Application Of Polymer Flame Retardants And New Technologies

Application Of Polymer Flame Retardants And New Technologies

With the development of society, the chemical synthetic materials and products industry has been widely applied in various fields. However, most chemical materials are flammable and combustible, and they produce dense smoke and toxic gases when burning, posing a huge threat to the environment and people's life safety.

Therefore, the demand for fire-resistant materials has given rise to and spurred the rapid development of the flame retardant industry. Since the 1980s, flame retardants have become the largest auxiliary material used in synthetic materials, second only to plasticizers.

According to the different main flame-retardant chemical elements in flame retardants, they can be roughly divided into three major categories: organic halogen, organic phosphorus, and inorganic. At present, the usage of halogen-free flame retardants in developed countries has greatly exceeded that of halogenated flame retardants, while developing countries are still the largest consumer area of halogenated flame retardants.

With the increasing requirements of environmental regulations and the gradual improvement of human health and environmental awareness, efficient, environmentally friendly, low-toxicity, and multifunctional flame retardants will inevitably become the future industry development trend.

I. Application of Halogenated Flame Retardants

Halogenated flame retardants include brominated flame retardants and chlorinated flame retardants. In terms of production volume, brominated flame retardants remain the largest variety of flame retardants in the global flame retardant industry at present.

The brominated flame retardants that are currently widely used mainly include the following categories:

Small molecule reactive flame retardants: These mainly include tetrabromobisphenol A, tribromophenol, and tetrabromophthalic anhydride diglycol ester, etc. They are mainly used to manufacture two types of brominated flame retardants or added as reactive components to the materials to be flame-retardant. Flame-retardant materials are prepared through chemical reactions with the materials to be flame-retardant.

Small molecule additive flame retardants: These mainly include decabromodiphenylethane, brominated triazine, octabrominated ether, methyl octabrominated ether, and ethyl-bis(tetrabromophthalimide), etc.

High molecular polymer flame retardants: Due to their good compatibility with polymers and stable physicochemical properties, they are the most environmentally friendly flame retardant variety among brominated flame retardants. They mainly include: brominated polystyrene, brominated epoxy resin, brominated SBS, and tetrabromobisphenol A polycarbonate oligomer, etc.

The bromine-based flame retardants are favored primarily due to their high flame retardancy efficiency and moderate pricing. Despite the fact that they produce a significant amount of smoke when burned, these materials offer excellent flame retardancy, require less quantity for effective protection, and have minimal impact on the properties of the products they are used in. In the short term, they maintain an irreplaceable position as the mainstay of flame retardants, and their intense competition with halogen-free flame retardants is expected to persist over the long term.

With technological advancements, efforts are being made globally to develop new types of bromine-based flame retardants. Currently, a new trend in the development of bromine-based flame retardants internationally is to continue increasing bromine content and enhance molecular weight.

For instance, PB-68 from Ferro Corporation in the United States, which is mainly brominated polystyrene with a molecular weight of 15,000 and a bromine content of up to 68%; Polybrominated Phenol Acrylate developed by Brominated Chemicals Fast Company and Ameribrom, which contains up to 70.5% bromine and has a molecular weight ranging from 30,000 to 80,000.

These flame retardants are particularly suitable for various types of engineering plastics, significantly outperforming many small molecule flame retardants in terms of migration resistance, compatibility, thermal stability, and flame retardancy. They have the potential to become the next generation of updated products.

In the future, the development and application of new halogen-based flame retardants may follow these trends:

(1) To counteract the impact on performance when used as additive assistants, the development of new bromine-based flame retardants with comprehensive excellent performance is underway. For example, the CP 44B polystyrene brominated by Kemira Corporation in the United States, which has excellent fluidity and thermal stability, can be well dispersed in materials and provides the material with bright, lasting color, gaining market favor.

(2) Utilizing modern polymerization and chemical synthesis techniques, new types of bromine-based flame retardants are being designed and synthesized to replace those that are restricted or soon to be restricted. For example, brominated copolymers prepared by copolymerizing styrene with butadiene and then adding bromine, serve as an alternative to hexabromocyclododecane flame retardants in expanded polystyrene.

Chlorine-based flame retardants, mainly represented by Polyvinyl Chloride (PVC) and Chlorinated Polyethylene (CPE), have the significant advantage of being cheaper than bromine-based flame retardants, making them widely used as well.

