Plant adhesive

Plant adhesives are mainly classified into starch glue, dextrin glue, soybean gum, gum arabic, rosin gum, carboxymethyl cellulose glue, lignin glue and the like.

First, starch glue

Starch gum is based on starch. The main source of starch is the roots and seeds of plants. Its molecular formula is (C 6 H 10 O 5 ), which is white, odorless and tasteless powdery or granular solid. Its properties and composition are shown in Table 1.

Table 1 Properties and composition of starch

Traits and composition corn starch Rice starch wheat starch Cassava starch Sweet potato starch Potato starch
shape polyhedron polyhedron Lens shape Bell Bell Oval
Diameter (um) 6-21 2-8 5-40 4-35 2-40 5-100
Average diameter (um) 16 4 20 17 18 50
Gelatinization temperature (°C) 77-78 75 75 67-78 75 65-66
composition(%) Moisture 13 13 13 12 12 18
protein 0.35 0.07 0.38 0.02 0.1 0
fat 0.04 0.06 0.07 0.1 0.1 0.05
Ash 0.08 0.1 0.17 0.16 0.3 0.6
Phosphorus pentoxide 0.05 0.02 0.15 0.02 0 0.18
Amylose 25 19 30 17 19 25

The starch itself is insoluble in water. When the starch is suspended in water, it expands as the heating temperature increases, and then ruptures and gelatinizes. The aqueous solution containing starch only produces turbidity at the initial stage of heating, and only becomes a viscous translucent liquid starch paste when the gelatinization temperature is reached.

The viscosity of the starch paste becomes smaller as the temperature increases, and the hardness and gel strength increase with cooling. In addition, the viscosity of the starch paste is also affected by the concentration, and the concentration increases accordingly.

The method for preparing starch glue includes heating method, alkali cooking method, amylase method and cold method, among which heating method and alkali cooking method are mainly used. The heating method is to add starch to water, stir evenly, and then stir to about 90 ° C while heating, and then keep it for 10-15 minutes, the ratio of starch to water is usually 10-15:85-90. The alkali cooking method is to add 10-15% starch water mixture, gradually add 5-10 parts of 10% sodium hydroxide solution under stirring, and gelatinize at room temperature to obtain starch glue.

In order to improve the performance of starch gel, in the actual preparation, various additives can be added according to different requirements, and the varieties and effects thereof are shown in Table 2.

Table 2 varieties and effects of starch additives
Additives Variety Dosage (%) effect
Crosslinker Borax 0.1-0.5 Improve bonding strength and water resistance
Same active agent Sodium fatty acid 0.5-1 Improve infiltration
Plasticizer Glycerin, ethylene glycol, calcium chloride 1-5 Improve toughness
Thinner Urea, boric acid 3-10 Reduce viscosity
Defoamer Ethanol, ether, silicone 0.1-0.5 Eliminate foam
preservative Phenol, boric acid 0.5-5 Improve mold resistance

In order to further improve the performance of the starch gel, the three hydroxyl groups at the 2, 3, and 6 positions in the starch molecule can be made to have a large chemical reactivity, and can be substituted with different chemical groups, as long as there is a low degree in the starch molecule. The substitution of starch gel can greatly improve the performance of the starch glue, not only the starch glue can maintain the original bonding strength, but also can increase the stability of the glue and improve the use value. The main modified starch gels are as follows:

1. Oxidized starch gel oxidized starch gel is also called chlorinated starch gel. This is a starch gel obtained by treating starch with hypochlorite to form a starch derivative, and then using it as a base system. Different derivatives can be obtained depending on the treatment method.

2. Starch Acetate Glue This is a starch gel obtained by heating starch and acetic acid in an acidic medium to obtain starch acetate, which is obtained as a base system, which has the characteristics of rapid curing and single component.

3, carboxy starch gel This is the starch in the alkaline medium with epichlorohydrin as a cross-linking agent to obtain a graft polymer, also known as carboxyl starch, and then as a base of the starch gel, which has High bonding strength.

4. Water-resistant starch glue This is a starch glue with good water resistance by reacting a hydrophilic group in a starch molecule with N-methylol acrylamide or polyethyleneimine to form a partially crosslinked structure. . In addition, the grafting reaction with the acrylic compound can also improve the stability of the glue.


<br> dextrin dextrin gum was incomplete hydrolysis of starch having the formula (C 6 H 10 O 5) .H 2 O. It is a yellow or white amorphous powder that dissolves in cold water to form a viscous liquid with a high bond strength. In fact, dextrin is an intermediate in the conversion of starch to glucose.

The dextrin made of dextrin as a matrix has higher bonding strength than starch gel, better water resistance and simpler operation process, and is usually used for rapid bonding at room temperature.

The dextrin can be obtained by treating the starch with acid or heat at a high temperature, or can form an incomplete hydrolysis product by the action of an amylase. At present, direct calcination and acid calcination are mainly used.

