4 PROCEDURE

4.1 Aging of samples

HALF OF THE PREPARED LINING SAMPLES—both wet and reactivated—plus the cast films were placed into an aging chamber.11 Both thermal and light aging occurred during the samples' exposure. The chamber was a Plexiglas box fitted with a General Electric 275 Watt Sunlamp Bulb regulated by a rheostat. A small fan kept air circulating in the chamber, and a Heathkit Relative Humidity Indicator monitored humidity inside the chamber.12 An attempt was made to regulate the humidity inside the chamber with a saturated solution of sodium iodide salts. Even so, the humidity fluctuated significantly, mostly in the 36%–40% range. Temperature averaged 46�–58� C (115�–136� F). Light falling on the tray holding the samples was about 500 footcandles. Over a one-month period the samples received 124.25 hours of exposure, equaling approximately 62,125 footcandle-hours. Even in this relatively short period the samples showed noticeable yellowing in both the clear films and the lining mockups. Control samples were kept under room conditions while the others were aging.

4.2 Peel Strength Testing (ASTM D-903-49)

A Scott CRE/500 peel strength tester was used to determine peel strengths for all samples.13 The machine was equipped with interchangeable load cells of 5 or 500 pounds. Where possible the 5-pound load cell was used. Calibrating the machine with a 500-gram weight made it possible to get an accurate estimate of the samples' peel strengths. The weight was hung from the clamp, and a reading was recorded on the same chart paper being used for the sample. All strengths were recorded in grams per linear inch. To get a measurement, the loose ends of the strips were clamped into the opposing jaws of the tester. Turning the tester on caused the clamps to move away from each other and the sample to be peeled apart. A recording device was used to chart the peel strengths so they could be graphically compared.

4.3 Measuring Change in Color

Yellowing was measured using a Minolta Chroma Meter CR-100.14 Data were collected from the aged and unaged samples of each type of adhesive and compared after statistical analysis.

4.4 Swelling of Cast Films

Samples of both aged and unaged cast films were cut into sections weighing approximately 0.5 grams each. These were weighed into glass vials using an analytical balance. Three solvents were tested for their effect on the adhesives: distilled water, toluene, and isopropanol. About 5 ml of the chosen solvent was added to the vials and left under room conditions for 24 hours. Excess solvent was decanted off, and the samples were left to dry for another 48 hours in the fume hood. The samples were weighed again. Percent swelling was calculated with the formula:15