Final answer:
The main difference between HDPE and LDPE is their density and branching structure. HDPE is more rigid and strong due to its low density and few branches, while LDPE is more flexible and less dense due to its high degree of branching.
Step-by-step explanation:
The main difference between High Density Polyethylene (HDPE) and Low Density Polyethylene (LDPE) is their density and branching structure. HDPE has a density of greater than or equal to 0.941 g/cm³ and contains few branches, resulting in a more rigid and strong polymer. LDPE, on the other hand, has a density range of 0.910-0.940 g/cm³ and has a high degree of branching, making it more flexible and less dense.