Compounding of magnesium hydroxide and zinc borate: a chemical duet that breaks through the UL94 V-0 level of flame retardancy of PE
On the stage of the plastics industry, polyethylene (PE) was once a "flammable and explosive" rebel - its hydrocarbon chain structure gives it lightness and flexibility, but also makes it the "best partner" of flames. It was not until the "flame retardant partners" of magnesium hydroxide and zinc borate came on stage together, pushing the flame retardancy of PE to the UL94 V-0 level with a delicate chemical reaction duet, that the game about fire and safety truly ushered in a subversive turning point.
1. The flame retardant dilemma of PE: a lone flame retardant brave man who can't stand alone
The limiting oxygen index of PE is only 17.4%. When it burns, the molten droplets splash and the smoke fills the air, like an out-of-control flame carnival. Traditional flame retardant solutions try to forcibly "extinguish the fire" with halogen or phosphorus-nitrogen compounds, but they are caught in a dilemma: either release carcinogenic smoke or make the material as brittle as thin paper. What is even more fatal is that the high filling amount of a single flame retardant (such as magnesium hydroxide needs to be added more than 65%) makes the mechanical properties of PE drop drastically, as if flame retardancy and strength are a pair of irreconcilable enemies.
Until scientists discovered that the combination of magnesium hydroxide and zinc borate can break this "zero-sum game".
2. The tacit understanding of the duet: a trio of synergistic effects
1. "Ice and Fire Concerto" of heat absorption and carbonization
Magnesium hydroxide is like a "calm ice mage". When it decomposes above 300℃, it absorbs heat and dehydrates, lowers the combustion temperature, and releases water vapor to dilute oxygen; while zinc borate is transformed into a "flame sculptor", catalyzing the cross-linking of PE molecules into carbon at high temperatures, forming a dense carbon layer covering the surface, isolating oxygen and heat transfer. The cooperation of this pair of partners has changed the combustion of PE from "a raging fire" to "a simmering fire extinguishing itself".
2. "Invisible shield" for smoke suppression and dripping resistance
Zinc ions in zinc borate capture free radicals during combustion and inhibit smoke generation; magnesium oxide generated by the decomposition of magnesium hydroxide combines with the carbon layer to form a ceramic barrier to prevent molten droplets from splashing. Experimental data show that the compound system can reduce the smoke release of PE by 80%, and the molten droplets completely disappear in the vertical combustion test.
3. "Unexpected counterattack" of mechanical properties
Traditional high-filling flame retardants often make PE as brittle as glass, but this pair of partners has achieved a "mechanical counterattack". The core-shell structured magnesium-zinc composite flame retardant (such as magnesium hydroxide coated with zinc borate) is evenly dispersed in the PE matrix, and the particles and molecular chains form physical entanglements. The tensile strength is increased to more than 10.0MPa against the trend, and the elongation at break exceeds 150%.
3. Golden Ratio: Precise Tango from Laboratory to Industry
The tacit understanding of this pair of partners depends on the precise control of the ratio:
65% magnesium hydroxide + 7% zinc borate: In the LLDPE/EAA system, the flame retardant performance reaches UL94 V-0 level, the peak heat release rate is reduced to below 270kW/m², and the impact strength is increased by 51.8%;
45% modified magnesium hydroxide + 5% red phosphorus synergist: The surface-coated magnesium hydroxide with silicone is compounded with zinc borate, the LOI value jumps to 34%, the tensile strength reaches 3.7MPa, and the dynamic mechanical properties are improved by 12%;
Nano-level golden ratio: When the particle size of magnesium hydroxide is locked at 3.1 microns and zinc borate is embedded in its surface as a nano-sheet layer, the flame retardant filling amount is reduced to below 50%, and the oxygen index of PE can still exceed 30%.
IV. Industrial Revolution: From Cable Sheath to New Energy Battlefield
On the production line of a new material factory in Hebei, ultrafine magnesium hydroxide and zinc borate are being compounded at the molecular level through ultrasonic cavitation technology. The modified flame-retardant PE composite material is quietly rewriting the industrial landscape:
New energy vehicle battery pack: In the needle puncture test, the compounding system delayed the thermal runaway time by 12 minutes, reduced the emission of smoke toxic gases by 80%, and passed the EU RoHS and UL94 V-0 dual certification;
5G base station cable sheath: The material remains flexible in extreme environments of -40℃ to 120℃, there is no droplet when burning, and the smoke density is less than 0.15;
Smart home appliance shell: Flame retardant performance is integrated with anti-UV and anti-static functions, becoming the "invisible safety guard" of high-end home appliances.
V. Future battlefield: the evolution of the flame retardant duo
The evolution of this chemical duo is far from stopping:
Nano-2.0: reduce the magnesium hydroxide particles to 100 nanometers, embed zinc borate in the form of quantum dots, and aim to reduce the flame retardant filling amount to less than 30%;
Bio-based armor: extract polysaccharide coating from seaweed, ｒｅｐｌａｃｅ silane coupling agent, and create zero-carbon flame retardant PE throughout the life cycle;
Intelligent response system: the temperature-sensitive zinc borate coating automatically thickens the carbon layer when it encounters fire, realizing a "dynamic fire barrier".
In the evolution history of flame retardant materials, the combination of magnesium hydroxide and zinc borate is like a chemical duet. They do not steal the show, but use UL94 V-0 certification and 16.1MPa tensile strength to prove that flame retardancy and performance are never multiple-choice questions. When PE transforms from a flammable material to a safety guard, this revolution has quietly rewritten the rules of the game in the polymer world - in the future, flame retardancy will be a perfect symbiosis of science and art.