Assemble quickly and teach children plastic knowledge

Assemble quickly and teach children plastic knowledge
Assemble quickly and teach children plastic knowledge

When I was in college, I met a girl from Chinese department. She knew that I was studying polymeric materials. Whenever I came across various plastic bags, I inadvertently asked what material they were made from. At time, editor had gone wrong way and professional courses were in disarray. Whenever I encounter such a situation, editor always pretends to look around, knocks, touches, pauses, and then categorically says: PE. It's okay to do it once or twice, but more times editor gets worried that if this keeps up, sooner or later it will be revealed. The plastics in this world can't be all polyethylene.

The vanity-driven editor began to pay attention to differences in appearance and feel of different plastic bags, which also pushed editor to slowly move along right path in life. The Power of Love~ In following, I will share what I have learned with everyone who works in industry or outside of it. If you have children in future, you can also let them gain health and knowledge and make them worship their parents.

1. The four most commonly used plastic bags?

1 LD (PE) high pressure plastic bag

Assemble quickly and teach children plastic knowledge

High-density polyethylene, also known as low-density polyethylene (LDPE), is translucent, and transparency of plastic bags is usually lower than that of high-density polyethylene. There are 3 main use cases:

A. Food packaging: cakes, candies, roasted seeds and nuts, biscuits, milk powder, salt, tea, etc.;

B. Fiber products packaging: shirts, clothing, needle cotton products, chemical fiber products;

C. Packaging of household chemicals.

2Low pressure polyethylene bag HL(PE)

Assemble quickly and teach children plastic knowledge

LDPE is also called High Density Polyethylene (HDPE). Due to its high crystallinity, its transparency is not very good and it is usually translucent. Clarity is worse than HDPE plastic bags. . There are 4 main use cases:

A, Garbage bag, garbage bag;

B, handbag, shopping bag, tote bag, vest;

C, storage bag;

D. Woven bag inner bag

3Polypropylene plastic bag (PP)

Assemble quickly and teach children plastic knowledge

Compared with polyethylene, crystallization ability of polypropylene in polypropylene plastic bags will be much weaker, especially atactic polypropylene, which has weakest crystallinity, and transparency of plastic bag products from it will be much higher.

Mainly used for packing textiles, needle cotton products, clothes, shirts, etc.

Due to non-polarity of material structure of first three plastic bags, they are not easy to color or print and require surface treatment for printing.

4Polyvinyl chloride plastic bag (PVC)

Assemble quickly and teach children plastic knowledge

PVC plastic bags are processed by PVC resin blow molding method. Compared with first three plastic bags, chlorine is introduced into material structure, which makes crystallization effect very weak and transparency of product. At same time, due to addition of chlorine, material itself has a certain polarity, which is convenient when printing and coloring. Its main purpose is twofold:

A. Gift package;

B, luggage bags, needle cotton packaging bags, cosmetics packaging bags;

Answer "PE", "PP" or "PVC" to see more articles

Second, diversified development of plastic bag components

Four commonly used plastic bags have been introduced above. Do you think editor can easily identify products on market? In fact, editor does not have a keen eye to recognize all materials, in fact, single-component materials for plastic bags are very few now, so it is difficult to quickly identify them at beginning.

Take physical education as an example!

Assemble quickly and teach children plastic knowledge

PE often appears in film, plate or rod, such as disposable plastic bags, because polarity in molecular structure of polyethylene is weak, surface energy is relatively low, and it is not easy to print, so pure polyethylene plastic bags are commonly used. It is colorless and translucent, and does not feel sticky like PVC film. In addition, polyethylene also has strong crystallinity, so polyethylene plates and rods are white and opaque.

This is an editor's resume in a book or in a lab. But when I went shopping at supermarket, I was dumbfounded when I saw this plastic bag:

Assemble quickly and teach children plastic knowledge

At time, editor was confused. What is this material? And plastic bag? What about colorless and translucent? Not comfortable typing? >(PE-LD+PE-LLD)-MD15

Well, it's a lot more exciting than you might have imagined.

I guess PE-LD should be LDPE, low density polyethylene, PE-LLD should be LLDPE, so what is MD15? It is impossible to guess about it, so we can only obediently check information.

After investigation, all-powerful editor finally found a credible claim:


Material name



Polyethylene terephthalate

polyethylene terephthalate



High density polyethylene

high density polyethylene



polyvinyl chloride

Polyvinyl chloride



Low density polyethylene

low density polyethylene







Ethylene vinyl acetate plastic

ethylene vinyl acetate plastic



polyterephthalic acid/adipic acid/diacetyl

poly(butylene adipate/terephthalate)



Polybutylene succinate

polybutylene succinate



Material name







Linear low density polyethylene

Linear low density polyethylene



Mid-density polyethylene

medium density polyethylene



Very low density polyethylene

Very low density polyethylene



Polyhydroxybutyrate valerate




Polylactic acid

polylactic acid or polylactide


Contextual advertising

Copolymer of carbon dioxide and propylene oxide

Copolymer of carbon dioxide and propylene



Polyvinyl alcohol

poly(vinyl alcohol)


This table is trustworthy because it is taken from Chinese national standard. Interested friends can directly search for GB21660-2008.

This standard also explains meaning of MD: MD is mineral powder, St is starch, and number is mass fraction (%) of additive.

In order for you, reader of this article, to actually use this form, here isfor example:

Example 1: Low density polyethylene with 30% (mass fraction) of starch (St), expressed as: >(PE-LD)-St30<

For blends containing multiple excipients, percentage of excipient must be described and enclosed in parentheses.

Example 2: Polypropylene containing 15% (w/w) mineral powder and 25% (w/w) starch (St), expressed as: >PP-(St25+MD15) PP-(St+MD) 40<

3. What do you know about commonly used plastic number plates?

Also, editor had secretly mastered numbers of commonly used general purpose plastics, and once I saw numbers, I could know what material it was made of. What do you know about digital identification of these commonly used plastics? If you do not know, then I suggest that you better not say that you are studying polymers (plastics, rubber), otherwise it will be completely embarrassing.

Assemble quickly and teach children plastic knowledge

In addition, "04" in three recycling arrows also corresponds to LDPE code name, and if there is no number in middle of arrow, it means that the plastic bag cannot be recycled.

Dear eyes, did you suddenly feel that your posture was lifted up? Collect quickly!