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Difference Between PP and HDPE

Difference Between PP and HDPE

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Today we will talk about the Difference Between PP and HDPE.


"PP" stands for "polypropylene". It is also called polypropylene. PP is a thermoplastic polymer made from a monomer called propylene. 

It is very resistant to acids, alkalis, and chemical solvents and is used in the production of textiles, packaging, automotive stationery, parts, reusable containers,

The crystallinity of PP is between LDPE, low-density polyethylene, and HDPE (high-density polyethylene). Most commercial polypropylenes are isotactic. 

PP has flexibility and toughness when copolymerized with ethylene. This characteristic makes it useful for engineering plastics.

Usually, it is opaque and colored. When unpigmented, it can be translucent, but it is not easy to make it transparent. It has high fatigue resistance.

The melting point of isotactic PP is 171 degrees Celsius; the melting temperature of commercial PP ranges from 160 degrees Celsius to 166 degrees Celsius.

Like sunlight, PP degrades from exposure to UV radiation and heat. When degraded, it shows intersections of cracks that become deeper with repeated exposure. This is due to the formation of carboxylic acids and aldehydes.


Molding and extrusion methods are used to melt polypropylene. They aid in the production of spun bonds and melt blown fibers. The molding technique used is called injection molding. Techniques such as injection-stretching and blow-molding are also used.

Application field

Different manufacturing methods result in different products being used. Some applications are filters, diapers, masks, cups, containers, auto parts, batteries, household items, etc.

High-density polyethylene

"HDPE" stands for "High-Density Polyethylene" or PEHD, polyethylene high density. HDPE is a polyethylene thermoplastic made from petroleum.


  • HDPE has higher tensile strength and intermolecular force than LDPE. This strength is due to its little branching at the molecular level.
  • It has increased specific strength because the density difference is outweighed by the density difference.
  • This is very difficult and opaque.
  • It can withstand high temperatures up to 110 degrees Celsius continuously and up to 120 degrees Celsius for shorter periods of time.
  • It cannot withstand autoclaving conditions.
  • HDPE is resistant to many solvents.


It is produced by the catalytic polymerization of ethylene. Polymerization can be carried out in suspension, gas phase, or solution phase reactors. To reduce branching, comonomers are added to HDPE at lower levels. These comonomers are butane, octane, and hexane.

Application field

HDPE has a variety of applications such as pyrotechnics, wood- plastic composites, composite wood, as a cell lining in landfills, water, which is chemically resistant, pipes, backpack frames, household utensils, plumbing steel by corrosion Liners, containers, plastic protective tubes for surgical applications, natural gas pipelines, etc.

Summary of Difference Between PP and HDPE

  1. "PP" stands for "polypropylene" and "polypropylene"; "HDPE" stands for "high-density polyethylene".
  2. Made of propylene; HDPE is made of petroleum.
  3. The crystallinity of PP is lower than that of HDPE.
  4. The melting range of PP is 160-166 degrees Celsius; HDPE can withstand temperatures up to 120 degrees Celsius.
  5. The molding and extrusion methods are used together with blow molding. HDPE is manufactured by polymerization, and comonomers are added to reduce branching.
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