1. Direct calcination method This is a method in which starch is first dried and then calcined by heating at a temperature of 190 to 230 °C. The resulting dextrin is slightly brownish.

2. Acid calcination method This is a method for promoting decomposition of starch by acid. The starch is first dried, then nitric acid and sulfuric acid (100 kg of starch is added to 200 ml of concentrated nitric acid and 300 ml of concentrated sulfuric acid, and the concentrated acid is diluted with 1001 of water in advance), uniformly mixed, and calcined by heating at 110-140 ° C.

When preparing a dextrin, it is usually necessary to add some additives to improve the performance. For example, adding an alkaline inorganic salt (such as borax, etc.), increasing the initial bonding strength, adding an acidic salt (such as sodium sulfite, etc.), removing the odor, adding an organic acid salt (such as sodium tartrate and sodium butyrate) to increase the toughness; Organic acids (such as tartaric acid, oxalic acid, butyric acid, etc.) improve the bonding strength.

Dextrin is mainly used for the bonding of wood, paper, leather, fabrics, etc. It can also be used as a sizing agent for fabrics and papers, as an excipient for pharmaceuticals, and for the preparation of inks.

Bean gum bean gum is mainly made from soybeans and is a vegetable protein glue. The soybean powder is extracted with a solvent, degreased, and dissolved in an alkali solution to obtain a crude protein, which is then refined into a protein. The soy gum is prepared by mixing protamine with water to form a certain concentration of glue.

At present, most of the raw materials used for extracting soy protein are the feet of soy products such as fans and tofu. Since these lower feet contain more moisture and are easily corroded by mold, it is possible to directly dry the waste or extract the soy protein. Post-drying method.

In the preparation of soy protein, the amount of alkali-dissolved calcium hydroxide has a significant effect on the properties of the glue. As shown in Table 3, too little or too much is used to obtain a good bonding effect.
Table III Effect of Calcium Hydroxide Amount on Adhesive Strength of Bean Gum
Calcium hydroxide dosage (%) Tensile strength (MPa) Impact situation
2.5 1.8 Not mushy
5 5.3 Not mushy
10 7.7 Paste, not frozen
20 7.7 Paste, not frozen
40 8.5 Paste, not frozen
60 6.3 Frozen
100 5.0 Solid
Under normal circumstances, the soy protein can be used together with water to form a glue, but in order to adjust the viscosity and prolong the use time of the glue, an appropriate amount of sodium chloride, copper chloride, sodium alginate, silicic acid can be added. Sodium, pectin and other additives. Table 4 lists typical formulations of bean gum.
Table 4 Typical Formulation of Bean Gum
Component Formula 1 Formula 2 Formula 3
Soy flour 100 100
Soy protein dry powder 100
water 300 300 700
Lime powder (lime: water = 1:4) 20 15 60
Sodium hydroxide 20 15 20
Sodium silicate (40 Baume) 40 20 48
Soybean gum is a non-water resistant adhesive, and the cured rubber layer cannot be wetted or soaked. In order to improve the water resistance, a small amount (usually about 3%) of sodium dodecyl phenyl ether sulfonate may be added to the glue. In addition, thiourea, potassium sulfonate, copper salt, low molecular epoxy resin, dimethylol urea, hexamethylenetetramine, etc. may also be added, and good effects can be obtained.

Soy gum is mainly used as an adhesive for the production of plywood and particleboard. However, due to its poor water resistance and the use of grain as the main raw material, it has been limited in use, and has been used less recently in recent years, and is mainly used as an additive for urea-formaldehyde resin and phenolic resin. The bonding strength of urea-formaldehyde resin glue using soybean gum as an extender is shown in Table 5.

Table 5: Adhesive strength of urea-formaldehyde resin glue as a bulking agent
Component 1 2 3 4 5 6 7 8
Urea-formaldehyde resin 100 100 100 100 100 100 100 100
Curing agent 20% ammonium chloride 5 7 9 12 0 0 0 0
10% hydrochloric acid 0 1 2 4 25 50 50 50
Soy flour 0 10 20 35 100 200 400 600
water 0 30 60 105 275 550 1150 1740
Bean gum ratio (%) - 40 80 140 375 750 1550 2340
Cold pressing bonding strength (MPa) birch normal 2.7 2.6 1.9 1.9 1.7 1.0 0.8
Water resistant 2.7 1.7 1.3 1.2 0.9 0.7 0.5
Liu Anmu normal 1.9 1.7 1.7 1.7 1.6 0.9 0.6 0.5
Water resistant 1.8 1.6 1.4 1.3 0.5
Hot pressing bonding strength (MPa) birch normal 3.6 3.0 3.1 2.9 2.5 1.9 1.3 0.8
Water resistant 3.1 2.0 1.8 1.6 1.2 1.0 0.5 0.3
Liu Anmu normal 2.3 1.9 1.8 1.8 1.8 1.5 1.0 0.9
Water resistant 2.0 1.8 1.6 1.3 1.5 0.9 0.2 0.1
Gum arabic

Acacia gum is a general term for gums obtained from gum trees grown in Arabia, Africa and Australia. It is a white to dark red hard and brittle solid with a density of 1.3-1.4 g/cm 3 . It is soluble in glycerin and water and insoluble in organic solvents. It is a long-chain polymer formed by conversion of potassium, calcium, magnesium salts and the like of arginic acid (C 10 H 18 O 9 ) to galactose and glucuronic acid.

