Multiple Internal Reflectance
Apparatus— Use an IR spectrophotometer capable of correcting for the blank spectrum and equipped with a multiple internal reflectance accessory and a KRS-5 internal reflection plate.
1 A KRS-5 crystal 2-mm thick having an angle of incidence of 45
provides a sufficient number of reflections.
Specimen Preparation— Cut two flat sections representative of the average wall thickness of the container, and trim them as necessary to obtain segments that are convenient for mounting in the multiple internal reflectance accessory. Taking care to avoid scratching the surfaces, wipe the specimens with dry paper or, if necessary, clean them with a soft cloth dampened with methanol, and permit them to dry. Securely mount the specimens on both sides of the KRS-5 internal reflection plate, ensuring adequate surface contact. Prior to mounting the specimens on the plate, they may be compressed to thin uniform films by exposing them to temperatures of about 177
under high pressures (15,000 psi or more).
General Procedure— Place the mounted specimen sections within the multiple internal reflectance accessory, and place the assembly in the specimen beam of the IR spectrophotometer. Adjust the specimen position and mirrors within the accessory to permit maximum light transmission of the unattenuated reference beam. (For a double-beam instrument, upon completing the adjustments in the accessory, attenuate the reference beam to permit full-scale deflection during the scanning of the specimen.) Determine the IR spectrum from 3500 to 600 cm–1 for polyethylene and polypropylene and from 4000 to 400 cm–1 for PET and PETG.
Thermal Analysis
General Procedure— Cut a section weighing about 12 mg, and place it in the test specimen pan.
[note—Intimate contact between the pan and the thermocouple is essential for reproducible results.
] Determine the thermogram under nitrogen, using the heating and cooling conditions as specified for the resin type and using equipment capable of performing the determinations as specified under
Thermal Analysis 891.
For Polyethylene— Determine the thermogram under nitrogen at temperatures between 40
and 200
at a heating rate between 2
and 10
per minute followed by cooling at a rate between 2
and 10
per minute to 40
.
For Polypropylene— Determine the thermogram under nitrogen at temperatures ranging from ambient to 30
above the melting point. Maintain the temperature for 10 minutes, then cool to 50
below the peak crystallization temperature at a rate of 10
to 20
per minute.
For Polyethylene Terephthalate— Heat the specimen from room temperature to 280
at a heating rate of about 20
per minute. Hold the specimen at 280
for 1 minute. Quickly cool the specimen to room temperature, and reheat it to 280
at a heating rate of about 5
per minute.
For Polyethylene Terephthalate G— Heat the specimen from room temperature to 120
at a heating rate of about 20
per minute. Hold the specimen at 120
for 1 minute. Quickly cool the specimen to room temperature, and reheat it to 120
at a heating rate of about 10
per minute.
Physicochemical Tests
The following tests, designed to determine physical and chemical properties of plastics and their extracts, are based on the extraction of the plastic material, and it is essential that the designated amount of the plastic be used. Also, the specified surface area must be available for extraction at the designated temperature.
Testing Parameters—
Extracting Medium— Unless otherwise directed in a specific test below, use
Purified Water (see monograph) as the
Extracting Medium, maintained at a temperature of 70
during the extraction of the
Sample Preparation. Sample Preparation Extract— Transfer the prepared
Sample Preparation to a suitable extraction flask, and add the required amount of
Extracting Medium. Extract by heating in a water bath at the temperature specified for the
Extracting Medium for 24 hours. Cool, but not below 20
. Pipet 20 mL of the prepared extract into a suitable container.
[note—Use this portion in the test for
Buffering Capacity.
] Immediately decant the remaining extract into a suitably cleansed container, and seal.
Nonvolatile Residue— Transfer, in suitable portions, 50.0 mL of the
Sample Preparation Extract to a suitable, tared crucible (preferably a fused-silica crucible that has been acid-cleaned), and evaporate the volatile matter on a steam bath. Similarly evaporate 50.0 mL of the
Blank in a second crucible.
[note—If an oily residue is expected, inspect the crucible repeatedly during the evaporation and drying period, and reduce the amount of heat if the oil tends to creep along the walls of the crucible.
] Dry at 105
for 1 hour: the difference between the amounts obtained from the
Sample Preparation Extract and the
Blank does not exceed 15 mg.
Residue on Ignition 281— [note—It is not necessary to perform this test when the
Nonvolatile Residue test result does not exceed 5 mg.
] Proceed with the residues obtained from the
Sample Preparation Extract and from the
Blank in the test for
Nonvolatile Residue above, using, if necessary, additional sulfuric acid but adding the same amount of sulfuric acid to each crucible: the difference between the amounts of residue on ignition obtained from the
Sample Preparation Extract and the
Blank does not exceed 5 mg.
Heavy Metals— Pipet 20 mL of the
Sample Preparation Extract, filtered if necessary, into one of two matched 50-mL color-comparison tubes. Adjust with 1 N acetic acid or 6 N ammonium hydroxide to a pH between 3.0 and 4.0, using short-range pH paper as an external indicator, dilute with water to about 35 mL, and mix.
Into the second color-comparison tube pipet 2 mL of
Standard Lead Solution (see
Heavy Metals 231), and add 20 mL of the
Blank. Adjust with 1 N acetic acid or 6 N ammonium hydroxide to a pH between 3.0 and 4.0, using short-range pH paper as an external indicator, dilute with water to about 35 mL, and mix. To each tube add 1.2 mL of thioacetamide–glycerin base TS and 2 mL of
pH 3.5 Acetate Buffer (see
Heavy Metals 231), dilute with water to 50 mL, and mix: any brown color produced within 10 minutes in the tube containing the
Sample Preparation Extract does not exceed that in the tube containing the
Standard Lead Solution, both tubes being viewed downward over a white surface (1 ppm in extract).
Buffering Capacity— Titrate the previously collected 20-mL portion of the Sample Preparation Extract potentiometrically to a pH of 7.0, using either 0.010 N hydrochloric acid or 0.010 N sodium hydroxide, as required. Treat a 20.0-mL portion of the Blank similarly: if the same titrant was required for both the Sample Preparation Extract and the Blank, the difference between the two volumes is not greater than 10.0 mL; and if acid was required for either the Sample Preparation Extract or the Blank and alkali for the other, the total of the two volumes required is not greater than 10.0 mL.
