Glass Transition Temperature (Tg) is a crucial property that determines whether a polymer behaves as a rigid, glassy material or a soft, flexible one. It can be compared to the thawing of a steak—Tg indicates whether the material remains frozen and brittle or has softened to a workable state.
Tg and Polymer Behavior
The flexibility of plastics and polymers is largely due to their long-chain molecular structure. At moderate temperatures, these chains can move past one another, giving the polymer a rubbery feel. However, as the temperature decreases, most polymers lose their flexibility, becoming more rigid and brittle. Beyond their Tg, they are prone to cracking and other forms of mechanical failure. This transition zone significantly impacts properties such as hardness, volume, elongation at break, and Young’s modulus.
Certain plastics, such as Polystyrene (PS), Acrylic (PMMA), and Polyethylene Terephthalate (PET), have a Tg higher than room temperature. This means they remain glassy and brittle under normal conditions. Unmodified Polyvinyl Chloride (PVC) also exhibits similar behavior. However, adding plasticizers to PVC can modify its mechanical properties, reducing stiffness and lowering its Tg to achieve flexibility over a desired temperature range.
On the other hand, polymers like Polypropylene (PP) and Polyethylene (PE) have a Tg below room temperature, meaning they stay in a rubbery state at standard conditions. These materials remain flexible and are less prone to breaking.
Since low-temperature performance is critical for many applications, testing the cold resistance of a polymer composite is an essential step in material selection. Polymers can be modified to meet specific low-temperature requirements for different projects.
Testing and Evaluating Low-Temperature Performance
E Squared is a U.S. manufacturer of coated fabrics, working closely with customers to help select the right materials for their applications. Our R&D laboratory conducts testing at temperatures as low as -65°F (-54°C) to ensure materials meet demanding low-temperature requirements. We offer customized solutions in PVC, TPU, PP, and PE and provide sample materials for evaluation.
Several standardized tests are used to assess polymer flexibility and brittleness at low temperatures:
ASTM D2136 – Low-Temperature Bend Test
This pass/fail test evaluates the flexibility of coated fabrics at a given temperature. The material is bent around a 1/8-inch rod, simulating bending over an embankment or roof edge during cold weather installations. It is widely used in the geomembrane and roofing industries.
ASTM D2137 – Brittleness Point Test
This test determines the temperature at which flexible polymers and coated fabrics exhibit fracture or cracking under impact force. Similar standards include ISO 812, ISO 974, and ASTM D746. This method is commonly applied to O-rings, gaskets, and rubber compounds.
ASTM D1790 – Brittleness Temperature of Plastic Sheeting by Impact
Used for thin plastic sheeting (1.00 mm or less), this test evaluates the lowest temperature at which the material exhibits brittle failure under impact conditions. It is particularly useful in PVC geomembrane testing (ASTM D7176).
ASTM D751 and Fed. Std. No. 191A Method 5874
These tests are commonly used for coated fabrics and roofing membranes. The specimen is subjected to low temperatures, then creased and pressed with a 10 lb. roller to check for cracks or flaking. Water or hydrostatic resistance is also measured. This test helps assess the overall durability and flexibility of the material at low temperatures.
Each of these tests focuses on specific mechanical properties such as bending, impact resistance, rolling, and folding behavior. Since different polymeric materials respond uniquely under these conditions, it is essential to select materials that not only meet minimum requirements but also withstand real-world operating conditions.
E Squared: Providing Custom Low-Temperature Solutions
At E Squared, we specialize in the manufacture of coated fabrics tailored to meet specific performance requirements. Our technical and sales teams work closely with customers to ensure the right material selection. Our R&D lab rigorously tests polymers at extreme temperatures to validate their suitability for various applications. We offer custom formulations for PVC, TPU, PP, and PE and can provide sample materials upon request.
For expert guidance and material evaluation, contact our team today.
Key Acronyms
- ASTM – American Society for Testing and Materials
- FGI – Fabricated Geomembrane Institute
- ISO – International Organization for Standardization
- PE – Polyethylene
- PET – Polyethylene Terephthalate
- PP – Polypropylene
- PMMA – Polymethyl Methacrylate
- PS – Polystyrene
- Tg – Glass Transition Temperature
References
- ASTM Standard D2136, 2019. Standard Test Method for Coated Fabrics—Low-Temperature Bend Test. ASTM International. DOI: 10.1520/D2136-19E01
- ASTM Standard D2137, 2018. Standard Test Methods for Rubber Property—Brittleness Point of Flexible Polymers and Coated Fabrics. ASTM International. DOI: 10.1520/D2137-11R18
- ASTM Standard D1790, 2021. Standard Test Method for Brittleness Temperature of Plastic Sheeting by Impact. ASTM International. DOI: 10.1520/D1790-21
- ASTM Standard D751, 2019. Standard Test Methods for Coated Fabrics. ASTM International. DOI: 10.1520/D0751-19
- Federal Standard Test Method No. 191A, 1978. FEDERAL STANDARD: TEXTILE TEST METHODS. U.S. Military Specs/Standards/Handbooks
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