Brief analysis of adhesive types and main physical and chemical performance indexes

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 swim bladder glue, etc.
; vegetable glue includes starch, dextrin, rosin, gum arabic, natural rubber, etc.
; mineral glue includes mineral wax, asphalt Wait for com" href="http://">coating online coatingol.
com .
Because of its abundant sources, low price and low toxicity, it is widely used in furniture, binding, packaging and handicraft processing.

Starch adhesive

After 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 natural and renewable resource that is non-toxic, harmless, inexpensive, biodegradable, and environmentally friendly.
The application in various industries is becoming more and more extensive.
Especially in recent years, the world's adhesive industrial production technology is developing in the direction of energy saving, low cost, harmlessness, high viscosity and solvent-free.

As a kind of green and environmentally friendly products, starch adhesive has attracted wide attention and great attention from the adhesive industry.

As far as the application and development of starch adhesives are concerned, the prospects of using corn starch oxidized starch adhesives are promising, with the most research applications.

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

Several common starch adhesives are introduced below:

Oxidized starch adhesive

The secretion agent made by the mixture of modified starch with low degree of polymerization containing aldehyde group and carboxyl group and water under the action of oxidant is heated and gelatinized or gelatinized at room temperature is a supported starch adhesive.

After the starch is oxidized, an oxidized starch with water solubility, wettability and bonding properties is formed.
The amount of oxidant is small, the degree of oxidation is not enough, the total amount of new functional groups generated by starch is reduced, the viscosity of the adhesive is increased, the initial viscosity is reduced, the fluidity is poor, and the amount is excessive, which causes the viscosity and initial viscosity of the adhesive to decrease.
Oxidation reaction time It has a great influence on the acidity, transparency and hydroxyl content of the adhesive.

Esterified starch adhesive

Esterified starch adhesives are non-degradable starch adhesives.

It imparts new functional groups to the starch through the esterification reaction between the hydroxyl groups of the starch molecule and other substances, thereby improving the performance of the starch adhesive.
Because the esterified starch is partially cross-linked, The viscosity is increased, the storage stability is better, the moisture-proof and anti-toxic properties are improved, and the glue layer can withstand high and low and alternate effects.

Grafted starch adhesive

The grafting of starch is to use physical and chemical methods to produce white from the starch molecular chain.

When encountering polymer monomers, a chain reaction is formed.
A side chain composed of polymer monomers is produced on the main chain of starch.

Cellulose Adhesive

Cellulose ether derivatives The cellulose ether derivatives used as adhesives mainly include methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose and other ethyl cellulose (EC): one A thermoplastic, non-water-soluble, non-ionic cellulose alkyl ether.

It has good chemical stability, strong alkali resistance, excellent electrical insulation and mechanical rheology.
It has the characteristics of maintaining strength and flexibility at high and low temperatures.

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.

Cellulose ester derivatives: mainly nitrocellulose and cellulose acetate.

Nitrocellulose: also known as cellulose nitrate.

Ester cellulose: also known as cellulose acetate.

In the presence of a sulfuric acid catalyst, the cellulose is acetic acidized with a mixture of acetic acid and ethanol, and then diluted acetic acid is added to hydrolyze the product to the desired degree of esterification.
Cellulose ester acid can be used to formulate solvent-based adhesives.
Compared with nitrocellulose, plastic products such as glasses and toys have excellent adhesion resistance and durability, but they have poor acid resistance, moisture resistance and weather resistance.

Protein adhesive

Protein adhesives are a type of natural adhesives with protein-containing materials as the main raw material.
Both animal protein and vegetable protein can be used to make adhesives.
According to the protein used, it can be divided into animal protein (fen glue, gelatin, complex protein glue, and albumin) and vegetable protein (soy gum, etc.
).
They generally have a higher bonding tension when dry, and are used in furniture manufacturing and wood product production.
However, its heat resistance and water resistance are poor, and animal protein adhesives are more important.

Soy protein glue: Plant protein is not only an important food raw material, but also has a wide range of applications in non-food fields.
With regard to soy protein adhesives, as early as 1923, Johnson applied for a patent for soy protein adhesives.
In 1930, the soy protein phenolic resin wood board adhesive (DuPont Measuring Division) failed to be used in large quantities due to its weak bonding strength and high production cost.
In recent decades, due to the expansion of the adhesive market, the acidity of global petroleum resources and environmental pollution have attracted attention, which has caused the adhesive industry to reconsider new natural adhesives, and soy protein adhesives have 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 prepare adhesives for wood bonding and plywood production.

Animal protein glue: Animal glue has been widely used in the furniture and wood processing industries.
Commonly used products include chairs, tables, cabinets and other furniture, models, toys, sporting goods, and layers.
The newer liquid animal glues with a solid content of 50%-60% include fast-curing and slow-curing types.
They are bonded to the frame board of the cabinet hard board, movable home assembly, difficult to laminate and other less suitable thermal animals.
Small and medium adhesive requirements for glue liquid.

