What is the difference between polyethylene from polypropylene?

Polyethylene and polypropylene are the most common plastics. They are used in many fields of human activity:

  • the production of films and packaging materials;
  • the production tubing;
  • production of thermal insulation materials, etc.

Perhaps, it’s hard to imagine that industry, wherever they were used. However, although their properties are largely similar but there are differences. So, what is the difference between polyethylene from polypropylene? We will consider below.

The content of the article

The difference in the chemical

In the names of both materials have the word «poly», which in Greek means «many». Most scientific terms are borrowings from the Greek or Latin languages – it just so happened long ago. That is «polyethylene» means «a lot of ethylene», and «polypropylene» – «a lot of propylene». What is the ethylene and propylene?

In normal conditions both of these chemicals are flammable gases. The formula of ethylene – С2Н4, the formula propylene – С3Н6. They occupy the first and second lines of the class of compounds called «alkenes» or «unsaturated acyclic hydrocarbons». Their General formula is СпН2п, that is, hydrogen atoms (H) in the molecule of any alkene is always twice that of carbon atoms (C). So, the third in the series will have a formula С4Н8, fourth – С5Н10, etc.

Polyethylene granules

With ethylene and propylene, we understand, go ahead. What is the difference between polyethylene from polypropylene, and the like of combustible gases get popular packing material? In the production of polyethylene and polypropylene is used special process. It is called «polymerization». Its essence is that the gas molecules get long chains, consisting of a large number of «bricks», each of which is a link С2Н4 (for polyethylene) or С3Н6 (for polypropylene). The material of these chain polymers have properties radically different from the properties of the original molecules, although chemical formula remains almost the same: (С2Н4)n and (С3Н6)n, where n is the number of links in the molecule of polyethylene or polypropylene.

to contents ↑the Difference between polyethylene and polypropylene in performance

These materials are neighbours in the group of alkenes, so the physical qualities have a lot in common. But propylene still has an overall higher strength characteristics. For example, on the hardness scale Brinell polyethylene has a rate of 1.4 to 2.5 kgf/mm2, and the polypropylene – 6,0-6,5 kgf/mm2. As per other indicators the differences are not so noticeable. Applications of both materials also have a lot of similarities.

They are used in the production of packaging materials, plastic utensils, pipes. Foamed polymers are demanded as insulating material. Widely used for the manufacture of copolymers (composed of different structural units, such as polyethylene and polypropylene or some other polymer). The production of insulators, household items, decorative items – list the areas where they are necessary, can be long.

One of the modifications of polyethylene – ultrahigh molecular weight high density polyethylene has very high strength characteristics. In this regard, the material is used where special strength is required. For example, when creating body armor, helmets, armor panelling. On a number of parameters characteristics higher than that of Kevlar, which is also used for making bulletproof vests.

to content ↑Comparative table

The table below will allow us to answer the question, what is the difference between polyethylene and polypropylene.

Polyethylene
Polypropylene

Chemical formula
(С2Н4)n
(С3Н6)n

Strength (Brinell)
1,4-2,5 kg/mm2
Of 6.0-6.5 kgf/mm2

Chemical properties
Resistant to most acids, is destroyed only when exposed to nitric acid (saturation 50%), and some other corrosive substances
Noticeable damaging impact: concentrated nitric acid, chlorosulfonic acid, some other caustic substances

The melting point
+103-137 degrees Celsius (different brands)
+130-171 ° C (different brands)

The scope of
Construction, manufacturing of packaging materials, plastic tableware, insulators, armour panels (ultrahigh molecular weight high density polyethylene) and more
Containers, and various films (including packaging), tubes, filaments, fibres and more

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