Everyone knows that plastics bring a lot of convenience to our lives, work and travel, but most of these plastics are extracted from petroleum, and the reserves of petroleum are limited. Not only will there be a day of exhaustion, but also in the exploitation and fractionation. When cracked oil becomes a variety of products, and further deep into the products we use, carbon emissions and incomplete sewage treatment will bring more harm to our environment, but this is not all. In the process of product use, and after the end of use, plastic has been destroying our ecological environment. Recently, various news media have reported a lot of plastic "white pollution", which threatens the living environment of various organisms including us. .

Polylactic acid material is an environmentally friendly material that can be completely biodegradable. The total amount of CO2 and water produced after degradation is balanced. It does not increase the greenhouse effect of the atmosphere, does not cause any pollution to the environment, and does not produce any toxic substances. . If it flows into soil, sewage, rivers and oceans, it can be completely decomposed into CO2 and water in 3-6 months under the action of bacteria and other microorganisms.

In terms of performance, PLA has good processing and use performance. It can be processed by traditional techniques such as injection molding, extrusion, and spinning. The fibers, films, sheets, and plates made from polypropylene (PP) and poly Ethylene (PE), polyester fibers (PET, PTT, PBT) and other general chemical materials have similar properties, which can gradually replace petrochemical fibers and petroleum plastics. Application areas include clothing, packaging, agriculture, home furnishing, auto parts, and 3D Printing, biomedicine, etc.

So there is no dispute that PLA is a degradable material, but how is it degraded step by step.

First of all, degradation is a micro-level matter, and it takes a long time. This is also the reason why materials can satisfy our use in normal environments. The clothes we wear and the plastic products we use are also degrading at the micro level, but some materials degrade very slowly, even taking hundreds of years. Therefore, degradation cannot be observed by our naked eyes. We only need to understand the truth and know that it is constantly going on.

From the initial chemistry, it is known that oxidation-reduction reactions are more common among chemical reactions of several substances. Natural organisms, including plants, animals, and microorganisms, are all accompanied by oxidation reactions in their metabolism and the reproduction of life, as well as birth, aging, sickness and death.

We should understand that the oxidative decomposition of organic substances in the cells of organisms produces carbon dioxide, water, and releases a large amount of energy. Biological oxidation and the combustion of organic substances in vitro are chemically the same in nature, and follow the general law of redox reactions. The amount of oxygen consumed, the final product, and the energy released are all the same, but the speed is different.

Oxidation reaction is one of the main ways of degradation, and different polymers have different molecular structures. The presence of oxygen can also aggravate the destructive effects of light, heat, radiation and mechanical forces on the polymer, causing it to undergo more complex degradation reactions. Polylactic acid molecules have ester bonds that are more sensitive to water and heat. Under high temperature, aerobic and humid environments, the ester bond breaks and degrades to varying degrees.

Then the polymerization of lactic acid is through the ring opening of lactide, and the lactic acid molecules are connected through ester bonds. During degradation, an oxidation reaction occurs, the ester chain is broken, and the long polymer chain is split into shorter parts, which become lactic acid molecules.

The carboxyl part of the lactic acid molecule is oxidized and decomposed into carbon dioxide (CO2) and water (H20). Then the oxidation of other functional groups also occurs simultaneously. The hydroxyl groups in the lactic acid molecule are also oxidized and converted into aldehyde groups and carboxyl groups, and then continue to be oxidized and decomposed into carbon dioxide and water, and the degradation continues.