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From the perspective of environment, plastic waste (Part 1)

Plastic waste (plastic waste)

Plastic waste refers to waste plastics or products that pollute the environment in daily life and other activities. There are many kinds of plastic wastes, the most common of which are discarded daily plastic products (such as waste plastic shoes, tablecloths, baby diapers, waste plastic bags or artificial leather bags, plastic cosmetic bottles, medicine certificates, etc.), and discarded agricultural plastic products (such as used shed films, mulch films, etc.). In particular, plastic packaging and disposable plastic products have become one of the main components of urban domestic waste, and are easy to be thrown away at will, affecting the urban landscape. This part of plastic waste is often called "plastics litters" in foreign countries

the impact of plastic waste on the environment

this problem should be analyzed from three aspects:

a. plastic has many varieties and uses, most of which are thermoplastics, so a considerable part of plastic waste can be recycled like paper products and metal products. Strengthen the recycling of this part of waste, and it will become waste with adverse effects on the environment only when it reaches the end of its life cycle after repeated use

b. at present, about 30% of the total plastic output belongs to disposable packaging products, medical and health products and mulching films with short service life. After use, some of them become municipal solid waste and enter the waste treatment system; Some of them are discarded at will and become garbage that hinders the landscape. At present, the proportion of plastic waste in the weight of municipal solid waste in western developed countries and major coastal cities of China has increased to about 8 ~ 10%, while the volume has reached more than 30%; Due to its light weight, large volume and difficult degradation, plastics not only increase the difficulty of waste treatment, but also occupy many limited land resources. Therefore, it has a certain impact on the environment

c. due to people's weak awareness of environmental protection and the lack of effective comprehensive waste management countermeasures and measures, some plastic wastes are scattered in nature, which not only pollutes the landscape on land and sea, destroys the ecological balance of the environment, and even endangers the lives of wild animals. This is what people used to call "white pollution"

measures to reduce or prevent the impact of plastic waste on the environment in foreign countries at present

the main countermeasures in foreign countries are to strengthen comprehensive treatment and adopt the policy of combining prevention and treatment such as volume reduction, reduction, recycling and degradation. The main measures are summarized as 3R and 1D. 3R refers to the reduction of plastic packaging waste; Reuse of plastic packaging products; Recycling of plastic packaging waste. 1D is to develop degradable plastics that are beneficial to the environment. Therefore, the current recycling and development of degradable plastics has become an important way for countries to prevent plastic waste from polluting the environment. At present, the profit margin of the coal and steel industry is still below the industrial average level

plastic degradation

the term plastic degradation refers to the end of the life cycle of polymer. As a result, the molecular weight of the polymer and the physical properties of the polymer materials (plastics) are reduced, which are typically manifested in the embrittlement, fragmentation, softening, hardening, loss of mechanical strength, etc. All plastics can be degraded, but there are difficulties. The aging and deterioration of plastics is a degradation phenomenon. However, in general, it takes decades or hundreds of years for plastics to degrade into fragments that are harmless to the environment (less harmful) or into CO2 and water and return to the natural cycle

degradable plastics

degradable plastics refers to the addition of some additives to plastics to promote their degradation function, or the synthesis of plastics with their own degradation properties, or plastics made of renewable natural raw materials, which can meet the original application performance requirements in the use and storage period, and after use, under specific environmental conditions, make it possible to significantly change its chemical structure in a relatively short time, It is a kind of plastic that causes mass loss of 20% - 80% of some sexual humidity

classification of degradable plastics

at present, according to the objective conditions or mechanisms that cause degradation, degradable plastics can be roughly divided into: biodegradable plastics, photodegradable plastics, oxidative degradable plastics and hydrolytic degradable plastics. They can be combined into degradable plastics with better performance, such as light/biodegradable plastics

photodegradable plastic: a kind of plastic degraded by sunlight

biodegradable plastics: a kind of plastics that are degraded by the action of microorganisms existing in nature, such as bacteria, molds (fungi) and algae. Biodegradable plastics can be divided into completely biodegradable plastics and destructive biodegradable plastics

oxidative degradation plastics: a kind of plastics degraded by oxidation

hydrolytic Degradable Plastics: a kind of plastics degraded by hydrolysis

environmental degradable plastics

a kind of plastics that are exposed to environmental conditions, such as light, heat, water, oxygen, pollutants, microorganisms, insects, as well as the combined action of wind, sand, rain and mechanical force, are the general term of degradable plastics

fully biodegradable plastics

fully biodegradable plastics are mainly made from natural polymers (such as starch, cellulose, chitin) or agricultural and sideline products through microbial fermentation or synthesis of biodegradable polymers, such as thermoplastic starch plastics, aliphatic polyester, polylactic acid, starch/polyvinyl alcohol, etc

destructive biodegradable plastics

currently, destructive biodegradable plastics mainly include starch modified (or filled) polyethylene PE, polypropylene PP, polyvinyl chloride PVC, polystyrene PS, etc

(to be continued)

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