Scientific understanding and environmental protection of flame retardants

With the widespread application of polymer materials and electronic consumer products, the incidence of fires is also increasing, and the harm it brings is even more shocking
.

The flame retardant properties of polymer materials are becoming more and more important, and flame retardants play an indispensable role in them.

 On June 14, 2017, a fire broke out in the Glenfellow Tower apartment in London, England, killing 79 people
.

 On June 14, 2017, a fire broke out in the Glenfellow Tower apartment in London, England, killing 79 people

 How doesflame retardant work? How does flame retardant work?

Flame retardants are used to improve the flame resistance of molecular materials, by increasing the ignition point of molecular materials, or reducing the burning speed of materials, thereby increasing rescue time, saving lives and reducing losses
.

According to the structure resistance, the fuel can be divided into macromolecular polymer type and small molecule type flame retardant; according to the method of use, it can be divided into additive type flame retardant and reactive flame retardant; according to whether the material contains halogen, it can be divided into It is a halogen flame retardant and a halogen-free flame retardant
.

Additive flame retardants are mostly used in thermoplastic polymer materials, do not chemically react with other components in the material, and only physically exist in the polymer materials

After the polymer material is ignited by an open flame, it will undergo a violent oxidation reaction and release a large amount of hydroxyl
.

Because the hydroxyl group is very active, it is easy to combine with other substances and produce water and other organic matter after the combination

In this process, how do flame retardants play a role? According to the three major elements of combustion-combustibles, combustibles and fire sources, the flame retardant principle of flame retardants can be summarized as follows:

1.

Flame retardant is achieved by absorbing heat.
For example, the inorganic flame retardant aluminum hydroxide decomposes at high temperature and releases crystal water, which evaporates into water vapor

1.
Flame retardant by absorbing heat,

　　2.

Dilute oxygen by generating non-combustible gas to slow down the combustion speed.

　2.

3.

4.
Capture the free radicals involved in the combustion reaction and inhibit the chain reaction of free radicals,

Combustion test of power switch with flame retardant (left) and without flame retardant (right)

Combustion test of power switch with flame retardant (left) and without flame retardant (right)

　　What are the types of flame retardants

　　What are the types of　　flame retardants　　What types of flame retardants are there

　　According to major categories, flame retardants can be divided into halogenated flame retardants and halogen-free flame retardants
.
Literally, the biggest difference between the two is that the former contains halogen, while the latter does not contain halogen
.
However, halogen-free is not absolutely halogen-free, but is defined according to its content
.
The definition of halogen-free is less than 900ppm of bromine and chlorine, and the total content of bromine and chlorine is less than 1500ppm
.
Halogenated flame retardants mainly refer to brominated flame retardants and chlorinated flame retardants.
Among them, brominated flame retardants are currently the most widely used and most widely used flame retardants
.

　　In the field of daily life and transportation, almost most flame retardant materials contain halogens.
Halogenated flame retardants have the characteristics of low addition amount, significant flame retardant effect and low price
.
In the addition of flame retardants, halogen elements have good compatibility with polymer materials, and will not affect the physical and chemical properties of the materials themselves
.

　　But at the same time, we cannot ignore that individual brominated flame retardants, such as hexabromocyclododecane, will release a large amount of smoke and toxic gases during the combustion process, which will bring difficulties to fire fighting, escape and recovery
.

　　When halogenated flame retardants face many controversies, we need to understand the following facts:

　　① Brominated flame retardants are still widely used worldwide, and the EU and many countries’ authorized lists and candidate lists only contain 2-3 halogenated flame retardants including hexabromocyclododecane.
However, the current brominated flame retardants There are more than 70 kinds of burning agents;

　　②Most brominated flame retardants have undergone rigorous evaluation and proved to be harmless to the human body and the environment, and some brominated flame retardants such as tetrabromobisphenol A are less toxic than table salt;

　　③Under correct operating conditions, the use and recycling process of brominated flame retardants will not generate new hazardous gases to the outside world, and the recyclability is better than other flame retardant systems;

　　④ Brominated flame retardants have a wide range of applicability and are suitable for almost all materials that require flame retardancy.
The research and application of brominated flame retardants have never stopped
.

　　Halogen-free flame retardants include phosphorus-based flame retardants, intumescent flame retardants, inorganic flame retardants, silicon-containing flame retardants, and bio-based flame retardants
.
Halogen-free flame retardants mostly contain phosphorus and nitrogen, which are mainly divided into

　　Phosphorus flame retardant

　　Phosphorus flame retardant

　　Phosphorus flame retardants are divided into inorganic phosphorus flame retardants and organic phosphorus flame retardants.
Modification of phosphorus flame retardants and compound flame retardants are the focus of its work
.
Phosphorus-based flame retardants mainly work in the initial stage of material decomposition in the fire, forming a protective film to isolate the heat and air from the outside
.

　　Intumescent flame retardant

　　Intumescent flame retardant

　　Intumescent flame retardants can effectively protect materials exposed to flames for a long time
.

　　Inorganic flame retardant

　　Inorganic flame retardant

　　Inorganic flame retardant has the characteristics of good thermal stability, flame retardant, non-volatile, no corrosive gas, and small amount of smoke.
It is the main raw material of low halogen halogen-free flame retardant system
.

　　Silicone flame retardant

　　Silicone flame retardant

　　Among the silicon-containing flame retardants, the Si-O-Si structure is stable, and has the characteristics of low toxicity, anti-dripping, promotion of char formation and smoke suppression during combustion
.

　　Bio-based flame retardants

　　Bio-based flame retardants

　　Although bio-based flame retardants are only in the initial stage of research, they have gradually become a hot spot of people's attention and research based on their advantages of low price, non-toxicity, and wide resources
.

