape stability, easy to color, and not easy to soften. As an adhesive, it is used to make tongs, paper boxes, paper bags, wallpaper and artificial wood.

Cellulose ester derivatives: mainly nitrocellulose and cellulose acetate. Nitrocellulose: Also known as cellulose nitrate, its nitrogen content is generally between 10% and 14% due to different degrees of esterification.

The high content is commonly known as fire cotton, which has been used in the manufacture of smokeless and colloidal gunpowder. The low content is commonly known as collodion. It is insoluble in water, but soluble in a mixed solvent of ethyl alcohol and ether, and the solution is collodion. Because the collodion solvent evaporates and forms a tough film, it is often used for bottle closures, wound protection and the first plastic celluloid in history.

If an appropriate amount of alkyd resin is added as a modifier and an appropriate amount of camphor is used as a toughening agent, it becomes a nitrocellulose adhesive, which is often used for bonding paper, cloth, leather, glass, metal and ceramics.

Cellulose acetate: Also known as cellulose acetate. In the presence of a sulfuric acid catalyst, cellulose is acetated with a mixture of acetic acid and ethanol, and then dilute acetic acid is added to hydrolyze the product to the desired degree of esterification.

Compared with nitrocellulose, cellulose acetate can be used to formulate solvent-based adhesives to bond plastic products such as glasses and toys. Compared with cellulose nitrate, it has excellent viscosity resistance and durability, but has poor acid resistance, moisture resistance and weather resistance.

protein glue

Protein adhesive is a kind of natural adhesive with protein-containing substances as the main raw material. Adhesives can be made from animal protein and vegetable protein. According to the protein used, it is divided into animal protein (fen glue, gelatin, complex protein glue, and albumin) and vegetable protein (bean gum, etc.). They generally have a high bond tension when dry and are used in furniture manufacturing and wood product production. However, its heat resistance and water resistance are poor, of which animal protein adhesives are more important.

Soy protein glue: Vegetable protein is not only an important food raw material, but also has a wide range of applications in non-food fields. Developed on soy protein adhesives, as early as 1923, Johnson applied for a patent for soy protein adhesives.

In 1930, the soybean protein phenolic resin board adhesive (DuPont Mass Division) was not widely used due to weak bonding strength and high production cost.

In recent decades, due to the expansion of the adhesive market, the acidity of global oil resources and environmental pollution have attracted attention, which made the adhesive industry reconsider new natural adhesives, resulting in soybean protein adhesives once again become a research hotspot.

Soybean adhesive is non-toxic, tasteless, easy to use, but has poor water resistance. Adding 0.1%~1.0% (mass) of cross-linking agents such as thiourea, carbon disulfide, tricarboxymethyl sulfide, etc. can improve water resistance, and make adhesives for wood bonding and plywood production.

Animal protein glues: Animal glues have been widely used in the furniture and wood processing industries. Commonly used products include furniture such as chairs, tables, cabinets, models, toys, sporting goods and deckers.

Newer liquid animal glues with a solids content of 50-60% include fast-cure and slow-cure types, which are used in the bonding of frame panels of hardboard cabinets, mobile home assembly, difficult laminates, and other less expensive thermal animals. Small and medium adhesive demand occasions for glue.

Animal glue is a basic type of adhesive used in adhesive tapes. These tapes can be used for common light duty retail bags as well as heavy duty tapes such as the sealing or packaging of solid fiber and corrugated boxes for shipments where fast mechanical operations and long lasting high bond strength are required.

At this time, the amount of bone glue is large, and the skin glue is often used alone or in combination with the bone glue. According to Coating Online, the adhesive used is generally formulated with a solid content of about 50%, and can be mixed with dextrin at 10% to 20% of the dry glue mass, as well as a small amount of wetting agent, plasticizer, gel inhibitor (when necessary).

Adhesive (60~63℃) is usually mixed with paint on the backing paper, and the deposition amount of solid is generally 25% of the mass of the paper base. Wet tape can be dried under tension with steam heated rollers or with adjustable air direct heaters.

In addition, animal glue applications include the manufacture of sandpaper and gauze abrasives, the sizing and coating of textiles and paper, and the binding of books and magazines.

Tannin adhesive

Tannin is an organic compound containing polyphenolic groups, widely present in the stem, bark, roots, leaves and fruits of plants. Mainly from wood processing bark scraps and plants with high tannin content. The tannin, formaldehyde and water are mixed and heated to obtain the tannin resin, then the curing agent and the filler are added, and the tannin adhesive is obtained by stirring evenly.

Tannin adhesive has good resistance to heat and humidity aging, and the performance of gluing wood is similar to that of phenolic adhesive. It is mainly used for gluing wood, etc.

lignin adhesive

Lignin is one of the main components of wood, and its content accounts for about 20-40% of wood, second only to cellulose. It is difficult to extract lignin directly from wood, and the main source is pulp waste liquid, which is extremely rich in resources.

