Some time ago, a customer asked if they purchased too many biodegradable plastic bags and put them in the warehouse for a long time, would they decompose? Furthermore, some netizens said that they buried the biodegradable plastic bag in the yard for half a year, but no trace of decomposition was found. Everyone knows that the main materials of biodegradable plastic bags on the market are PLA+PBAT. Next, let’s take a look at the decomposition diagram of PLA:
In fact, PLA (polylactic acid), the main component of degradable plastic bags, is not easily decomposed. Like natural biodegradable polymers and silk, it will not decompose during use. Cotton or silk products are generally biodegraded (moulded) from the dirty place when they are placed deep in the cabinet in midsummer. In other words, the beginning of biodegradation requires a high-temperature, high-humidity environment and a source of microbial nutrients, as does polylactic acid. Since the introduction of polylactic acid is generally “plastics that can be reduced in soil”, it is often the case that the above-mentioned consumers think that degradable plastic bags will be decomposed casually and lose their use value.
From the above, the decomposition of degradable plastic bags is inseparable from the conditions of temperature and humidity. At room temperature (25°C), the hydrolysis starts after half a year, and the biodegradation starts nearly a year later. In the initial decomposition, microorganisms have little effect, which is also an important feature of degradable plastic bags.
However, under high temperature (60~70℃) and high humidity (50%~60%) environments like composting, decomposition will proceed quickly. As shown in the figure above, the decomposition of the degradable plastic bag (polylactic acid) in the compost at 60°C begins with hydrolysis. The average molecular weight of the degradable plastic bag is 10,000. When the molecular weight becomes 20,000, it becomes brittle, and when it becomes 10,000, it becomes crushed. At the same time, it begins to biodegrade into lactic acid and lactic acid oligomers, releasing carbon dioxide. The decomposition mechanism of these two stages is characteristic of degradable plastic bags (polylactic acid). Therefore, for degradable plastic bags, the best treatment method is to compost.