SEVERAL CHARACTERISTICS DISTINGUISH POLYETHYLENE AND POLYPROPYLENE

Q: What are the performance characteristics of polypropylene and polyethylene and how do they compare?

A: In order to understand the difference between polypropylene and polyethylene, we need to take a look at their origins. Both of these fibers are referred to as olefin, which can be any member of a class of unsaturated hydrocarbons, characteristically exhibiting a good deal of chemical activity. In addition, these chemicals form oily liquids when combined with other substances. This characteristic is what gives them the name olefin, which means oil forming.

Ethylene is a colorless flammable gas derived from natural gas and petroleum. It is the base substance for polyethylene fiber, which is manufactured from polymerized ethylene resin in monofilament form.

Propylene is also a flammable gas and is derived from petroleum hydrocarbon cracking. It is the polymers and copolymers that form polypropylene fiber.

Also helpful is an understanding of the term polymer. These heavy molecular chainlike structures are the building blocks with which all kinds of substances are linked to form fibers and other plastics such as resins and films. When something is polymerized, it is formed into this special structure. Polymers are produced by joining two or more monomers. In this case, ethylene is the monomer of polyethylene and propylene is the monomer of polypropylene.

Polyethylene fibers have low moisture regain and low specific gravity. They are very resistance to mildew and insect attach, and exhibit the same tensile strength under wet or dry conditions. If coloring is required, it must be added before spinning, because the fiber does not dye. Polyethylene has a relatively low melting point and can be heat-sealed successfully. It is also more elastic compared to polypropylene.

Like polyethylene, polypropylene has a low specific gravity and is not easily damaged by mildew and insects. That is where the similarities end. Polypropylene fibers are stronger than polyethylene, more resilient, and will not become fibrous under stress, as polyethylene will. It has some advantages over other fibers in the weaving process when coverage is important, because it provides more coverage per pound. Compared to polyethylene, polypropylene has a high melting point and does not heat-seal well, as it tends to crystallize after melting.

 

SEVERAL CHARACTERISTICS DISTINGUISH POLYETHYLENE AND POLYPROPYLENE
Polyethylene Polypropylene
Low specific gravity Low specific gravity
Resists mildew and insects Resists mildew and insects
Same tensile strength, wet or dry Stronger of the two
Melting point: 230-250°F Melting point: 325-340°F
Must be pigmented before spinning Can be dyed
Can be heat-sealed Doesn’t heat-seal well
More elastic of the two More resilient of the two
Low moisture regain Will not become fibrous under stress

Del Swanson: Director of Information Central
Article taken from: Industrial Fabric Products Review Magazine October 1986