II. Application of Halogen-free Flame Retardants

• Inorganic Phosphorus Flame Retardants

Inorganic phosphorus flame retardants mainly include red phosphorus, phosphate and ammonium polyphosphate.

Red phosphorus is a flame retardant with excellent performance, characterized by its high efficiency, smoke suppression, and low toxicity. However, it is prone to moisture absorption and oxidation, which can release highly toxic gases. Its dust can be explosive and it has a dark red color, which greatly limits its use.

To address these drawbacks, surface treatment of red phosphorus is a major research focus, with microencapsulation being the most effective method.

The future development of red phosphorus surface treatment should focus on:

1.Modifying the encapsulating material to have multifunctional properties such as thermal stability, plasticization, and flame retardancy, developing multifunctional microencapsulated red phosphorus flame retardants.

2.Studying the effective combination of various flame retardants with red phosphorus flame retardants and microencapsulating them to enhance flame retardancy and improve the mechanical properties of materials.

3.Developing smoke suppression technologies, as smoke suppression is more critical than fire prevention in fires. Red phosphorus has smoke suppression effects, and suitable smoke suppressants can be sought for combination.

Ammonium polyphosphate and its corresponding intumescent flame retardants are currently active research areas in phosphorus-based flame retardants. Long-chain ammonium polyphosphate (APP) has a high content of P/N flame retardant elements, good thermal stability, and is nearly neutral, making it compatible with other substances. It has enduring flame retardant properties and has developed rapidly.

APP appears as a white powder, with a decomposition temperature greater than 256°C. It is water-soluble when the degree of polymerization is between 10 and 20, and insoluble in water when the degree of polymerization is greater than 20. APP is less expensive than organic flame retardants, has low toxicity, and good thermal stability, making it suitable for use alone or in combination with other flame retardants in plastics.

At high temperatures, APP quickly decomposes into ammonia and polyphosphoric acid. Ammonia can dilute the concentration of oxygen in the gas phase, thus preventing combustion. Polyphosphoric acid is a strong dehydrating agent that can cause polymers to dehydrate and carbonize, forming a carbon layer that isolates the polymer from oxygen, preventing combustion in the solid phase.

The intumescent flame retardant system based on APP is a hot topic in the research of halogen-free flame retardant polyolefins and shows good development prospects in the processing and modification of polypropylene. Domestic research on the intumescent flame retardant system combined with cage phosphate esters or salts and APP has good heat resistance and flame retardancy.

APP has a wide range of applications and can be used as a fire extinguishing agent for large-scale fire extinguishing in forests and oil fields, and can also be formulated into intumescent fireproof coatings.

• Organophosphorus Flame Retardants

Most of the phosphate ester is liquid, poor heat resistance, volatility, compatibility is not ideal, in the combustion of dripping material. In order to avoid the above shortcomings, the development of some polymer polycondensation type phosphate ester has become one of the future development direction of phosphate ester flame retardant.

In addition, the nitrogen-containing phosphate ester containing nitrogen and phosphorus two elements at the same time, flame retardant effect than only phosphorus-containing compounds is better, phosphate ester system has become another direction of development of flame retardants.

Diethyl Aluminum Phosphinate (ADP) is a product that is insoluble in water and organic solvents, but soluble in strong acid and strong base solutions. It has many advantages such as high phosphorus content, high thermal stability, non-toxicity, low smoke, small particle size, low specific gravity, good dispersion, easy coloring, and low density (1.2 kg/L). As an efficient flame retardant, it can be widely used in the flame retardation of thermoplastic plastics (such as PA, PBT), fibers, and textiles.

Piperazine Pyrophosphate (PAPP), also known as Polyphosphoric Acid Piperazine (Focused Phosphoric Acid Piperazine), is a halogen-free, environmentally friendly, intumescent flame retardant designed with phosphorus and nitrogen as the main flame retardant elements.

PAPP appears as a white powder and has characteristics such as high carbonization efficiency, good thermal stability, and low smoke and non-toxicity. It can be used in flame-retardant products such as polypropylene (PP), polyethylene (PE), polyurethane (PU), acrylonitrile-butadiene-styrene (ABS), and epoxy resin (EP), and has great potential for future market development.

• Nitrogen Flame Retardant

Nitrogen-based flame retardants are developed later than other flame retardants, and their flame retardancy is not too good, and they are mostly used in combination with other flame retardants.

