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Degradation mechanism of biodegradable plastics
 
 
 
Detail
 

The degradation mechanism of biodegradable plastics is that biodegradable plastics are caused by bacteria and other microorganisms

3. 1: biophysical effect, which causes mechanical destruction of the polymer due to the growth of its cells after microbial erosion;

2:

Biological chemistry, the action of microorganisms on polymers and new substances;

3. The direct action of enzyme, the microbial erosion part

Causes plastic to split or oxidize.

Biodegradable plastics can be divided into complete biodegradable plastics and biodestructive plastics according to their degradation characteristics.

(1) complete biodegradable plastic: refers to the total decomposition of carbon dioxide and water in a certain period of time under the action of microorganisms

Of compounds.

(2) destructive biodegradable plastics: the polymer can only be decomposed into scattered fragments under the action of microorganisms.

According to its origin, it can be divided into microbial synthetic materials, chemical synthetic materials, natural polymer materials and mixed materials

And so on.

(1) microbiological synthesis: microbial synthesis polymer is a kind of material produced by the biological fermentation method, mainly

Microbial polyester and microbial polysaccharides were included in the study.

At present, the bacteria can be used to synthesize microbial polyester

There are more than 80 kinds.

This kind of product has high biological decomposition and good thermoplastic and easy forming process but in heat resistance and mechanical strength

3

There are still problems in performance, and the cost is too high. It has not yet been well applied and is now trying to switch to various other sources of carbon

Reduce costs.

(2) chemical synforming: chemical synforming materials are mostly fatty group polyesters introduced in the molecular structure of esters

The esters in nature are easily decomposed by microorganisms or enzymes.

For this type of degradable plastics it is still necessary to study how to control it

Chemical structure, so that it completely decomposes.

In addition, the cost cannot be ignored.

(3) natural macromolecular type: starch, vitamin, chitosan, protein and so on are natural high polymer material, this kind of material

The source is abundant, can be completely biodegradable, and the product is safe and non-toxic, and therefore more and more attention.

However, natural polymers

Although the material is completely biodegradable, it has poor thermal and mechanical properties and cannot meet the performance requirements of engineering materials.

Therefore, the current research direction is through natural macromolecule modification, the natural polymer degradable plastic with practical value is obtained.

(4) mixed plastic: a mixture of two or more polymers, at least one of which is divided into living organisms

Can degrade, this component USES starch, cellulose and so on natural macromolecule, the starch is much more.

Starch mixtures of creatures

There are three types of degradable plastic: starch filled biodegradable plastic, starch grafted biodegradable plastic, starch matrix

Biodegradable plastics.

Photodegradable plastic refers to the role of the plastic in absorbing ultraviolet light under the sunlight and causing the key to weaken.

Long chains split into smaller fragments with lower relative molecular weight, the integrity of the polymer is destroyed, and the physical property is degraded.

The lower

The particles of relative molecular weight are further oxidized in the air, resulting in free radical chain reaction, which can be degraded into energy

Biodegradable low molecular weight compounds are finally completely oxidized to CO2 and H2O.

The degradation of photodegradable plastic mainly depends on the effect of ultraviolet ray.

The activation energy of the plastic oxidation reaction is approximately

20.91 ~ 46.3 KJ/mol, the pyrolysis activation energy is 125.4 ~ 334.4 KJ/mol, the dissociation energy of various chemical bonds can be obtained

167.2 ~ 418KJ/mol, and natural light consists of visible, infrared and ultraviolet light, only uv light to plastic

The degradation works.

When a large molecule of plastic absorbs ultraviolet light, it will be in a state of excited state and thus can be degraded

Sex.

Ultraviolet light is mainly derived from solar radiation.

Its wavelength range is 290 ~ 400 nm.

Although uv light only makes up the sun

It's about 6% of the radiation, but it's equivalent to 292.6 ~ 418KJ/mol of light energy.

That's about 6 percent of the uv light

The energy is very powerful in attacking the chemical structure of plastic polymer, and it is very powerful in the process of photochemical degradation, such as breaking chain and breaking chain

Energy is sufficient to cut off most of the bonding force in the plastic.

The absorption and absorption of solar radiation by traditional plastics

The rate is limited and the number of reactive molecules is small, and there is no sharp photodegradation in sunlight.

because

When the photosensitive group is introduced into the polymer chain, it can be triggered after absorbing ultraviolet light, causing the polymer to break down from the weak bond.

The resulting lower relative molecular mass can further oxidize in the air, resulting in free radical breaking chain reaction

At the same time, further degradation, namely the famous photodegradation of Norrish, can accelerate the photosensitization of polymer materials

Degradation.

In addition, natural environments such as oxygen, heat and water also accelerate the process of photodegradation.

The product of photodegradation (powder) is in

Nature continues to be degraded by environmental microbes into CO2 and H2O, into the benign ecological cycle of nature.

There are two methods of preparation of photodegradable plastics: one is to introduce the photosensitive group (such as carbonyl) into the polymer structure

The copolymerization formed photodegradation plastic;

Another is the addition of photodecomposition agents to the polymer materials, which are absorbed by the photodecomposition agent

The photoenergy (mainly uv) produces free radicals, and then causes the macromolecules to oxidize and react to deterioration

In addition, it can be called adding photosensitive dosage form photodegradable plastic.

Photodegradable plastic begins to age under ultraviolet light, and oxygen in the air is involved in this change, so it's real

The quality is photooxidative degradation, but this process of natural degradation is slow, so it is not, strictly speaking, health

Plastic.

4

Light/biodegradable photodegradation of a class of plastics combined with microorganisms (which include synthetic polymers and adding light or raw material

It has the characteristics of light and microbial degradable plastics at the same time.

Water degradable plastic is used to add water absorbent material in plastic, and it can be dissolved in water after use. It is mainly used in medicine

Medicine hygienic equipment (such as medical gloves) is easy to destroy and disinfect.


 
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