Lignin is not used as an adhesive alone, but a phenolic resin polymer obtained by the action of the phenolic group of lignin and formaldehyde as an adhesive. In order to improve water resistance, it can be used in combination with ring-loaded isopropane epoxy isocyanate, stupid phenol, resorcinol and other compounds. Lignin adhesives are mainly used for bonding plywood and particleboard. However, its viscosity is high and the color is deep, and after improvement, the scope of application can be expanded.

Arabic gum

Gum arabic, also known as acacia gum, is an exudate from the wild locust family tree. Named because of its prolific production in Arab countries. Gum arabic is mainly composed of lower molecular weight polysaccharides and higher molecular weight acacia glycoproteins. Due to the good water solubility of gum arabic, formulation is very simple, requiring neither heat nor accelerators. Gum Arabic dries extremely quickly. It can be used for bonding optical lenses, gluing stamps, pasting trademark labels, bonding food packaging and printing and dyeing auxiliaries.

Inorganic adhesive

Adhesives formulated with inorganic substances, such as phosphates, phosphates, sulfates, boron salts, metal oxides, etc., are called inorganic adhesives. Its characteristics:

(1) High temperature resistance, can withstand 1000 ℃ or higher temperature:
(2) Good anti-aging properties:
(3) Small shrinkage
(4) Great brittleness. The elastic modulus is a foot order higher than that of organic adhesives:
(5) Water resistance, acid and alkali resistance are poor.

Do you know? Adhesives have other uses besides sticking.

Anti-corrosion: The steam pipes of ships are mostly covered with aluminum silicate and asbestos to achieve thermal insulation, but due to leakage or alternating cold and heat, condensate water is generated, which accumulates on the outer wall of the bottom steam pipes; and the steam pipes are exposed to high temperature for a long time, soluble salts The role of the outer wall corrosion is very serious.

To this end, water glass series adhesives can be used as coating materials on the bottom layer of aluminum silicate to form a coating with an enamel-like structure. In mechanical installation, components are often bolted. Long-term exposure to air for bolted devices can cause crevice corrosion. In the process of mechanical work, sometimes the bolts are loosened due to severe vibration.

In order to solve this problem, the connecting components can be bonded with inorganic adhesives in the mechanical installation, and then connected with bolts. This can not only play a role in reinforcement, but also play a role in anti-corrosion.

Biomedical: The composition of the material hydroxyapatite bioceramic is close to the inorganic component of human bone, has good biocompatibility, can form a strong chemical bond with bone, and is an ideal hard tissue replacement material.

However, the general elastic modulus of the prepared HA implants is high and the strength is low, and the activity is not ideal. Phosphate glass adhesive is selected, and the HA raw material powder is bonded together at a lower temperature than the traditional sintering temperature through the action of the adhesive, thereby reducing the elastic modulus and ensuring the material activity.

Cohesion Technologies Ltd. announced that they have developed a Coseal sealant that can be used for cardiac bonding and has been successfully used clinically. Through the comparative use of 21 cases of cardiac surgery in Europe, it was found that the use of Coseal surgery significantly reduced surgical adhesions compared with other methods. Subsequent preliminary clinical studies showed that Coseal sealant has great potential in cardiac, gynecological and abdominal surgery.

The application of adhesives in medicine is known as a new growth point in the adhesive industry. Structural glue composed of epoxy resin or unsaturated polyester.

In defense technology: Stealth submarines are one of the symbols of the modernization of naval equipment. An important method of submarine stealth is to lay sound-absorbing tiles on the submarine shell. The sound-absorbing tile is a kind of rubber with sound-absorbing properties.

In order to realize the firm combination of the muffler tile and the steel plate of the boat wall, it is necessary to rely on the adhesive. Used in the military field: tank maintenance, military boat assembly, military aircraft light bombers, missile warhead thermal protection layer bonding, preparation of camouflage materials, anti-terrorism and anti-terrorism.

Is it amazing? Don’t look at our little adhesive, there is a lot of knowledge in it.

The main physical and chemical properties of the adhesive

Operation time
Maximum time interval between adhesive mixing and pairing of parts to be bonded

Initial curing time
Time to Removable Strength Allows Adequate Strength for Handling Bonds, including Moving Parts from Fixtures

full cure time
Time required to achieve final mechanical properties after adhesive mixing

storage period
Under certain conditions, the adhesive can still maintain its handling properties and the storage time of the specified strength

bond strength
Under the action of external force, the stress required to make the interface between the adhesive and the adherend in the adhesive part break down or its vicinity

Shear strength
Shear strength refers to the shear force that the unit bonding surface can withstand when the bonding part is damaged, and its unit is expressed in MPa (N/mm2)

Uneven pull-off strength
The maximum load that the joint can bear when subjected to uneven pull-off force, because the load is mostly concentrated on two edges or one edge of the adhesive layer, and the force is per unit length rather than per unit area, and the unit is KN/m

Tensile Strength
Tensile strength, also known as uniform pull-off strength and positive tensile strength, refers to the tensile force per unit area when the adhesion is damaged by force, and the unit is expressed in MPa (N/mm2).

peel strength
Peel strength is the maximum load per unit width that can withstand when the bonded parts are separated under the specified peeling conditions, and its unit is expressed in KN/m