Breaking the Ice: Successfully Freezing Liquids in Glass Bottles (2024)

Moulded borosilicate 3.3 glass bottles offer many benefits as industrial packaging for APIs, including high light-transparency, a well characterized extractables profile, and impermeability to gases and water vapor. However, glass can be vulnerable to the effects of liquid water, which is an adversary due to its corrosive (hydrolytic) behaviour. But the "universal solvent" also has another trick up its sleeve, which manifests itself during freezing - expansion. This makes freezing aqueous liquids in glass bottles a challenging task due to the risk of breakage due to the ice expansion. In this article, I will discuss these issues and explore possible solutions to mitigate the risk. DURAN® bottles are often used for the storage and shipments of HPAPI's, the high value of these materials and hazardous nature mean that failure of the bottles during freezing can lead to a significant economic loss, production down time, and a serious threat to process technician safety.

Issues

Breakage

Glass bottles are brittle and can break under extreme conditions, such as sudden temperature changes. When a liquid is frozen in a glass bottle, it expands and exerts pressure on the glass walls. If the pressure exceeds the strength of the glass, the bottle will break.

Expansion

Aqueous liquids expand when they freeze, which can cause the glass bottle to rupture. The amount of expansion depends on the type of liquid and the temperature at which it freezes. For example, water expands by about 9% when it freezes, which can create significant pressure on the glass bottle. Analysis shows that water ice is a very strong material. In the normal freezing of water, the initially formed ice forms a jacket around still, unfrozen water. During subsequent freezing, pressure develops within still unfrozen water, and at some point the ice jacket breaks. The nature of this breakage and the thickness of the ice jacket at the breaking point depend on the initial volume of water. The larger the initial volume of water, the thicker is the ice jacket and the more explosive is the breakage [1].

Solutions

Choose the right glass type

The type of glass used for the bottle can influence its ability to withstand the thermal shock of freezing. Borosilicate 3.3 glass is a type of glass that is resistant to thermal shock and is commonly used for laboratory glassware. It has a low coefficient of thermal expansion, making it less susceptible to breakage or rupture due to temperature changes. Using borosilicate 3.3 Type I glass bottles can mitigate the risk of breakage.

Use new, unused glass bottles

The strength of glass and its susceptibility to breakage depend on the presence of surface flaws and the amount of tensile stress applied, rather than the glass composition itself [2]. The Griffith equation and other theoretical formulas can be used to establish two general principles: a) the larger the surface flaws, the less tensile stress that can be applied before glass breakage, and b) glass items with minimal defects can withstand much higher levels of tensile stress before fracturing occurs. Using new, unused glass bottles for freezing will have fewer and smaller surface scratches than older used bottles. It is good practice to thoroughly visually inspected the bottles prior to use, and not use any bottles with signs of scratches, chips, or manufacturing defects such as bubbles or stones.

Leave room for expansion

To avoid pressure build-up inside the bottle, leave some space for the liquid to expand when it freezes. Typically, it is recommended to fill the bottle up to 75% capacity to allow for expansion. Ideally the bottles should be frozen slanted at an angle of 45° to enlarge the surface area and allow for the expansion of the freezing liquid. Alternatively, use bottles with a wider diameter to reduce pressure on the glass walls.

Slow / step-wise cooling and thawing

Rapid cooling can create thermal shock, which can cause the glass to break. Slow cooling can help to reduce the risk of breakage or rupture. When working at low temperatures, the effect of any expansion of a DURAN® bottle’s contents must be borne in mind. During cooling and thawing care must be taken to ensure that the temperature difference does not exceed 100 °C. In practice, therefore, step-wise cooling and thawing are recommended.

Conclusion

Freezing aqueous liquids in glass bottles can be a challenging task, but with the right precautions, it can be done safely. Choosing the right glass bottle, leaving room for expansion, and slow cooling can mitigate the risk of breakage or rupture. By following these solutions, researchers and scientists can freeze aqueous liquids in glass bottles with confidence.

References:

[1] Susanta Chatterji, Aspects of the freezing process in a porous material–water system: Part 1. Freezing and the properties of water and ice, Cement and Concrete Research, Volume 29, Issue 4, April 1999, Pages 627-630, ISSN 0008-8846, http://dx.doi.org/10.1016/S0008-8846(99)00035-6

[2] Shelby, J.E. Introduction to Glass Science and Technology. 2nd Ed. London: RSC 2005 Page 191