ASTM D4020-11

1.1 This specification provides for the identification of virgin, natural color, unmodified homopolymer ultra-high-molecular-weight polyethylene (UHMW-PE) plastics molding and extrusion materials. This identification is made in such a manner that the seller and purchaser can agree on the acceptability of different commercial lots or shipments.

1.2 This specification also provides guidance for the characterization of UHMWPE materials based on various mechanical, thermal, electrical, and other analyses.

1.3 It is not intended to differentiate between various molecular weight grades of ultra-high-molecular-weight polyethylene commercially available.

1.4 It is not the function of this specification to provide specific engineering data for design purposes.

1.5 Ultra-high-molecular-weight polyethylenes, as defined in this specification, are those linear polymers of ethylene which have a relative viscosity of 1.44 or greater, in accordance with the test procedures described herein.

1.6 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.7 The following precautionary caveat pertains only to the test method portions in Section 7 and the Annex and Appendixes, of this specification: 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.

Note 1 - This standard and ISO 11542-1 address the same subject matter, but differ in technical content. ISO 11542-1 provides a classification system based on various characteristics and a range of viscosity numbers determined in accordance with ISO 1628-3.

X2.1.1 This test method covers determination of the impact strength of UHMW-PE, which is extremely impact resistant. When tested in accordance with Test Method D256, Method A, UHMW-PE generally gives the NBF type of failure, rendering the test result invalid. This test method specifies the same type of pendulum impact test machine as that given in Test Method D256 but introduces a much higher degree of stress concentration into the specimen by double notching with a razor blade. Application of this test method shall be limited to the characterization of virgin, unmodified UHMW-PE resins, not commercially processed products. It is advised that the user be familiar with Test Method D256 before attempting to use this test method.

X2.1.2 The values stated in SI units are to be regarded as the standard.

Note X2.1 - This test method and Annex B of ISO 11542-2 address the same subject matter, but differ in technical content and results shall not be compared between the two test methods.

X4.1.1 This test method covers the determination of elongational stress as a characterization of the melt viscosity of UHMW-PE. The melt flow rate in accordance with test method D1238 cannot be determined for this material because ultra high molecular weight polyethylene does not have a melt flow. The elongational stress is also be referred to as ZST and flow value, or both.

X4.1.2 Application of this test method shall be limited to virgin, unmodified resin. The elongational stress method is invalid on a previous thermally-processed material due to possible crosslinking.

Note X4.1 - This test method is identical to to Annex A of ISO 11542-2 in the measurement of elongational stress. It is not equivalent to ISO 11542-2 in any other measurement or section

X5.1.1 The measurement of molecular weight of UHMW-PE is nearly impossible to measure by techniques normally used to measure molecular weight of other polymers. Techniques such as gel permeation chromatography (GPC) and light scattering used for other polymers are not useful for UHMW-PE.

X5.1.2 The dilute viscosity test method can provide satisfactory correlations for viscosity average molecular weight within a specific manufacturing process, but this does not necessarily apply for another manufacturing process. As a result, at least five equations have been developed to describe the molecular weight of UHMW-PE.

X5.1.3 Fig. X5.1 shows the relationship between the five equations with respect to nominal viscosity average molecular weight versus intrinsic viscosity.

X5.1.4 This appendix is being provided only as a reference. Only Eq 1 listed in 3.2.1.1 of this specification shall be used to present data to the industry.

X6.1.1 This method is used to determine the resistance of materials to abrasion, measured in terms of percent weight loss, by rotating test specimens in a slurry consisting of 20 grit aluminum oxide and water.

X6.1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

Note X6.1 - There is no known ISO equivalent to this method.