Difference between polyethylene and polypropylene.

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

  • production of films and packaging materials;
  • pipe production;
  • manufacture of thermal insulation materials, etc.

Perhaps it is even difficult to imagine the industry where they are not used. However, although their properties are similar in many respects, there are also differences. So, what is the difference between polyethylene and polypropylene? Consider below.

Chemical differences

The names of both materials contain the word “ poly ", which in Greek means" a lot. " Most of our scientific terms are borrowings from the Greek or Latin languages ​​- this has been the custom for a long time. That is, "polyethylene" means "a lot of ethylene", and "polypropylene" means "a lot of propylene". What are ethylene and propylene?

Under normal conditions, both of these chemical compounds are flammable gases. The ethylene formula is C2H4, the propylene formula is C3H6. They occupy the first and second lines of the class of compounds, which is called "alkenes", or "acyclic unsaturated hydrocarbons". Their general formula is CnH2n, that is, there are always twice as many hydrogen atoms (H) in a molecule of any alkene as there are carbon atoms (C). This means that the third in the row will have the formula C4H8, the fourth - C5H10, etc.

Polyethylene granules

We have dealt with ethylene and propylene, let's move on. What is the difference between polyethylene and polypropylene, and how is a popular packaging material obtained from combustible gases? A special process is used in the production of polyethylene and polypropylene. It is called "polymerization". Its essence is that long chains are obtained from gas molecules, consisting of a huge number of "bricks", each of which is a link C2H4(for polyethylene) or C3H6(for polypropylene). The material from such polymer chains has properties that are fundamentally different from those of the initial molecules, although the chemical formula remains almost the same: (C2H4)nand (C3H6)n, where n is the number of units in a polyethylene or polypropylene molecule.

Comparison of performance

These materials are neighbors in the group of alkenes, therefore, in terms of physical properties, they have much in common. But propylene still has generally higher strength characteristics. For example, according to the Brinell hardness scale, polyethylene has an indicator of 1.4-2.5 kgf / mm², and polypropylene - 6.0-6.5 kgf / mm². For the rest of the indicators, the differences are not so noticeable. The areas of application of both materials also have many similarities.

They are used in the production of packaging materials, plastic dishes, pipes. Foamed polymers are in demand as an insulating material. They are widely used for the manufacture of copolymers (they include various structural units, for example, polyethylene and polypropylene or some other polymer). The production of dielectrics, household items, decorative items - it can take a long time to list the areas where you cannot do without them.

One of the modifications of polyethylene - ultra-high-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, armored panels. For a number of parameters, its characteristics are higher than that of Kevlar, which is also used for the manufacture of body armor.

Table

The table below will give the most complete answer to the question, what is the difference between polyethylene and polypropylene.

Polyethylene Polypropylene
Chemical formula(C2H4)n(C3H6)n
Strength (Brinell)1.4-2.5 kgf / mm²6.0-6.5 kgf / mm²
Chemical propertiesResistant to most acids, degrades only when exposed to nitric acid (saturation not less than 50 percent) and some other corrosive substancesA noticeable destructive effect is exerted by: concentrated nitric acid, chlorosulfonic acid, some other corrosive substances
Melting point103- 137 degrees Celsius (various brands)130-171 degrees Celsius (various brands)
ApplicationsConstruction, production of packaging materials, plastic dishes, dielectrics, armor panels (ultra high molecular weight polyethylene of high density) and much moreContainers, various films (including packaging), pipes, threads, fibers and much more
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