The term «polymer» only refers to using small molecules (called «monomer», needn't be of one type) multiple times to build a larger molecule. E.g., if you would use the small molecule thrice to get a larger one, it were a trimer, if four times, a tetramer to be more specific; but these were all examples of «polymers». The term does not tell if the material were of industrial / artificial (like for a PET bottle), or biological origin (e.g., lignin, chitin, cotton, or kreatin).
Given the small size of molecules, even tiny particles known as microplastic consist of many polymer molecules each. Like if the band of a tagliatelle would just be cut into smaller and smaller pieces and still count as a noodle. The fine mechanical division / chopping into smaller and smaller fragments only increases the accessible area per unit of weight. Similar to a combustion engine, this material then spread out may yield a combustion more efficient with less smoke and soot than, e.g., a torch, or a candle. Not all polymers burn equally well, even if finely divided.
The «problem» with wood, compared to natural gas - chemically speaking - is that it consists of many different compounds. Beside the lignin, there are a number of minerals, sugars, fluids, resins, etc. and water present in a tree; each with its own characteristics. Some will catch fire quickly no matter what, like human hair. Some need to be heated first so that fire nibbles them away. Meanwhile others may be heated and then burn as gases, rather than as solid or liquid, sometimes liberated like in an explosion. Some materials require much air (wind) per unit of mass to burn, or otherwise would just smoulder; so now equally soil, weather and topography of the terrain enter the the set of parameters yielding a typical wild fire with incomplete combustion and smoke.