What Is a Foaming Agent?

The so-called foaming agent is the substance that makes the target substance pores ^[1] . It can be divided into three categories: chemical foaming agents, physical foaming agents and surfactants. Chemical foaming agents are those compounds that can release carbon dioxide and nitrogen gas after thermal decomposition, and form pores in the polymer composition; physical foaming agents are foam pores that change through the physical form of a substance , That is, formed by the expansion of compressed gas, volatilization of liquid, or dissolution of solids; foaming agents have high surface activity, can effectively reduce the surface tension of liquids, and arrange a two-electron layer on the surface of the liquid film to surround the air , Forming bubbles, and then a single bubble to form a foam.

Chinese name: Foaming agent
Classification: Chemical, physical, surfactant
Exterior: Light yellow liquid

Density: 1.01 1.02 g / cm3
Solid content: 35%
PH value: 9 10

Foaming agent concept

1 Foaming agent concept 1

Chemical foaming agents are divided into inorganic foaming agents and organic foaming agents ^[2] .

Organic foaming agents are mainly of the following categories:

1. Azo compounds

2. Sulfonyl hydrazide

3 Nitroso compounds ^[2] .

Inorganic foaming agents are mainly of the following categories:

Carbonate: An inorganic foaming agent. The most commonly used are calcium carbonate, magnesium carbonate, and sodium bicarbonate. Among them, sodium bicarbonate is a white powder with a specific gravity of 2.16. The decomposition temperature is about 100-140 ° C, and a part of CO _{2 is} released, and the entire CO ₂ is lost by 270 ° C. Soluble in water but insoluble in alcohol.

Water glass: Sodium silicate, when mixed with glass powder and heated to about 850 ° C, it reacts with glass and emits a large amount of gas, and at the same time, it can strengthen the compressive and tensile strength of the material. .

Silicon Carbide: The main foaming agent used in the current production of foam glass industry, which emits a large amount of gas when sintered at 800-900 ° C.

Carbon black: It is also a very easy-to-use foaming agent. It emits CO ₂ when heated, and the foaming effect is good, but the disadvantage is that the price is higher.

Commonly used physical blowing agents are low-boiling alkanes and fluorocarbons. Physical foaming agent is a compound type physical foaming agent, which not only has the advantages of high foaming ratio, good foam stability, low bleeding, etc., but also can play a certain role in modifying magnesite cement and reduce product halogen Frost probability. Physical foaming agents have been widely used in the production of foamed magnesite products such as fire-resistant panels and lightweight partition boards, and in some products (magnesite fire door cores, etc.) have a key role in the success or failure.

Physical and chemical properties of magnesium blowing agent Magatto:

Appearance: light yellow liquid Density: 1.01 1.02 g / cm ³ Solid content: 35% PH value: 9 10

1. N-pentane

2. N-hexane

3 N-heptane

4 Petroleum ether (naphtha)

5. Trichlorofluoromethane (Freon11 for short)

6. Dichlorodifluoromethane (Freon12 for short)

7. Dichlorotetrafluoroethane (Freon114 for short)

Active agent

The anionic surfactant aqueous solution generates a large amount of foam when mechanical force is introduced into the air, and is widely used in the field of paper plasterboard and foam concrete ^[3] .

The essence of the blowing agent is its surface activity. Without surface activity, it cannot be foamed and cannot be a foaming agent. Surface activity is the core of foaming.

Commonly used surfactant foaming agents are:

1. Sodium lauryl sulfate (K12)

2. Fatty alcohol polyoxyethylene ether sodium sulfate (AES)

3 Rosin soap foaming agent

4 Animal and vegetable protein foaming agents

5. Pulp waste liquid and so on.

2 Foaming agent concept 2

Foaming agent in a broad sense and a narrow sense. Foaming agents have two concepts: broad sense and narrow sense. There are some differences between these two concepts, which can distinguish non-applicable foaming agents from applied foaming agents.

Broad blowing agent refers to all surfactants or surface active substances whose aqueous solution can produce a large amount of foam when air is introduced. Because most surfactants and surface-active substances have a large amount of foaming ability, the broad-spectrum foaming agents include most surfactants and surface-active substances. Therefore, the broad range of foaming agents is very wide and there are many types, the performance and quality of which are very different, and they have very wide selectivity.

In the broad sense, there are no strict requirements on the technical properties such as the expansion factor (foaming capacity) and foam stability (availability) of the foaming agent. It only indicates that it has a certain ability to generate a large amount of foam. Can the generated foam have practical use? There is no definition ^[4] .

