Ordinary plastic bags containing polyethylene cannot biodegrade, but they can be photodegraded. So how was the data that plastic bags take 500 years to decompose obtained? The internal energy of the sun is the key to its effectiveness. When placed in sunlight, the polymer chain inside the polyethylene weakens and then begins to break. That is, the broken polyethylene molecules become particles that can only be seen under a microscope. However, scientists have not been able to determine how long it takes for plastic bags to decompose. Some say it's 500 years, and more conservative estimates are 1,000 years. Some plastic experts believe that all of these data are just different ways of saying the same thing, that is, "it takes a very, very long time."
Degradation time of compostable garbage bags
If only degradation materials are added to compostable garbage bags, they are not truly fully degradable, they only split the degradable compostable garbage bags into small pieces, which are still polyethylene and will not decompose. Fully degradable biodegradable garbage bags have a degradation cycle of 180 days (6 months), according to some manufacturers, some say it is one year, and some say three years. Regardless of which degradation cycle it is, it is difficult for individuals to complete the degradation test. Now, the environmentally friendly decomposition is relatively fast, and it may decompose within one year. There are also faster ones. The environmentally friendly plastic bags abandoned after the Beijing Olympics can decompose in 72 days.
Generally speaking, there are no completely environmentally friendly plastic bags, only some plastic bags that add some ingredients and are easily degraded. That is, degradable plastics. In the production process of plastic packaging products, a certain amount of additives (such as starch, modified starch, or other cellulose, photosensitizer, biodegradable agent, etc.) are added to make the stability of plastic packaging materials decrease and it is easier to degrade in natural environment. Experiments show that most degradable plastics compostable garbage bags begin to thin, lose weight, and decrease in strength after being exposed to normal environments for 3 months, gradually cracking into pieces. If these pieces are buried in garbage or soil, the degradation effect is not significant.
Good prospects for the development of compostable garbage bags
At present, the industrialized production of biomass plastic garbage bags mainly includes two categories. One is natural high molecular weight polymers such as starch and plant cellulose, which are modified and processed alone or in different proportions with other biodegradable plastics or common plastics. Then, fully or partially biodegradable plastics are produced through thermoplastic processing, such as starch-based plastics. The other is to directly synthesize biodegradable plastic garbage bags by synthesizing renewable resources such as starch and molasses through dust or genetic engineering, such as polyhydroxyalkanoates (PIIA), etc.; or to use agricultural and sideline products such as starch and straw as raw materials, and synthesize monomers through fermentation, and then chemically synthesize biodegradable plastics compostable garbage bags, such as polylactic acid, etc.