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Last time we learned about the types of degradable plastics. What will we learn today? Let’s look down together——

1. Will the large-scale production of biodegradable plastics lead to a food crisis?

At present, the global production capacity of biodegradable plastics is about 1 million tons, with an annual growth rate of about 20% to 30%. Biodegradable plastics such as PBAT from fossil sources are still dominated. Among these plastics, the biodegradable plastics prepared from corn starch are mainly polylactic acid. The current global production capacity of polylactic acid is about 280,000 tons/year, and the apparent consumption is about 160,000 tons/year. Even if the polylactic acid production capacity construction in some reports is realized in recent years, the biodegradable plastics prepared from corn starch as raw materials will only be about one million tons, which will not have a fundamental impact on food. In the past five years or even longer, the impact of the development of biodegradable plastics on the food crisis is very low.

2. What is compostable biodegradable plastic?

Composting is an aerobic process for producing compost. Compostability refers to the ability of a material to be biodegraded during the composting process. If a material, including paper, plastic, etc., is claimed to have compostability, it must state that the material biodegrades and disintegrates in a composting system (as shown in the standard test method) and is fully biodegradable in the end use of the compost. . Compost must meet relevant quality standards. Quality criteria such as low heavy metal content, no biological toxicity, and no clearly distinguishable residues.

3. What is the difference between industrial composting and household composting?

Fertilizer is an organic soil conditioner derived from the biological decomposition of a mixture. The mixture consists mainly of plant residues, sometimes with some organic material and a certain amount of inorganic matter. The raw materials for composting can be organic solid waste from urban and rural areas, such as agricultural crop straw, rural breeding manure, urban domestic waste, kitchen waste, municipal sludge, food industry waste, etc.

Composting, a processing method for producing compost, is a biochemical process that uses microorganisms widely found in nature to controlly promote the conversion of degradable organic matter in solid waste into stable humus. Composting can be divided into aerobic composting and anaerobic composting based on the growth process of microorganisms and whether they provide oxygen. Aerobic composting is the process of decomposing organic matter in the presence of oxygen. The final products are CO2, H2O, and heat. And humus, anaerobic composting means that under anaerobic conditions, anaerobic microorganisms degrade organic matter into CH4, CO2, H2O, heat and humus. Composting generally refers to aerobic composting.

Industrial composting refers to a process in which microorganisms degrade solid and semi-solid organic matter aerobically at medium or high temperatures under controlled conditions to produce stable humus. The general cycle is 180 days, but with changes in aerobic composting technology, the shortest time is 30 days or even shorter.

Home composting refers to the process of aerobically composting household food waste or garden waste to produce compost for home use. Home composting takes longer than industrial composting, but generally does not exceed one year at most.

Whether it is industrial composting or household composting, the organic waste processed should have the following characteristics:

a) Biodegradability (i.e. the original biodegradability of the material);

b) Disintegration performance during composting;

c) Will not adversely affect the biological decomposition process;

d) Adverse effects on the quality of the final compost, such as excessive amounts of harmful elements.

4. Can biodegradable plastics be disposed of only in compost?

This is not necessarily the case. Biodegradable plastics can biodegrade under composting conditions, can also biodegrade under other conditions such as anaerobic digestion equipment, and can also biodegrade under natural environments such as soil, seawater, etc., but the specifics depend on the chemical structure of the plastic and the formula of the product. etc. and are related to degradation environmental conditions. It is incorrect to make a general statement that biodegradable plastics can only be disposed of in compost.

Materials such as PHA and PBAT are relatively easy to biodegrade under seawater, soil, and compost conditions, while PLA is relatively easy to biodegrade under compost conditions, and the degradation cycle or speed under seawater and soil conditions will be relatively slower.

