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Background: I was cooking eggs (very difficult) with a plastic spatula which was not very good, so when I set it on the border of the pan it began melting. In order to keep cooking, I reached for a wooden spoon which can touch the pan without melting.

This led me to wonder about the behaviors of the materials. For example, if I had left the plastic spatula it would have melted, but if I had turned up the temperature enough it would have actually ignited and caught a flame. If I had done the same with the wooden spoon, it wouldn't melt as I turned up the temperature but it would ignite eventually.

So why is it that certain materials (plastic in this case) will go through the process of melting, then igniting, but wood just seems to skip the melting and go straight into ignition?

My only guess is that somehow wood has a melting point higher than its ignition point, but I am not even sure if that makes physical sense. A Google search led me to a strange-looking forum with disappointing answers. My understanding of thermodynamics is only as far as the math goes, but I am conceptually blind in this area. Maybe someone can shed some more light.

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    $\begingroup$ Either the spatula was made of entirely inappropriate plastics or you're cooking your eggs way too hot. Go easy on them; don't scorch the flavor out of them. $\endgroup$
    – dmckee --- ex-moderator kitten
    Commented Jun 21, 2016 at 23:47
  • $\begingroup$ @dmckee I like them well done but it was indeed a very sorry spatula $\endgroup$
    – M Barbosa
    Commented Jun 21, 2016 at 23:53
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    $\begingroup$ A polymer chemist could probably give a better answer than me. Nevertheless, wood is composed of a very large molecular weight, highly cross-linked polymer, composed of glucose monomers. All the cross links between molecules ensure that wood doesn't dissolve in water and doesn't melt. For an "analogy" to this, vulcanized rubber is also highly cross linked in its chemical structure. Have you ever seen an old tire melt before burning? $\endgroup$
    – David White
    Commented Jun 21, 2016 at 23:54
  • $\begingroup$ @DavidWhite a polymer chemist wouldn't have made sense, so great answer. Come to think of it most things that are "fiber-y" do not melt before burning (meats, plants, etc...). $\endgroup$
    – M Barbosa
    Commented Jun 22, 2016 at 0:00
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    $\begingroup$ Also surprising that the liquid egg goes through a process of solidifying when cooked:) $\endgroup$
    – philip_0008
    Commented Jun 22, 2016 at 0:57

1 Answer 1

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When a substance undergoes a phase change such as melting, its chemical makeup remains the same. However, when heat is added to wood, the wood oxidizes before it would be able to melt. Wood contains long-chain organic molecules that decompose into products such as charcoal, water, methanol, and carbon dioxide upon heating. The physical structure of wood is destroyed in the process, and the resulting material cannot return to the original matter. As a result of the chemical, irreversible breakdown of its components, wood does not melt. Fore more details see http://www.yalescientific.org/2010/05/everyday-qa-can-you-melt-a-wooden-log/

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    $\begingroup$ when we say a wood log is ignited, it is the combustible gas emitted by the log being ignited but not the wood itself (well, you can say that is wood ignition. But I want to point this out). Heat breakdown wood long chain molecular and release flameble gas. Unfortunately, heat cannot melt wood before break its molecular. Others such as wax can be melt. $\endgroup$
    – user115350
    Commented Jun 22, 2016 at 5:31
  • $\begingroup$ An interesting side (chemistry) question, I think, would be what would happen to wood continuously heated in vacuum. $\endgroup$
    – Declan
    Commented Jun 22, 2016 at 5:32
  • $\begingroup$ .. Oh.. Sorry. I just followed your link :) $\endgroup$
    – Declan
    Commented Jun 22, 2016 at 5:33
  • $\begingroup$ @user115350: Strictly-speaking, both the released gasses and the wood itself ignite and burn; the gasses produce the large flames rising above the wood, and the wood itself produces the glow coming directly off the burning logs. $\endgroup$
    – Vikki
    Commented Sep 19, 2018 at 23:08
  • $\begingroup$ @Declan: It's called destructive distillation of wood, and produces charcoal, tar, and various other volatiles. $\endgroup$
    – Vikki
    Commented Sep 19, 2018 at 23:09

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