If you work in a laboratory that deals with cryogenic samples, you may have wondered what kind of lab plastic can you use in liquid nitrogen storage. Liquid nitrogen is one of the most commonly used cryogenic liquids in research labs, as it can preserve biological, genomic, and diagnostic samples at very low temperatures. However, liquid nitrogen also poses some challenges and hazards for lab workers, especially when it comes to choosing the right containers and materials for storage.
In this blog post, we will discuss the hazards of liquid nitrogen, the factors to consider when selecting lab plastic for liquid nitrogen storage, and some examples of lab plastic that can be used in liquid nitrogen storage. By the end of this post, you will have a better understanding of how to safely and effectively store your cryogenic samples in liquid nitrogen.
The Hazards of Liquid Nitrogen
Liquid nitrogen has a boiling point of -196°C, which means that it can rapidly freeze skin tissue and eye fluid, resulting in cold burns, frostbite, and permanent eye damage even by brief exposure. Therefore, it is essential to wear appropriate personal protective equipment (PPE) such as gloves, goggles, and lab coats when handling liquid nitrogen.
Liquid nitrogen expands 695 times in volume when it vaporizes and has no warning properties such as odor or color. Hence, if sufficient liquid nitrogen is vaporized so as to reduce the oxygen percentage to below 19.5%, there is a risk of oxygen deficiency which may cause unconsciousness or death. To prevent this, liquid nitrogen should be handled in well-ventilated areas and never stored in a confined space.
Without adequate venting or pressure-relief devices on the containers, enormous pressures can build upon cryogen evaporation. Users must make sure that cryogenic liquids are never contained in a closed system and use a pressure relief vessel or a venting lid to protect against pressure build-up.
The Factors to Consider When Selecting Lab Plastic for Liquid Nitrogen Storage
Given these hazards, what kind of lab plastic can you use in liquid nitrogen storage? The answer is not simple, as different types of plastic have different properties and characteristics that affect their suitability for cryogenic applications. Some general factors to consider are:
- Impact resistance: Plastic materials that can withstand the extremely low temperatures without becoming brittle or cracking should be used. Materials such as carbon steel, plastic and rubber become brittle at these temperatures.
- Thermal expansion: Plastic materials that have low coefficients of thermal expansion and contraction should be used. Materials that expand or contract significantly when exposed to temperature changes can cause leaks or cracks in the containers.
- Chemical resistance: Plastic materials that are resistant to chemical reactions with liquid nitrogen or other substances in the samples should be used. Materials that react with liquid nitrogen or the samples can cause contamination or degradation of the samples.
- Biocompatibility: Plastic materials that are compatible with biological samples and do not leach harmful substances should be used. Materials that are not biocompatible can affect the quality or viability of the samples.
The Examples of Lab Plastic That Can Be Used in Liquid Nitrogen Storage
Some examples of lab plastic that can be used in liquid nitrogen storage are:
- Polypropylene (PP): PP is a thermoplastic polymer that has high impact resistance, low thermal expansion, good chemical resistance, and good biocompatibility. PP is widely used for cryogenic vials, tubes, boxes, racks, and containers that store biological samples in liquid nitrogen .
- Polycarbonate (PC): PC is a thermoplastic polymer that has high impact resistance, moderate thermal expansion, moderate chemical resistance, and good biocompatibility. PC is often used for cryogenic vessels, transfer devices, and accessories that transport or store liquid nitrogen .
- Polytetrafluoroethylene (PTFE): PTFE is a fluoropolymer that has high impact resistance, low thermal expansion, excellent chemical resistance, and good biocompatibility. PTFE is sometimes used for cryogenic valves, fittings, gaskets, and seals that control or regulate the flow of liquid nitrogen.
Conclusion
Choosing the right lab plastic for liquid nitrogen storage depends on several factors such as impact resistance, thermal expansion, chemical resistance, and biocompatibility. Some common lab plastic materials that can be used in liquid nitrogen storage are polypropylene, polycarbonate, and polytetrafluoroethylene. However, users should always follow the manufacturer’s instructions and specifications for each product and application.
