Knowledge of plastic bags - Chapter 1.

2022-10-10 09:41:17 Monica

Plastic bags are bags made of plastic (commonly used plastics include polypropylene, polyester, nylon, etc.) as the main raw material. They are essential items in people's daily life and are often used to hold other items. It is widely used because of its advantages of low cost, extremely light weight, large capacity and easy storage, but it has been banned from production and use in some countries due to its extremely long degradation cycle and difficult handling.

Since June 1, 2008, China has implemented a plastic restriction order: a system of paid use of plastic shopping bags has been implemented in all supermarkets, shopping malls, bazaars and other commodity retail places. Manufacture, sale and use of plastic shopping bags with a thickness of less than 0.025 mm.

In March 2018, the Panama government said it had decided to ban single-use plastic bags in stores in order to reduce the amount of marine debris in the Pacific and Caribbean.

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Development History

Cybertron discovered the plasticity of nitrocellulose, and that things made from it were impermeable to water. He made some beautiful rice bowls, cups, bottles and teapots out of it with great interest. He admired these masterpieces of his own, and he wrote to his friend Faraday, a famous scientist, about this unexpected result. It's a pity that Faraday didn't care at that time until a photographer appeared. Photographer Alexander Parks has many hobbies, photography is one of them. In the 19th century, people couldn't buy ready-made photographic film and chemicals as they do today, and often had to make what they needed themselves. So every photographer must also be a chemist.

The "ancestor" of this amazing material is the most abundant cellulose in plants.

In 1845, Cybertron, a chemist living in Basel, a city in northwestern Switzerland, accidentally encountered concentrated sulfuric acid and concentrated nitric acid on the table while doing an experiment at home. He hurriedly picked up his wife's cloth apron to wipe the table. mixed acid. After the fuss, he hung the apron to dry by the stove. Unexpectedly, the apron burned with a "pop" and turned to ashes in an instant. Cybertron returned to the laboratory with this "major discovery", and repeated "accidents". After many experiments, Cybertron finally found the reason: the main component of the original cloth apron was cellulose, which was in contact with the mixture of concentrated nitric acid and concentrated sulfuric acid to form nitrocellulose resin, which was later widely used nitrocellulose. .

One of the materials used in photography is "collagen", which is a solution of "nitrocellulose", ie, a solution of nitrocellulose in alcohol and ether. At the time it was used to glue light-sensitive chemicals to glass to create an equivalent similar to photographic film.

In the 1850s, Parks looked at different ways of dealing with collodion. One day he tried mixing collodion with camphor. To his surprise, the mixing resulted in a bendable, hard material. Parks called the substance "Paxine," and that was the first plastic.

Parks made all kinds of objects out of "Paxine": combs, pens, buttons and jewelry prints. Parks, however, was not very business-minded and lost money on his own business ventures. In the 20th century, people began to discover new uses for plastics. Almost everything in the home can be made of some kind of plastic.

It was left to other inventors to continue to develop and profit from Parks' work. John Wesley Hayat, a printer from New York, saw the opportunity in 1868, when a company that made billiards complained of a shortage of ivory. Hayat improved the manufacturing process, and gave "Pakxin" a new name - "celluloid" (false ivory - translation). He got a ready market from billiard manufacturers, and it wasn't long before he was making a variety of products out of plastic.

Early plastics were prone to fire, which limited the range of products that could be made from it. The first plastic to successfully withstand high temperatures was "Bakerlite".

In 1909, Baekeland in the United States synthesized phenolic plastics for the first time. In the 1930s, nylon was introduced, which was described as "a fiber made of coal, air and water, thinner than spider silk, stronger than steel, and better than silk". Their appearance laid the foundation for the invention and production of various plastics thereafter. Due to the development of the petrochemical industry in the Second World War, the raw material of plastics replaced coal with petroleum, and the plastics manufacturing industry also developed rapidly.

Plastic is a very light substance that can be softened by heating it at a very low temperature, and it can be shaped into anything you want. Plastic products are bright in color, light in weight, not afraid of falling, economical and durable. Its advent not only brings a lot of convenience to people's lives, but also greatly promotes the development of the industry.

However, it is less than 100 years since the invention of plastics. If people were ecstatic about their birth at that time, they now have to take great pains to deal with these things that are flooded in life and pose a great threat to the human living environment. Plastics are chemical petroleum products derived from petroleum or coal that are difficult to degrade naturally once produced. Plastic buried in the ground for 200 years will not rot and degrade. A large amount of plastic waste is buried underground, which will destroy the permeability of the soil, make the soil compact, and affect the growth of plants. If livestock accidentally eat plastic mixed with feed or left in the wild, it can also cause death due to digestive tract obstruction.

From 2012, Hungary will completely ban the use of plastic bags. In 2012, Hungary used an average of 160 to 170 plastic bags per person, while in 2018, the number of plastic bags used per person in Hungary was 80.

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Plastic consumption

The annual output of plastics in China is 30 million tons, and the consumption is more than 6 million tons. If plastic bags are calculated based on 15% of the annual plastic waste, the world's annual plastic waste is 15 million tons, China's annual plastic waste is more than 1 million tons, and the proportion of waste plastics in the garbage accounts for 40%, such a large amount. The waste plastics are buried underground as garbage, which will undoubtedly bring more pressure to the arable land that is already lacking.

While plastic brings convenience to people's lives, it also brings unmanageable troubles to the environment. People call the disaster caused by plastic to the environment "white pollution".

In many countries, waste plastics are disposed of by incineration (regeneration of thermal energy) or by reprocessing (regeneration of products). These two methods enable waste plastics to be recycled and achieve the purpose of saving resources. However, since waste plastics will produce gases that are harmful to the human body and pollute the environment when incinerated or reprocessed, it can be said that the disposal of waste plastics will still be a major headache in environmental protection work until 2021.

plastic use

High pressure polyethylene plastic bag

The invention of plastic bags has brought great convenience to human life, but more and more people do not know how to use it effectively and environmentally, which has led to the globalization of plastic bag pollution.

Compared with traditional plastic bags, the advantages of environmentally friendly bags:

1. The water-soluble speed can be selected by design, completely dissolved in water, non-toxic and non-polluting;

2. Strong stretch and good tension;

3. High transparency and good gloss;

4. High softness and good touch;

5. Good oil and solvent resistance, heat sealable and printable;

6. Low air permeability and good gas barrier;

7, can add plastic buckle or self-adhesive bag;

8. Excellent antistatic performance, no dust collection, etc.

9. Can be degraded by water, air, sunlight and biology. Usually about a month, it can be decomposed into harmless substances.

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Plastic properties

Commonly used food plastic bags are mostly made of polyethylene film, which is non-toxic, so it can be used to hold food. There is also a film made of polyvinyl chloride, which itself is non-toxic, but the additives added according to the use of the film are often harmful to the human body and have certain toxicity. Therefore, such films and plastic bags made of the films are not suitable for containing food. To identify polyvinyl chloride plastic bags and polyethylene plastic bags, the following simple method can be used for identification.

Polyethylene film (non-toxic)

The film is milky white and translucent (it is especially obvious when several layers are stacked), it is smooth to the touch, as if there is a wax layer on the surface, shaking with force, the sound is brittle, flammable in case of fire, the flame is yellow, and there is sticky dripping when burning , and the smell of burning candles.

PVC film (generally toxic)

If no pigment is added, it is transparent, the surface is sticky to the touch, shakes vigorously, the sound is low, and it is not easy to burn in case of fire.