Biodegradable polymer materials

In order to protect the global environment, it is necessary to clearly separate and distinguish the sphere of life of human activities from the natural environment of the earth, and it should be possible to make the human sphere of activity a closed system, thereby reducing the emissions of difficult-to-decompose materials. Further, the waste discharged into the earth's environment must be converted into easily decomposable substances, making it part of the natural material cycle.

At present, there are several types of pollution in nature, such as “white” (plastic products) and “black” (rubber products). The perpetrators of these pollutions are polymer materials. Therefore, the development of biodegradable products is necessary and urgently needed.

Biodegradable plastic

The ideal biodegradable plastic is a polymer material that has excellent performance, can be completely decomposed by environmental microorganisms after being discarded, and is eventually inorganicized to become a component of the carbon cycle in nature. As we all know, "paper" is a typical biodegradable material, and "synthetic plastic" is a typical polymer material. Then, biodegradable plastics are polymer materials that combine the properties of both paper and synthetic plastics.

In order to establish a methodology that can simultaneously control the biodegradability and physical properties of polymer materials, various countries in the world are conducting active research on both basic and applied aspects. Since 1990, international conferences on biodegradable plastics have been held in the United States, Europe and Japan. According to relevant reports, a variety of biodegradable polymer materials have been successfully developed. Some of them have already achieved industrial-scale production and some have been put to practical use.

There are four major ways in which polymers degrade: microbial degradation, large-scale biodegradation, photodegradation, and chemical degradation. The definition of photodegradable and biodegradable plastics refers to a class of plastic called photo-biodegradable plastics that undergo photooxidative degradation by natural sunlight and can be further degraded by microorganisms after photodegradation reaches a decay period.
Light-biodegradable plastics are mostly polyolefin plastics supplemented with suitable photosensitizers, biodegradants, oxidizers, and degradation control agents (including stabilizing, accelerating control agents, and biodegradable sensitizers).

Such degradable plastics can be divided into two categories: one is starch-added light-biodegradable plastics, and the other is the use of metal chelates as photosensitizers, whose photodegradation products can eventually be biodegraded. Representative products are Ecostar Plus, Polyclean and so on. Light-biodegradable plastic is actually an improved type of photodegradable plastic, and its application area is substantially the same as that of photodegradable plastic.

Photodegradable plastics can only degrade under sunlight. Plastics that can degrade into small molecules into the ecological cycle are only a very small part. Most plastics only gradually disintegrate into fragments or powders that may not be visible to the naked eye, but their long-term absorption by microorganisms in the soil is not known. When plastic waste is partially buried in the soil or the entire landfill is buried in the ground, it will not be degraded due to lack of light or lack of oxygen and lack of water. It can only change the pollution from visible to invisible, and brings about more ecological environment. Large potential hazards. Therefore, the development of biodegradable plastics will have a positive significance for the entire biosphere.
However, although there are many researches and reports on degradable plastics, many specific problems cannot be solved and the promotion is very difficult. The outlook is not optimistic. The reasons are: First, because biodegradable plastic bags have low load bearing capacity, they cannot meet the requirements of customers for multiple loading and repeated use; second, the biodegradable plastic bags have a dull yellow color and low transparency, giving people a sense of not being clean and ugly. It is not safe to use it. Third, the price is high. Because the business is a free gift, the cost is hard to accept.

Another example is to solve the environmental pollution problem of EPS fast food lunch boxes. Try to replace it with a paper lunch box or a degradable plastic lunch box. However, due to the following reasons, it is very difficult to promote: First, EPS intensity, light weight, good insulation; Second, the price of paper boxes is 1.5 to 2.5 times the EPS; Third, even if the use of degradable PP lunch box, its performance is better than On EPS. Recently, the relevant departments in our country require the use of plant fibers to make disposable tableware instead of EPS. However, due to the use of a polymeric hot melt in the molding process of such plant fiber cutlery, there are still handling problems and the control of pesticide content remaining in plant fiber dishes.

Therefore, the development and research of degradable plastics still have a long way to go.

Waste rubber regeneration cycle

In order to solve the problem of "black" pollution, recycling of waste rubber becomes inevitable. The rubber wastes are mainly recycled through two methods: prototype reuse or reorganization and physical and chemical regeneration.
Reuse or remodeling of prototypes is mainly used for scrap tires, such as retreading of tires, artificial fishing rods, ship protection, road bedding, lifebuoys, track cushions, shoe soles, sports facilities, etc., in particular, large amounts of tires are refurbished and the economic benefits are high. The retreading method is generally scraped off the outer layer of the waste tire, pasted raw rubber, and then vulcanized.

Physical and chemical recycling

The rubber waste can be prepared into a rubber powder or a fine rubber powder. The rubber powder has many uses, for example, it can be blended into a rubber material instead of a part of the raw rubber, and the activated rubber powder or the rubber powder can be used to manufacture various rubber products ( Such as automobile tires, conveyor belts; rubber powder can also be mixed with asphalt, used for highway construction and housing construction; rubber powder and plastic blend the nature, can make waterproof membrane, agricultural water-saving irrigation pipe, silencer board and floor , water pipes and tubing, packaging materials, bathtubs and water tanks, etc.; can also make paints, paints and adhesives; and produce activated carbon.

Reclaimed rubber refers to the product obtained by desulfurizing and re-vulcanizing the vulcanizate. Because the reclaimed rubber process performance is superior to the rubber powder, it is beneficial to mix and rubberize the rubber in the rubber product by adding an appropriate amount of reclaimed rubber. There are several ways to make reclaimed rubber.