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Significance and Use
There are three types of olefinic groups present in sufficient concentrations to warrant consideration, one or more of that can normally be found in any polyethylene. The three types are trans-vinylene, R-CH=CH-R′, sometimes referred to as trans-internal unsaturation; vinylidene or pendent methylene, RR′C-CH2; and vinyl unsaturation, R-CH=CH2, also referred to as terminal unsaturation.
The type and quantity of these groups can influence the chemical and physical properties of the resin. Information concerning their presence can also be used to characterize or identify unknown resins or blends of resins.
Additives can interfere with unsaturation measurements. The use is cautioned to determine which additives are present and if there any absorbance bands caused by additive presence that overlap or interfere with unsaturation absorbance bands used in this test method in the range of 1050 to 850 cm–1. If overlapping bands occur, the method is not applicable.
Interference fringes resulting from smooth sample surfaces can cause measurement errors. This test method requires the use of aluminum foil in the compression molding of samples to provide an adequately rough surface to minimize interference fringes.
1.1 This test method covers most types of polyethylene, those ethylene plastics consisting of ethylene and α-olefin comonomers longer than propylene, and blends of the above in any ratio.
1.2 The values stated in SI units are to be regarded as the standard.
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 hazards statements are given in Section 8. Note 1—There is no known ISO equivalent for this standard.
Note 1—There is no known ISO equivalent for this standard.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D792 Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement
D1505 Test Method for Density of Plastics by the Density-Gradient Technique
D3124 Test Method for Vinylidene Unsaturation in Polyethylene by Infrared Spectrophotometry
E131 Terminology Relating to Molecular Spectroscopy
E168 Practices for General Techniques of Infrared Quantitative Analysis
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E275 Practice for Describing and Measuring Performance of Ultraviolet and Visible Spectrophotometers
ICS Number Code 83.080.20 (Thermoplastic materials)
UNSPSC Code 13111016(Polyethylene)
ASTM D6248-98(2012)e1, Standard Test Method for Vinyl and Trans Unsaturation in Polyethylene by Infrared Spectrophotometry, ASTM International, West Conshohocken, PA, 2012, www.astm.orgBack to Top