Narrowly defined foaming agent Narrowly defined foaming agent refers to those that can not only produce a large amount of foam, but also have excellent properties, can meet the technical requirements for foaming of various products, and can really be used to produce actual surfactants or surfactants. substance. The biggest difference between it and the generalized foaming agent is its application value, and its outstanding performance is reflected in its application value. Its excellent performance is characterized by particularly strong foaming capacity, large foam volume per unit volume, very stable foam, long-term non-defoaming, fine foam, and good compatibility with the use medium, etc. ^[4] .

The narrowly defined foaming agent is a practically applied foaming agent. Generally speaking, the foaming agent refers to such a narrowly defined foaming agent. Only narrowly defined blowing agents have research and development value

Foamed concrete foaming agent belongs to a narrow sense.

Advantages and disadvantages of foaming agent

Vegetative

The plant-based cement foaming agent uses imported high-quality natural plant polymer materials as raw materials and is produced through a series of complex chemical reactions. The product is a light yellow, pure and transparent oily liquid ^[5] . Insensitive to hard water, non-toxic, odorless, and no sediment. The PH value is close to neutral, non-corrosive to cement and metal, and does not cause pollution to the environment. The foaming agent is resistant to storage, is not easy to deteriorate, has excellent foaming performance, rich foam, and moderate foam stability. Foaming cement made with this foaming agent has the characteristics of low consumption, low cost, and stable quality. Each barrel of foaming agent (200kg) can produce about 500 cubic meters of foaming cement, so it is widely used in floor heating projects and In roof insulation works, construction costs can be significantly reduced.

Disadvantages: 1. Because the internal pores of the foamed cement made with the foaming agent are connected, the foamed cement has good air permeability and poor permeability resistance, and cannot be used in water resistance projects.

2. Compared with foaming cement made of animal foaming agent at the same density, its thermal insulation performance and compressive strength are slightly damaged, so its application in some projects with special requirements is limited.

3. Due to the restriction of the foam stability of the plant-based foaming agent, the thickness of the one-time pouring foam cement generally does not exceed 200 mm, otherwise the surface collapse is likely to occur.

Blowing agent animal

Animal cement foaming agent uses selected animal (bovine, sheep) keratin as the main raw material, and is made by heating, dissolving, diluting, filtering and shrinking at high temperature after a series of hydrolysis reactions ^[5] . It adopts foaming equipment and manufacturing technology to produce. The production process adopts strict quality management. The product is a dark brown viscous liquid with low impurity content, light irritating odor, uniform quality, good quality consistency, good foamability and excellent. The foam stability is a new generation animal-based cement foaming agent. Due to the high surface strength of the foam produced by the foaming agent, the foam is extremely stable. The foam of the foamed cement produced by the foaming agent has a closed state independently of each other. it is good.

1. At the same density, compared with foamed cement made with plant-based foaming agents, its sealing and thermal insulation properties are better, and its strength is higher.

2. Due to its excellent foam stability, the thickness of the one-time poured foamed cement can reach more than 1.5 meters without collapse, so it is suitable for the production of foamed bricks, lightweight boards, and lightweight walls.

Disadvantages: 1. Due to the complicated production process, the product cost is high. 2. The foaming agent is less foamy than the plant-based foaming agent, and the consumption of foaming cement is high. 3. It has a certain irritating odor, which can only disappear after being made into foamed cement.

Selection points of foaming agent

The problems of organic foaming agents are: (1) small gas volume, generally only 15% -30% of inorganic foaming foaming agents, large residues, including water and volatile substances, and sometimes odor And surface frosting: (2), the foaming decomposition has a large amount of heat, which is difficult to remove, especially when the thickness of the product wall is large, it will cause the internal plastic to overheat and decompose, reducing performance; (3), almost all It is flammable and has low decomposition temperature. Care should be taken in storage and use.

The ideal chemical blowing agent should meet the following requirements:

1) The temperature range of decomposition gas should be narrow

2) The rate of gas release should be fast and the gas generation rate should be controllable

3) The released gas should be non-toxic, non-corrosive, and non-combustible. Nitrogen is best, but carbon dioxide is also possible. You can also try nitrogen dioxide, but nitrogen dioxide is corrosive and it is best not to use it.

4) The chemical foaming agent should be easy to disperse uniformly. It is best to mix with plastic.

5), cheap, stable storage, non-toxic.

6) The residue after decomposition should be non-toxic, colorless, odorless, and will not affect the physical, chemical and mechanical properties of plastics, and be chemically inert, without affecting the melting rate and solidification of plastics.

7) During the decomposition, it should not exotherm a lot, and it will not affect the melting and solidification of the plastic.

8) The residue after decomposition has good compatibility with the resin, and there is no blooming or dialysis of the residue.