5. Can biodegradable plastics be completely degraded in soil?

Since conditions such as temperature, moisture, and microorganisms are uncontrollable in natural soil, the conditions are relatively uncontrollable compared to the controlled conditions in the composting process. At present, judging from the application of biodegradable mulch films and the results of laboratory and field degradation experiments, most biodegradable plastics can be biodegraded under field soil conditions, such as PBAT, PHA, PCL, PBS, etc., within 5 months under normal climate conditions. It can be completely degraded when buried in the soil and will not have any impact on plants; materials like PLA degrade relatively slowly and take a long time, but after being blended with materials such as PBAT, experimental results show that it can also be degraded within about half a year. Completely degraded.

6. How long does it take for biodegradable plastics to degrade under natural conditions?

The public is particularly concerned about how long it takes for biodegradable plastics to degrade under natural conditions, and this is indeed the case. However, the degradation time is related to natural conditions and the structure and formula of the plastic, and cannot be generalized. If natural conditions do not give microorganisms some suitable conditions for growth or life activities, the degradation of biodegradable plastics and even natural polymers such as paper, straw, wood, etc. will be relatively slow. When we go to suburban woodlands or mountains, we can This is also true when you see some branches, wood or paper on the sand that have not been degraded by the environment for a long time.

Judging from the nationwide demonstration applications of biodegradable mulch films made of PBAT materials in the past five years, they can be completely degraded in 4 to 5 months. In actual mulching applications, even if the crops are not completely degraded when harvested, they will still be degraded after plowing. can be completely degraded.

Materials such as PHA and PBAT can be completely degraded in about 30-60 days under sea water and (25±3) ℃ conditions.

7. Will the degradation products of biodegradable plastics or degradation cause secondary environmental hazards?

Everyone is particularly concerned about whether the degraded products of biodegradable plastics will cause secondary harm to the environment. Therefore, heavy metal content indicators have been added to the degradation performance requirements of biodegradable plastics and strict requirements have been imposed.

Ecotoxicity tests including phytotoxicity tests, earthworm toxicity tests, etc. were conducted on the composted compost of compostable plastics.

In addition to stipulating the degradation performance and heavy metal content of soil-degradable biodegradable mulch films, new international standards also stipulate ecotoxicity.

Therefore, from the current perspective, biodegradable plastics that meet the standard requirements will not cause secondary harm to the environment after degradation.

8. Can biodegradable plastics be recycled?

Biodegradable plastic is actually a special variety of plastics. Its recycling and reuse are not much different from traditional plastics. It can be physically recycled and reused, that is, melting, regeneration and reprocessing.

It’s just that because it has biodegradable properties, it has more ways to be biorecycled than traditional plastics (such as composting), and it can no longer be recycled when used in mulch films. In addition, the chemical structure of biodegradable plastics is mainly based on ester bonds, which is easy to be degraded by alkali, acid or alcohol. Therefore, it can be chemically recycled compared to transmission plastics, and the material can be recycled and regenerated through the use of monomer recycling methods. use.

9. What is the difference between landfilling or incineration of biodegradable plastics and traditional plastics or traditional organic waste?

Some reports believe that biodegradable plastics will produce secondary hazards such as dioxins when incinerated compared to traditional plastics. However, biodegradable plastic is a type of traditional plastic, and its polymer structure does not contain chlorine elements, etc., and there will be no dioxin exhaust gas when incinerated. In addition, the polyester structure of biodegradable plastics determines that compared with traditional plastics such as polyethylene, the organic carbon content in the main chain is lower, making it easier to fully burn when incinerated. When incinerated, biodegradable plastics do not produce more waste gas than traditional plastics.

In addition, there is concern that biodegradable plastics will release more harmful gases when landfilling. Since most modern landfills currently use some devices that collect biogas for energy recovery during the landfill process, even if the biogas is not recycled, there will still be corresponding organic waste. Measures for biogas release after landfill. The solid content of plastic in landfills is less than 7%, and the current amount of biodegradable plastics is less than 1% of traditional plastics. Therefore, even if it is landfilled, there will be no more methane impact on the landfill. question.

I learned a lot today, pick up a notebook and take notes~