For a long time, the “white pollution” of plastic bags has been a big stone in the hearts of the public, making it difficult for us with conscience to buy things.
Then, there is the concept of biodegradable plastic bags. Everyone seems to see the hope that they can buy and buy quickly.
Is it true? I recently visited a large plastics company to gain a deep understanding of the process and technology of biodegradable plastic bags. When I came back to do some research, I found that the saying “degradable plastic bags are more environmentally friendly” is not valid.
1 There are many “fake” biodegradable plastic bags on the market
Most of the biodegradable plastic bags available to consumers on the market are fake concepts.
1) “Stone Plastic Environmental Protection Bag”
The so-called “stone plastic environmental protection bag”, as the name suggests, is made of calcium carbonate fillers added to polyethylene plastics. Calcium carbonate is indeed one of the main components of stone. Adding calcium carbonate filler can reduce the use of polyethylene plastic, and polyethylene comes from non-renewable petrochemical resources. From this perspective, the stone plastic environmental protection bag saves non-renewable petrochemical resources and has a certain environmental value.
But this has nothing to do with degradability. Polyethylene is still the same polyethylene. What’s more, when this kind of bag is discarded, it becomes brittle by weathering, and it is easier to produce plastic dust particles, which may be more harmful to the environment.
Therefore, the stone plastic environmental protection bag is a plastic bag mixed with stone powder. The plastic dust produced after “degradation” enters the environment, and then enters animals and human bodies through food and water sources, which is even worse.
2) Starch-based plastic bags
Bio-based (or starch-based) plastic, the standard number is QB/T 4012-2008, and its ingredients are made of ordinary HDPE/LDPE with starch and N kinds of additives, among which the starch content is more than 15%
The principle of degradation is that the produced bag has many honeycomb-like holes on the surface under the microscope, which effectively increases the contact area of the product with the air, and after the starch component is decomposed, the other plastic components contact the air with a larger area, which speeds up Oxidation speed, coupled with some degradation-promoting ingredients in starch-based plastics, will cause the bag to disintegrate into very small particles in a short period of time.
Starch-based plastic bags, similar to stone plastic environmental protection bags, use starch instead of stone powder. Starch is indeed easy to decompose, but the same polyethylene is still polyethylene. After the bag collapses, it becomes polyethylene particles and enters the environment, which is not environmentally friendly.
3) Even selling dog meat by hanging sheep’s heads altogether
2 There are truly biodegradable plastic bags, but there are very few on the market
So what exactly is degradation?
Degradation refers to high molecular polymers that undergo biological and/or chemical reactions (bacterial decomposition, oxidation, light, etc.) into small molecular substances such as water, carbon dioxide, and methane.
This is a process of changing the chemical structure of a substance.
The main material of plastic bags, PE (polyethylene), has a tight molecular structure, and it will take hundreds of years to gradually degrade. To find a plastic bag that can quickly degrade in a short time, new materials must be needed.
Indeed, there are already real biodegradable plastic bags: PBAT, PLA, etc.
PBAT-is a copolymer of aliphatic (butylene adipate) and aromatic (butylene terephthalate), which combines the excellent degradation performance of aliphatic polyester and the good mechanical properties of aromatic polyester . The processing performance of PBAT is very similar to that of LDPE, and the film can be blown with LDPE processing equipment.
PLA-Polylactic acid is made from starch raw materials proposed by renewable plant resources (such as corn, cassava, etc.). Starch raw materials are saccharified to obtain glucose, which is then fermented by glucose and certain strains to produce high-purity lactic acid, and then a certain molecular weight polylactic acid is synthesized by chemical synthesis. It has good biodegradability. After use, it can be completely degraded by microorganisms in nature under specific conditions, and finally produce carbon dioxide and water.
Seeing the difference between this price and volume, I seem to suddenly understand something. . .
So what if the price drops to the same as ordinary plastic bags?
3 Even if the price is reduced, fully degradable plastic bags are still not so environmentally friendly.
1) First of all, recycling channels are not supported.
There are still a large number of ordinary plastic bags on the market. The recycling methods of these two types of plastic bags are completely different, and they are very difficult to distinguish in actual use.
Therefore, the recycling process will likely be mixed together, so two situations will occur:
- a) Sent to compost to degrade, fully degradable plastic bags are no problem, ordinary plastic bags cannot be degraded, and finally affect the composting treatment
- b) Sent to recycling, ordinary plastic bags can also be re-granulated, fully degradable plastics become impurities, resulting in unqualified recycled materials
Unless, overnight, all ordinary plastic bags can disappear and all are replaced by fully degradable plastic bags.
The elimination of outdated production capacity is very difficult to happen suddenly.
2) In addition, fully degradable plastic bags are produced using a large amount of food as raw materials.
According to the current consumption of plastic bags in our country, all plastic bags should be replaced by fully degradable plastic bags. Experts have calculated that it will take about one grain output in Hunan Province.
Now that food still depends on imports, how can there be extra plastic bags for you? ?
3) Secondly, the degradation of fully degradable plastic bags is conditional.
According to the manufacturer, under industrial composting conditions, rapid degradation can be completed within 6 months. Industrial composting specifically refers to a composting environment with a high temperature of 50-60 degrees, a certain humidity, and fermentation of specific strains.
And some research institutions and environmental protection volunteers have done experiments in real environment:
- In 2014, Central South University of Forestry and Technology simulated natural soil, 12 months PLA plastic test, and its quality only lost 0.23% after 12 months;
- In 2017, the 400-day test at the University of Myroit, Germany, placed in seawater and fresh water, and finally only about 0.5% of the mass loss of PLA;
- Volunteers in Beijing did a similar experiment in the park. After burying for 210 days, only a small part of it was degraded.
Conclusion: Under the current circumstances, the degradable plastic bag does not have sufficient environmental protection properties, so use it with caution.