Ethylene Propylene Diene Monomer (EPDM): Synthesis, Properties and Industrial Applications

Ethylene Propylene Diene Monomer (EPDM): Synthesis, Properties and Industrial Applications

Ethylene Propylene Diene Monomer (EPDM) is a saturated carbon chain elastomer. With its excellent weatherability, ozone resistance, and wide temperature adaptability, it has become the core material in the fields of building seals, automotive parts, cable insulation, and more.

I. Chemical Structure and Synthesis Method of EPDM

1. Chemical Composition and Third Monomer Selection

EPDM is a ternary copolymer of ethylene (E), propylene (P), and non-conjugated diene (D), with the diene serving as a crosslinking site (third monomer). The main types include:

• Ethylidene norbornene (ENB): High vulcanization activity and crosslinking density (accounts for over 70% of global EPDM production)

• Dicyclopentadiene (DCPD): Low cost, but slower vulcanization rate

• 1,4-Hexadiene (HD): Excellent heat resistance, suitable for high-temperature vulcanization systems

Typical molecular structure formula:

-(CH}_2{CH}_2)_x-(CH}_2CH(CH}_3)_y-(Diene)_z

The ethylene content (45-75%), propylene content (25-55%), and third monomer content (1-10%) together determine the material properties.

2. Industrial Production Processes

The mainstream processes are solution polymerization and gas-phase polymerization.

Production Process:

1. Raw material refining: Purity of ethylene and propylene >99.9%, and dienes must have polymerization inhibitors removed.

2. Polymerization reaction: Continuous injection of catalyst, reaction time 1-3 hours

3. Monomer recovery: Unreacted monomers are separated by flash vaporization (recovery rate >95%)

4. Post-processing: Water washing to remove ash → extrusion dewatering → fluidized bed drying

Major global manufacturers include Dow Chemical (USA), LANXESS (Germany), JSR (Japan), and Sinopec (China).

II. Classification and Grade System of EPDM Raw Rubber

1. Classification by Ethylene Content

2. Classification by Third Monomer Type

• ENB Type: Mooney viscosity ML(1+4) 125℃ 40-80, vulcanization speed index (t90) 3-10 min.

• DCPD Type: Mooney viscosity ML(1+4) 125℃ 30-60, t90 10-20 min.

• HD Type: Heat resistance up to 150℃ (ENB type is 130℃)

3. Classification by Mooney Viscosity

III. Physical Properties of EPDM

1. Hardness

• Test Standard: ASTM D2240 (Shore A)

• Range: Unfilled rubber 30-50 Shore A, up to 40-90 Shore A after carbon black reinforcement.

• Adjustment: Increasing N550 carbon black by 20 phr raises hardness by ~10 degrees; adding 10 phr paraffin oil decreases hardness by 3-5 degrees.

2. Mooney Viscosity

• Test Condition: ML(1+4) 125℃

• Typical Value: Raw rubber 30-100, high ethylene grade >70

• Processing Impact: High Mooney rubber requires extended mixing time or addition of flow aids (e.g., PE wax)

3. Density

• Range: 0.86-0.87 g/cm³ (pure rubber) → 1.10-1.30 g/cm³ (filled with 50 phr carbon black)

• Comparison: Lower than natural rubber (0.92 g/cm³) and nitrile rubber (1.15 g/cm³)

4. Aging Resistance

• Thermal Oxidative Aging: Tensile strength retention >80% after 150℃×168h (requires antioxidant MB 1 phr + TMQ 2 phr)

• Ozone Aging: No cracks after 500 hours at 50pphm ozone concentration (natural rubber only lasts 24 hours)

5. Elasticity

• Resilience: 50-70% for vulcanized rubber (higher than NBR, lower than natural rubber)

• Dynamic Properties: Loss factor (tanδ) 0.05-0.15, suitable for low heat generation parts

6. Low-Temperature Flexibility

• Embrittlement Temperature: -60℃ (low ethylene grade) to -40℃ (high ethylene grade)

• TR70 Value: Maintains 70% modulus of elasticity at -50℃

7. Stress Relaxation

• Data: Retention >60% after 1000 hours at 100% constant tensile stress.

• Improvement: Adding 5 phr nano-silica increases retention to 75%

8. Compression Set

• Test Standard: ASTM D395 Method B (125℃×22h)

• Typical Value: Peroxide vulcanization system <20%, sulfur vulcanization system 25-35%

9. Other Key Properties

• Electrical Insulation: Volume resistivity >1×10¹⁵ Ω·cm (suitable for 10 kV cables)

• Water Vapor Resistance: Volume change <3% after 28 days at 100℃

• Fatigue Resistance: Dynamic flex life >5 million cycles (ASTM D430)

IV. Chemical Properties of EPDM

1. Solvent Resistance

• Polar Solvents: Resistant to alcohols, ketones (swelling rate in acetone <10%)

• Non-Polar Solvents: Swelling rate of 30-50% in mineral oil (improvement needed with CR blending)

• Acid and Alkali Resistance: Resistant to 10% HCl or NaOH solutions (volume change <5%)

2. Resistance to Chemical Media

V. Mixing and Vulcanization Process Points

1. Mixing Process Optimization

• Equipment Selection: Recommended use of internal mixers (filling factor 0.65-0.75)

Charging Order:

1. Raw rubber mastication (100-120℃×2min)

2. Zinc oxide/stearic acid

3. Carbon black/filler

4. Plasticizer (paraffin oil)

5. Vulcanizing agent (peroxide or sulfur)

• Temperature Control: Discharge temperature ≤130℃ (sulfur system) or ≤110℃ (peroxide system)

2. Vulcanization System Design

3. Vulcanization Condition Control

• Platen Vulcanization: 160℃×15-30 min (sulfur system) or 170℃×5-10 min (peroxide system)

• Continuous Vulcanization: Salt bath (230℃×2 min) or microwave (2.45 GHz×90 sec)

4. Common Issues and Countermeasures

• Scorching: Cooler water temperature in internal mixer (<20℃), add 0.3 phr CTP

• Bubble Defects: Preheat pre-formed rubber at 60℃ for 30 min, molding pressure >15 MPa

• Uneven Vulcanization: Use stepwise heating (120℃→160℃) or post-vulcanization (150℃×2h)