Polyethylene: branching affects the density

Polyethylene (PE) use is extensive due to how easy one can tweak its density. Generally, PE has low strength, hardness, and rigidity but high flexibility. Yet, we can tune these properties with the number of branches on the polymer chains.

Linear polyethylene (i.e., no branching) packs closely, giving us high-density polyethylene (HDPE). Low-density polyethylene (LDPE) has, on the other hand, a lot of branches. These branches push neighboring chains further away, lowering the density. This low density gives a softer and more flexible polymer with a lower strength compared to HDPE.

Figure 1: Illustrations of a high-density bottle, a low-density bottle, and the structure of the polymers that compose both objects.