　　There are many types of halogen-free flame retardants, but they face a common problem-it is difficult to achieve a good flame retardant effect, and it has an impact on the mechanical and processing properties of the material
.
Therefore, halogenated flame retardants and halogen-free flame retardants have their own advantages and disadvantages.
When choosing flame retardants, people should fully consider the structure of the flame-retardant substrate, use environment, and recycling
.

　　Scientifically understand the environmental protection of flame retardants

　　Scientifically understand the environmental protection of　　flame retardants　　Scientifically understand the environmental protection of flame retardants

　　In recent years, halogen-free flame retardants have become more and more popular
.
For a long time and even now, the wrong view that "halogen flame retardants are toxic and harmful, and halogen-free flame retardants are environmentally friendly, is the future development direction of flame retardants" is deeply rooted in the hearts of the people
.
The view that flame retardants "non-halogenated = environmental protection" has become popular
.

　　To explore its origins, one is that after the adverse effects of individual flame retardants appear, people use partiality to extend this adverse effect to the entire halogenated flame retardants; second, misinterpretation and out of context of individual research results; third, due to The difficulty of detecting the structure of compounds exceeds the difficulty of detecting elements.
For convenience, people only judge whether compounds contain halogens.
Fourth, they are used by individuals, companies, and research institutes for profit.
Propagating that halogens are harmful and halogen-free is environmental protection.
Downstream manufacturers abandon the use of all halogen-containing flame retardants in order to conduct blue ocean marketing and so on
.
In fact, according to the internationally accepted chemical classification and labeling system, among all the more than 70 commercial brominated flame retardants, only TBBA (tetrabromobisphenol A) and HBCD (hexabromocyclododecane) are two products.
It is clearly defined as toxic and harmful
.
Some halogen-free flame retardants, such as most phosphate esters, some phosphates, and hypophosphites, carry environmentally hazardous substances labels
.
Therefore, there is no scientific basis for judging whether it is environmentally friendly by containing a certain chemical element!

One, two, three, four,

　　There is no regulation that restricts the entire halogen family, or exempts or supports halogen-free
.
Sided emphasis on non-halogenated only bring a lot of harm to society: First, it makes the concept confuse, mislead the public; second is to destroy science-based chemicals assessment and management system, to mislead regulators to take a one-sided policy measures; three It is to force manufacturers to adopt immature halogen-free alternative products, or to reduce the flame retardant level, thereby amplifying the risk of fire, threatening the safety of life and property; fourth is to increase unnecessary inspection and testing, increase the cost of manufacturers, and ultimately increase the burden on consumers ; Fifth, breaking the original auxiliary agent supply market pattern, reducing the number of auxiliary suppliers, increasing the concentration of supply, and increasing the risk of monopoly; sixth, widening the gap between domestic electronic product manufacturers and world-class manufacturers, and weakening Improve the competitiveness of domestic brands
.

One is two is three is four is five is six is

　　The flame retardant industry should flourish.
Different flame retardants have different application fields.
They should be selected by the market within the framework of compliance with regulatory laws and regulations, instead of unilaterally advocating and emphasizing halogen-free due to individual issues
.

　　It is true that the pursuit of environmental protection is a necessary condition for the sustainable development of flame retardants, but it should not be too extreme, and the nature of environmental protection must be understood first
.
Environmental protection means environmental friendliness.
As a chemical, flame retardants need to meet three conditions to be environmentally friendly
.
First, from the perspective of the chemical structure itself , it should achieve two attributes: environmental non-PBT and non-toxic and harmless to the human body
.
Specifically, environmental non-PBT refers to chemicals that have little impact on persistent pollution, bioaccumulation, mobility, and ecotoxicity, and are non-toxic to humans and have no impact on human health
.
Second, the entire life cycle has a small impact on the environment , which is mainly reflected in the low carbon footprint, low environmental release, and low comprehensive energy consumption during the entire process from product production, manufacturing, transportation, use to disposal, and the need to control the process The waste should be properly treated, and it is best to be recyclable
.
Third, the product has the necessary physical and chemical properties , can achieve the use performance, make the best use of the material, and meet the regulatory requirements of relevant laws and regulations
.
When the flame retardant meets these three conditions, it can meet the principles of green chemistry and find the future direction of environmentally friendly development
.

First, from the perspective of the chemical structure itself.
Second, the impact on the environment during the entire life cycle is small.
Third, the product has the necessary physical and chemical properties.

　　As we all know, as far as the product itself is concerned, chemicals can only cause corresponding hazards when they enter the organism
.
As for polymer compounds, because the molecules are too large, it is difficult to penetrate biological cell membranes and participate in systemic circulation and metabolism, so they are unlikely to produce bioaccumulation
.
Therefore, macromolecular polymerized flame retardants are one of the green development directions
.
From traditional polymer bromine-based flame retardants, polymer phosphorus-based flame retardants, etc.
, to today’s new silicone-based flame retardants, polymeric nitrogen-phosphorus flame retardants, etc.
, they are all environmentally friendly to flame retardants.
Exploration and pursuit in a friendly direction
.

　　To sum up, we must hold a scientific and rational attitude to the understanding of flame retardants, and must not be heard
.
As people's awareness of environmental protection has increased, reducing harm to people's health has attracted more and more attention.
The development of flame retardants in an environmentally friendly direction is bound to be the future trend
.

　　(Note: This article is the first prize of the second "Scientific Understanding of Flame Retardants" College Essay Competition organized by the Flame Retardant Materials Professional Committee of the China Petroleum and Chemical Industry Federation
.
The author is: Yang Lijie and Wang Wenwen, Beijing University of Chemical Technology)