Difference Between PP VS 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.

More rigid and more heat resistant, PP is commonly used for hot food storage containers. PP strength can be said to be between LDPE and HDPE. In addition to the thermal vest and some parts of the car, PP is also one of the ingredients used in disposable baby diapers and sanitary napkins.

Just like LDPE, PP is considered a plastic that is safe enough to be used together with food and drinks. But despite having good quality, PP is not easily recycled and can cause asthma and hormonal disorders in humans.

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”, polyethylene high-density. HDPE is polyethylene thermoplastic which is made by using petroleum.

Special enough when compared to other types of plastic, HDPE has a single polymer chain that is quite long which makes this type of plastic quite solid, strong, and thicker than PET (Polyethylene Terephthalate).

HDPE is usually used as shopping bags, milk cartons, juice bottles, shampoo bottles and bottles of medicine. The special one is easy to recycle, HDPE is also relatively more stable than PET. HDPE is considered a type of plastic that is safe enough to be used with food and drinks (food grade), although some studies show that if it is exposed to UV light for a long time, HDPE can produce chemicals similar to estrogen (one of the hormones in humans) that can damage the hormone system.

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, HDPE is very hard and stronv, and 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. HDPE is resistant to a variety of solvents.

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.

Source: differencebetween.net