Question

What makes HDPE have higher density and strength as compared to LDPE?

Answer 1

Hint: As we know that HDPE stands for High Density Polyethylene and LDPE stands for Low density Polyethylene. These are thermoplastics which come under the family of polyolefins. These are petrochemical based plastics that include polypropylene and polyethylene. Polyethylene (PE) is widely used in the world as it has a simple structure and is readily available.

Complete answer:
We need to know that both HDPE and LDPE are derived from Polyethylene (PE). PE is produced by polymerising ethylene. Treating PE differently produces HDPE and LDPE. These polymers have different properties because of the different structure of the molecules.
LDPE polymer has side branches. Imagine this as a straight line of molecules, within which another chain branches off. And another from that, and so on. The side chains constrain the polymer from lining up in a straight line or orderly arrangement. Because of these irregularities arise, which leads to lowering its density. LDPE doesn’t have a crystalline structure. The force of attraction between polymer molecules is thus weakened.
HDPE on the other hand lines up regularly. Take the example of army soldiers in formation, in an organized row, column, that’s how HDPE will be.
HDPE is crystalline unlike LDPE. It has a formidable structure that makes it denser than LDPE. The forces of attraction are also strong in HDPE.
HDPE is more durable and can resist high temperatures. Because of the absence of branching in HDPE, the molecules are tightly packed together making it dense and has higher resilience than LDPE.

Note:
Now we can see that there are also some similarities between HDPE and LDPE like; both are lightweight, have high impact strength, resistant to chemicals, water vapour, have high recyclability and always have low manufacturing cost.