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Polyethylene RAW Materils

Do you know if polyethylene raw materials are thermoplastic or thermoset? Generally, polymers are divided into two categories: thermoplastic and thermoset. Thermoplastics are materials that easily deform, flow, and can be molded multiple times under heat, allowing for repeated use.

Thermosets are polymeric materials that, upon heating, cure, take shape, harden after forming, and no longer change shape or flow when heated.

Both types of polymers are used to produce polyethylene pipes and fittings.

The main difference between thermoplastics and thermosets is that products made from thermoplastics can be melted again and transformed into other products through extrusion or molding processes.

However, products derived from thermosets, due to their non-melting and insoluble nature, cannot undergo a reversal process and be remelted into new products.

This is because a thermoset product will decompose upon heating before it reaches its melting point, as its decomposition temperature is lower than its melting temperature; however, this characteristic allows us to create very strong compounds by combining thermoset polymers with reinforcements.

Fiberglass-reinforced pipes are one of the most common types of thermoset pipes.

It is worth mentioning that polyethylene raw materials, along with polypropylene and polyvinyl chloride (PVC), fall into the category of thermoplastics.

These polymers can be shaped in their molten state and turned into various products such as pipes and fittings, including: injection-molded polyethylene fittings, screw-type polyethylene fittings, handmade (mitre) polyethylene fittings, branch polyethylene fittings, electrofusion polyethylene fittings, and valves.

 

The production of polyethylene raw materials involves the polymerization process, which is the chemical bonding of small molecular units called monomers to form large hydrocarbons known as polymers or macromolecules.

One of the most common polymers is the polyethylene molecule, which is created by the repeated connection of ethylene units. Ethylene is a colorless gas composed of two carbon atoms with a double bond and four hydrogen atoms.

In the polyethylene raw material production process, the double bond between the two carbon atoms is broken, making them ready to bond with another atom.

Next, individual ethylene units, whose double bonds have been broken, are placed next to each other and form chemical bonds. This bonding continues until the reaction stops, the chain length becomes fixed, and the large polyethylene molecule is formed.

The polymerization of ethylene occurs in reactor systems, using different catalysts under various pressure and temperature conditions.

Polyethylene raw materials are either produced using only the ethylene monomer, referred to as homopolymers, or in the polymerization process, co-monomers such as butene, propene, hexene, and octene are used; this method is known as co-polymerization, and the resulting polymers are called copolymers.

 

 

Important Parameters in Polyethylene Raw Materials
Density, crystallinity, molecular weight, and molecular weight distribution are among the key indices that play a decisive role in the physical properties and final characteristics of polyethylene. Please follow items A to D for more familiarity with these indices.

A) Density of Polyethylene Raw Materials
Polyethylene molecules have different densities based on the number of side branches in their molecular arrangement. Generally, the higher the pressure under which ethylene is polymerized into polyethylene, the more branching occurs in the main chain, and the number of side branches increases.

This increase in the number of side branches results in a decrease in density, producing a lighter polyethylene. This is because the presence of side branches prevents the tight packing of chains.

In fact, polyethylene molecules are classified by density into the following types:

– Low-Density Polyethylene (LDPE) – produced under high-pressure conditions.
– Linear-Low-Density Polyethylene (LLDPE) – an advancement towards lower-pressure processes.
– Medium-Density Polyethylene – produced under both high and low-pressure conditions.
– High-Density Polyethylene (HDPE) – produced under low-pressure using a small amount of co-monomer, resulting in a copolymer.
– High-Density Polyethylene (HDPE) – produced under low-pressure without the presence of co-monomer, resulting in a homopolymer.

In general:

High-pressure polymerization → Many side branches → Less structural compactness → Lower density

Low-pressure polymerization → Fewer side branches → More structural compactness → Higher density