What determines the strength of a plastic bag?

Not all plastic bags have the same strength capacity. The strongest type of plastic bag depends on how the plastic is manufactured. In fact, different types of plastic bags were developed just for their strength properties. The strongest plastic bags are made of HDPE or high-density polyethylene. Material changes that determine thickness and strength occur during the polymerization process.

 

The strength of plastic bags depends on the way ethylene reacts during the polymerization process. To make polyethylene, small molecules of ethylene combine together to form a chain of molecules called a polymer. From this main chain, branches can begin to form. The more branches that are formed, the thinner and less dense the resulting polyethylene is. In order to make denser, stronger polyethylene, fewer branches must be formed.

For example, if the polymer has a relatively straight main chain with few branches, it is called high-density polyethylene. HDPE is made of tightly packed molecules, which not only makes it denser but also less flexible. It can be used to make plastic bags that are stronger and more durable than lower density plastics.

If the polymer chain has many branches that form along the main chain, it may be MDPE or LDPE. medium density polyethylene and low density polyethylene are more flexible and have less resistance than HDPE.