The degradable plastic degradation needs to meet temperature and humidity conditions
According to different materials, degradable plastics is divided into bio-based biodegradable plastics (such as polylactic acid (PLA), polyhydroxyalkanoate (PHA), etc.) and petroleum-based biodegradable plastics (such as polyadipate/terephthalate). Diester (PBAT), polycaprolactone (PCL), etc.]. What we call "degradable plastics" is currently the collective name of "bio-based biodegradable plastics".
Among the broad categories of "degradable plastics", the most common one is polylactic acid (PLA). PLA is made up of lactic acid produced by starch fermentation. Because the raw materials are derived from plants and the “degradable” promotion, it is easily mistaken for an excellent environmental friendly material. In addition, compared with other degradable materials, PLA's production technology is mature and the cost is low. It has also been promoted as a substitute for disposable plastics in some industries and places.
However, the biodegradability of PLA is not unconditional, and it is not completely without environmental hazards. PLA biodegradation needs to meet the two most basic conditions: 50%-60% humidity and 50-70 degrees Celsius. Under these conditions, it is possible for microorganisms to gradually decompose the PLA over several months or even longer. The problem is viewed from another perspective, that is, PLA cannot be degraded in an environment that does not satisfy the temperature and humidity conditions.
Degradable plastics are not more environmental friendly than the traditional plastics
Some research results show that in fresh water or seawater, the degradation rate of PLA is almost the same as that of ordinary plastics. Even in the hot Mediterranean region, PLA does not degrade well in natural soils.
In a report called "The fate of so-called biodegradable polymers in seawater and freshwater," the researchers did an experiment. They hot-pressed different biodegradable plastics (PCL, PLA, Ecoflex, PET, etc.) into films with an average thickness of 320 ± 20 μm, and placed them in artificial seawater and fresh water at 25 ° C for one year. The water in the experiment was updated every two weeks.
It can be seen that the PLA plastic film has almost no loss in quality even in the sea water or fresh water for 300 days.
So, what do you think about degradable plastics inside the plastics industry? The European Plastics Association once publicly replied to the relevant questions of netizens' questions on the official website and expressed their attitude. They said that to evaluate the environmental impact of any object, a comprehensive recyclable evaluation mechanism and a cost evaluation mechanism should be used. Accordingly, we cannot believe that biodegradable plastics are more environmentally friendly than traditional non-degradable plastics.
All in all, if the degradation conditions cannot be satisfied, the "degradable plastic" is basically the same as ordinary plastics, and it will become plastic garbage, which becomes micro-plastic, polluting the ocean and water.