Animal glue is a basic type of adhesive used in adhesive tapes.
These tapes can be used for common light-weight retail packaging bags, as well as heavy-duty tapes, such as the sealing or packaging of solid fibers and corrugated boxes for shipping goods.
Such occasions require rapid mechanical operation and long-lasting high bonding strength.
At this time, the amount of bone glue is large, and skin glue is often used alone or in combination with bone glue.
According to Coating Online, the adhesive used is generally formulated with a solid content of about 50%, and can be blended with dextrin at 10% to 20% of the dry glue quality, as well as a small amount of wetting agent, plasticizer, and gel inhibitor (when necessary).
Adhesive (60~63℃) is usually mixed with paint on the backing paper, and the solid deposit is generally 25% of the paper base mass.
The wet tape can be dried with a steam heated roller under tension, or can be dried with a direct heater with adjustable air.

In addition, the application of animal glue also includes 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 polyphenol groups, which is widely present in the stems, barks, roots, leaves and fruits of plants.
It is mainly derived from wood processing leftovers from bark and plants with high tannin content.
Tannin, formaldehyde and water are mixed, heated to prepare tannin resin, then curing agent and filler are added, and the tannin adhesive is obtained by stirring evenly.
Tannin adhesives have good resistance to damp and heat aging.
The performance of bonding wood is similar to that of phenolic adhesives.
It is mainly used for bonding wood.

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.
Lignin is difficult to extract 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 base of lignin and formaldehyde as an adhesive.
In order to improve water resistance, it can be used in combination with ring-loaded isopropanol epoxy isocyanate, stupid phenol, resorcinol and other compounds.
Lignin adhesives are mainly used for bonding plywood and particleboard.
But its high viscosity, deep color, and after improvement, the scope of application can be expanded.

Arabic adhesive

Gum arabic, also known as acacia gum, is a kind of gum fluid from wild Robiniaceae trees.
It is named because it is prolific in Arab countries.
Gum arabic is mainly composed of polysaccharides with lower molecular weight and arabinose glycoproteins with higher molecular weight.
Due to the good water solubility of gum arabic, the preparation is very simple, neither heating nor accelerator is needed.
Gum Arabic liquid dries extremely fast.
It can be used for optical lens bonding, stamp gluing, trademark label pasting, food packaging bonding 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 temperatures of 1000°C or higher:

(2) Good aging resistance:

(3) Small shrinkage

(4) High brittleness.
The modulus of elasticity is several orders higher than that of organic adhesives:

(5) Poor water resistance, acid and alkali resistance.

Do you all know? In addition to the adhesive effect, adhesives have other uses.

Anti-corrosion: The steam pipes of ships are mostly coated with aluminum silicate and asbestos to achieve the purpose of insulation.
However, due to leakage or alternating cold and heat, condensate water is collected on the outer wall of the bottom steam pipe; and the steam pipe is exposed to high temperature and soluble salt The corrosion of the outer wall is very serious.
For this reason, water glass series adhesive can be used as coating material on the aluminum silicate bottom layer to form a coating of enamel-like structure.
Its thermal expansion coefficient is similar to that of the pipe material, and the heat should be small and will not be cracked.
In mechanical installation, components are often fixed by bolts.
Devices fixed by bolts are exposed to the air for a long time, and crevice corrosion will occur.
In the process of mechanical work, the bolts are sometimes loosened due to severe vibration.
In order to solve this problem, the connecting members can be bonded with inorganic adhesives in the mechanical installation, and then connected with bolts.
This can not only play the role of reinforcement, but also play a role in anti-corrosion.

Biomedicine: The composition of the material hydroxyapatite bioceramics is close to the inorganic components of human bone.
It has good biocompatibility and can form a firm chemical bond with bone.
It is an ideal hard tissue substitute material.
However, the general elastic modulus of the prepared HA implant is high, but 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 activity of the material.
Cohesion Technology Co.
, Ltd.
announced that they have developed a Coseal sealant that can be used for heart bonding, and it has been successfully used clinically.
Through the comparative use of 21 heart surgeries in Europe, it was found that the use of Coseal surgery significantly reduced surgical adhesions than other methods.
Subsequent pre-clinical studies have shown that Coseal sealant has great development potential in heart, gynecological and abdominal surgery.
The application of adhesives in medicine is hailed as a new growth point in the adhesive industry.
Structural glue composed of epoxy resin or unsaturated polyester.

In national defense technology: Stealth submarine is one of the symbols of the modernization of naval equipment.
An important method for submarine stealth is to lay anechoic tiles on the submarine hull.
Acoustic tile is a kind of rubber with sound absorption properties.
In order to achieve a firm combination of anechoic tile and boat wall steel plate, it is necessary to rely on adhesive.
Used in the military field: tank maintenance, military boat assembly, used in 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 adhesives, they are very knowledgeable.

The main physical and chemical performance indicators of the adhesive

Operating time

The maximum time interval between the mixing of the adhesive and the pairing of the parts to be bonded

Initial curing time

Time to reach the removable strength, allowing the processing of sufficient strength of the bonded parts, including moving the parts from the fixture

Full curing time

The time required to obtain the final mechanical properties after the adhesive is mixed

Shelf life

Under certain conditions, the adhesive can still maintain its operating performance and the specified strength for storage time

Bonding strength

Under the action of external force, the stress required to cause damage to the interface between the adhesive and the adherend or the vicinity thereof

Shear strength

Shear strength refers to the shear force that the unit bonding surface can withstand when the bonding part is broken, 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 the two edges or one edge of the adhesive layer, and the force is per unit length rather than 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 viscous force is broken, and the unit is expressed in MPa (N/mm2)

Peel strength

Peel strength is the maximum load that can be borne by the unit width when the adhesive is separated under specified peeling conditions, and its unit is expressed in KN/m