Imagine a rubber band in your hand, which is usually bouncy and soft. But what happens if you throw it into a fire or put it in a very, very hot place? It doesn't just "melt" and be done with it - it will undergo a "big transformation", and the process is quite dramatic!
Temperature: About as hot as a car in the summer (70-120°C).
Changes: The rubber will become super soft, even a little sticky, like chewed gum. The elasticity will also deteriorate, and it may "deflate" if you pull it, and it can't go back.
Why? Because the heat makes the "noodle-like" molecular chains (polymer chains) in the rubber easier to slide, so the whole thing becomes soft.
Temperature: Much hotter than the pan for frying steak (over 200°C).
Changes: At this time, the rubber can't hold up! High temperature is like an "invisible pair of scissors" that starts to cut: the rubber molecular chain itself (those "noodles" are cut into small pieces). More importantly, the "small bridges" (called "cross-links") that connect these "noodles" are also cut! This is like removing the "skeleton" of a rubber band.
Consequence: Completely inelastic, the rubber band can never bounce back again.
Smoke and oil: Some of the debris produced after cutting turns into smoke (gas) and escapes, and some turns into oily things and remains on the surface.
Sticky hands and strange smells: The remaining things are sticky and black, and may also emit unpleasant odors.
Temperature: Reach the "ignition point" (300-600°C, depending on the type of rubber).
Changes: If there is air (oxygen) around, the rubber will really burn! Flames jump out.
Thick black smoke: The smoke from burning rubber is particularly black and thick, and it is full of carbon particles (soot).
Toxic gas: This black smoke is no joke! There are many dangerous things hidden in it:
Carbon monoxide (CO): Inhaling too much will cause poisoning, which is fatal! (It is the same as gas poisoning)
Pungent acidic gas: If the rubber is treated with sulfur (such as tires), it will release sulfides and choke people.
Other highly toxic substances: Some synthetic rubbers may even produce super dangerous toxic gases such as hydrogen cyanide (HCN) or hydrogen chloride (HCl) when burned!
The remaining slag: In the end, a piece of black and brittle "coke" is left.
Oil-like liquid: It can be used as fuel or chemical raw material.
Carbon powder: Black powder, rubber factories can recycle and reuse it themselves (for example, add it back to new tires).
Steel wire: If you are dealing with old tires, the steel wire inside can also be recycled. (This is called "thermal cracking")
Safety first! Rubber fire is very dangerous! Black smoke is toxic and blocks vision, and inhaling toxic gases has serious consequences (especially when escaping from a fire). Don't burn rubber garbage indiscriminately!
Make things more durable: Factories that make rubber products must control the temperature (for example, when making tires) and cannot let it "overheat and fall apart."
Choose the right material: For hot places like the engine compartment of a car, you must use rubber that is particularly resistant to high temperatures (such as silicone).
Turn waste into treasure: The "thermal cracking" mentioned above is a good way to recycle old tires and other rubber waste. It does not burn or bury, and can also produce fuel and raw materials.
When rubber is heated to ultra-high temperatures, it does not melt quietly, but will: First become soft and sticky (like chewing gum), then "fall apart" and emit smoke and oil (molecular chains and connecting bonds are "cut"). If there is air, it will burn violently, producing highly toxic black smoke and coke. But if there is no air (special treatment), it can decompose into useful things such as oil and carbon powder
So, next time you see rubber in an extremely hot environment or on fire, be extra careful of the thick black and toxic smoke! Understanding this process is very helpful for us to use rubber safely and deal with rubber waste.
