ASTM D1928-96

1.1 This practice covers the preparation of compression-molded test sheets of Types I, II, III, and IV polyethylene plastics (Specification D 1248). This practice includes both branched and linear polyethylenes. Two of the procedures given provide for compression-molded sheets to be conditioned by first heating each material above its melting point for a period of time sufficient to erase its prior thermal history and then cooling it from the melt state at a controlled rate while maintaining the required dimensions of the sheet. The third procedure provides for molded test sheets to be prepared by cooling the platens of the compression press, and hence the molten polyethylene plastic, at a controlled rate. Three cooling schedules are provided for as follows:

1.1.1 Procedure A , in which the temperature of the initially molten plaque is lowered at a rate of 5 + 0.5°C/h (9 + 0.9°F/h).

Note 1-It is recognized that Procedure A may not be applicable to material containing carbon black due to difficulties, at times, with sheets containing voids. If it is not possible to mold a void-free sheet, Procedure B or C should be selected.

1.1.2 Procedure B , in which the initially molten plaque is chilled very rapidly under specified conditions in water, and

1.1.3 Procedure C , in which the temperature of the platens of the molding press, and hence of the initially molten plaque, is lowered at a rate of 15 + 2°C/min (27 + 3.6°F/min).

1.2 This practice method also covers the preparation of test specimens from compression molded test sheets.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in 7.5.1.

Note 2- Although this practice and ISO 293-1986(E) differ in some details, data obtained using either method should be technically equivalent.