Blocking Load - ASTM D3354
Blocking load is the load required to separate two parallel layers of polyethylene film with a 100 cm² contact area.
Blocking is the undesirable adhesion between layers of plastic, particularly films.
Testing may either be performed using a two-pan balance, or a machine specifically designed to measure blocking load.
Testing with a two-pan balance
One pan of the balance is replaced by a pair of aluminum blocks, one stationary and one connected to the balance. Film specimens are attached to the two aluminum blocks. When the balance is zeroed the two aluminum blocks are in contact. The blocking load is applied by adding water to the balance pan at a rate of 90 ml/min.
Blocking Load Test
Once the films separate, the volume of water added to the pan (in milliliters) is multiplied by 0.9975 to obtain the blocking load (in grams). This multiplication is performed to account for the density of water not being exactly 1 g/ml.
Testing with a blocking load machine
A blocking load machine automatically applies a load to separate the films and displays the blocking load directly. The test is essentially the same as that of the two-pan balance, in that a lever lifts one specimen off another.