How long can biodegradable garbage bags decompose

Ordinary plastic bags containing polyethylene cannot undergo biodegradation, but they can undergo photodegradation. So, how did you get the data that plastic bags take 500 years to decompose? The energy within the sun is the key to its effectiveness. When exposed to sunlight, the polymer chains inside polyethylene will weaken and then begin to burst. That is to say, the polyethylene molecules after explosion will become particles that can only be seen under a microscope. However, so far scientists are unable to determine how long it will take for plastic bags to break down. Some say it will take 500 years, while others are more conservative in estimating it at 1000 years. According to some plastic experts, all of these data simply state the same fact in different ways, which means "it will take a very, very long time".
If only biodegradable materials are added to the degradable garbage bag and it is truly fully degraded, the degradable garbage bag is only divided into small fragments, which are still polyethylene and will not degrade. Fully biodegradable garbage bags, some manufacturers say the degradation cycle is 180 days (half a year), some manufacturers say it is one year, and some manufacturers say it is three years. Regardless of the degradation cycle, it is difficult for individuals to complete degradation testing.
The environmentally friendly decomposition methods currently used are relatively fast and may decompose within a year. There are also faster, Olympic environmentally friendly plastic bags that can decompose within 72 days after disposal.
Generally speaking, there are no completely environmentally friendly plastic bags, and only some plastic bags can be easily degraded after adding some ingredients. That is, biodegradable plastic. Adding a certain amount of additives (such as starch, modified starch, or other cellulose, photosensitizers, biodegradable agents, etc.) to the production process of plastic packaging products can reduce the stability of plastic packaging materials and make them easier to degrade in the natural environment. At present, there are 19 units in the Beijing region that develop or produce degradable plastics. Experiments have shown that most biodegradable plastics begin to thin, lose weight, decrease strength, and gradually crack into fragments after being exposed to a general environment for 3 months. If these fragments are buried in garbage or soil, the degradation effect is not significant. There are four shortcomings in using degradable plastics: firstly, it consumes more food; Secondly, the use of biodegradable plastic products cannot completely eliminate "visual pollution"; Thirdly, due to technical reasons, the use of biodegradable plastic products cannot completely solve the "potential harm" to the environment; Fourthly, biodegradable plastics are difficult to recycle due to their special additives.