Both LDPE as HDPE are polyethylene types. The difference between the two types is that LDPE is made under high pressure, unlike HDPE. LDPE has many more side branches in its molecular structure, so LDPE has good transverse tear strength. The welding temperature of LDPE is somewhat lower than that of HDPE (around 10 degrees).
Because the molecular structure has more side branches, the water vapour permeability of LDPE is worse than that of HDPE. This is about a factor of 2.5.
The advantage of the molecular structure with side branches is that this makes LDPE suitable for shrink films. As LDPE film is heated again, the molecules want to return to their original state, which means that in addition to a longitudinal contraction, a latitudinal contraction can also occur. HDPE only shrinks longitudinally.
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This article was published on: 02-01-2021.