How Low Temps Impact Plastics
While the effects of high temperatures on plastic materials are well-known, low temperatures can also have a structural impact on most plastics. At room temperature, typical thermoplastics and other plastics are semi-flexible and have a low failure rate under stress. However, they act much differently when they are at a low temperature. Since plastics are increasingly becoming part of modern manufacturing and construction, understanding this effect is important.
When plastics reach extremely cold temperatures, they tend to harden and become more brittle. At this point, they become similar in structure and function to glass. This tendency can create problems if the plastic is under strain because it increases the risk of fracture or breakage. Cold temperatures can also cause a change in the dimensions of a plastic component, which then changes its wear behavior, friction, and overall mechanical properties. Plastic is exposed to various temperatures, including extreme heat and cold in many applications, including flying and boating. This is why exploring the effect of low temperatures on plastics is so essential.
Introduction to Low-Temperature Plastic Testing
To choose the best plastic for a particular application, manufacturers must know how it performs at extreme temperatures, including low temperatures. With the wide range of plastic products in today’s market, each one behaves differently under these stressful situations, and that’s why testing is vital.
Manufacturers often use ultra-low deep freezers to test plastics at low temperatures. The freezer creates a stable low temperature inside a cabinet, allowing the plastic to remain at that temperature for a set period of time. After the plastic reaches the desired temperature, the manufacturer tests the material to see how its structure and properties change.
Factors Affecting Plastic Material Properties at Low Temperatures
When looking for plastics that will withstand low temperatures well, manufacturers have specific features they need. These include:
- Thermal expansion rate – When plastics go through temperature changes, they can change in density and size. Therefore, most applications desire a low thermal expansion rate.
- Thermal conductivity – Proper thermal conductivity is important if the plastic needs to allow or prevent heat transfer.
- Wear rate – The wear rate of a plastic often changes when it is at a low temperature, so manufacturers must understand this change when choosing products for thermal insulators or cryogenic purposes.
The Role of Polymer Chemistry in Low-Temperature Plastic Performance
Polymers consist of long chain molecules that are entangled together. This chemical makeup allows the molecules to slither and move over each other, keeping the plastic flexible. However, when the temperature lowers, they go through what chemists call a glass transition. This transition changes them from movable molecular chains to stiff molecular chains.
The glass transition happens over various temperatures, so chemists can’t rate this change with one particular temperature. However, the glass transition premature threshold, the lowest temperature in that range, is the defined low temperature for that particular plastic. After that point, the impact resistance of the plastic lowers while the failure rate due to cracking and breaking increases.
Because of the many types of plastics on the market, the glass transition temperature varies significantly. For example, PTFE has a glass transition temperature of 130 degrees Celsius, while PVDF has a transition temperature of -45 degrees Celsius.
Testing Methods for Assessing Plastic Materials at Low Temperatures
Testing plastics for cold temperature resistance typically involves placing them in an ultra-deep freeze. Still, the actual factors tested after subjecting the plastics to these temperatures depend on the goal. Manufacturers can look at four specific factors when testing plastics at low temperatures. These low premature testing options look at the following:
- Retraction - This test measures how much a particular plastic retracts at a specific temperature.
- Crystallization - This is a measure of the increase in hardness of the plastic after it has been stored at a particular temperature.
- Brittleness - This test will determine the lowest possible temperature the plastic can withstand without becoming so brittle that it fails.
- Stiffening - Finally, stiffening testing, also known as torsion testing, measures how stiff a plastic is compared to its temperature. This is sometimes called the Gehman test.
By taking plastics through testing in each of these areas, manufacturers can have a good understanding of how they perform under extremely cold temperatures.
For Cold Temperature Rated Plastics, Trust Piedmont Plastics
If you have a cold temperature application and need the right plastic product, trust the experts at Piedmont Plastics to help you find it. Reach out to our plastic experts today to discuss your needs and find the right thermoplastic product to handle it well.