Environmental stress crack resistance (ESCR)

Environment stress cracking (ESC) is the accelerated brittle failure of a polymeric material from a combination of environment and stress. The incidence of depends on the material properties, the environment conditions and the type and level of stress.

Pira can perform comparative ESCR tests on ethylene plastics using the "Bell test method" detailed in ASTM D1693.

"Bell test" for ethylene plastics (ASTM D1693)

38mm x 13mm test pieces are punched out from the material sheet and a 19mm notch cut into the specimen. The depth of the notch is made relative to the thickness of the test piece. Ten replicate specimens are then bent into a U-shape and inserted into a specimen holder with the cut imperfections facing outwards.

The entire specimen holder is then placed into a test tube and the tube filled with the test chemical. The tube is sealed with a foil-wrapped cork and placed into a temperature controlled bath at the test temperature. The specimens are then inspected at regular intervals and the number of specimens that show splitting at right angles to the notch is noted.

ESCR of containers (ASTM D2561)

Under certain conditions of stress, and in the presence of environments such as soaps, wetting agents, oils, or detergents, blow-moulded polyethylene containers may exhibit mechanical failure by cracking at stresses appreciably below those that would cause cracking in the absence of these environments.

Test methods described in ASTM D2561 can be used to measure the environmental stress- crack resistance of containers, which is the summation of the influence of container design, resin, blow-moulding conditions, post treatment, or other factors that can affect this property.

Contact:

Doug Leatherdale
email: doug.leatherdale@pira-international.com
Tel: +44 1372 80 2108