What is PLA? Why shouldn't PLA replace single-use plastic?

PLA refers to "polylactic acid" (Polylactic acid or Polylactide, referred to as PLA). It is a biodegradable plastic commonly used in many countries. It is mainly made of plant starch such as sugarcane, corn, potato and other carbohydrates as raw materials. It is mostly used to make plastic substitutes such as disposable tableware, packaging boxes, fresh trays, and cosmetic packaging.

Biodegradable plastics such as PLA may sound environmentally friendly at first glance, as if they can decompose in the natural environment, but they are not. PLA must be degraded by microorganisms under a certain temperature and humidity, usually in an industrial composting environment. Therefore, when PLA products flow into oceans, forests, and rivers, they will not be easily decomposed like ordinary plastics.

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Even though PLA can be decomposed in an industrial composting environment, most countries currently do not have corresponding treatment systems and cannot handle a huge amount of PLA products, so they can only be sent to incinerators. In addition, PLA and PET (polyethylene terephthalate, recycling symbol number 1, mostly made into PET bottles) are similar in appearance and difficult to identify, which makes PLA classification more difficult, and if it is mixed with PET, the value of recycling will be reduced.

Replacing materials cannot solve the problem, stopping "one-time use" is the sticking point

Plastic reduction awareness is on the rise. In response to global trends, many businesses choose to replace single-use plastic packaging and disposable tableware with biodegradable plastics such as PLA, but this cannot really solve the problem of plastic pollution.

As early as 2018, the European Parliament has voted that biodegradable plastics cannot solve the problem of plastic pollution. Since Greenpeace promoted plastic reduction in retail channels in 2019, it has continued to call for "replacing single-use plastic packaging with bare-bones, reusable, and recyclable containers." It should not continue to be "disposable" with another material, otherwise the problems of raw material sustainability and waste pollution will not be resolved.

In order to promote the industry to stop replacing single-use plastic packaging with PLA, the Greenpeace team conducted experiments in 2021, obtained PLA beverage cups, straws, and trays from supermarkets, and placed them in simulated natural environments, namely in soil, on soil, and on sea water. After 60 days of observation, it was found that these PLA products remained in their original state and were not decomposed. In order to reveal to the industry and the public: PLA is not a solution. Please refer the link below:

https://www.youtube.com/watch?v=HvxJ38YqL4o

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Bio-based plastics are not equal to biodegradable plastics

Biobased plastics and biodegradable plastics are two different concepts, but consumers often confuse them, and some manufacturers deliberately confuse them. You should distinguish them clearly.

bio-based plastic

Bio-based plastics refer to components of biological origin, which are then processed into plastics. The common ones are polylactic acid (PLA) plastics that are fermented from starch to lactic acid, and then polymerized; Coca-Cola used sugarcane and the waste generated in the sugarcane production process to produce plant PET bottles (PET); or the bagasse straws that exploded in Taiwan a few years ago (this is a bit controversial, because the main body is still PLA); and the media also reported that the Czech depot Skoda launched a beet bagasse. The residue after the grass becomes biofuel becomes the material of interior door panels, A-pillars and other parts. These are all cases of using biomaterials as polymers, which can replace plastics from petroleum materials, but using biomaterials does not mean that they can be biodegradable, which is a place that many people misunderstand.

biodegradable plastic

Biodegradable plastics refer to substances that are more easily decomposed by microorganisms than traditional plastics under certain conditions, and their sources can be petroleum or bio-based plastics. However, there are differences in the decomposition of plastics. Some of them just disintegrate or decompose. That is, plastics seem to be decomposed, but they are actually decomposed into small particles such as powder due to oxidation or photolysis. The essence is still plastic polymers. But another class of biodegradable plastics, specifically known as "biocompostable plastics," refers to the decomposition process that produces compost or humus, which is a bioavailable smaller molecule that can be added to industrial compost along with organic waste, or directly degraded into carbon dioxide. It is conceivable that this kind of biodegradable plastic is the goal of environmental protection in the minds of many people.

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In 2019 alone, 59% of the biodegradable plastics produced globally were made into plastic bags, food bags, food boxes, beverage cups and cosmetic packaging, and plasticizers or other chemicals were still added during the manufacturing process to meet usage needs; complex materials also made it impossible to recycle, all of which raised concerns about the environment and health.

Blind spots of biodegradable plastic (PLA)

At present, the most commonly known biodegradable plastic on the market is PLA. PLA is often used in the form of transparent cold drink cups, transparent salad boxes, transparent egg boxes, knives and forks, and plastic bags. The PLA material is classified as No. 7 other plastics. PLA is believed by some to be an environmentally friendly material, but is PLA really as ideal as everyone imagines?

PLA cannot be recycled with other plastics

PLA has different properties from other plastics, so it cannot be mixed with other plastics for recycling. It can even be said that mixing other plastics with PLA will greatly hinder its value and feasibility of recycling. At present, PLA and other plastics have to be sorted manually, so this is a major problem in the current plastic recycling system. But many companies don't understand this and use PLA blindly. It is also because PLA must go through an independent recycling system, and most countries lack a mechanism for remanufacturing PLA, so in fact, even if PLA is sorted, most of it is sent to incineration and cannot be recycled (Recycle).

PLA is difficult to decompose in the natural environment

The misunderstanding of PLA caused by many people is that PLA will decompose into natural nutrients or return to carbon dioxide in the natural environment, such as being buried in the soil. In fact, this is from the imagination of many people, or from the deliberate misleading marketing of manufacturers. Someone did an experiment before, and buried the PLA packaging in the soil for half a year, but the appearance of the PLA was still intact and there was no trace of decomposition. In fact, according to previous research by Japanese scholars, PLA must be ideally decomposed under specific conditions, that is, it must be in an anaerobic environment with high enough humidity, above 55 degrees C, and 90% of it can be decomposed within 60 days. So it’s definitely not something so beautiful that can be decomposed by just burying it.

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Taiwan conducts scientific composting degradation experiments on PLA

Scholars Ding Yahan and Luo Kaiyin from the Department of Agricultural Chemistry at National Taiwan University conducted a scientific report, which was published in Taiwan Journal of Agricultural Chemistry and Food Science in March 2021, discussing "Research on the degradation conditions of biodegradable plastic polylactic acid (Taiwanese Journal of Agricultural Chemistry and Food Science (March, 2021) 59(1):11-17). A series of experiments have been done on how PLA can be degraded more quickly.

pre-processing

The degradation of PLA is preferably pre-treated by ultraviolet irradiation to destroy the surface of PLA to facilitate subsequent fermentation. Irradiating UVC for more than 12 hours and UVB for more than 24 hours can accelerate the subsequent decomposition of compost.

Fermentation conditions

Anaerobic solid-state fermentation is the best composting condition, adding rice straw as carbon source and chicken manure as nitrogen source (nitrogen-to-carbon ratio 20), moisture content 60%, and temperature 50°C.

As you can see, the composting degradation reaction of PLA requires these special conditions to achieve degradation in about a month without foul smell. Therefore, the decomposition of PLA is not as easy as the outside world imagines, and it is difficult to achieve 100%.

So far, there is no perfect biodegradable plastic. It is not the plastic that claims to be 100% biodegradable. We can rest assured that as a responsible consumer, we should try our best to reduce the use of plastic (Reduce), recycle as much as possible (Reuse), and do a good job of recycling (Recycle).