This is quite easy, with their different densities, particularly with the HDPE having a density less than one, and the PVC having a density greater than one.
The density of water is 1 g/ml. Materials with a density less than this will float, materials with a density greater than this will sink.
.092g/ml<1g/ml, so the HDPE will float, if placed in a container of water. 1.406g/ml>1g/ml so the PVC will sink if placed in a container of water.
To sort these two plastics, find a container that can hold water, and add enough water that you can separate the floating HDPE from the PVC that sank.