Degradable Plastics Knowledge Series (3)

Degradable Plastics Knowledge Series (3)

Question: Can microorganisms degrade polymers containing benzene rings in backbone?

Because backbone of polymers containing benzene rings is relatively stable, many people think that biodegradable plastics containing benzene rings cannot be degraded by microorganisms, but since biodegradable aromatic polymers, due to their special chemical structure, there are also microorganisms that can decompose benzene rings in nature, so they can also be biodegraded, and toxicity of decomposition products does not harm environment. The figure below shows changes in organic carbon and its microorganisms (hyphae) during decomposition of PBAT.

Degradable Plastics Knowledge Series (3)

Fig.2 Mineralization and surface settlement of films of three PBAT variants during 6-week incubation in soil

Degradable Plastics Knowledge Series (3)

Fig. Fig. 4. NanoSIMS images obtained after prolonged spray erosion of a PBAT film

(Image Source:Biodegradation of Synthetic Polymers in Soils: Tracking Carbon to CO2 and Microbial Biomass, Zumstein et al., SCIENCE ADVANCES, 4: eaas9024, 2018, July)

Organic carbon in each structural unit of chemical structure of PBAT is decomposed by microorganisms in soil, including filamentous fungi, with formation of new substances. Studies have shown that decomposition of organic carbon has not caused any harm to plants Influence.

Question. How dissatisfied is public with decomposing plastic?

(1) Biodegradable plastic is considered to degrade when exposed to air or use

Some consumers may mistakenly believe that biodegradable plastic will degrade during use or when exposed to air, because biodegradable plastic requires temperature, humidity, and microorganisms to degrade. It will not degrade during use or storage.

(2) Biodegradable in any environment

Because of different varieties and different chemical structures, biodegradable plastics have different degradation behavior under different conditions. In addition, decomposition also requires certain external environmental conditions, as mentioned above. Therefore, biodegradable plastics cannot be used in any environment. Decomposition. At present, most biodegradable plastics decompose in soil, sea water, compost and other environments under suitable temperature and humidity conditions, and are decomposed by microorganisms.

It is therefore recommended to recycle biodegradable plastics like traditional plastics after they have been used and discarded. Those that can be physically recycled can be recycled first, and those that are not easily recycled or difficult to recycle are recommended. undergo biological or chemical processing.

(3) Biodegradable plastic can only be composted

The conditions and environment of decomposition of biodegradable plastics may be different. They can decompose in compost, soil, river water, sea water and other environments when temperature and humidity and their microorganisms are suitable, so it is not only under conditions of composting It can decompose, and biodegradable in conditions such as soil. But since composting is a controlled state, biodegradation process is relatively easier to control.

Q: Can biodegradable plastic be recycled? How to recycle?

Biodegradable plastics are a special kind of plastics. Their recycling and reuse is not much different from traditional plastics. They can be physically recycled and reused, i.e. regenerated by melting and reprocessing.fight.

Just because it has characteristics of biodegradation, it has more biorecycling methods than traditional plastics (such as composting) and can no longer be recycled when plastic film is applied.

In addition, chemical structure of biodegradable plastics is mainly based on ester bonds, which are easily broken down by alkali, acid or alcohol, so they can be chemically recycled compared to transmission plastics.

Q: Will biodegradable plastic affect recycling of conventional plastic?

More than 160 types of traditional plastics are currently widely used. One of them is biodegradable plastic, which is currently used in small quantities. The recycling of traditional plastics is influenced by blending of biodegradable plastics. The complexity of traditional plastic hybrid system will not matter much due to addition of one type of degradable plastic. It is possible that in some recycling systems, such as PET bottle recycling system, more PLA materials will make things more difficult. but PET bottles. The recycling system will also cause difficulties due to use of new types of non-degradable polyester bottles, such as traditional plastics such as PBT and PEN. From a modern sorting system using infrared sorting method, it is quite possible to realize separate processing. So this question is just subjective opinion of some people who did not consider technical improvement of original disposal system.

Q: What is role of biodegradable plastic in waste sorting and recycling? What else can a waste sorting and disposal system do to fully reflect importance of degrading biodegradable plastics?

In terms of design and use value, biodegradable plastics are used in case of biochemical disposal of single-use products and mixing them with organic waste after use or when they are difficult to recycle, such as mulching products after use. The function of biodegradation of degradable plastics can be reflected more fully.

However, since global waste classification and waste disposal is not reasonable, even in developed countries such as Europe and United States, waste classification and disposal are very standardized, there will always be a part of plastic packaging that will be released into natural environment unintentionally or intentionally Among them, if these products can be replaced with biodegradable plastics, risk of environmental pollution can also be reduced. Therefore, use of biodegradable plastics can also be seen as a preventive measure to avoid environmental pollution caused by unintentional release of plastic waste outside closed waste system.

In addition, with improvement of classification system and removedwaste management in my country by adjusting formula of biodegradable plastic garbage bags, it is more suitable for biochemical treatment process of urban organic household waste to solve problem of current residential area. Throwing food waste bins every day, you need to take initiative to break bag and cause personal hygiene problems.