Recycling and Recycling Technology of Biodegradable Plastics (5)

Recycling and Recycling Technology of Biodegradable Plastics (5)


The purpose of the aforementioned material recycling, heat recycling and chemical recycling is to regenerate the same or another raw material”, “return to raw material basic substances”, “energy (heat) recovery, utilization ”, while biological recycling refers to the use of biological functions for recycling, including regeneration and transformation operations. In contrast, the latter is rather vague, and there are some overlaps in the category with the above-mentioned forms of recycling. Therefore, if these four concepts are simply juxtaposed, there may be room for discussion.

Since the concept of biological recycling is relatively new. Although there is a clear definition of this concept in ISO related materials, there are not many descriptions, and even people who have been engaged in related research for a long time are not very accustomed to it. And now, the so-called “biological” or “biological”, so far there is no accurate definition.

1.Biological recycling and reuse in the recycling system

Many unused resources in the resource cycle can be used as biomass resources. In other words, a wide variety of biomass resources are utilized in various forms, so it is impossible to introduce them one by one. The picture shows the cycle of food production, consumption. On the right is (cultivation) agriculture, livestock industry, forestry, etc., which can produce various resources such as cultivated biomass. Furthermore, the food in it, or the food material, generates waste (by-product) at various stages.

Recycling and Recycling Technology of Biodegradable Plastics (5)
Circulation of unused (biomass) resources around the production of food materials

There are 10 million tons of domestic waste involved in the food recycling law, and about 10 million tons of household waste other than this. The forms of effective use of these, which are marked with boxes in the figure, are mainly in the form of heat energy and useful substances (including compost). Among them, there are four recycling methods including material recycling, thermal recycling, chemical recycling and biological recycling.

The higher the picture, the higher the ranking (meaning, convenience, practicality, economy). It can be seen that, firstly, high value-added substances, human food, and livestock feed, and secondly, the use of convenient high-fluid fuels (methane, fuel cells) is more advantageous. Fertilizers like composting and the like are again. The technology has entered the practical stage, which means that the price must be reduced to a suitable range. The utilization of agricultural materials in the form of agricultural materials is now mostly limited by the price. Simple incineration is at the bottom, but if it is changed to electricity/heat utilization or waste power generation, the position will be higher.

In these application forms, excluding the lowest combustion and the secondary electricity/heat utilization, an example of biological recycling can be seen.

In the classification of new functional ecological materials, food processing residues and food residue sugars undergo lactic acid fermentation to produce lactic acid, which can be regarded as either biological recycling or chemical recycling. The resulting lactic acid is then polymerized to form a bio-based polymer, PLA.

In the classification of the utilization forms of food materials and feeds, food processing residues and food residues are also fermented and decomposed under the action of aerobic microorganisms to be used to produce new fermented foods, and livestock with improved nutrition and digestibility. Feed, etc., is also a kind of biological recycling.

In the classification of fluid fuel production, the technology of producing biogas under the action of methane bacteria using livestock excrement and urine and BOD wastewater from food factories as raw materials has already been implemented and has high practicability. Methane gas itself has a low calorific value and is also mixed with carbon dioxide gas, so it needs to be refined if it is used in a combustion battery. Moreover, the reaction is highly temperature-dependent, so the reaction efficiency will be lower in a cold environment. However, on the one hand, it can be used as a purification treatment method for high-concentration BOD wastewater, and the treatment residue can also be used as fertilizer, which will undoubtedly become one of the biological recycling technologies.

In the classification of fertilization or soil improvement materials, composting can have positive effects on both soil improvement and waste disposal, so it has attracted attention for a long time. One of its biggest features is that most of the objects of composting are substances derived from our human food production and consumption activities, and then the final product compost can be used for food production and agriculture, thus forming a cycle. Although composting has existed for a long time, there are still many problems that need to be solved urgently, and in order to correctly evaluate and fix the composting technology, it is also necessary to organize data.

2.Biorecycling of biodegradable plastics and biodegradable bio-based polymers

Biorecycling of plastics starts with the difference between biodegradable plastics and biobased polymers.

