Test Methods for Resistance of Glass Containers to Chemical Attack
What is the Chemical Attack Resistance of Glass Containers?
The chemical attack resistance of glass containers describes the material’s ability to resist dissolution, leaching, and surface degradation when in contact with the liquids they contain. When a glass container holds an aqueous solution — whether a beverage, a pharmaceutical preparation, a laboratory reagent, or a household chemical product — the glass surface can react with the liquid, releasing ionic species (primarily sodium, potassium, calcium, silica, and boron) into the product. This process is called glass leaching or glass corrosion.
Controlling glass leaching is critical for pharmaceutical product stability, beverage flavour integrity, and safety compliance across the glass packaging, laboratory equipment, and speciality glass industries.
Why Chemical Resistance Testing Matters
Glass leaching can cause:
- Pharmaceutical product degradation: Alkaline leachates from soda-lime glass can raise solution pH, catalysing drug hydrolysis or precipitation
- Particulate contamination: Severely leached glass surfaces shed glass flake particles into parenteral solutions, creating an injectable contamination risk
- Flavour changes in beverages: Leached ionic species can impart off-tastes to stored beverages
- Regulatory non-compliance: USP, EP, and ISO standards impose strict limits on glass container extractables for pharmaceutical packaging
Glass Hydrolytic Resistance Classification
Glass containers for pharmaceutical use are classified by hydrolytic resistance into four types per USP <660> and ISO 4802:
- Type I (Borosilicate glass): Highest hydrolytic resistance — for most injectable pharmaceutical preparations
- Type II (Treated soda-lime glass): Surface-treated to improve resistance for neutral and acidic aqueous preparations
- Type III (Soda-lime glass): Moderate resistance — for non-aqueous parenterals and dry solids
- Type NP (Soda-lime glass, non-parenteral): For oral and topical products only
Key Test Methods for Chemical Attack Resistance
ASTM C225 — Resistance of Glass Containers to Chemical Attack (Powder Method)
ASTM C225 grinds glass containers to powder and leaches the powder with purified water at 121°C in an autoclave for 30 minutes. The extract is titrated with sulphuric acid to measure the total alkalinity (mEq/g) released — a direct measure of glass dissolution rate. This method characterises the bulk glass composition’s hydrolytic resistance.
ASTM C724 — Acid Resistance of Ceramic Decorations on Glass
Tests the chemical durability of enamel decorations on glass containers against standardised acid attack, relevant for decorated beverage bottles.
USP <660> — Containers — Glass (Powdered Glass and Whole Container Tests)
USP <660> specifies both the powdered glass test (measuring bulk glass hydrolytic resistance) and the whole container test (measuring leachate from the internal surface). The whole container test autoclaves water-filled containers at 121°C for 60 minutes and titrates the extracted water.
ISO 719 and ISO 720 — Hydrolytic Resistance of Glass Grains
ISO 719 (hydrolytic class HGB 1–5) and ISO 720 (hydrolytic class HGA 1–3) define European hydrolytic resistance classification using the powdered glass method, providing a standardised framework for glass type designation.
ISO 4802 — Hydrolytic Resistance of the Inner Surfaces of Glass Containers
Tests the resistance of the interior surface specifically — measuring the amount of material leached from the inner surface of filled and autoclaved glass containers, per ISO 4802-1 (flame emission spectroscopy) and ISO 4802-2 (titrimetric method).
Industrial Applications
In pharmaceutical packaging, all primary glass containers for injectable products must be qualified to USP <660> Type I or Type II requirements. In beverage packaging, chemical resistance testing verifies that glass containers do not leach metallic impurities that could affect product safety or taste. In laboratory glassware, the borosilicate glass chemical resistance is validated against acids, alkalis, and organic solvents.
Conclusion
Chemical attack resistance testing is essential for determining how well glass containers resist leaching, dissolution, and surface degradation when exposed to the products they store. This is particularly critical in beverage, laboratory, and speciality chemical applications, where even minor ionic leaching can affect product stability, safety, taste, and regulatory compliance.
Standards such as ASTM C225, USP <660>, and ISO 4802 provide standardised methods to classify glass types and verify hydrolytic resistance. These tests help ensure that glass containers meet the required performance for safe storage and long-term product integrity.
Why Choose Infinita Lab for Glass Chemical Resistance Testing?
Infinita Lab provides ASTM C225, USP <660>, ISO 719, ISO 720, and ISO 4802 chemical resistance testing for glass containers through our nationwide accredited materials and analytical testing laboratory network.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you.
Frequently Asked Questions (FAQs)
What is Type I glass? Type I is borosilicate glass, offering the highest hydrolytic resistance and commonly used for injectable pharmaceutical products.
What is the powder method? In this method, the glass is crushed into powder and exposed to purified water under controlled conditions to measure alkali release.
Can chemical attack affect injectable products? Yes. Poor resistance can cause glass flakes, pH drift, and contamination, which are critical risks in parenteral formulations.
What is the difference between the powdered glass test and the whole container test for glass chemical resistance? The powdered glass test measures the hydrolytic resistance of the bulk glass composition by leaching glass powder — it characterises the material itself. The whole container test leaches the internal surface of intact containers — it measures the combined effect of glass composition and any surface treatments applied after forming.
How does surface treatment improve the chemical resistance of Type II glass? Type II glass is produced by treating the interior surface of formed soda-lime glass containers with sulphur dioxide, ammonium sulphate, or fluorine gas at high temperature. This converts the surface layer from sodium-rich soda-lime glass to a more chemically resistant silica-rich composition, dramatically reducing sodium leaching.
