Wood does not melt. Right? We burn wood to produce energy. Wood is a natural composite made up of cellulose, lignin and water. If you heat wood, during the process the water boils first and evaporates. Then the lignin and cellulose. Both lignin and cellulose which are composed of long-chain organic molecules will react with oxygen and burn.
Even in a vacuum, these molecular chains due to their long-chain structure are so tangled that they can’t be wiggle free before they reach temperatures high enough to break their bonds.
Hence, they can’t be converted into the liquid form. Rather, they break down into smaller substances like methane and organic compounds containing carbon and hydrogen, like charcoal, methanol, carbon dioxide etc.