What is the difference between photodegradation and biodegradation?

Photodegradation and biodegradation are two different degradation processes that differ in their mechanism of action, environmental conditions, and areas of application. Here are the main differences between the two based on the search results:

1. Mechanism of action:

Photodegradation: Mainly due to the action of light, especially the irradiation of ultraviolet rays, which leads to the photooxidation of polymer materials, and then introduces photosensitive functional groups into the material chain, causing the chain to break, and eventually leading to the decomposition of the material. Photodegradable plastics are divided into copolymer type and additive type, the former is synthesized by copolymer, and the latter is prepared by adding photosensitizer to the plastic substrate.

Biodegradation: refers to the process in which materials are gradually decomposed into smaller molecules through the action of microorganisms in living organisms or in a specific biological environment, and finally converted into harmless substances such as water and carbon dioxide. Biodegradable materials include biodegradable metals, bioceramics and polymer materials.

2. Environmental conditions:

Photodegradation usually requires the presence of light, especially ultraviolet light, and it occurs mainly on the surface of the soil or under light conditions.

Biodegradation, on the other hand, relies on the presence of microorganisms and can take place in soil, compost or in a specific biological environment, without necessarily requiring light.

3. Applications:

Photodegradable materials are often used to reduce the environmental pollution of plastics, for example by adding photosensitizers to promote the decomposition of plastics.

Biodegradable materials are widely used in the medical field, such as surgical sutures, drug controlled release systems, etc., as well as in the environmental protection field, such as degradable plastic bags.

4. Degradation products:

The end product of photodegradation may still be a small molecule that is not degradable and may still be potentially harmful to the environment.

The end product of biodegradation is usually harmless and can be absorbed by the natural environment or converted into other harmless substances.

5. Degradation efficiency:

The efficiency of photodegradation is affected by factors such as light intensity, photosensitivity of the material, etc.

The efficiency of biodegradation is affected by factors such as microbial species, ambient temperature, humidity, etc.

6. Standards and Specifications:

According to the current GB/T 20197-2006 standard, although photodegradable plastics and thermal-oxygen degradable plastics comply with the national standard, they may be deleted by the revised standard, because they only lead to changes in the size of plastics, and the degradation process may produce microplastics, which are harmful to the environment.

The implementation standard for biodegradable plastics is GB/T 38082-2019, which requires that the biodegradation rate must reach a certain standard, and it needs to pass ecotoxicology tests.

In summary, photodegradation and biodegradation have obvious differences in degradation mechanism, conditions, applications and effects.