In recent years, on the basis of the original food containers, mulch for cultivation, garbage bags and other products, rope-shaped, ribbon-shaped, mesh-shaped biodegradable products used in the production and distribution of vegetables, and some stationery have appeared. In particular, the mulch film for cultivation does not need to be recycled after use, as long as it is ploughed into the soil, and there is no need to worry about environmental issues, thus making a great contribution to the labor-saving of agricultural operations.

As long as the biodegradable plastic meets the mentioned standards, it does not matter even if the source of petrochemical resources is confirmed as long as the biodegradability is confirmed. Biomass products focus on the carbon dioxide reduction effect, which has important environmental protection significance, and will vigorously develop uses other than biodegradability in the future, which are feasible directions in the automotive and electronic industries.

BiodegradabilityPetroleum plasticBio-based polymers(Saving petrochemical resources and suppressing the increase of greenhouse gases)
No biodegradabilityPE, PP, PS, PVC, phenol resin, etc.PTT, Soy Polyol, PU
biodegradable(One of the options to solve the problem of waste disposal)Aliphatic polyester, aliphatic/aromatic polyesterPLA, starch resin, PHA
1) Polyester of 1,3 propylene glycol and petrochemical-derived terephthalic acid obtained by fermentation;
2) PU synthesized from polyols derived from soybean oil;
3) Among the aliphatic polyesters, the technology of producing PBS from biomass raw materials such as waste paper has been developed;
4) Microbially produced polyester (PHA).

At present, resin materials derived from biomass are called “bio-based polymers”. For a long time, the main body of the definition of biodegradable plastics (green plastics) is biodegradability, while bio-based polymers are based on the origin of raw materials. Therefore, these two concepts cannot be confused. Existing plastics are classified by these two discriminant indicators and listed in the table. Although most plastics are neither biodegradable nor derived from biomass, it is necessary to determine which of these four categories the new materials that will appear in the future belong. But as far as the existing plastics are concerned, there are corresponding materials in the four categories. Among them, biodegradable petroleum-based plastics and bio-based polymers can be directly used as objects for biological recycling. Also, it should be emphasized that not all bio-based polymers are biodegradable.

Recycling and Recycling Technology of Biodegradable Plastics (5)
Decomposition mechanism of PLA under composting environment

The production of bio-based polymers derived from biomass is closely related to bio-recycling. The following will focus on the bio-recycling of bio-degradable plastics and bio-based polymers after use. The relevant content of the biodegradation mechanism has been introduced before. The representative biodegradable bio-based polymer, PLA, is decomposed in the representative biorecycling and recycling process-composting environment. The mechanism is shown in the figure. Substances smaller than oligomers are metabolized by microorganisms and completely decomposed into carbon dioxide and water, rather than turning back into plastic materials and their main constituents. So some people think that this route is one-way and cannot be called recycling. Others believe that water and carbon dioxide can also be absorbed by plants and become biomass resources again, so they should also be included in biological recycling and reuse (Figure). And even if it is discontinued in the middle stage, the intermediate product of plastic can also be used as an active ingredient of composting.

Recycling and Recycling Technology of Biodegradable Plastics (5)
When PLA products are decomposed and incinerated, the carbon dioxide produced is absorbed and fixed by plants and will not be released into the atmosphere, so PLA is also known as a “carbon neutral” material.

The value of biodegradable materials in biorecycling is more in terms of supplementary materials. To thoroughly sort and recycle household waste, we need kitchen waste collection mesh bags and garbage bags that can be easily sorted, discharged, and directly put into composting.

In the design of garbage bags, the collection time should also be taken into account, so that they cannot be biodegraded during the household storage period. Since this was not noticed in the initial product, there was a case of decomposing and giving off a bad smell during storage.

The largest attempt at biorecycling and recycling of biodegradable bio-based polymers was held in Aichi from March to September 2005. A total of 120,000 reusable food utensils in 12 categories, 20 million in 24 types of disposable food utensils, and about 550,000 garbage bags have been invested (Figure 8-15). Among them, some disposable food utensils, garbage bags and some damaged reusable food utensils are collected together with household garbage, mixed with livestock manure, etc., and then composted. The compost produced is used by nearby farmers, and vegetables and fruits are grown to supply the venue.

Recycling and Recycling Technology of Biodegradable Plastics (5)
Reusable containers used in the theme restaurant of the Expo

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