Difference Between PP and HDPE

PP vs HDPE

PP
“PP” stands for “polypropylene.” It is also referred to as polypropene. PP is a thermoplastic polymer which is made from a monomer called propylene. It is very resistant to acids, bases, and chemical solvents and used for producing textiles, packaging, stationary, components of automobiles, reusable containers, etc.
Properties

PP has crystallinity intermediate to LDPE, low-density polyethylene, and HDPE, high-density polyethylene. Most of the commercial polypropene is isotactic. PP is flexible and tough when copolymerized with ethylene. This property allows it to be used for engineering plastic.
Generally, it is opaque and colored. When uncolored, it can be translucent but not easily made transparent. It is fatigue resistant to a very high degree.
Isotactic PP melts at 171 degree Celsius; commercial PP melts at a range starting from 160 degrees to 166 degrees Celsius.
PP degrades from exposure to UV radiation and heat, as in sunlight. When degrading, it shows a crisscross of cracks which become deeper with repeated exposure. This is due to the formation of carboxylic acids and aldehydes.

Manufacturing

Molding and extrusion methods are used to melt the polypropylene. They help in the production of spun-bond and melt-blown fibers. The shaping technique used is called injected molding. Some techniques like injection-stretch and blow molding are also used.

Applications

Different manufacturing methods result in different products for use. Some applications are: filters, nappies, face masks, cups, containers, automotive parts, batteries, housewares, etc.

HDPE

“HDPE” stands for “high-density polyethylene” or PEHD, polyethylene high-density. HDPE is polyethylene thermoplastic which is made by using petroleum.

Properties

HDPE has more tensile strength and intermolecular force than LDPE. This strength is due to the little branching it has at its molecular level.

It has a specific strength which is increased because the difference in density is exceeded by the difference in density.

It is very hard and opaque.

It can withstand very high temperatures up to 110 degrees Celsius continuously and, for shorter spans of time, temperatures as high as 120 degrees Celsius.

It cannot withstand autoclaving conditions.

HDPE is resistant to a variety of solvents.

Manufacturing

It is made by a catalytic polymerization of ethylene. Polymerization is done either in suspension, gas, or solution-phase reactors. To reduce the branching, comonomers are added to HDPE at lower levels. These comonomers are butane, octane, and hexane.

Applications

HDPE has varied applications like the pyrotechnics trade, wood plastic composites, composite wood, in landfills as a cell lining, water pipes, backpacking frames, housewares, piping systems which are chemical resistant, steel pipes that are protected by corrosion linings, containers, plastic surgery applications, natural gas pipes, etc.

Summary:

1.“PP” stands for “polypropylene” and “polypropene”; “HDPE” stands for “high-density polyethylene.”
2.It is made from propylene; HDPE is made from petroleum.
3.The crystallinity of PP is less than HDPE.
4.The melting range of PP is 160-166 degrees Celsius; HDPE can withstand temperatures as high as 120 degrees Celsius.
5.Molding and extrusion methods are used along with blow molding for its manufacturing. HDPE is manufactured by polymerization and comonomers are added to reduce branching.
6.They have varied applications.

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