Which polymer is better for packaging PP or HDPE?
Posted by philiplam on March 5th, 2019
It depends on the requirement of the packing for the product whether for food items or for other use. Properties like chemical resistance, gas and moisture permeability of the packaging, impact strength, abrasion resistance, transparency, UV resistance, etc decides what material to used for packaging. Lastly the cost and aesthetic value also decide what material should be used for packaging.
High Density Polyethylene is a rigid, tough and strong polymer of natural milky color. HDPE has very good stress crack resistance as well as high impact strength and melt strength. Density of HDPE is 0.93 to 0.97 g/cm3.
And due to this translucent or opaque nature, it is used where transparency of the packaging is not required and the packaging require good impact strength and chemical resistance and very good resistance towards water and oxygen permeability.
HDPE is used for beverages, food and chemicals bottles and containers, also used in coating of chemical resistant piping.
Polypropylene is used in a wide variety of applications, including food packaging, textiles, laboratory equipment, automotive components, etc. It is unusually resistant to many chemical solvents, bases and acids. It is much less brittle than HDPE. PP has very good resistance to fatigue but less impact resistant than HDPE.
PP can be amorphous and crystalline and depending on that it will have different properties and uses. Density of amorphous PP is 0.855 g/cm3 and crystalline PP is 0.946 g/cm3.
Due to amorphous nature and low density of PP than HDPE, which is more crystalline, PP is transparent and used in cups and containers for food packaging. Crystalline PP is also used as food containers for high strength and chemical resistance but has low impact resistance than HDPE.
And due to good fatigue resistance plastic caps such as those on flip-top bottles, are made from PP.
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