Biodegradable materials can be divided roughly into two categories, according to their biodegradation processes:

For totally biodegradable materials, such as natural polymer cellulose, synthetic polycaprolactone, etc., decomposition results mainly from:

1. Rapid growth of microorganisms, leading to the physical collapse of plastic structures.

2. The biochemical action of microorganisms, enzyme catalysis, and acid-base catalysis under various types of hydrolysis.

3. Free-radical-chain degradation caused by various other factors.

Decomposition also occurs in biologically disintegrating materials, such as starch and polyethylene mixtures, which decompose mainly due to the destruction of additives and weakening of the polymer chain, so that the molecular weight of the polymer degrades to the extent that microorganisms can digest it, decomposing the materials into carbon dioxide (CO2) and water.

Currently, semi-biodegradable plastics include starch-modified polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS), triphenyl phosphate (TPE), etc. Studies have shown that starch-based biodegradable plastics enter landfills and double-degrade without exposure to sunlight. Through anaerobic digestion and decomposition of methanobacteria, the pH value, dry solid percentage, and volatile solid change, these biodegradable plastics ultimately decompose into carbon dioxide (CO2) and methane (CH4).