Why is it that when I hold a plastic bottle over a flame, it melts- but wood burns?

Question

If I hold a metal can or a plastic bottle over an open flame, it melts. But if I do the same with a wooden stick or a sheet of newspaper, it burns. Why is this?

Answer 1

It comes down to how hot a material needs to get to burn. All materials burn, even concrete! Everything has a combustion point, it is just that some are higher than others

Both plastic and metal DO burn, but at a much higher temperature than wood and paper (which is essentially wood). So while the metal and plastic melts, if you continued to heat it it would burn. With wood and paper it is destroyed pretty quickly at a lower temperature.

Answer 2

first of all, not all materials have a combustion point.  Things that melt have a property call the crystallization temperature.  this is the temperature that when you pass with an increase in temperature, the material becomes soft, and the molecules are able to move.  This produces the melting you talk about in plastics and metals.  If you ever notice, metal does not catch on fire like newspaper.  newspaper does not have a crystallization temperature that is used.  It burns because the bonds retain so much potential energy that the energy is released at one time, instead of over time like in plastics and metals which is observed by a molten flow of material.  The burning is the carbon bonds and oxygen bonds being released.  This is also why it is harder to burn ash ( not as much oxygen in it anymore).

Answer 3

Wood does not actually burn, only the vapors driven off by heat.  The plastic melts when hot enough but will not burn unless hot enough to drive off vapors that can mix with oxygen.  Some plastics vaporize more easily than others.  Metals generally do not burn with an open flame unless finely divided into a powder that permits better mixing with oxygen.

Answer 4

All substances will eventually burn when heated enough. Some materials melt prior to that, some don't.

The combustion temperature of wood and paper is lower than their melting temperature, so they burn before they have a chance to melt.