翻譯 chemistry

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Pyrolysis
As the resin becomes hotter it thermally decomposes and the smaller molecules produced in this way join the other burning molecules and contribute to the flame. By this stage the wood that is immediately beneath the burning surface, where there is no oxygen, starts to undergo a type of thermal decomposition known as pyrolysis. This is a reaction in which the large polymer molecules of cellulose, hemicellulose and lignin break down into smaller molecules. The absence of oxygen ensures that ignition does not occur. This causes a large volume of gas to be produced within the wood. As the gas pressure increases the gas forces its way out, simultaneously opening up the structure of the wood and making it porous. Once the small molecules from pyrolysis reach the surface they instantly burst into flames and contribute to the heating effect.