The addition of nitrogen flame retardant can promote the carbonization of phosphorus system, which has synergistic effect. In addition, nitrogen and antimony also have synergistic effect.

Nitrogen-based flame retardants mainly include melamine and melamine cyanurate, which can be used in polyurethane and polyamide. At present, the main topic is to develop nitrogen flame retardants with high nitrogen content, high-temperature dispersion and matching with polymers.

• Inorganic Flame Retardant

Antimony trioxide as a typical halogen flame retardant co-effective flame retardant, its own no flame retardant effect, need and bromine or chlorine halogenated flame retardant compound use, has the characteristics of high charcoal, flame retardant effect is obvious, and magnesium hydroxide has co-effective flame retardant effect.

Aluminum hydroxide (ATH) is the most representative among inorganic metal compound flame retardants, accounting for over 40% of inorganic flame retardants. It has three functions: flame retardancy, smoke suppression, and filling, without causing secondary pollution. It can also produce a synergistic effect with a variety of substances, is non-volatile, non-toxic, has low corrosiveness, and is cost-effective.

The flame retardant effect of aluminum hydroxide occurs when it undergoes dehydration and heat absorption at temperatures above 200°C, with a heat absorption capacity of 1968 J/g, which can suppress the early temperature rise of materials. However, aluminum hydroxide has the disadvantage of requiring a large amount to be added; typically, more than 50% must be incorporated to achieve good flame retardant effects.

To overcome this drawback, methods such as granulation technology can be used to develop ultrafine particles, narrowing the particle size distribution; improved coating techniques can enhance its dispersion in polymers; and treatment with macromolecular bonding can be applied. Zinc borate also has a synergistic flame retardant effect with aluminum hydroxide.

• Silicon Flame Retardants

Silicon-based flame retardants can be categorized into inorganic and organic types based on their composition and structure.

Inorganic silicon flame retardants are primarily composed of SiO2, which serves both as a reinforcing agent and a flame retardant. The flame retardation mechanism involves the formation of a SiO2 layer when the polymer material burns, which acts as a barrier to combustion and provides a shielding effect. SiO2 is rarely used alone and is often combined with halides for enhanced performance.

Organic silicon polymer flame retardants are characterized by their high efficiency, non-toxicity, low smoke emission, drip prevention, and environmental friendliness, with minimal impact on the properties of the finished products. The flame retardation mechanism for these materials involves the formation of silicon carbide when the polymer burns, which prevents the escape of volatile combustion products, isolates oxygen from the resin, and prevents the dripping of the molten material, thereby achieving the goal of flame retardation.

The main types of organic silicon flame retardants include silicone oils, silicone resins, silicone rubbers, and organosilicon alkanolamides.

GE's SFR100, developed by General Electric in the United States, provides excellent flame retardancy for polyolefins and also improves the processing and mechanical properties of the resin. It imparts superior flame retardancy and smoke suppression to the matrix, making it suitable for applications with strict fire safety requirements where conventional flame retardant systems are not adequate.

Dow Corning, a company known for its silicone products, has developed a silicon resin micropowder that is an efficient flame retardant. Different grades of this product can be used in polyolefins, polyesters, polyamides, and polystyrenes.

In Japan, a polysiloxane PC has been developed as one of the latest halogen-free flame retardant resins. It has received the German "Blue Angel" environmental certification and is being marketed globally to manufacturers in the electrical and other industries.

YINSU Flame Retardant specializes in providing efficient and environmentally friendly flame retardant solutions, and its products cover a wide range of key flame retardants. The main red phosphorus flame retardant, after special surface treatment, overcomes the shortcomings of traditional red phosphorus and is characterized by high efficiency, smoke suppression and low toxicity, and is suitable for a wide range of polymer materials.

The company's antimony trioxide substitutes provide an environmentally friendly upgrade option for traditional halogen flame retardant systems, while maintaining excellent flame retardant effects. Organic phosphorus flame retardant series, with its high phosphorus content and good compatibility, are suitable for a wide range of materials such as thermoplastics, fibers and textiles, effectively enhancing the flame retardant properties of the materials. In addition, the carbon-forming agent products perform well in promoting the formation of protective carbon layers in materials, further enhancing the fire safety of materials.

YINSU Flame Retardant's flame retardants are widely used in many industries such as electronic and electrical appliances, construction materials, automobile manufacturing, textiles, etc., helping customers to meet the strict fire safety standards and promoting the green development of the industry.