9) The decomposition temperature of the foaming agent should be the same as the melting temperature of the resin.

The above are the main points of the foaming agent selection, and the specific needs to be selected according to the required conditions ^[6] .

Selection of blowing agent type

Foamed magnesite cement is different from ordinary magnesite cement, the bulk density is generally controlled at 500kg / m ³ ; below, some products such as fire-resistant door core boards require a lower bulk density, generally controlled at 250 340kg / m ³ ; Therefore, the foaming magnesite cement has relatively high requirements for foaming agents. There are many types of foaming agents on the market, and the quality is uneven, which leads to producers being overwhelmed by the choice of foaming agents. The selection of foaming agent in foamed magnesite cement is briefly described.

Fully understand the types of foaming agents: different types of foaming agents have different foaming powers, and foam stability is not the same, so there are certain limitations during use. For example, the rosin foaming agent does not have good foam stability and expansion ratio, so it can only be used for foaming magnesia cement with a volume greater than 600 / m ³ ; it cannot be used for 500 / m³. ; The following low-density foamed magnesite cement; anionic synthetic surfactant foaming agent has fast foaming, large foam volume, but poor foam stability, and low-density (500 / m ³ ) foamed magnesite Difficult to produce; relatively good foaming power and foam stability of protein-based foaming agents, but the foam viscosity is large, not conducive to mechanized production; composite foaming agents have good foaming power and foam stability The specific technical indicators of foaming agents also vary.

Classification of blowing agents

Rubber foaming agent, glass foaming agent, cement foaming agent, concrete foaming agent, plastic foaming agent, polyurethane foaming agent.

Formation and development of foaming agent

Adding some fillers to the plastic can improve some properties of the plastic, which is more suitable for some special applications. In order to reduce the density and hardness of plastic, or to enhance its heat insulation or sound insulation, the most ideal filler is voids. Plastics containing voids or cells are classified as foam. With the degree of foaming, that is, the difference in volume share of foam caused by voids, the performance of foam plastics may be quite different from that of basic plastics. A foaming agent is a chemical that can be added to plastics. At the appropriate time in the processing process, it will emit gas and form cells in the plastic.

The formation of plastic foam can generally be divided into four stages. In the first stage, the blowing agent must be completely uniformly dispersed in the polymer, which is usually in a liquid or molten state. The blowing agent can form a true solution in the polymer at this time, or it can simply be dispersed uniformly in the polymer to form a two-phase system. In the second stage, after a large number of individual bubbles are formed, the system is transformed into a system in which gas is dispersed in a liquid. Nucleating agents are often added at this time to promote the formation of a large number of small bubbles. Nucleating agents are generally very fine inert particles that provide sites for the formation of a new gas phase.

In the third stage, the initially formed cells are constantly expanding. This is because more gas diffuses through the polymer and enters the cells. If this period is long enough, the individual cells will contact each other. If the wall separating individual cells breaks, larger cells will be formed by this coalescence. If the foam is mainly formed through the interconnection of cells, it is called an open-cell foam. If the foam is formed by disconnected cells, it is called a closed-cell foam. If cell coalescence is allowed to proceed indefinitely, the foam will collapse because the gas is all automatically separated from the polymer.

In the fourth stage, when the polymer viscosity increases and the cells can no longer grow, the foam stabilizes. Polymer cooling can be increased by cooling, crosslinking or other methods. The last three stages of the foaming process can be as short as a fraction of a second, and the longest will not exceed a few seconds. The formation of foam requires the polymer to be liquid. For this purpose, the polymer can be dissolved or plasticized by heating. The production process of foam plastic is almost the same as any ordinary plastic production process, usually through extrusion, rotational molding and injection molding, as well as plasticizing paste processing and thermoforming. For the same reason, basically any kind of plastic can be made into foam. Polyvinyl chloride (both hard and soft), polystyrene, polypropylene, ABS, and polyethylene have all been made into foam on an industrial scale. The same is true of heat-resistant engineering plastics and thermosetting polymers. ^[7]

Development Prospects of Foaming Agents

Only after understanding the type of foaming agent, can its performance characteristics be understood, which is unique when selecting a foaming agent. Generally speaking, taking the compound road is the prospect of the foaming industry ^[8] . At present, the most commonly used common physical blowing agent is a combination of anionic surfactants and foam stabilizers, or foam stabilizers with excellent compatibility with animal and plant surfactants; anionic surfactants are fatty alcohol polyoxygen Sodium vinyl ether sulfate, sodium lauryl sulfate, etc. are the mainstream. Silicone polyether emulsions are the most ideal foam stabilization systems.