Polymer Flame Retardant Black Technology: Charring Technology and Anti-dripping Cheats

Moreover, the char-forming technology also has a hidden "super power"-smoke suppression. The research shows that for every 1/3 increase in char formation, the smoke emission can be reduced by 1/2. This means that when the char content of the polymer reaches 30%, it can not only effectively retard the flame, but also make the maximum specific optical density (Dm) less than 100, which greatly reduces the smoke hazard at the fire site and strives for precious time for escape and rescue.

In the flame retardant mechanism, phosphorus-containing flame retardants can dehydrate some oxygen-containing polymers such as epoxy resin, polyurethane, unsaturated polyester and other char-forming positive ions into char; Boron-containing flame retardants such as zinc borate can also form char; Intumescent flame retardant is achieved by charring technology, so it has the best charring property.

大部分聚合物的成炭率如下表所示：

Char-forming flame retardants, such as phosphate, boron and intumescent flame retardants, are added; Cross-linking agent such as PE, PP, PVC, PS can be added to cross-link to form carbon;

ABS can be grafted to form copolymer, which can realize the purpose of char formation. Add char-forming agent to form char. Typical char-forming agents such as pentaerythritol, isocyanate, melamine derivatives, cellulose and its derivatives, PPO, PF, PEI, PC, PI, PA, TPU, etc. These char-forming agents can only form char by themselves and cannot catalyze other materials to form char, so the addition amount should be above 5%.

Adding synergistic agent for catalytic char formation, such as metal oxide and aluminosilicate, such as zeolite, talcum powder, kaolin and hydrotalcite, can catalyze other components to form char, and the addition amount is below 5%. For example, adding 1% zinc oxide can improve the oxygen index of ABS flame retardant formula by 5%.

In fire, melt dripping during polymer combustion is a big problem. These droplets may ignite the objects below, leading to the rapid spread of fire. Therefore, anti-dripping technology is like a "safety lock" for fire prevention, which is very important.

Many polymers (such as PE, PP, HIPS, PA, PC, etc.) are prone to melt dripping, which requires us to modify them with anti-dripping properties. The carbonization technology is one of the key means to resist dripping. Common methods are as follows:

• Adding crosslinking agent: crosslinking can not only promote char formation, but also effectively prevent melt dripping. For example, when triallyl triisocyanate (TAIC) or dicumyl peroxide (DCP) is added to PP, the surface char formation increases during combustion, and the melt is not easy to drip at high temperature.

• Add char-forming agent: You can also directly add char-forming agent, such as Dstone DFCA-01, which is an efficient char-forming agent compounded by hybridization of various silicone, with good compatibility, good dispersibility, good processability, good temperature resistance, environmental protection and non-toxicity, and meets REACH/RoHS requirements.

• Add anti-dripping agent: PTFE (F4) is a "star material" for anti-dripping. It can play a fibrotic role in polymer processing and significantly increase the melt strength and elastic modulus. Even if the melt is elongated, it will not drip because of its high strength, thus reducing flame spread. There are pure PTFE and modified PTFE on the market.
  

• Inorganic fillers: inorganic fillers such as talcum powder, organic montmorillonite and metal oxides can also play an anti-dripping role. Organic montmorillonite, in particular, is not only char-forming but also migration-resistant, killing two birds with one stone.

• Adding compatilizer: The addition of compatilizer can improve the compatibility of formula components, thus increasing the char yield, improving the compactness of combustion carbon layer and playing an anti-dripping role.

Article Source Reference: Chain Plastic Network, Internet Data

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