Glass Transition Temperature (Tg): When Rubber Becomes Brittle as Glass.

Glass Transition Temperature (Tg): When Rubber Becomes Brittle as Glass

Problem Statement

High-temperature applications expose rubber components to thermal stress, leading to brittleness and failure. A client reported premature cracking in EPDM seals operating at 120°C, below the material’s rated maximum temperature of 150°C. Root cause analysis identified the glass transition temperature (Tg) as the critical factor.

Material Science Analysis

At Tg, rubber transitions from a flexible, elastomeric state to a rigid, glass-like state. EPDM’s Tg (-50°C to -40°C) is low, but its molecular structure lacks resistance to oxidative degradation at elevated temperatures. FKM, with a Tg of -20°C to 0°C, outperforms EPDM due to its fluorine content, which provides superior thermal stability and chemical resistance.

Technical Specs

• Material: FKM (Fluorocarbon Rubber)
• Shore A Hardness: 70-90
• Tensile Strength: 15-20 MPa
• Elongation at Break: 100-200%
• Temperature Range: -20°C to 200°C
• Compression Set: ≤20% (22 hrs at 200°C)

Technical Comparison

Material	Tg (°C)	Temperature Range (°C)	Chemical Resistance	Compression Set (%)
FKM	-20 to 0	-20 to 200	Excellent	≤20
EPDM	-50 to -40	-50 to 150	Good	≤30
Silicone	-120 to -100	-60 to 230	Fair	≤25

Standard Compliance

RubberQ adheres to IATF 16949 standards for batch-to-batch consistency. Our in-house compounding ensures precise control over polymer ratios, fillers, and curing agents. Materials meet ASTM D2000 for performance and ISO 3601 for sealing applications.

CTA

For custom material compound development or IATF 16949 documentation, consult RubberQ’s engineering department.