Glass containers may react with chemicals present in food, beverages, or pharmaceutical products, producing harmful substances that seep into the product. For safe packaging and storage, ASTM C225 determines the reactivity of glass with the chemicals present in the product.
Since many products are sterilized for packing, the test specifies autoclave conditions during testing. Autoclave represents some of the most extreme conditions that the containers will experience. ASTM C225 employs three test methods, any of which can be used to follow specifications laid out by a customer, an agency, or the United States Pharmacopeia.
The three methods employed in ASTM C225 are:
Test Method B-A
Test Method B-A is used to test glass containers intended to store products with a pH under 5. The glass bottles are partially filled with a dilute acid, acting as the attacking medium. They are placed inside the autoclave and the temperature is adjusted to 121°C.
Test Method B-W
Test Method B-W is used to test glass containers intended to store products with a pH of 5.0 or over. The glass bottles are partially filled with distilled water, acting as the attacking medium. They are placed inside the autoclave and the temperature is adjusted to 121°C.
Test Method P-W
Test Method P-W in ASTM C225 is an autoclave test conducted at 121°C on powdered samples with pure water as the attacking medium. It is a hydrolytic autoclave test used for evaluating samples from untreated glass containers. It is often used for testing containers with a capacity too little to permit measurements of solubility by other tests. It is also used in conjunction with the B-W test method to distinguish whether the internal surface of a container has been treated to improve its durability.
For ASTM C225, three glass bottles are tested if the bottles are of 168 cm3 (6-oz) capacity or over. If the bottles are smaller than 168 cm3 capacity, a sufficient number of bottles are selected such that the contents can be combined to form three sets to give 100 ml/set.
The following data is calculated in ASTM C225 testing:
Test Method B-A:
The results are reported as milliliters of 0.020N acid consumed in the test.
Calculated as follows:
A = V – 0.98B
V = 0.020N NaOH solution equivalent to 100 ml of the attacking medium.
B = 0.020N NaOH solution used in the titration of 100 ml of bottle extract.
0.98 = factor applied to the titration.
Test Method B-W:
The results are reported as milliliters of 0.020N H₂SO₄ required for titration of the sample, minus milliliters required for titration of the blank.
Test Method P-W:
The results are reported as the milliliters of 0.020N H₂SO₄ used to neutralize the extract from 10 g of glass, minus milliliters required for titration of the blank.
ASTM C225 uses an autoclave to determine the resistance of glass containers to chemical attacks.