An aqueous solution of gum arabic can form a strong film after drying, but is more brittle. In order to improve the brittleness and improve the toughness, an appropriate amount of ethylene glycol, glycerin, polyethylene glycol or the like may be added as a plasticizer, but the drying speed of the glue may be affected.

Acacia gum is used as an adhesive and can be formulated separately with water. It can also be formulated by adding plasticizer, starch, gum tragacanth, thymol and the like. Generally, it is not necessary to heat when preparing, as long as it is stirred at room temperature until it is evenly transparent.

Acacia gum is mainly used for bonding optical lenses, food packaging, etc., as a sizing material for stamps and trademark labels, as an outer film material for latent curing adhesive microcapsules, and as an excipient for drugs.

Rosin gum rosin is based on rosin. Rosin is obtained from the rosin resin (also known as raw rosin or turpentine) secreted by pine trees by distillation to remove turpentine. It is a transparent, light yellow to dark brown glassy brittle substance with a special odor. Do not dissolve in water, soluble in alcohol, ether, acetone, benzene, carbon disulfide, turpentine, oil and alkali solution. The main components are unsaturated compounds such as rosin acid and rosin anhydride, usually containing 80-90% of rosin acid. Has greater activity. Its properties vary depending on color, acidity, softening point, and transparency.

In general, the lighter the color, the better the performance; the greater the rosin acid content, the greater the acidity and the higher the softening point.

The rosin gum can be obtained by directly dissolving rosin in an organic solvent; it can also be made into a water-soluble gum by alkalization.

1. Solvent-type rosin gum It is prepared by directly preparing rosin and a solvent, and the solvent capable of dissolving rosin can be used, and can be appropriately adjusted according to the type and solid content of the solvent. For example, as a rosin agent for bonding metal foil wrapping paper, a solvent having a low boiling point (such as diethyl ether, acetone, benzene, etc.) can be used; for use as a rosin gum for preparing fly paper, etc., a solvent having a high boiling point (such as hydrazine) can be used. Sesame oil, etc.). When preparing, it is generally stirred under heating.

2. Water-soluble rosin gum which is obtained by alkalizing rosin from an alkali solution. The method of alkalization includes adding rosin directly to the lye, adding an alkali solution to the molten rosin, and adding an emulsifier in excess to the base. Water-soluble rosin gum has higher bonding strength and low cost, and is suitable for a large number of applications.

Rosin gum can be directly used for the bonding of metal materials, especially metal foil packaging materials, and also for the manufacture of sticky paper. The lacquer obtained by co-melting rosin gum with inorganic fillers (such as chalk, gypsum, etc.) and inorganic pigments (such as cinnabar, iron red, etc.) is a traditional hot melt adhesive, which can be used for sealing documents and instruments. In addition, rosin is also a commonly used tackifier for pressure sensitive adhesives and hot melt adhesives.

Carboxymethyl Cellulose Gum Carboxymethyl Cellulose Gum is commonly known as chemical paste, which is prepared from carboxymethyl cellulose (CMC for short) and an appropriate amount of water. The utility model has the advantages of good transparency, rapid curing, good high and low temperature performance, direct heating, hot glue bonding, and room temperature bonding.

Carboxymethylcellulose is a type of cellulose ether having a molecular formula of (C 6 H 9 O 4 .OCH 2 COOH ), and its sodium salt is usually used. It is obtained by reacting cellulose with chloroacetic acid in a sodium hydroxide solution and replacing the chlorine on the hydroxyl group with a carboxymethyl group. It is a white powder with strong hygroscopicity. It is soluble in water and forms a viscous liquid. It is very stable to heat and light.

Carboxymethylcellulose gum is mainly used as an adhesive for tablet powders. It is used for the bonding of paper and other materials. It can also be used for the sizing of fabric warp yarns and the bonding of powder materials in the production of ceramic products.

The lignin gum lignin gum is based on lignin, which is the second only substance in wood, which is colorless or light yellow resin. It is mainly extracted from pulp waste liquid. The thiolignin which is a monosulfite structure is extracted from the kraft pulp; the sulfonate-structured sulfonic acid lignin is extracted from the sulfite pulp.

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